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In this study, we aimed to assess the capacity of a physics-based earthquake simulator to improve our understanding of the seismogenic process. In this respect, we applied a previously tested earthquake simulator to two well-known and completely different seismogenic fault systems, namely the Italian Apennines and the Nankai subduction in Japan, for which long historical records of strong earthquakes are available. They are characterized by different fault mechanisms, fault sizes, and slip rates. Because of the difference in slip rates, the time scale of the seismicity patterns is different for the two systems (several hundreds of years for the Apennines and a few tens of years for the Nankai Fault). The results of simulations that produced synthetic catalogues of 100,000 years show these significant long-term seismicity patterns characterizing the seismic cycles for both seismogenic areas as follows: The average stress and the occurrence rate of earthquakes increase in the long term as the next major earthquake approaches; while the average stress increases uniformly, the occurrence rate stops increasing well in advance of the mainshocks; the b-value exhibits a long-term increase before major earthquakes and a fast decrease shortly before the mainshocks. Even if no specific statistical tool was applied for the quantification of the similarities between the seismicity patterns of the two seismic areas, such similarities are clearly justified by the large number of seismic cycles included in the 100,000-year synthetic catalogues. The paper includes a discussion on the capability of the simulation algorithm to reliably represent the real long-term seismogenic process. This question is difficult to answer because the available historical observations are of too short a duration to provide significant statistical results. In spite of the limitations characterizing the use of earthquake simulators for time-dependent earthquake hazard assessment, and the lack of convincing mechanistic explanations of the specific seismic patterns reproduced by our simulator algorithm, our results encourage further investigations into the application of simulators for the development of seismogenic models, including short-term features. [ABSTRACT FROM AUTHOR]

GIL/GIS bus is widely used in the field of power transmission and distribution, and the demand for lightweight is becoming more and more prominent. To reduce the weight of the bus and ensure the safety and reliability of the structure, a new 6σ robust design method of the GIL/GIS bus based on electric‐thermal‐mechanical co‐simulation is proposed. Taking a 550 kV/5000A bus as the initial structure, considering the uncertainty of product size and performance, a 6σ robust lightweight model of bus insulation electric field strength, current temperature rise, and mechanical stress multi‐performance co‐simulation is established. The finite element numerical calculation method is used to calculate and analyze the performance parameters of the bus. The Kriging surrogate model is used to form the response surface, and the optimal bus structure is obtained by genetic algorithm. The results show that after the robustness optimization, the performance of the bus meets the design requirements, the weight per meter decreased from 65.11 to 39.12 kg, and the lightweight effect is remarkable. Compared with the traditional deterministic optimization design, the reliability of the structure is improved. The new method of the GIL/GIS bus lightweight design proposed in this study has high feasibility and application prospects, which can provide new ideas for the development of gas‐insulated electrical equipment. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Earthquakes with magnitudes of 6–7 have been reported even in various active tectonic settings where fault deformation topography have not been detected. Therefore, delineating concealed active faults generating such earthquakes is necessary to reduce earthquake damage; however, few studies exist to provide its clues regarding such faults. The 1984 Western Nagano Earthquake in Japan was a main shock with a magnitude of Mj 6.8 and a depth of 2 km at the source. Solid bedrocks are well‐exposed in the earthquake source region; however, no surface rupture have been identified, and the active fault is known to be concealed. In this study, we collected data on striations observed in fractures by geological survey around the source area of the 1984 Western Nagano Earthquake. Using the collected data, the multiple inverse method was used to estimate the stresses that affected the striation formation. Consequently, stresses similar to acting faults in this area were detected in minor faults around the known concealed active fault. This suggests that the minor faults might be part of the damage zone that has been developed around the concealed active fault. Some minor faults were recognized in Quaternary volcanic rocks, confirming that they experienced displacements recently. This study indicates the possibility of detecting concealed active faults in the bedrock by geological survey. Plain Language Summary: The activity of active faults causes earthquakes. Therefore, it is crucial to understand the distribution of active faults to prepare for earthquakes in advance. However, earthquakes can also occur where active faults have not been recognized. In this case, the active fault cannot be recognized on the surface but might be concealed. In this study, we collected data on many slip marks on fractures in the bedrock where a concealed active fault has been inferred and estimated the stress required to form the slip marks to examine whether a clue to the existence of a concealed active fault can be obtained from a surface approach. Consequently, similar stresses to currently acting faults in this area were obtained in the area directly above the concealed active fault. This discovery shows that there are many recently moved slip marks directly above the concealed active fault, which might be related to the activity of the fault. This result indicates the possibility of recognizing the concealed active fault from surface approaches. Key Points: We collected minor faults‐slip data around the 1984 Western Nagano Earthquake region, and conducted a multiple inverse methodAs results, the minor faults were active in the recent stress are concentrated just above the concealed active faultIt shows the possibility of understanding the existence of the concealed active fault by using our method even in no active fault areas [ABSTRACT FROM AUTHOR]

The global tobacco epidemic, claiming over 8 million lives annually, constitutes a formidable public health threat. Fatalities arise from both direct tobacco use and exposure to second-hand smoke. Smoking prevalence, notably in Japan, varies across age groups with distinct patterns indicating higher rates among those aged 40 years and above. Persistent concerns surround the significance of smoking behavior in individuals aged 20 to 30 years, given the potential for early adulthood behavior to contribute to long-term health impacts. The emergence of heated tobacco products adds complexity with a substantial percentage of individuals aged 20 to 30 years using these alternatives. This study analyzed data from 15,333 individuals aged 20 to 39 years, collected through Japan's "Comprehensive Survey of Living Conditions 2017". Compliant with the Japan Statistics Act, a secondary analysis employed multivariate logistic analysis to examine concerns and stress sources by sex and smoking behavior, adjusting for various variables. As a result, no statistically significant associations were found between smoking in men and concerns or stress. However, in women who smoked, significant associations were observed between smoking and specific stressors, such as work-related concerns, financial stress, and stress from a lack of personal free time. This study emphasizes the necessity of considering gender differences and social backgrounds in designing targeted smoking-prevention programs, aiming to enhance overall health longevity and comprehensively reduce lifelong smoking rates in this demographic. [ABSTRACT FROM AUTHOR]

Knowledge of the state of stress in subducting slabs is essential for understanding their mechanical behavior and the physical processes that generate earthquakes. Here, we develop a framework which uses a high-resolution focal mechanism catalog to determine the change in the position of the neutral plane before and after the M9 Tohoku-oki earthquake to determine that the deviatoric stress within the slab at intermediate depths must be very low (~1 MPa). We show that by combining the static stress calculated from coseismic slip distributions with the stress orientations before and after the mainshock, we can determine the full deviatoric stress tensor within the subducting slab at intermediate depths. These results preclude earthquake source mechanisms that require large background driving stresses, favoring a mechanically weak subducting slab, thus providing quantitative constraints on the physical processes that generate intermediate-depth earthquakes. [ABSTRACT FROM AUTHOR]

As megathrust earthquakes often have source areas in offshore regions, offshore seismic observations are important. However, the detection capability and resolution of offshore earthquake locations are low owing to the small number of permanent offshore seismic stations. Recently, distributed acoustic sensing (DAS) measurements, which use a fiber-optic cable as a high-density strain rate sensor, have been used for seismic observations. To evaluate the detectability of earthquakes using DAS measurements, locate earthquakes near the cable, and derive the empirical relationship between the magnitude and DAS S-wave strain rate amplitude, we conducted DAS measurements for 4 months using an offshore fiber-optic cable in the Tsugaru Strait, where various types of earthquakes were observed. In this observation, some earthquakes with magnitudes smaller than one or not listed in the earthquake catalog by the Japan Meteorological Agency (JMA) were observed. This suggests a high seismic detection capability for DAS measurements near the cable. We located earthquakes in the Tsugaru Strait by manually picking the arrivals of P- and S-waves. The hypocenters of events near the cable were located near those of the JMA catalog at a kilometer resolution; therefore, DAS data have the potential to locate earthquakes near the cable. In this study, an equation related to the maximum S-wave strain rate amplitude, hypocentral distance, and earthquake magnitude was derived. When the hypocentral distance increased by one order, the amplitude of the S-wave strain rate decreased by approximately 1.8 orders. This attenuation was larger than that derived mainly from inland DAS data in previous studies, which may be due to the difference in scattering or intrinsic attenuation between the inland and offshore regions. Using the derived equation, the magnitude of an earthquake can be estimated using the DAS data. We compared the S-wave amplitudes of the DAS strain rate and the acceleration of the permanent inland stations. The relationship between these two amplitudes is comparable to an apparent S-wave velocity of approximately 710 m/s in the sediment. [ABSTRACT FROM AUTHOR]

Maximum shear stress along an active deformation zone marking the subduction plate interface is important for understanding earthquake phenomena and is an important input parameter in subduction zone thermomechanical modeling. However, such maximum shear stress is difficult to measure directly at depths more than a few kilometers and is generally estimated by simulation using a range of input parameters with large associated uncertainties. In addition, estimated values generally represent maximum shear stress conditions over short observation timescales, which may not be directly applicable to long-timescale subduction zone modeling. Rocks originally located deep in subduction zones can record information about deformation processes, including maximum shear stress conditions, occurring in regions that cannot be directly accessed. The estimated maximum shear stress is likely to be representative of maximum shear stress experienced over geological timescales and be suitable to use in subduction zone modeling over timescales of millions to tens of millions of years. In this study, we estimated maximum shear stress along a subduction plate interface by using samples from the Sanbagawa metamorphic belt of southwestern (SW) Japan, in which slivers of mantle-wedge-derived serpentinite are widely distributed and in direct contact with metasedimentary rocks derived from the subducted oceanic plate. These areas can be related to the zone of active deformation along the subduction plate interface. To obtain estimates of maximum shear stress at the subduction interface, we focused on the microstructure of quartz-rich metamorphic rocks – quartz is the main component of the rocks we collected and its deformation stress is assumed to be roughly representative of the stress experienced by the surrounding rock and plate interface deformation zone. Maximum shear stress was calculated by applying deformation temperatures estimated by the crystallographic orientation of quartz (the quartz c -axis fabric opening-angle thermometer) and the apparent grain size of dynamically recrystallized quartz in a thin section to an appropriate piezometer. Combined with information on sample deformation depth, estimated from the P – T (pressure–temperature) path and deformation temperatures, it is suggested that there was nearly constant maximum shear stress of 15–41 MPa in the depth range of about 15–30 km, assuming plane stress conditions even when uncertainties related to the measurement direction of thin section and piezometer differences are included. The Sanbagawa belt formed in a warm subduction zone. Deep slow earthquakes are commonly observed in modern-day warm subduction zones such as SW Japan, which has a similar thermal structure to the Sanbagawa belt. In addition, deep slow earthquakes are commonly observed to be concentrated in a domain under the shallow part of the mantle wedge. Samples showed the depth conditions near the mantle wedge, suggesting that these samples were formed in a region with features similar to the deep slow earthquake domain. Estimated maximum shear stress may not only be useful for long-timescale subduction zone modeling but also represent the initial conditions from which slow earthquakes in the same domain nucleated. [ABSTRACT FROM AUTHOR]

This article examines a case study involving a 3D‐printed titanium "aero base handlebar" that failed and caused a crash during the Japan 2020 Olympics. The failure was attributed to the handlebar's design, which did not meet the increasing demands of customers in terms of safety, cost, reliability, and comfort. The handlebar was created using in‐house Altair product tools like Inspire Studio, SIMSOLID, and SULIS. Static structural analysis was conducted by estimating boundary forces. The analysis revealed that the original handlebar design, with a width of 50 mm, did not meet the required safety standards. To address safety concerns, the article proposed moving the arms forward by 35 mm (1.37 in.) to create clearance and attempting to secure a modified aero handlebar with an 85 mm width. The modified design incorporated a lattice structure, which exhibited higher levels of deformation and stresses, as well as lower maximum fatigue damage compared to the original 50 mm design. These results highlight the importance of considering customer expectations for safety, reliability, and comfort. Company Altair's advanced proprietary software, including Inspire Studio, SIMSOLID, and SULIS, in addition to employing lattice optimization methods, can support designers and engineers in fulfilling these requirements and creating products that are both safer and more reliable. [ABSTRACT FROM AUTHOR]

Evaluating the mechanical properties of gas (primarily methane) hydrate-bearing sediments is essential for commercial production as a next-generation resource and understanding the global carbon cycle. Triaxial and uniaxial compression tests have been conducted on synthetic gas hydrate and natural core samples recovered from deep-sea beds using pressure coring techniques. The results show that four factors are vital in establishing the strength of hydrate-bearing sediments: hydrate saturation, effective confining stress, porosity, and strain rate. However, no study has evaluated these factors in a unified and quantitative manner, and even if the physical properties of the reservoir are known in detail from logging, predicting the strength has been challenging. In this study, pressure cores were drilled and recovered from the Eastern Nankai Trough in April 2018 after Japan's second offshore production test, and triaxial or uniaxial compression tests were performed on 12 pressure core samples brought back to the laboratory. The mechanical properties of the hydrate-bearing sediments were classified with previous obtained results from 53 pressure cores and 223 synthetic cores, and empirical equations for triaxial compressive strength and deformation modulus were proposed as functions of gas hydrate saturation, effective confining pressure, porosity, and strain rate. The obtained equations were found to correlate well with the experimental data and can predict the strength and deformation modulus from logging data. [ABSTRACT FROM AUTHOR]

This research paper focuses on evaluating the log piling technique as a sustainable, cost-effective, and environmentally friendly solution for reducing soil liquefaction risks during earthquakes. Although this method has been used extensively in Japan, mainly aiming for complete soil layer penetration, its economic viability is questionable in cases requiring very deep soil improvements. The study highlights that shallow ground improvement can notably enhance the seismic behavior of the soil-improvementstructure system, as evidenced by the reduced total and penetration settlements caused by liquefaction. The paper presents a methodology for determining the optimal dimensions of the modified ground zone using both small and medium-scale 1-g shaking table tests. The small-scale tests involve a detailed parametric study, examining variables like improvement width, pile spacing, and the depth-to-thickness ratio of the improved layer. Medium-scale tests, on the other hand, are geared towards identifying the minimum effective pile length. This approach provides a practical guideline for engineers to implement log piling for small residential buildings. Additionally, the paper utilizes finite element method (FEM) effective stress analysis, incorporating a PLAXIS 2Dbased constitutive model (PM4Sand) calibrated with laboratory undrained cyclic torsional tests. This model accounts for the changes in effective stress during seismic activities. Finally, the study correlates its numerical findings with the results from the 1-g shaking table experiments, offering a well-rounded perspective on the effectiveness of log piling in mitigating liquefaction risks during seismic events. [ABSTRACT FROM AUTHOR]

For a comprehensive understanding of the Nankai Trough seismogenic zone, the Integrated Ocean Drilling Program/International Ocean Discovery Program (IODP) conducted a deep ocean drilling project referred to as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) from 2007 to 2019 off the Kii Peninsula, Japan. To investigate the subduction zone's physical properties and reveal the sediments' compressive strength, we carried out consolidated-undrained triaxial compression tests with pore water pressure measurements on NanTroSEIZE core samples. The core samples used were retrieved from depths of approximately 400m below the seafloor at sites C0006 and C0007 with ~4000m water depths. The rocks are Pliocene siltstones with a porosity of ~50%, classified as sedimentary soft rocks. As a result of the triaxial compression tests, the cohesion ccu and internal frictional angle φcu derived from the total stress analyses ranged in 1.8-1.9 MPa and 15-17°, respectively. In addition, the cohesion ccu and internal frictional angle φcu determined by the effective stress analyses were within 1.6-2.2 MPa and 18-28°, respectively. All the specimens tested caused brittle failure and formed clear shear fractures. In the case of these brittle failures, we found that post-failure specimen area correction when calculating differential stress in post-failure might cause a nonnegligible underestimation of the differential stresses. Therefore, we suggest that the area correction for undrained triaxial compressive tests of soft rocks should be conducted until reaching their peak strength if brittle failure occurs. [ABSTRACT FROM AUTHOR]

Cement with fly ash has rarely been used in Japan, mainly because its strength development is slower than ordinary Portland cement. In this research, the effect of the new type of fly ash (which was modified by the electrostatic belt separation method) with high alite (C3S) cement on cracking resistance of precast concrete prepared by steam curing was studied. The mechanical and shrinkage properties of the proposed fly ash concrete were compared with those of concrete made using OPC cement without fly ash. In order to study the cracking tendency of precast concrete with the proposed cement with fly ash, thermal stress analysis was conducted, taking into consideration the experimental data of concrete properties with the different concrete mix proportions. A standard precast concrete box culvert model was used in this 3D FEM analysis, and the distribution of temperature and relative humidity in the cross-section and induced restraint stress during and after steam curing were discussed. Steam-cured concrete with fly ash and high alite cement developed higher compressive strength on the first day of age than concrete with OPC. The proposed fly ash concrete developed high cracking resistance in the early days. On the other hand, the results showed that the drying shrinkage at later ages was the main cause of cracking. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of 10 years of research on models of the megathrust earthquake cycles and crustal deformation associated with the 2011 Tohoku-oki earthquake. Several earthquake cycle models have been proposed for the northeast Japan subduction zone to elucidate why megathrust earthquakes occur at intervals of approximately 600 years and why large slips occurred in the shallow subduction zone. A model that considers a strong asperity in the shallow plate interface, and a hierarchical asperity model that considers the scale dependence of the critical displacement of the rate- and state-dependent friction law have been proposed. Modeling with dynamic weakening of faults has also been proposed. In the model using the shallow friction characteristics obtained by the Japan Trench Fast Drilling Project, rupture from depth can propagate to the trench, resulting in shallow large slips. Submarine crustal deformation has been observed for the first time in addition to dense observations of the inland crustal deformation. The observation of the seafloor deformation near the trench showed that viscoelastic relaxation played an important role in short-term postseismic deformation near the trench. The effects of the low-viscosity region at the oceanic lithosphere and asthenosphere boundary, and the cold forearc mantle wedge (cold nose) have been discussed. Simulations using the nonlinear flow law of rock in the mantle, where a power–law relationship holds between stress and strain rate, and the fault friction law at the plate boundary, show that the Tohoku-oki earthquake caused large stress fluctuations, resulting in a sudden viscosity decrease and rapid flow in the asthenosphere below the oceanic lithosphere. The simulations of the crustal deformation associated with the Tohoku-oki earthquake cycle also indicate that in the later stage of the earthquake cycle, the Pacific coastal region begins to subside due to the increasing slip deficit rate on the deeper parts of the plate interface. These results explain the subsidence of the Pacific coast of northeast Japan observed for about 100 years prior to the Tohoku-oki earthquake. In the future, a model that explains the long-term crust and mantle deformation during the entire Tohoku-oki earthquake cycle must be constructed. [ABSTRACT FROM AUTHOR]

Absolute maximum shear stress ("shear stress" in this study) along the subduction plate interface is important for understanding earthquake phenomena and is an important input parameter in subduction zone thermomechanical modelling. However, such shear stress is difficult to measure directly at depths more than a few kilometers and is generally estimated by simulation using a range of input parameters with large associated uncertainties. In addition, estimated values generally represent shear stress conditions over short observation timescales, which may not be directly applicable to long-timescale subduction zone modelling. Rocks originally located deep in subduction zones can record information about deformation processes, such as shear stress conditions, occurring in regions that cannot be directly accessed. The estimated shear stress is likely to be representative of shear stress experienced over geological timescales and be suitable to use in subduction zone modelling over time scales of millions to tens of millions of years. In this study, we estimated shear stress along a subduction plate interface by using samples from the Sanbagawa metamorphic belt of Southwest (SW) Japan, in which slivers of mantle wedge-derived serpentinite are widely distributed and in direct contact with metasedimentary rocks derived from the subducted oceanic plate. These areas can be related to the ancient subduction plate interface. To obtain estimates of shear stress at the subduction interface, we focused on the microstructure of quartz-rich metamorphic rocks--quartz is the main component of the rocks we collected and its deformation stress is assumed to be representative of the region. Shear stress was calculated by applying deformation temperatures estimated by the crystallographic orientation of quartz (the quartz c-axis fabric opening-angle thermometer), and the apparent grain size of dynamically recrystallized quartz in a thin section to an appropriate piezometer. Combined with information on sample deformation depth, estimated from P-T path and deformation temperatures, it is suggested that there was nearly constant shear stress of 16-41 MPa in the depth range 17-27 km, assuming plane stress conditions even when uncertainties related to measurement direction of thin section and piezometer differences are included. The Sanbagawa belt formed in a warm subduction zone. Deep slow earthquakes are commonly observed in modern-day warm subduction zones such as SW Japan, which has a similar thermal structure to the Sanbagawa belt. In addition, deep slow earthquakes are commonly observed to be concentrated in a domain under the shallow part of the mantle wedge. Samples showed the depth conditions near the mantle wedge, suggesting that these samples were formed in a region with features similar to the deep slow earthquakes domain. Estimated shear stress may not only be useful to long-timescale subduction zone modelling but also represent the initial conditions from which slow earthquakes in the same domain nucleated. [ABSTRACT FROM AUTHOR]

Absolute maximum shear stress ("shear stress" in this study) along the subduction plate interface is important for understanding earthquake phenomena and is an important input parameter in subduction zone thermomechanical modelling. However, such shear stress is difficult to measure directly at depths more than a few kilometers and is generally estimated by simulation using a range of input parameters with large associated uncertainties. In addition, estimated values generally represent shear stress conditions over short observation timescales, which may not be directly applicable to long-timescale subduction zone modelling. Rocks originally located deep in subduction zones can record information about deformation processes, such as shear stress conditions, occurring in regions that cannot be directly accessed. The estimated shear stress is likely to be representative of shear stress experienced over geological timescales and be suitable to use in subduction zone modelling over time scales of millions to tens of millions of years. In this study, we estimated shear stress along a subduction plate interface by using samples from the Sanbagawa metamorphic belt of Southwest (SW) Japan, in which slivers of mantle wedge-derived serpentinite are widely distributed and in direct contact with metasedimentary rocks derived from the subducted oceanic plate. These areas can be related to the ancient subduction plate interface. To obtain estimates of shear stress at the subduction interface, we focused on the microstructure of quartz-rich metamorphic rocks—quartz is the main component of the rocks we collected and its deformation stress is assumed to be representative of the region. Shear stress was calculated by applying deformation temperatures estimated by the crystallographic orientation of quartz (the quartz c-axis fabric opening-angle thermometer), and the apparent grain size of dynamically recrystallized quartz in a thin section to an appropriate piezometer. Combined with information on sample deformation depth, estimated from P–T path and deformation temperatures, it is suggested that there was nearly constant shear stress of 16–41 MPa in the depth range 17–27 km, assuming plane stress conditions even when uncertainties related to measurement direction of thin section and piezometer differences are included. The Sanbagawa belt formed in a warm subduction zone. Deep slow earthquakes are commonly observed in modern-day warm subduction zones such as SW Japan, which has a similar thermal structure to the Sanbagawa belt. In addition, deep slow earthquakes are commonly observed to be concentrated in a domain under the shallow part of the mantle wedge. Samples showed the depth conditions near the mantle wedge, suggesting that these samples were formed in a region with features similar to the deep slow earthquakes domain. Estimated shear stress may not only be useful to long-timescale subduction zone modelling but also represent the initial conditions from which slow earthquakes in the same domain nucleated. [ABSTRACT FROM AUTHOR]

A cosmic muon imaging system is essentially a particle tracking detector as known from experimental High Energy Physics. The Multiwire Proportional Chamber (MWPC) once revolutionized this field of science, and as such it is a viable choice as the core element of an imaging system. Long term construction and operation experience was gathered from a Japanese–Hungarian collaboration that gave rise to the MWPC-based Muon Observatory System (MMOS), and is being used in Japan at the Sakurajima volcano. The present paper attempts to draw conclusions on the thermal and mechanical limits of the system, based on controlled measurements and detailed simulations. High temperature behavior and effects of thermal cycling and conditioning are presented, which appear to consistently allow one to propose quality control criteria. Regarding mechanical stability, the relation between gluing quality (tensile strength) and expected stress from vibration (during transportation) determines the safety factor to avoid damages. Both of these are presented and quantified in the paper using a conservative and austere approach, with mechanical simulations validated with experimental modal testing data. One can conclude that mechanical stress during industrial standard air freight shipping conditions is nearly a factor of three below the calculated maximum stress. [ABSTRACT FROM AUTHOR]

Stress state is a long-sought but poorly known parameter on subduction megathrusts and in overlying accretionary wedges in general. We used direct observations made during drilling of Integrated Ocean Drilling Program (IODP) borehole C0002 to a depth of 3058 m below the seafloor (mbsf) in the Nankai subduction zone of southwestern Japan to constrain in situ pore pressure and stress state in the deep interior of an accretionary wedge for the first time. These data included downhole pressure, active pumping tests, and logging and sample measurements. We found a nearly linear gradient in minimum horizontal principal stress (Shmin) and show that it remained consistently smaller than the vertical stress (Sv), definitively ruling out a thrust-faulting stress regime to at least 3 km depth, and to within ~2 km above the subduction megathrust. At 3000 mbsf, the estimated effective stresses were: Sv = 33 MPa, SHmax = 25-36 MPa, and Shmin = 18.5-21 MPa. We therefore interpret that the stress state throughout the drilled interval, which lies entirely in the hanging wall of the active megathrust, lies in a normal or strike-slip faulting regime (Sv ≥ SHmax > Shmin). Total differential stresses are below ~18 MPa. We conclude that (1) basal traction along the megathrust must be small in order to permit both locking (and frictional sliding at failure) of the décollement and such low differential stresses deep within the upper plate; and (2) although differential stresses may remain low all the way to the plate boundary at ~5000 mbsf, SHmax must transition to become greater than the vertical stress-either spatially below the base of the borehole or temporally leading up to megathrust fault rupture-in order to drive thrust motion along the plate boundary as observed in great earthquakes and in recurring very low-frequency earthquakes and slow-slip events. [ABSTRACT FROM AUTHOR]

Geodetic and seismological observations have shown discrepancies between azimuths of maximum contraction (strain rate) and maximum compression (stress). These discrepancies can be the results of the superposition of localized or transient mechanical processes such as fault coupling during seismic cycles. Rich sets of recent geophysical data allow us to conduct spatiotemporal imaging of the discrepancies. Here, we estimate the spatiotemporal evolution in the strain-rate fields of the Japanese Islands with optimized smoothing distances from 1997 to 2021 using Global Navigation Satellite System (GNSS) data, and investigate how the maximum contraction axes of horizontal strain rates differ from those of horizontal stress based on earthquake focal mechanisms. Several characteristic results are observed for each region within the Japanese Islands. Both azimuths of the strain rates and stress differ by more than 60° over hundreds of kilometers from the Kanto region to along the Nankai Trough, related to seismotectonics due to the dual subduction of the Philippine Sea plate and the Pacific plate beneath the Japanese Islands. The differences in the azimuths imply the effect of the very long-term stable subduction of the Pacific plate. We find that the azimuthal differences tend to be small along tectonic zones with active inland earthquakes and high strain rates on the back-arc sides. We also find that the 2011 off the Pacific coast of Tohoku earthquake caused notable azimuthal differences in the strain rates and the stress in the Tohoku region. The strength of fault may cause lower response sensitivity of seismological stress to major earthquakes than geodetic strain rate. Our dataset has wide spatiotemporal coverage and can serve as a basis for further research, for example, to estimate the current fault conditions during seismic cycles. [ABSTRACT FROM AUTHOR]

Quantifying the stress distribution or finding mechanically coupled areas on the plate interface is fundamentally important for conjecturing megathrust earthquakes that may occur in the future. Kinematically coupled areas, or slip deficit distributions, on plate interfaces were commonly estimated by geodetic‐data analyses. However, mechanically coupled areas are not identical to the kinematically coupled areas. The present study develops an inversion method to estimate the stress rate distribution as mechanically coupled areas. We apply this method to the Nankai trough subduction zone, southwestern Japan to detect mechanically coupled areas. Some of the estimated coupled areas correspond to the rupture areas of historical earthquakes. Others are in a deeper part, which may release the stress as aseismic slip. We then construct a rupture scenario that can occur in the Nankai trough in the future based on the estimated mechanical coupling, assuming that an effective stress accumulation period is 100 years. The scenario consists of a foreshock of MW 8.0 followed by an afterslip of MW 7.7 and a mainshock of MW 8.2. Although the moment magnitude of the afterslip is slightly smaller than the foreshock, the strain energy released by the foreshock is significantly larger than the afterslip. In order to compare events when the stress drops are significantly different, it is useful to use the minimum released strain energy, or available energy, to characterize the magnitude of the events. Plain Language Summary: The driving force that generates huge earthquakes originates from the frictional locking between overriding continental plate and subducting oceanic plate. How strong and which parts are locked along the plate interface provide us with critical information for megathrust earthquakes that may occur in the future. Significantly coupled areas along the plate interface can be detected by the analysis of ground deformation. However, it is difficult to obtain correct information about the stress of the locking. To quantify the coupling along the plate interface, this study develops a method to estimate the stress rate based on elastic mechanics. We apply the method to the Nankai trough, in southwestern Japan, to estimate the plate locking. Then, by using the estimated locking information, we create a scenario for a sequence of earthquakes. This consists of a foreshock, a mainshock, and a slow slip between the foreshock and the mainshock. This study provides a method to obtain critical information about the mechanics on the plate boundary based on which we can create megathrust rupture scenarios. Key Points: An inversion method for the shear stress rate distribution along a plate boundary is developedMechanically coupled areas are identified on the plate interface in the Nankai troughA possible scenario for a megathrust earthquake after an afterslip of a foreshock is proposed based on the coupling distribution [ABSTRACT FROM AUTHOR]

The high‐temperature canned electric‐actuated valve permanent magnet synchronous motor (CEAV‐PMSM) directly drives the valve load, which is prone to eccentricity operation, causing greater system vibration and shortening the valve operating life. In order to analyze the electromagnetic and structural characteristics of CEAV‐PMSM under different eccentricity faults, this paper uses analytical methods to derive the magnetic field distribution of the motor under normal and eccentricity conditions. Then, the Maxwell Stress Tensor method is used to derive the expression of the radial electromagnetic force under normal and eccentricity conditions, and the order of space–time harmonics that have a greater impact on CEAV‐PMSM are summarized. After that, the electromagnetic performance comparison of the three pole‐slot combinations under different eccentricity conditions, and the harmonic orders during eccentricity is analyzed by Fourier transform to obtain the optimal pole‐slot combination, which verified the correctness of the analytical calculations. In addition, the influence of different eccentricity conditions on the radial force density and unbalanced magnetic pull are studied. On this basis, the vibration response of the motor under eccentricity is analyzed, and the influence of the canned sleeve on the vibration performance of the motor is discussed. Finally, the modal analysis of CEAV‐PMSM is carried out to prevent the occurrence of resonance under eccentricity, which provides some references for reducing the vibration and noise of the canned electric‐actuated valve. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Aseismic megathrust slip downdip of the seismogenic zone is accommodated by either steady creep or episodic slow slip events (SSEs). However, the geological conditions defining the rheology of megathrust slip remain elusive. We examined exhumed subduction mélanges on Kyushu, Japan, which deformed at ∼370–500°C under greenschist to epidote‐amphibolite facies conditions, comparable to warm‐slab environments. The mélanges recorded fluid release and viscous shear localization associated with metasomatic reactions between juxtaposed metapelitic and metabasaltic rocks. Metasomatic reactions caused albitization of metapelite, resulting in depth‐dependent changes to megathrust rheology. In a mélange deformed at ∼370°C, very fine grained reaction products (metasomatic albite) facilitated grain boundary diffusion creep at stresses of ∼45 MPa, less than those in the surrounding metabasalt. Mineralogical and chemical changes during metasomatic reactions, and their field content, imply an onset of albite metasomatism at ∼350°C. Albite metasomatism therefore potentially contributed to decreased megathrust strength around the inferred thermally controlled base of the seismogenic zone. In a mélange deformed near the mantle wedge corner at ∼500°C, metasomatic reactions promoted local quartz vein formation and localized viscous shear at slow slip strain rates, during which the coarse‐grained metasomatic albite behaved as relatively rigid blocks in a viscous matrix. We suggest that albite metasomatism can facilitate changes in a megathrust slip mode with depth and may explain why slip mode changes from creep to SSEs with tremor with increasing depth. Plain Language Summary: Along tectonic plate boundaries, where one plate slips beneath another, plate movement occurs by processes including large and devastating earthquakes slipping at meters/second, very small earthquakes called tectonic tremor, slow slip events (SSEs) slipping at millimeters/day, and steady creep slipping at centimeters/year. However, the factors controlling where these different slip styles occur remain poorly understood. On Kyushu, Japan, ancient plate boundary rocks have been exposed by uplift and erosion. Our measurements of structures and rock chemistry in these rocks revealed that chemical reactions between subducted basalts and sediments may influence the plate boundary slip behavior. In rocks that deformed near ∼370°C, chemical reactions produced very fine grained rocks that caused local weakening within the plate boundary. This could explain why the plate boundary slip behavior changes from frictional to viscous near the downdip of the seismogenic zone at ∼350°C. In rocks that deformed at ∼500°C, near where slow slip and tremor events occur, chemical reactions promoted quartz vein formation that may represent tremor and localized viscous shear at faster strain rates than in surrounding rocks. This could explain the occurrence of tectonic tremors and SSEs. Key Points: Exhumed mélange shear zones deformed downdip of the seismogenic zone recorded albite metasomatism during subductionVery fine grained albite facilitated shear zone weakening by grain boundary diffusion creep near the base of the seismogenic zoneAlbite metasomatism promoted viscous shear localization at an increased strain rate near the mantle wedge corner [ABSTRACT FROM AUTHOR]

It is easy to draw stress trajectories to investigate the present stress field by interpolating stress orientations determined at control points. However, challenges arise when we deal with the trajectories of paleostresses, because neighboring control points may have the stress orientations of different tectonic phases. We must choose coeval stresses to draw the trajectories. Recent stress inversion techniques can separate stresses from heterogeneous data from fault, dilational fractures, etc. Natural data sets from those structures are often heterogeneous, and age data are usually not enough to classify the stresses by age. As a result, an unsupervised classification problem of the inversion results must be solved to draw the trajectories. Here, we propose a simple and heuristic procedure for this problem. We assume smooth trajectories during each of the phases. The smoothness makes density-based clustering adoptable to solve the problem. The heterogeneity of data sets allows the additional partition of the clusters. As a worked exercise for this technique, the trajectories of minimum horizontal stress orientations were drawn based on the paleostresses determined from the attitudes of felsic dikes and quartz veins formed in mid Cretaceous orogeny in the North Kitakami Terrain, northern Japan. The orogen-parallel and orogen-perpendicular extensional stress fields delineated by the present technique were probably the manifestations, respectively, of the gravitational collapse of the orogen and of regional extensional tectonics in the Far East. • Stress inversion techniques can separate paleostresses from a heterogeneous data set. • They are thought to be the stress conditions of different tectonic phases. • The paleostresses must be sorted into coeval groups to draw stress trajectories. • Density-based clustering was adopted for this purpose. • Worked exercises with artificial and natural data are presented. [ABSTRACT FROM AUTHOR]

In order to reveal the secular deformation evolution and strain accumulation progress along subduction zone, we focus on high-precision Global Navigation Satellite System (GNSS) data processing, GNSS time series analysis and regional spatiotemporal filtering. The GNSS position time series is modeled as a combination of the long-term plate movements, short-term noise and the frequency-dependent variations and tectonic deformation information. Common Mode Errors (CME) is removed and the deformation signals is then extracted from the residual time series by Principal Component Analysis (PCA). Combing the filtered displacement array and the dynamic regional strain array derived from GNSS baseline, a spatiotemporal tectonic evolution map is exhibited obviously. We process the data recorded by GEONET over the 2003–2011 period in middle Japan island and reveal the dynamic evolution of crustal deformation along subduction zone. The results show that the regional reference frame transformation by constraining one site location and one stable GNSS baseline direction can further improve the Signal-to-Noise Ratio (SNR) of GNSS observations. A integrated analysis combining the baseline length with azimuth change can show the crustal motion feature more comprehensively. The observed behaviors agree well with the simulation experiment results of the rock rupture in the laboratory. We divide the pre-seismic deformation into four stages, the stable linear strain accumulation stage, the formation stage of the local locked area, local decoupling stage, and strain release stage. We also give an appropriate dynamical model for the interplate coupling to explain the observed deformation characteristics. Research result provides some of the observational new evidence for inter-seismic deformation anomaly detection and the medium- to longer-term seismic hazard assessments. [ABSTRACT FROM AUTHOR]

Application of Raman spectroscopy of carbonaceous material thermometry to samples of metasedimentary rock from the low‐grade Sanbagawa belt in the central Kii peninsula reveals a progressive decrease in temperature from ~390 °C close to the northern boundary, a major continental shear zone—the median tectonic line (MTL)—to ~270 °C and ~7 km to the south and roughly constant temperature distribution thereafter. Within the Sanbagawa belt, the thermal structure is not significantly modified by slip‐on fault boundaries between different geological units or folding. Meso‐ and microstructural observations combined with strain analysis using detrital grains in meta‐mudstone indicate a similar deformation history throughout the area and no correlation between ductile strain and temperature gradients. These observations suggest the observed thermal structure was developed after the main stages of ductile deformation of the Sanbagawa belt were complete and are not due to localized preferential exhumation along with the MTL. The observations also require a heat source along with the MTL. Order of magnitude estimates suggest the influx of warm fluid along the MTL are viable causes of the observed thermal anomaly. Although shear heating would be another possible explanation, thermal calculations require anomalous fast slip rates along the MTL and much greater frictional strength than generally considered reasonable. For these reasons, fluid infiltration is our preferred model. [ABSTRACT FROM AUTHOR]

Tide-embankment walls protecting coastal roads frequently contain numerous windows so that pedestrians and drivers can view the scenery without experiencing reduced sunlight. Tide-embankment windows must withstand extreme climatic conditions. However, the effects of temperature extremes on acrylic boards have rarely been studied. This paper proposes a simple method for constructing a high-temperature environment and a method for measuring strain on an acrylic plate. The deformation and strain of a 40-mm-thick acrylic tide-embankment window were determined experimentally and numerically in this study in a high-temperature environment, obtaining similar results; additionally, the numerical method was subsequently used to simulate a low-temperature environment. Because thermal conductivity was low, the internal temperature of the thick acrylic board did not immediately change with the temperature of the surface, and thermal expansion and contraction of the board were restrained. Temperature-induced deformation effects were low across the entire range of temperatures and heating rates recorded in coastal Japan. [ABSTRACT FROM AUTHOR]

We present field and microstructural data from an exhumed subduction complex in the Ryukyu arc, Japan, where epidote-blueschist, Triassic, Tomuru metamorphic rocks with block-in-matrix structure crop out. With the aim to constrain epidote-blueschist rheology, we investigate fabric development and infer deformation mechanisms of blocks and matrix through microstructural analyses on the main fabric-forming minerals: glaucophane, epidote and albite. The blocks have a poorly developed, discontinuous foliation. In contrast, the matrix has a well-developed, continuous foliation. Glaucophane is the principal foliation-forming phase, arranged in interconnected layers that surround epidote and albite, which suggests that glaucophane controls epidote-blueschist rheology. Deformation mechanisms inferred from petrographic and electron backscatter diffraction (EBSD) analysis are similar in blocks and matrix, with glaucophane deformed by diffusion creep accompanied by reaction-driven creep, albite by diffusion creep, and epidote by brittle fracture and incipient dislocation creep, based on degrees of internal misorientations, lattice preferred orientation (LPO) development and grain size. During deformation, shear stress must have been relatively low, which is implied by the predominance of diffusion and reaction creep as the dominant deformation mechanisms, and by the small viscosity contrast between blocks and matrix, reflected by their similarity in dominant deformation mechanism. • Epidote-blueschist rheology is guided by diffusion creep of glaucophane. • Microstructures imply low shear stress at deformation on the deep plate interface. • Diffusion creep is unlikely to accommodate stress transients on the plate interface. [ABSTRACT FROM AUTHOR]

In recent years, the sewer system in Japan is becoming obsolete. It is, therefore, necessary to reinforce or repair without stopping sewer functions by applying a suitable water stopping method. In this study, a multi-layered sewer pipe plug consisting of a protective sheet and inner and outer rubber balls is focused since it can be installed and removed at the construction site in a short time conveniently. This sewer pipe plug has several advantages dealing with various diameters compared to the conventional type. In this study, the rupture test is conducted to improve the water stopping performance. The fractured position of the protective sheet of the sewer pipe plug is investigated experimentally. It is clarified that the maximum stress around the flange portion can be reduced by decreasing the flange inner diameter. [ABSTRACT FROM AUTHOR]

Triggering of volcano seismic activity and eruptions by tides, atmosphere pressure, rainfall, and earthquakes have been in constant debate. However, there is limited evidence concerning the triggering of very‐long‐period signals (VLPs), which are closely linked to volcano conduit dynamics. Persistent and repetitive VLP event beneath the Aso volcano, historically termed long‐period tremor (LPT), manifests episodic pressurization and depressurization events in a crack‐like shallow conduit. Here we show that LPT activity display no appreciable spectral peaks associated with major diurnal/semidiurnal tidal constituents or barometric pressure. Instead, passing surface waves of ∼0.01 m/s from the 2011 Tohoku earthquake elevated LPT activity and preferentially increased the likelihood of depressurization events. We suggest that the hydrothermal reservoir near the LPT source behaves like a confined (unconfined) aquifer against short‐period (long‐period) stress. A high stress rate of ∼102 Pa/s is sufficient to enhance the permeability of the conduit plug/wall and preferentially promotes depressurization events. Plain Language Summary: At one of the most active volcanoes in Japan, Aso volcano, long‐period tremor (LPT) was first discovered in the 1930s by Prof. Sassa in Kyoto University and such LPT activity have persisted since. It offers a unique natural laboratory and controlled experiment to systematically explore how periodic loadings trigger or modulate LPT activity in a persistently degassing volcano equipped with a well‐developed hydrothermal system. After carefully considering the background noise level modulated by the local wind and meteorological condition, we find no evidence of modulation or triggering by tides, barometric pressure, or temperature. Systematic analysis of surface wave amplitudes from great earthquakes suggests a common triggering threshold (∼0.01 m/s) shared by LPT (pressure change events) in Aso and volcano‐tectonic earthquakes (brittle failure events) in some geothermal areas, supporting key processes of pressure oscillations and unclogging fractures by dynamic stress. Key Points: Repetitive very‐long‐period signals (VLP) in Aso volcano (aka long‐period tremor, LPT) do not show detectable response against major tidal constituents, barometric pressure and temperatureStrong surface waves from the 2011 Tohoku earthquake (> 0.01 m/s) preferentially modulate depressurization LPT events for several daysResponse of hydrothermal reservoir to pressure change induced by periodic loadings is likely stress‐rate dependent [ABSTRACT FROM AUTHOR]

In recent years, local downpours frequently occur in various parts of Japan, and embankments are destroyed by these downpours. Many embankments are historical products of flood control that have been reinforced as they age by raising their height. However, the structure of the river embankment was developed based on information from disasters that actually occurred, and analysis of the destruction of the structure was not considered in design. Furthermore, until now, mechanisms of levee collapse have been discussed, but they have not been fully elucidated. Therefore, in this study, embankment analysis considering difference of layer thickness was performed by using the unsaturated soil / water / air coupled element finite method analysis program (DACSAR-MP). Stress behavior in the embankment during the rise of the river water level due to rainfall was analytically expressed, and the effect of the stress was considered to analytically investigate the collapse mechanism of the river embankment. From this work, it was analytically confirmed that embankment failure mode differed depending on differences in the speed of water level rise. [ABSTRACT FROM AUTHOR]

Background. Assessment of physiological states by measuring biomarkers, such as cortisol, has significantly contributed to the monitoring of health, welfare and management of animals. Immunoreactive cortisol in hair (hC) has been used widely for deciphering 'stressful' past-events in various wild and captive animals. However, no such studies have been done in long-lived mammals. Methods. In this first exploratory study in elephants, we assessed (i) tail-hair growth rate (TGR) and (ii) hC levels in tail-hair samples from six captive Asian elephants from two zoos in Japan for comparing hC levels with zoo-keepers' records of distinct biological events over a c.0.5-2.0-year period. Tail-hair samples were cut into segments (based on monthly growth rate), pulverized or minced and a validated cortisol enzyme- immunoassay employed to measure hC levels. Results. When the hC levels of all individuals were compared with the keepers' records, a posteriori, most of the high hC levels were found to be associated with 'stressful' or distinct behavioural events such as pathological (anaemia, colic infection, skin infection, oral sores), psychosocial (reluctance in entering the enclosure, presence of a calf) and husbandry practice-related (contact trials/ space sharing) conditions, indicating that tail-hair indeed can be a potential 'retrospective' calendar of physiological health of an animal. Conclusions. Our observations open up the possibility of using the tail-hair as an alternative matrix to reconstruct the physiological history of elephants. [ABSTRACT FROM AUTHOR]

This study investigates various types of seismicity changes that occurred in several regions in and around the Tohoku District, prior to the 2011 M 9.0 Tohoku–Oki earthquake. In particular, we focus on the seismicity anomalies that were revealed not only in inland local areas but also in a wide area for several years before the 2008 M 7.2 earthquake in the inland Tohoku District. We reconsider these seismicity anomalies in nearly identical regions, which persisted in the extended period up until the M9 mega event. This suggests that the stress changes due to transient slow slips on the Pacific Plate boundary are more likely to be the cause of the wider seismicity changes than the slips beneath the inland earthquake. To confirm the significance, we use the two-stage stationary epidemic-type aftershock sequence model and explore the relationship between seismicity changes and stress rate changes due to slow slip by means of global navigation satellite system geodetic observations. [ABSTRACT FROM AUTHOR]

The characteristics of shallow low‐frequency earthquakes (LFEs) are related to stress changes on the shallow plate boundary, which are important for understanding the megathrust earthquake cycle. The 5 September 2004 off the Kii Peninsula earthquakes (MJMA = 7.1, 7.4) occurred near the Nankai trough subduction zone, off southwest Japan. Ocean bottom seismometer observations from 22 September to 30 November 2004 detected many shallow LFEs among the ordinary aftershocks. During the observation period, the frequency of shallow LFEs steadily decayed with the exception of episodic activities, which were very sensitive to stress changes caused by tides and the 23 October 2004 Niigata earthquake (MJMA = 6.8). We also confirmed correlations between shallow LFEs and shallow very low frequency earthquakes, which suggest that these slow events represent the same slip phenomenon. These findings will contribute to clarifying the impact of LFEs on megathrust earthquakes. Key Points: We detected shallow low‐frequency earthquakes (LFEs) after the 2004 off Kii Peninsula earthquakes by using ocean bottom seismometersSome shallow LFEs are associated with very low frequency earthquakes, which suggests both slow earthquakes represent the same phenomenonEpisodic shallow LFEs are stochastic yet sensitive to stress changes caused by both the 2004 Niigata earthquake and tidal effects [ABSTRACT FROM AUTHOR]

Purpose: Retrievability, connecting strength, and ease of laboratory work are important but conflictingprerequisites for the success of an implant superstructure, particularly with regard to immediate function. To resolve this issue, a telescopic magnetic attachment system has been developed for implant-supported removable dentures. The splinting effect of the attachment was evaluated for stress distribution and elevation with an in vitro model of three implants in an edentulous mandible. Materials and Methods: Two types of telescopic magnetic attachments were prepared; the inclination angles of the axial wall of the abutment were 2.5 and 6.0 degrees. Three types of three-unit superstructures-a screw-retained superstructure and two telescopic magnet-retained superstructures-were fabricated. Static loads of 24.5, 49, and 98 N were applied vertically at three loading points on one side of each occlusal table. The elevation was measured as the height at which the magnet-retained superstructure detached from the abutment (on the other side of the prosthesis). In addition, by means of strain gauges, the stress distribution around the implants was evaluated and compared among the superstructures with the same three loads applied at six different points. Results: The magnet-retained superstructure with the axial wall inclined at 2.5 degrees did not detach from the abutment. The differences in stress distribution between the screw-retained and magnet-retained superstructures with a 2.5-degree inclination were found to be statistically insignificant. The magnet-retained superstructure with a 6-degree inclination detachedfrom the abutment, and the stress was concentrated during loading to a cantilever site. Conclusion: Because of its stress distribution and elevation, the new telescopic magnetic attachment, which has properties such as splinting the implants, ease of fabrication, and retrievability, is expected to be a viable alternative for the retention of implant-supported removable dentures. [ABSTRACT FROM AUTHOR]

The three‐dimensional (3‐D) deformation field associated with the 2016 Central Tottori earthquake is retrieved from advanced land observing satellite 2 interferometric synthetic aperture radar (InSAR) observations with four different viewing geometries, that is, ascending/descending tracks and left‐/right‐looking modes. The strain model and variance component estimation (SM, VCE, SM‐VCE) method is exploited and improved to integrate the InSAR observations with different viewing geometries so that the 3‐D deformation field is not affected by the inconsistent coverage of SAR footprints or the gross errors in InSAR observations. The obtained results are consistent with GNSS observations, indicating that the improved SM‐VCE method, known as SM‐RVCE in this paper, is capable of retrieving an accurate and spatially complete 3‐D deformation field for this earthquake. In addition, the precision of the InSAR observations and the estimated 3‐D deformation are quantitatively assessed by the SM‐RVCE method. Finally, on the basis of the estimated 3‐D coseismic deformation, the source parameters of this event are inverted, revealing an asperity with a maximum strike‐parallel slip of ~1.1 m concentrated at depths between 2 and 10 km. The estimated seismic moment is 2.4 × 1018 Nm, which corresponds to a Mw 6.2 event. Key Points: We retrieve the 3‐D deformation field of the 2016 Central Tottori earthquake from left‐ and right‐looking InSAR observationsWe conduct a precision assessment for InSAR observations based on the variance component estimation (VCE) methodWe employ the robust VCE method to mitigate the effects of gross InSAR errors such as unwrapping errors on the 3‐D deformation [ABSTRACT FROM AUTHOR]

• An axial loading test of square steel-tubed reinforced UHSC columns was conducted. • The load-bearing capacity and failure mode of the specimens were investigated. • Confining stress by the steel tube and transverse reinforcement was estimated. • The size effect and confined effect of UHSC columns were discussed. Steel-tubed reinforced concrete (STRC) columns with ultra-high-strength concrete (UHSC; compressive strength greater than 120 MPa) are currently used in some super high-rise buildings in Japan and other Asian countries. To properly evaluate the seismic performance of steel-tubed reinforced ultra-high-strength concrete (STR-UHSC) columns, it is necessary to understand their behavior under axial compression. However, there are few studies on the axial behavior of square STRC columns, particularly with UHSC. Therefore, axial compression tests were conducted on four square STR-UHSC columns with the test variables being the amount of transverse reinforcement and the presence of the steel tube. The concrete compressive strength used was over 170 MPa. The test result showed that the presence of the steel tube and the amount of the transverse reinforcement had no significant effect on the load-bearing capacity but greatly improved the post-peak behavior. To discuss the influence of the size effect and confining effect on the concrete compressive strength, a database of 56 plain and reinforced concrete columns with UHSC, including four specimens of this study was constructed. A new formula was proposed to evaluate the concrete compressive strength under the size effect and confining effect based on the regression analysis of the database. The proposed formula well simulated the measured peak load with a proper amount of contributions from concrete and longitudinal reinforcement. Finally, axial load-axial strain relationships were simulated using the proposed concrete stress–strain relationship. The axial behavior of each specimen was well simulated by considering the size effect and confining effect of the steel tube as well as the transverse reinforcement on the ultimate strain. [ABSTRACT FROM AUTHOR]

The overriding lithosphere is occasionally stretched parallel to the consuming plate boundary. Such arc-parallel extension manifests itself mostly in forearc regions. Here, we report unique arc-parallel extension, which affected only the backarc regions with arc-parallel strain and stress gradients. The extension took place in the backarc regions of the northern Ryukyu and western SW Japan arcs in the Middle Miocene. The extension was evidenced by NW-SE trending normal faults in the extensional zone and paleostresses that were determined from dike orientations. To determine the age of and spatial extent of this zone, we analyzed fault-slip data from the Amakusa region, northern Ryukyu arc, where early middle Miocene intrusions allowed us to judge the magmatism to be older than the faults that affected Cretaceous and Eocene formations. The slip senses of the faults have been controversial in Amakusa. As a result, the region was found to have belonged to the extensional zone. The extensional zone is 300–400 km long and ∼100 km wide. We also found that the arc-parallel extension resulted in crustal strain with a southwestward increasing trend along the zone. The strain magnitudes showed a negative correlation with distance from the Okinawa Trough. This correlation is explained by the increasing stress magnitude toward the trough. We suggest that the stalled rift propagation of the northern Okinawa Trough caused the unique arc-parallel extension in the Middle Miocene. • Middle Miocene arc-parallel extension in the backarc regions of western Japan. • The extension followed widespread magmatism in the SW Japan and northern Ryukyu arcs. • Extensional strains in the regions had an increasing trend toward the Okinawa Trough. • No mechanism but a stress gradient though the regions account for the trend. • The gradient was caused by the stalled rift propagation in the Okinawa Trough. [ABSTRACT FROM AUTHOR]

Seismic activity and focal mechanisms are governed by the effective stress field that is a combined result of regional tectonic processes and local stress perturbation. This study investigates the regional variation in the stress field in the eastern continental margin of the Eurasian plate around the Korean Peninsula and Japanese islands using a damped stress inversion technique based on the focal mechanism solutions of regional earthquakes. The dominant compressional stress is directed ENE–WSW around the Korean Peninsula and eastern China, E–W at the central East Sea and northern and southern Japan, NW–SE at central Japan, and N–S around the northern Nankai trough. The dominant compression direction changes rapidly in the East Sea and Japanese islands, which may be due to the combined effects of tectonic loading in the subduction zones off the Japanese islands and the India-Eurasia plate boundary. The crustal stress fields around the subduction zones off the Japanese islands present characteristic depth-dependent orientations. The orientations of the largest horizontal stress components, σ H , in the subduction zones are subparallel with the plate convergence directions at shallow depths. The σ H orientations are observed to rotate clockwise with the depth owing to slab subduction and lithospheric deformation. The regional stress field around the Japanese islands was perturbed temporally by the 2011 M9.0 Tohoku-Oki megathrust earthquake. The regional stress field was recovered in a couple of years. The stress field and tectonic structures are mutually affected, causing stress field distortion and a localized mixture of earthquakes in different faulting types. [ABSTRACT FROM AUTHOR]

Temperature gradient type ESSO test is one of the most popular test methods for evaluating the brittle crack arrest toughness, $$K_{ca}$$ . However, test conditions which are specimen shape, tab plate shape, applied stress and temperature gradient affect $$K_{ca}$$ . This document reports effects of specimen geometries that are specimen width, tab plate length, tab plate thickness and tab plate width on $$K_{ca}$$ evaluation. In addition, effects of applied stress and temperature gradient have also been investigated. Temperature gradient type ESSO tests are conducted at three different steel mills in Japan. Then, test conditions were varied and test results were compared. In the result, influence range of effect specimen width, tab plate thickness, applied stress and temperature gradient were demonstrated. The applicable range of specimen geometry, applied stress and temperature gradient were clarified and implemented to the brittle crack arrest standard. [ABSTRACT FROM AUTHOR]

Repeating earthquakes, the sequence of stress accumulation and release at isolated small asperities on a plate interface, can be regarded as a renewal process in statistics. From such a point of view, we modelled a sequence of repeating earthquakes and developed an objective Bayesian method to estimate the space-time distribution of interplate slip rates from the recurrence intervals of repeating earthquakes. The space-time distribution of slip rates is represented by the superposition of tri-cubic B-splines. The knots of B-splines in time are unequally allocated for representing co-seismic abrupt and post-seismic rapid changes in slip rates. In addition, to avoid overfitting, smoothness constraints are imposed and their optimal weights are determined by Akaike's Bayesian Information Criterion. We applied this method to the complete data set of repeating earthquakes in northeast Japan for about 18 yr before the 2011 Tohoku-oki earthquake, and revealed spatiotemporal variations of interplate slip rates off the Hokkaido-Tohoku region, where the 1994 Sanriku-oki (M7.6), 2003 Tokachi-oki (M8.0), 2004 Kushiro-oki (M7.1), and 2008 Ibaraki-oki (M7.0) earthquakes occurred. First, we confirmed the reciprocal correlation between the spatial distribution of average slip rates for a seismically calm period (1996-2000) and that of average slip-deficit rates, which has been estimated from GPS array data. Then, we examined the temporal variations of slip rates associated with the large interplate earthquakes in detail. [ABSTRACT FROM AUTHOR]

Most of the seismicity in inland Kyushu, southwest Japan occur in the localized intraplate shear zones which are Beppu-Shimabara Graben (BSG) and left-lateral shear zone (LSZ). One of the largest fault systems in Japan (Median Tectonic Line—MTL), and subduction zone of the Philippine Sea Plate also exist near Kyushu. These suggest that the island arc, such as Kyushu has a complex deformation process. This study estimated the anelastic strain rate in the lower crust and the interplate coupling rate via inversion analysis using Global Navigation Satellite System data to elucidate the seismotectonics. Deformation in the lower crust and interplate coupling were modeled by cuboid volumetric sources and a back slip model, respectively. To stabilize the solution, a L2 regularization constraint was applied to the anelastic strain rate. Further, constraints on direction and smoothing to the slip deficit rate were applied. These strength of the constraints were determined via the minimum value of the Akaike Bayesian information criterion. The analyses showed that the anelastic strain rate of the BSG and LSZ was ∼0.6 ×10−6 yr−1, and BSG was related to MTL activity. The findings also suggest that this anelastic deformation in the lower crust created a stress concentration zone in the upper crust of BSG and LSZ, with a stress change rate of ∼6–10 kPa·yr−1. The value is consistent with the stress drop and recurrence interval of regional earthquakes, suggesting that the seismicity around BSG and LSZ is strongly influenced by anelastic deformation in the lower crust. It is also suggested that BSG and LSZ development is influenced by slab rollback, and a subducting ridge. Lastly, a comparison between the deviatoric stress field estimated using focal mechanisms and the anelastic strain rate suggests the existence of a shear zone consisting of weak faults south of BSG. • This study estimated the anelastic strain rate in the lower crust. • The anelastic strain rate in the lower crust of the BSG and LSZ was ∼0.6×10−6·yr−1. • Lower crust anelastic deformation creates stress concentration in the upper crust. • Plate geometry changes indirectly controls the anelastic deformation of island arc. [ABSTRACT FROM AUTHOR]

We discuss elastostatic effects on Mt. Fuji, the tallest volcano in Japan, due to historic earthquakes in Japan. The 1707 Hoei eruption, which was the most explosive historic eruption of Mt. Fuji, occurred 49 days after the Hoei earthquake (Mw 8.7) along the Nankai Trough. It was previously suggested that the Hoei earthquake induced compression of a basaltic magma reservoir and unclamping of a dike-intruded region at depth, possibly triggering magma mixing and the subsequent Plinian eruption. Here, we show that the 1707 Hoei earthquake was a special case of induced volumetric strain and normal stress changes around the magma reservoir and pathway of Mt. Fuji. The 2011 Tohoku earthquake (Mw 9), along the Japan Trench, dilated the magma reservoir. It has been proposed that dilation of a magma reservoir drives the ascent of gas bubbles with magma and further depressurization, leading to a volcanic eruption. In fact, seismicity notably increased around Mt. Fuji during the first month after the 2011 Tohoku earthquake, even when we statistically exclude aftershocks, but the small amount of strain change (< 1 μ strain) may have limited the ascent of magma. For many historic earthquakes, the magma reservoir was compressed and the magma pathway was wholly clamped. This type of interaction has little potential to mechanically trigger the deformation of a volcano. Thus, Mt. Fuji may be less susceptible to elastostatic effects because of its location relative to the sources of large tectonic earthquakes. As an exception, a possible local earthquake in the Fujikawa-kako fault zone could induce a large amount of magma reservoir dilation beneath the southern flank of Mt. Fuji. [ABSTRACT FROM AUTHOR]

SUMMARY We developed the 550-kV disconnectors that strengthened earthquake proofing by the addition of the damper unit and weight reduction of conductive part based on the damage of the 550-kV disconnectors by the Great East Japan earthquake (March 11, 2011) and inspected the earthquake proofing performance by shake table test. In shake table test, we performed the test by the artificial seismic wave that varied in phase characteristic in addition to the test by resonance method. And, in a high-level earthquake area, we analyzed it about the influence that a phase characteristic of the artificial seismic wave gave to stress to occur in disconnectors. As a result, it is thought that the stress to occur in disconnectors is decided by a primary natural frequency basically because a bending strain to occur to the disconnectors in the time when the resonance frequency ingredient becomes the big acceleration response value grows big. But, on a particular phase condition, it was confirmed that the bending strain to occur in disconnectors might grow big conspicuously. As for this, the possibility is thought about by influence of higher natural frequency doing superposition. [ABSTRACT FROM AUTHOR]

We investigated a detailed spatial distribution of principal stress axis orientations in the source area of the 2003 M6.4 Northern Miyagi Prefecture earthquake that occurred in the forearc of northeastern Japan. Aftershock hypocentres were precisely relocated by applying the double difference method to arrival time data obtained at temporary stations as well as at surrounding routine stations. We picked many P-wave polarity data from seismograms at these stations, which enabled us to obtain 312 well-determined focal mechanism solutions. Stress tensor inversions were performed by using these focal mechanism data. The results show that quite a lot of focal mechanisms are difficult to explain by the uniform stress field, especially near the large slip area of the main-shock rupture. Stress tensor inversions at the location of individual earthquakes show that σ1 axes are orientated mainly to WSW-ENE in the northern part of the source area, while they are oriented to NW-SE in the southern part. This spatial pattern is roughly similar to those of the static stress change by the main shock, which suggests that the observed spatially heterogeneous stress field was formed by the static stress change. If this is the case, the deviatoric stress magnitude before the main shock was very small. Another possibility is the heterogeneous stress field observed after the main shock had existed even before the main shock, although we do not know why it was formed. Unfavourable orientation of the main shock fault with respect to this stress field suggests that the fault is not strong in this case too. [ABSTRACT FROM AUTHOR]

Coseismic deformation depends on both the source fault and on the elastic properties of the crust. Large coseismic deformation associated with the 2011 Mw 9.0 Tohoku-oki earthquake enabled us to investigate strain anomalies from crustal inhomogeneity. Concentrated contractional strain was observed in the Echigo Plain (Niigata-Kobe Tectonic Zone) before the Tohoku-oki earthquake, whereas continuous and campaign global navigation satellite system measurements show a widespread distribution of coseismic extensional strain in and around the plain. A 1-D displacement profile shows high strain (7.2 ± 0.7 microstrain) in a 17 km long section across the Echigo Plain and low strain (3.3 ± 0.4 microstrain) along a 15 km long section east of the plain, despite the latter being closer to the megathrust fault source. We performed numerical modelling of coseismic deformation using a heterogeneous subsurface structure and successfully reproduced excess extension in the plain, which is filled by low-rigidity sediments. This study demonstrates the importance of considering heterogeneous crust in deformation modelling. [ABSTRACT FROM AUTHOR]

The stress conditions of the ductile-to-brittle regime have been assessed along the Asuke Shear Zone (ASZ), which strikes NE–SW in the Cretaceous Ryoke granite terrain in SW Japan. Along the ASZ, pseudotachylyte and mylonitized pseudotachylyte are locally developed together with cataclasite. The simultaneous operation of dislocation creep and grain-size-sensitive creep, as indicated by the coexistence of the Z-maximum and relatively random c -axis lattice preferred orientations as well as the sizes of dynamically recrystallized quartz grains (6.40–7.79 μm) in the mylonitized pseudotachylyte, suggest differential stresses of 110–130 MPa at ∼300 °C. The e -twin morphology, twinning ratio, and distribution of the glide direction on the e- twin plane of the twinned calcite in the amygdules of the pseudotachylyte suggest the stress conditions of the σ 1 and σ 3 axes trend 228° and 320° and plunge 55° and 1°, respectively, and indicate differential stresses of 40–80 MPa at 150–200 °C. Based on kinematic indicators in the fault rocks, the stress conditions estimated from calcite twins, and the cooling history of the granitic protolith, the ASZ is inferred to have been activated under a stress state that caused sinistral normal movements before and after pseudotachylyte formation at 70–50 Ma. [ABSTRACT FROM AUTHOR]

Safety countermeasures have been implemented in nuclear power plants in Japan under the new nuclear regulation. The importance of structural integrity of components which are attacked by tornado missile has been growing as one of the countermeasures. In the case of impact analysis for tornado missile, strain rate dependency needs to be considered in the stress strain relationship, which is different from static analysis. However, it is difficult to obtain the data of stress strain relationship which strain rate is over 103 s−1 due to the restriction of test equipment. Therefore, a new method to estimate strain rate dependency of stress strain relationship on the high strain rate condition was developed. An inverse analysis using the deformation data obtained by the Taylor impact test and FEM analysis was applied in the method. Stress strain relationship estimated by the method was verified by comparing it to Split Hopkinson Bar (SHB) test result. It was confirmed that the method could estimate strain rate dependency of stress strain relationship accurately. [ABSTRACT FROM AUTHOR]

We extracted tectonic crustal deformation caused by the interplate coupling between the Pacific and North American plates from GNSS time series data at land-based stations in the Tohoku district, northeastern Japan, during the period from 21 March 1996 to 7 March 2011. Next, we estimated the spatiotemporal distributions of the slip deficit rates between the two plates prior to the 2011 Tohoku-oki earthquake for the 1997–2010 period by performing time-dependent inversion analysis. As a result, two strongly coupled regions were identified. One is located off the coast of Iwate Prefecture, whose reliability may not be high, where coseismic slip of the Tohoku-oki earthquake was small, indicating that this area may be a source region for a future megathrust earthquake. The other is a region with strong and continuous interplate coupling of more than 8 cm/yr from 1997 to 2010 in and around the epicenter of the Tohoku-oki earthquake. This area coincides with the area where coseismic slip greater than 20 m was estimated. Decrease of interplate coupling by approximately 0.4 cm/yr was identified at the downdip side of the region during the period from 2003 to 2008, reaching a coupling of 1.5 cm/yr in 2008, which would yield an increase in shear stress at its shallower strongly coupled region. We also identified that in 2010, the strongly coupled region rapidly expanded in southwestern and downdip directions. These results suggest that the shear stressing rate in the strongly coupled region might be accelerated, reaching rupture strength because of these two effects, thereby causing the main shock. • Strong coupled region was identified near the epicenter of the Tohoku-oki earthquake. • Decrease in coupling at the downdip of the coupled region was found before the event. • The coupled region rapidly expanded in southern and downdip directions in 2010. • Another possible coupled region was unruptured by the event, being a possible future large event. [ABSTRACT FROM AUTHOR]

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In order to investigate the spatial distribution of the crustal stress state across NE Japan, we determined 1370 focal mechanisms by picking P-wave polarities from seismograms observed by temporary and permanent seismic networks densely deployed in this area. We applied stress tensor inversions to these data, plus to those routinely determined. The results show that the stress state in NE Japan is heterogeneous in space, which is different from previous results that showed that the NE Japan arc is characterized by margin normal compression. The orientations of the maximum compressional stress (σ1.) axes are significantly different with 95% confidence limits between the arc–backarc region and the forearc region. The arc–backarc region is characterized by spatially uniform margin normal compression. However, the north and south parts of the forearc region have the σ1 axis oriented nearly N–S and vertical, respectively. The region in between has a similar stress orientation to the arc–backarc region. Moreover, the stress regime in the arc–backarc region varies spatially in response to change in the surface altitude. Beneath regions of relatively low altitudes, a reverse faulting stress regime is dominant. However, regions of higher altitudes are characterized by a strike–slip faulting stress regime. Numerical model calculations, in which gravitational and buoyancy forces caused by topography are incorporated, show that differential stresses of about 15–25 MPa are needed to explain the lateral variation of the stress regime observed in the arc–backarc region. This suggests that the background deviatoric stress magnitude in NE Japan is very low. [ABSTRACT FROM AUTHOR]