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In this paper, a scalable end-to-end tree boosting system called XGBoost has been applied for predicting the magnitude of an earthquake from the early part of earthquake waveform data. This model uses the features extracted from the early P wave phase of the records as an input. The model's effectiveness has been verified by using data on earthquakes occurring in the Eurasian plate of Japan Islands from 1996 to 2021. Feature engineering has given 29 new features identified from the early P wave phase of the record, which show a high correlation with the magnitude of an earthquake. The comparison of predicted and actual magnitude shows that a trained XGboost model, which uses a single input record for magnitude prediction, gives an average prediction error of 0.004 ± 0.57 for earthquakes in the test dataset. In contrast, the average prediction error of –1.1 ± 0.80 and –0.65 ± 0.69 has been obtained for the magnitude estimated from conventional τc and Pd methods using the same test dataset. It is further seen that the average predicted magnitude of a single earthquake of magnitude 4.5 and 6.1 (MJMA) obtained by using multiple nearfield records using XGBoost model is 4.58 ± 0.33 and 6.32 ± 0.29, which is close to the actual magnitude of the earthquake. The results presented in this paper clearly show that the structured data can be effectively used by complex machine learning or deep learning models to predict earthquake magnitude from single or multiple records. [ABSTRACT FROM AUTHOR]

Recent geodetic measurements have detected recurrent slow slip events (SSEs) in many subduction zones. Numerical simulations suggest that the recurrence intervals and magnitudes of such SSEs decrease in the later stage of the interseismic period. Therefore, activities of SSEs and their temporal variations in recurrence intervals and magnitudes provide important clues for evaluating future large earthquakes. However, our knowledge of recurrent SSEs before the establishment of dense observation networks is limited. Here, we report a possible SSE in 1973 beneath the Kii peninsula along the Nankai subduction zone, southwest Japan, where magnitude 8 class earthquakes such as the 1944 Tonankai and 1946 Nankai earthquakes repeatedly occur. The possible SSE was detected by a horizontal pendulum tiltmeter installed in 1947 at the Kishu observatory. We recovered and converted the original tilt records from 1969 to 1974 drawn on bromide (light sensitive) papers to digital tilt records. In late-November 1973, there was a slow transient signal down to the northeast of about 1.4 μrad, lasting about 1–3 days. Assuming this crustal deformation was due to an SSE, we searched for a possible fault model by adopting the already-known SSE models occurring from 1996 to 2012 as template models. Among the 42 template fault models, five models were able to qualitatively explain the direction of the observed tilt change. The centroids of these fault models were located about 30–60 km to the west of the observatory. In the source region, two magnitude 5 class earthquakes occurred before the initiation of the transient signal, and thus may be related to the occurrence of the possible SSE. In contrast, the magnitude of the calculated tilt change was about 1–2 order smaller than that of the observed tilt change. This discrepancy could be partly explained by a slip amount larger than that in the template models, which suggests that the possible SSE in 1973 was larger than those detected by recent observations. Further investigation of historical data on crustal deformation will reveal more about the temporal change in the recurrence intervals and magnitudes of SSEs during earthquake cycles of large earthquakes. [ABSTRACT FROM AUTHOR]

A cross-region prediction model named SeisEML (an acronym for Seismological Ensemble Machine Learning) has been developed in this paper to predict the peak ground acceleration (PGA) at a given site during an earthquake. The SeisEML model consists of hybridized models, kernel-based algorithms, tree regression algorithms, and regression algorithms. The model ablation study is conducted to examine the performance and the selection of meta-machine learning models in the SeisEML. The training and testing dataset consists of 20852 and 6256 accelerograms recorded by the Kyoshin Network, Japan. The mean absolute error (MAE) and root mean square error (RMSE) have been utilized to compare the predicted peak ground acceleration (PGA) for the test data. The SeisEML model yields approximately half the MAE and RMSE values obtained with conventional attenuation relations. The SeisEML model has been used to compute Japan's iso acceleration contour map of three earthquakes ( M JMA 7.4, 6.6, and 6.1). The qualitative comparison of iso acceleration contours obtained from actual and predicted PGA using SeisEML clearly shows that the model can reliably predict the PGA distribution during an earthquake compared to the regional ground motion prediction equation (GMPE). The cross-region prediction was performed on the datasets of the Iranian earthquakes using SeisEML. The comparison of predicted and observed peak ground acceleration in terms of MAE and RMSE shows that the machine learning model's performance is superior to the regional attenuation relation. The predictions of PGA from the developed ML model indicate that this trained model has the potential for predicting regional and global scenarios with similar tectonic setups. The ML model developed in this paper can considerably enhance the reliability of PGA prediction for seismic hazard mapping of any region and can serve as a reliable substitute for GMPEs. [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]

We studied the earthquake detection capacity of DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis) operating in the Nankai Trough, a target region monitored for future megathrust earthquakes. The focus of this paper was to evaluate the impact on this capacity from the malfunction of parts of the network. For this purpose, the completeness magnitude, above which all earthquakes are considered to be detected by a seismic network, was used. Then, a catalog that includes events observed by DONET was used. We found spatiotemporal variability of completeness magnitude, ranging from values below 1 in one of the areas where stations are densely deployed to values above 2 at the periphery and outside of the DONET area. We conducted a simulation computation for cases of malfunction of densely distributed stations. The results showed that completeness estimates in the area near the malfunctioning stations were about 1 magnitude larger. This implies that malfunction repair and/or replacement with new stations would be desirable because they pronouncedly affect earthquake monitoring. We then demonstrated an example of how to use the information of completeness magnitude as prior knowledge to compute the b value of the Gutenberg-Richter distribution. The result indicates the b value as a proxy that can help to image stress heterogeneity when there is a magnitude-6 class slow slip event on the Nankai Trough plate boundary. [ABSTRACT FROM AUTHOR]

Though there is now a substantial body of research on the relationship between nonprofits and the state, examples from non-Western countries have been lacking in the nonprofit literature in English. This paper attempts to fill this gap using nonprofit cases in three key districts in Fukushima after the Great East Japan Earthquake. By focusing on these cases, this study captures the complex nature of the relationship between the nonprofit sector and state in Japan during a period of increased activity of both the nonprofit sector and the state. The idea of the nonprofit sector, state, and market as relatively separate and with different interests, influences discussions on themes related to the nonprofit sector (e.g., business-like behavior). The study suggests how the Japanese case can contribute in uncovering assumptions that are embedded in the existing understanding of the nonprofit sector, based primarily on Western examples. [ABSTRACT FROM AUTHOR]

The motivation of this study stems from a retaining wall made of waste tires. The wall did not suffer any earthquake or tsunami-induced damage during the 2011 Off the Pacific Coast of Tohoku Earthquake, Japan. This paper deals with a case study on this tire retaining wall. Results from a series of field and laboratory investigations are first described. A numerical simulation is also described in which whole tires were used as protective layers in an embankment. The results show that confining effect of each tire, friction between the tires, ductility, and damping inherent in tires contribute towards the excellent performance of the retaining wall during the earthquake loading. The case study also reveals that it is the isolation mechanism due to the vibration absorption capability of rubber particles in tires, which could protect tire retaining structure during the earthquake. [ABSTRACT FROM AUTHOR]

Shikoku island, southwestern Japan lies in the western Nankai Trough and showcases along-strike segmentation of slow earthquake behavior. Whether the spatial variation of tremor behavior reflects the regional differences in structure/source properties and how much such differences can be recognized by the seismic signals themselves are two questions addressed in this paper. Taking advantage of advanced methods in recognizing and classifying signals using machine learning approaches, we attempt to answer them by conducting signal classification experiments in Shikoku. Based on the tremor catalog from 1 June 2014 to 31 March 2015, the tremors recorded in four different areas were treated as different classes and segmented into 60-s-long signals. The number of tremors in four different areas (A to D, from west to east) reached 15,000, 31,000, 10,000, and 16,000, respectively. To efficiently distinguish between tremors from different areas, we applied a k-nearest neighbor (k-NN) classifier with Fisher's class separability criteria to select the optimal feature subset. The resulting classification performance reached more than 90% at all 12 stations. We further designed a triangle test to select the features that can better represent the differences in source properties between areas. We found that the most efficient features were associated with (1) the number of peaks in the temporal evolution of discrete Fourier transforms and (2) the energy distribution in the autocorrelation function (ACF). To match the difference in behavior revealed by the ACF, the size of the tremor zone, which mainly controls how long the seismic energy lasts in a tremor episode, was determined to be largest in Area B and smallest in Area C. The heterogeneity of the asperities in a tremor zone, which may control how spiky the tremor signals developed over time, was determined to be strong in Areas B and C. Together with previously documented variations in slow earthquake behavior in the same area, we finally propose a conceptual model that provides a better understanding of the regional differences in the tremor source properties in Shikoku, Japan. [ABSTRACT FROM AUTHOR]

Slow earthquakes are episodic slow fault slips. They form a fundamental component of interplate deformation processes, along with fast, regular earthquakes. Recent seismological and geodetic observations have revealed detailed slow earthquake activity along the Japan Trench—the subduction zone where the March 11, 2011, moment magnitude (Mw) 9.0 Tohoku-Oki earthquake occurred. In this paper, we review observational, experimental, and simulation studies on slow earthquakes along the Japan Trench and their research history. By compiling the observations of slow earthquakes (e.g., tectonic tremors, very-low-frequency earthquakes, and slow slip events) and related fault slip phenomena (e.g., small repeating earthquakes, earthquake swarms, and foreshocks of large interplate earthquakes), we present an integrated slow earthquake distribution along the Japan Trench. Slow and megathrust earthquakes are spatially complementary in distribution, and slow earthquakes sometimes trigger fast earthquakes in their vicinities. An approximately 200-km-long along-strike gap of seismic slow earthquakes (i.e., tectonic tremors and very-low-frequency earthquakes) corresponds with the huge interplate locked zone of the central Japan Trench. The Mw 9.0 Tohoku-Oki earthquake ruptured this locked zone, but the rupture terminated without propagating deep into the slow-earthquake-genic regions in the northern and southern Japan Trench. Slow earthquakes are involved in both the rupture initiation and termination processes of megathrust earthquakes in the Japan Trench. We then compared the integrated slow earthquake distribution with the crustal structure of the Japan Trench (e.g., interplate sedimentary units, subducting seamounts, petit-spot volcanoes, horst and graben structures, residual gravity, seismic velocity structure, and plate boundary reflection intensity) and described the geological environment of the slow-earthquake-genic regions (e.g., water sources, pressure–temperature conditions, and metamorphism). The integrated slow earthquake distribution enabled us to comprehensively discuss the role of slow earthquakes in the occurrence process of the Tohoku-Oki earthquake. The correspondences of the slow earthquake distribution with the crustal structure and geological environment provide insights into the slow-earthquake-genesis in the Japan Trench and imply that highly overpressured fluids are key to understanding the complex slow earthquake distribution. Furthermore, we propose that detailed monitoring of slow earthquake activity can improve the forecasts of interplate seismicity along the Japan Trench. [ABSTRACT FROM AUTHOR]

A modified k-nearest-neighbors method is introduced that provides an efficient nonlinear estimate of the intensity of a point process (field) based on locations of events. The method is applied to perform a detailed statistical analysis of the spatial structure of the seismic intensity field (in the context of this paper, the term "intensity" refers to the intensity of the seismic field, and should not be mistaken for the intensity of ground motion caused by an earthquake). The proposed method requires neither a preliminarily delineated area nor a normalization procedure for the estimates. In contrast to many interpolation methods, estimates based on the proposed method are statistically justified. The "uncertainty relation" between the spatial smoothing effect and random errors is established for the method in an explicit form. A procedure for choosing the number of nearest neighbors k* that controls the effective radius of smoothing is suggested. The proposed method is applied to analyze the seismic intensity field in two seismogenic regions surrounding the Kuril Islands and Japan during the period from 1904 to 2011. Spots of increased seismic activity in these regions are localized by the new method, and some quantitative statistical characteristics of these spots are determined and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we explore the Western Pacific subduction impact on the geodynamics of the Asian continent. The data on migration of slow strain and earthquakes from the Nankai, Japan and Kuril-Kamchatka segments of the Western Pacific subduction zone deep into mainland Asia are analyzed. The calculations performed on five profiles, crossing the Kuril Islands, the Japanese Archipelago and Sakhalin Island toward the Asian continent, have revealed the transverse migration of earthquakes from the Japan–Kuril-Kamchatka subduction zone. The velocities of hypocenter migration of M ≥ 4.5 earthquakes from the Kuril-Kamchatka Trench via northern and central Sakhalin vary from 6 to 17 km/year, on average, at different depths. The profiles crossing the islands of Hokkaido and Sakhalin show the M ≥ 4.earthquake migration from the Kuril and Japan trenches at velocities of 8–27 km/year. [ABSTRACT FROM AUTHOR]

The Kumamoto area includes 11 municipalities and a population of about one million. The area represents the largest total use of groundwater in Japan. The main recharging area for this groundwater used to be paddy fields for rice production located along the mid-stream section of the Shirakawa River. In the past few decades, the area of paddy fields has rapidly decreased due to the Japanese government's rice production adjustment policy and urbanization. In consequence, the groundwater recharge decreased from 656.2 million m3 in 1992 to 606.9 million m3 in 2006. Thus, groundwater recharge from paddy fields only might not be sufficient for groundwater demand in the future. For this reason, an artificial recharge system was established to increase groundwater recharge. In this study, we review the history of groundwater management and results of 14 years' operation of a large-scale artificial groundwater recharge project in the Kumamoto area. We visualize the resilience of the groundwater management and recharge project by influence of the 2016 Kumamoto Earthquake. It is shown that through an integrated approach of all societal groundwater stakeholders, a sustainable groundwater management can be achieved. The hydrological methods in this integrated approach quantify recharging groundwater volumes for different types of recharge fields by use of 170 local experimental observations. Results and experiences outlined in this paper can be used by planners and managers of dwindling groundwater resources to build resilient systems for groundwater recharge by involving all societal stakeholders through an integrated approach. [ABSTRACT FROM AUTHOR]

Crustal earthquakes are generally recognized as having recurrence periods of more than 1000 years. However, in northern Ibaraki Prefecture, Japan, two moderate-sized earthquakes occurred on almost the same fault plane in 2011 and 2016. Moreover, it has been reported that the slip distributions derived from crustal deformation data from these two events are almost identical. We performed a near-field waveform inversion analysis to estimate the details of the spatiotemporal distribution of the co-seismic rupture. Our results reveal large slip areas during each earthquake at different locations across the bend of the fault plane. These results indicate that the shear stress of the fault area where the main slip occurred during the 2011 event was not rebuilt in such a short period, a phenomenon that had not previously been discussed for this sequence. Our results also suggest that the fault geometry affected such complex fault ruptures. [ABSTRACT FROM AUTHOR]

In this paper, we deal with evacuation decision making of people in the disaster area. By threshold model, we discuss whether all agents decide to evacuate or not. It is reported that not all people in the affected area evacuated during the Great East Japan Earthquake. But, many evacuation simulations treat that all people evacuate. In the previous work, on the assumption that all people decide to evacuate, we dealt with the needed time to make all people evacuate if psychological conditions exist at the time of disaster. In this paper, we deal with the condition that not all people decide to evacuate and focus on contagion of evacuation decision making on real map. We found that for contagion of evacuation decision making, local neighborhood and connection of sub network is necessary. [ABSTRACT FROM AUTHOR]

This research aims to explore detailed spatial distribution characteristics, identify key factors weight, and establish an accurate susceptibility regionalization model of coseismic landslides by the Mw 6.6 Iburi, Japan, earthquake sequence of 6 September 2018. Based on the remote sensing interpretation database, 5,977 individual coseismic landslides were delineated, which occupies an area of about 15.26 km2. The relationship between eight key factors and spatial distribution of coseismic landslides were precisely analyzed by the landslide area density (LAD) and landslide point density (LPD) curves. In order to obtain the weight of eight key factors more accurately, this paper compares the similarities and differences of the two curves in the earthquakes with similar magnitude, which was included the Lushan and Jiuzhaigou earthquake in China. According to the weight of eight key factors, the improved weight of evidence method was used to produce the susceptibility regionalization map of coseismic landslides in the Iburi earthquake. The results show that the improved weight of evidence method has better precision and can provide a scientific coseismic landslides susceptibility regionalization map for disaster prevention and mitigation in the Iburi earthquake. [ABSTRACT FROM AUTHOR]

This analysis is an extension of the studies based on the space–time–magnitude domain nearest-neighborhood distances (ƞ) obtained from two successive earthquakes. We included epicentral depth as a parameter, and established a new analytical solution for seismicity clustering in the space–time–depth–magnitude domain. The proposed technique was applied to SW Japan seismic observation data for 2011–2018, and revealed that the temporal, spatial, and epicentral (T, R, E) components of the joint distribution for ƞ were prominently bimodal, indicating the presence of two, statistically distinct, earthquake populations. We used the Lomb–Scargle periodogram (LSP) to generate a power spectrum preceding the Kumamoto earthquake, and detected the periodic component of unequally spaced points for log10ƞ (logarithmic scale of ƞ). The LSP showed a dominant peak corresponding to the time period between foreshocks and aftershocks, due to the highest number of recorded ƞ observations. The technique presented in this paper can be applied globally for any time period and any seismotectonic zone preceding large earthquakes of interest. [ABSTRACT FROM AUTHOR]

Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. B Correction: Progress in Earth and Planetary Science (2023) 10:8 b https://doi.org/10.1186/s40645-023-00540-8 After publication of this article (Ikehara et al. [1]), it was brought to our attention that one of the reviewer's name in the acknowledgments of the paper is incorrect, it should be changed from Dr J.N. Prost to Dr J.N. Proust. [Extracted from the article]

This paper examines the effects of the 2012 revisions to the damage predictions of an anticipated Nankai Trough megathrust earthquake on subsequent inter-municipality migration in Japan's coastal areas. We find that an increase in predicted tsunami height—rather than anticipated seismic movements—after the 2012 revision is associated with a subsequent reduction in net migration. While the reducing effect of tsunami predictions on in-migration persisted throughout the study period, the effect on out-migration was only temporary. Moreover, working-age people are more likely to respond to tsunami risk and avoid moving to municipalities with a high tsunami risk after the revisions. [ABSTRACT FROM AUTHOR]

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The Ou Backbone Range in the Tohoku Region of Japan is bounded on its both sides by two major active fault systems: the Western Fault Zone of Kitakami Lowland in the east and the Eastern Fault Zone of Yokote Basin in the west. Although these two systems are primary active fault systems in the region, information on their long-term activity characteristics is still quite limited. Therefore, we analyzed the normalized channel steepness indexes of river valleys trending perpendicular to the range front along both flanks of the Ou Backbone Range. Our results show that the eastern flank has gentler river valleys, whereas rivers along the northwestern flank are steeper. Our field investigation shows that knickpoints in this area are mostly related to local lithologic boundaries or are check dams along the valleys, thus the river systems are likely under steady-state conditions. Hence, the steeper river valleys in northwestern Ou Backbone Range indicate a higher uplift rate of the area. Because both fault systems are primarily dip-slip reverse faults and do not have significant variations in their subsurface geometry, the faster uplift suggests that the northern segment of the Eastern Fault Zone of Yokote Basin has a higher slip rate. This is consistent with results of previous studies, and the fact that the rupture of the 1896 Rikuu earthquake, the only historical surface-rupturing event in this region, was only limited along the northern segment of this fault system. [ABSTRACT FROM AUTHOR]

The 2016 Kumamoto earthquake first occurred on April 14, 2016 with magnitude 6.5 in Kumamoto, Japan as a foreshock. Subsequently, after 28 h, an even larger earthquake occurred with magnitude 7.3 as the main shock on April 16, 2016. These earthquakes were caused by two active faults: the Futagawa and Hinagu faults. This paper proposes a landslide susceptibility calculation method that considers the geomaterial strength reduction from peak to residual state and ground motion directivity. Although there is a lack of information regarding the strength parameters of geomaterials in the slopes, a parametric analysis with various strength parameters of friction angle and cohesion was carried out. To simulate the actual landslides triggered by the 2016 Kumamoto earthquake, the best combination of friction angle and cohesion in each lithology was optimized by a proposed weighted prediction rate. Based on the calculated permanent seismic displacement, a landslide susceptibility map was produced to show the degree of susceptibility over a wide area comprising 100 km2. The proposed regional landslide susceptibility map will be valuable for estimating the locations of possible slope failures and the extent of damage, as well as for planning field reconnaissance and preventing secondary disasters immediately after earthquakes. [ABSTRACT FROM AUTHOR]

The positive relationship between trust and happiness has been demonstrated by the literature. However, it is not clear how much this relationship depends on environmental conditions. The Great East Japan Earthquake of 2011 is considered one of the most catastrophic events in human history. This disaster caused not only physical damage for Japanese people, but also perceived damage. Using individual-level panel data from Japan covering the period 2009-2012, this paper attempts to probe how the relationship between trust and happiness was influenced by the Great East Japan Earthquake by comparing the same individuals before and after the earthquake. A fixed-effects estimation showed that there is a statistically well-determined positive relationship between trust and happiness and this relationship was strengthened by disaster, especially for residents in the damaged area. We argue that social trust is a substitute for formal institutions and markets, which mitigates the effect of disaster-related shock on psychological conditions such as happiness. Therefore, a trustful society is invulnerable to a gigantic disaster. [ABSTRACT FROM AUTHOR]

Sliding of natural and artificial slopes generally occurs during or following strong earthquakes. Such sliding is greatly affected by a combination of geological conditions and earthquake loading. Earthquake-induced landslides often cause more damage to infrastructure and human lives than the earthquake itself. Pseudo-static analysis is widely implemented as one of several design methods used in engineering practice to assess the seismic stability of natural and artificial slopes. However, the most important issue of pseudo-static analysis is to select the most appropriate method for measuring seismic coefficient. In order to investigate this, back analysis was conducted for surficial slides subjected to strong ground motion during the 2004 Mid-Niigata prefecture earthquake in Japan. This paper surveyed the stochastic properties of earthquake-induced surficial slides and clearly showed that the obtained results were applicable to back analysis of shear strength and seismic coefficient. In back analysis, soil properties such as soil strength and density and sliding depth were assumed as random variables owing to their uncertainties. Seismic coefficient is also assumed to be a random variable and varies with distance from the epicenter fault line. The analysis of 4504 recorded surficial slides clearly shows a unique relationship of landslide occurrence ratio with slope angle and distance from the epicenter fault line. This study’s results enhance the calculation of the shear strength of weathered soil covering slopes and the horizontal seismic coefficient through back analysis procedure. By considering possible stochastic properties of variables, some case studies were implemented in the back analysis. [ABSTRACT FROM AUTHOR]

Sassa and others in the Disaster Prevention Research Institute (DPRI), Kyoto University, developed a series of undrained ring-shear apparatus to physically simulate landslide initiation and motion, from DPRI-3 (Sassa ) to DPRI-7 (Sassa et al., Landslides 1(1):7-19, ). The maximum undrained capacities in the DPRI series ranged from 300 to 650 kPa. Sassa and others in the International Consortium on Landslides (ICL) have developed a new series of undrained ring-shear apparatus (ICL-1and ICL-2) for two projects of the International Programme on Landslides (IPL-161 and IPL-175). Both projects are supported by the Science and Technology Research Partnership for Sustainable Development Program (SATREPS) of Japan. ICL-1 was developed to create a compact and transportable apparatus for practical use in Croatia; one set was donated to Croatia in 2012. ICL-2 was developed in 2012-2013 to simulate the initiation and motion of megaslides of more than 100 m in thickness. The successful undrained capacity of ICL-2 is 3 MPa. This apparatus was applied to simulate possible conditions for the initiation and motion of the 1792 Unzen-Mayuyama megaslide (volume, 3.4 × 10 m; maximum depth, 400 m) triggered by an earthquake. The megaslide and resulting tsunami killed about 15,000 people. The Unzen Restoration Office of the Ministry of Land, Infrastructure and Transport (MLIT) of Japan systematically collected various papers and reports and published two summary leaflets: one in English in 2002 and an extended version in Japanese in 2003. Samples were taken from the source area (for initiation) and the moving area (for motion). The hazard area was estimated by the integrated landslide simulation model LS-RAPID, using parameters obtained with the ICL-2 undrained ring-shear apparatus. The estimated hazard area agrees reasonably with the landslide moving area reported in the Ministry leaflets. [ABSTRACT FROM AUTHOR]

The paper analyzes the data of manual ionograms processing of hourly measurements of the critical frequency foF2 of the F2 ionospheric layer at the Wakkanai ionospheric vertical sounding station (Japan) in a geomagnetically quiet environment before a series of earthquakes with magnitude M > 6.0, for which the station entered the earthquake preparation zone, in order to detect possible Ionospheric Disturbances Preceding Earthquakes (IDPE), and to determine their quantitative characteristics. Detected IDPE, in the opinion of the authors, can be related to the processes of preparation of the corresponding earthquakes, i.e., to be Ionospheric Precursors of Earthquakes (IPE). [ABSTRACT FROM AUTHOR]

We calculated stress drops for 2875 small intraslab earthquakes at intermediate depths beneath Tohoku, Japan. We applied an S-coda-wave spectral ratio method to almost 900,000 event pairs. Detailed velocity values for the oceanic crust (OC) were adopted from previous observational studies. The median stress drops in the OC are about half those in the oceanic mantle (OM). The median stress drop for earthquakes in the OC decreases from depths of 70 to 120 km and increases from 120 to 170 km. Our preferred interpretation is that the rigidity in the OC decreases and then increases with depth due to combined effects of the dehydration associated with the eclogite formation and the increasing temperature with depth. These depth variations are consistent with results of a similar study beneath Hokkaido. The median stress drops in the oceanic plate beneath Tohoku are generally smaller than those beneath Hokkaido. Previous studies imaging the seismic structure at shallow depths and b-value analyses of intraslab earthquakes indicate that the near-trench region of the oceanic plate off Tohoku is more hydrated than that off Hokkaido. Taken together, these results suggest that differences in the degree of hydration of the oceanic plate in the near-trench regions could produce the different behaviors of stress drops of intermediate-depth earthquakes observed in Tohoku and Hokkaido. [ABSTRACT FROM AUTHOR]

This study explored closed-circuit television (CCTV) networks in northeastern Toyama Prefecture, Japan, as a new data source for tsunami detection following the 2024 Noto Peninsula earthquake. We analyzed CCTV footage and extracted time-series water level fluctuations at Yokoyama, Shimoiino, and Ekko. Spectral analysis of these waveforms revealed several long-period peaks (more than 100 s) in power spectral density (PSD), suggesting the presence of tsunami components. Notably, relatively large PSD peaks at approximately 5–10 min were observed at all CCTV locations in this study and at offshore wave observation points (Tanaka and Toyama). At Yokoyama, a maximum run-up of approximately 3 m was confirmed around 16:28. Although water level fluctuations at Shimoiino and Ekko were detected, identifying tsunami components proved challenging due to their small magnitude compared to other wave components. Despite these challenges, this study demonstrates the potential of CCTV networks for tsunami detection, and further research is needed to achieve real-time detection. [ABSTRACT FROM AUTHOR]

The 2007 Chuetsu Oki earthquake (M = 6.6) triggered more than one hundred slope failures in the northwest part of Niigata prefecture, Japan. A reconnaissance survey conducted by the authors revealed that although most of the failures were only a few meters deep, they still caused significant damage to roads, railways, and houses. It was also found that a vast number of shallow slides were concentrated along the coastal line of the Japan Sea, while only few, but relatively larger failures occurred in a mountainous part of the study area, which is located in a considerable distance from the earthquake's epicenter. This paper summarizes the reconnaissance observations, describes the geologic characteristics of the area covered by landslides, provides characterization of major types of the landslides, and examines the causes and mechanisms of typical failures. In addition, this paper seeks to investigate the mechanism of the Ohzumi landslide, the largest slide triggered by the Chuetsu Oki earthquake. For this purpose, a comprehensive analysis that included field investigation and laboratory testing of soils samples was performed. Results of field investigation suggested that the failure plane of the Ohzumi landslide formed in a saturated layer of sandy soil near a boundary with bedrock. Data from undrained cyclic loading triaxial compression tests indicated that the sandy material was highly susceptible to generation of high excess pore-water pressures during earthquake loading. On the basis of the obtained results and the outcome of seismic response and slope stability analyses, the authors posited an explanation on the mechanism of the Ohzumi landslide. [ABSTRACT FROM AUTHOR]

The evolution of seismo-ionospheric disturbances accompanied strong destructive earthquakes in the region of Kuril and Japan Islands on October 4, 1994, September 25, 2003, and November 15, 2006 is studied in the paper. For determination of the dynamics of spatial-temporal and amplitude parameters of disturbances in the total electron content (TEC) on the basis of the Japan network of receiving GPS stations GEONET and Korean network KGN, the method of drawing 'distance-time' diagrams and quasi-optimal algorithm of spatial-temporal processing of the GPS network data was used. The ionospheric response was detected at a distance D from the epicenter up 2500 km. The maximal value of the disturbance amplitude is observed at D = 400-600 km. For the September 25, 2003 and November 15, 2006 earthquakes, the velocity V of propagation of the dominant disturbance mode is independent of the distance and equal to 850 and 1100 m/s, respectively. At a distance D ∼ 600 km, the wave disturbance from the main shock of the October 4, 1994 earthquake is split into two modes: the velocity of the 'fast mode' of the disturbance increases with distance from 1500 to 2400 m/s, while the velocity of the 'slow mode' V = 600 m/s does not depend on D. Possible interpretation of the obtained results is given. [ABSTRACT FROM AUTHOR]

Dense strong motion observation networks provided us with valuable data for studying strong motion generation from large earthquakes. From kinematic waveform inversion of seismic data, the slip distribution on the fault surface of large earthquakes is known to be spatially heterogeneous. Because heterogeneities in the slip and stress drop distributions control the generation of near-source ground motion, it is important to characterize these heterogeneities for past earthquakes in constructing a source model for reliable prediction of strong ground motion. The stress changes during large earthquakes on the faults recently occurring in Japan are estimated from the detailed slip models obtained by the kinematic waveform inversion. The stress drops on and off asperities are summarized on the basis of the stress change distributions obtained here. In this paper, we define the asperity to be a rectangular area whose slip is 1.5 or more times larger than the average slip over the fault according to the previous study for inland crustal earthquakes. The average static stress drops on the asperities of the earthquakes studied here are in the range 6-23 MPa, whereas those off the asperities are below 3 MPa. We compiled the stress drop on the asperities together with a data set from previous studies of other inland earthquakes in Japan and elsewhere. The static stress drop on the asperity depends on its depth, and we obtained an empirical relationship between the static stress drop and the asperity's depth. Moreover, surface-breaking asperities seemed to have smaller stress drops than buried asperities. Simple ground motion simulations using the characterized asperity source models reveal that deep asperities generate larger ground motion than shallow asperities, because of the different stress drops of the asperities. These characteristics can be used for advanced source modeling in strong ground motion prediction for inland crustal earthquakes. [ABSTRACT FROM AUTHOR]

new method for wave propagation modeling is introduced in this paper. By using the constraint optimization (Lagrange multiplier) method, the sum of weighted squared Fourier amplitudes is minimized when subjected to a constraint. The sum of the maximum amplitudes obtained from all output models is normalized to unity and is taken as a constraint. In this method, all the actual time histories are considered as outputs and dealt with equally. Independently of the combinations of time histories (or the first time history selected) during the analysis, the method captures the relationship of actual time histories by showing clear peaks. This paper describes the formulation of the models and illustrates the advantage of this method over the normalized input-output minimization (NIOM) method. The Mod-NIOM is then used to analyze the time histories of the Hyogoken-nanbu earthquake recorded at the Port Island vertical array site in Kobe, which suffered from liquefaction caused by the strong motions during the main shock. This method showed good correlations between the observed time histories at the site even though the surface time history was greatly modified by the liquefaction. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various articles within the issue on topics including greenhouse gas emission reduction assessment tools and reduction strategies; forests and their role in providing global goods; and damage from Great Japan Earthquake and Tsunami.

A method which we developed for spatio-temporal data processing is employed to yield the source coordinates of the September 25, 2003 Hokkaido earthquake (magnitude 8.3), the switch-on time, and the propagation velocity of the earthquake-induced ionospheric disturbance. Distribution of total electron content (TEC) variations obtained from the GPS sites located in the near-field area of the earthquake epicenter is used for the data analysis. Parameters calculated in this paper are in good agreement with the real location of the earthquake epicenter, the real shock time (seismic data), and the results obtained earlier for ionospheric disturbances due to strong earthquakes. [ABSTRACT FROM AUTHOR]

On October 21, 2016, an earthquake with Japan Meteorological Agency (JMA) magnitude 6.6 hit the central part of Tottori Prefecture, Japan. This paper demonstrates two notable effects of the surface geology on strong ground motions due to the earthquake. One is a predominant period issue observed over a large area. A seismic intensity of 6 lower on the JMA scale was registered at three sites in the disaster area. However, the peak ground acceleration ranged from 0.3 to 1.4 G at the three sites because of the varying peak periods of observed strong ground motions. The spectral properties of the observations also reflect the damage around the sites. Three-component microtremors were observed in the area; the predominant ground period distributions based on horizontal to vertical spectral ratios were provided by the authors. The peak periods of the strong motion records agree well with predominant periods estimated from microtremor observations at a rather hard site; however, the predominant periods of the microtremors are slightly shorter than those of the main shock at the other two soft sites. We checked the nonlinear effect at the sites by comparing the site responses to small events and the main shock. The peak periods of the main shock were longer than those of the weak motions at the sites. This phenomenon indicates a nonlinear site effect due to large ground motions caused by the main shock. A horizontal component of the accelerogram showed rather pulsating swings that indicate cyclic mobility behavior, especially at a site close to a pond shore; ground subsidence of ~20 cm was observed around the site. The peak periods of weak motions agree well with those of the microtremor observations. This implies an important issue that the predominant periods estimated by microtremors are not sufficient to estimate the effect of surface geology for disaster mitigation. We have to estimate the predominant periods under large ground motions considering the nonlinear site response of soft sediment sites. [ABSTRACT FROM AUTHOR]

The Noto region in Japan has been experiencing earthquake swarm activity since mid-2018, with repeated rises and falls in activity. Crustal deformation (expansion and uplift) observed there since the end of 2020 has been connected to crustal fluids. Studies in other regions have suggested that tides are related to earthquake swarm activities associated with crustal fluids. Therefore, we investigated whether tides are also involved in the Noto earthquake swarm activity. Our results suggest a tidal correlation only at greater depths in the southern part of the analyzed area ('region Sd'). There, we inferred that an increase in pore fluid pressure caused by the inflow of deep fluids may have led to a decrease in fault fracture strength, making the local seismicity relatively susceptible to the effects of tidal forces. The significantly high value in region Sd of the scaling parameter b of the Gutenberg–Richter law (describing the earthquake magnitude–frequency distribution) and observed crustal deformation are consistent with this interpretation. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via the original article. [ABSTRACT FROM AUTHOR]

To create effective risk mitigation policies and improve risk communications, it is important to understand how individuals perceive ambiguity about certain risks. A significant number of studies have demonstrated that an individual's behavior is sensitive to ambiguity. Therefore, this study explores how Japanese homeowners perceive ambiguity about earthquake and house destruction risks by focusing on two research questions: (1) To what degree do people perceive ambiguity? and (2) What are the factors that affect the degree of perceived ambiguity? We administered a survey to 1200 homeowners in Japan. Respondents were asked to state their subjective probabilities and ambiguities about earthquake and house destruction risks. Next, we examined the socioeconomic characteristics affecting their perceived ambiguities by applying a sample selection model. The findings reveal four aspects related to ambiguity. First, some homeowners perceived considerable ambiguity, while the majority observed small degrees of it. Second, on average, homeowners perceived less ambiguity about house destruction risk compared to earthquake risk. Third, socioeconomic characteristics and house attributes had an effect on the perception of ambiguity. Finally, from the perspective of creating policies that mitigate house destruction risks due to earthquakes, seismic diagnoses can help correct subjective risks and reduce the perceived ambiguity regarding them. [ABSTRACT FROM AUTHOR]

Over the past years, many scholars emphasized the importance of maintaining social relations which were built before disasters into temporary housing communities. However, reality is that most of the temporary housing complexes need to develop newly community relations due to the difficulties of maintaining community ties built before disasters. This paper attempts to find community management issues in newly developed temporary housing communities and argues solutions to the issues of constructing social capital. Key findings from this study are summarized as follows: From bonding aspect, the challenges of community management in temporary housing are leadership, ownership, and participation. One of the suggestions to solve these challenges is to employ community organizers, and a union of existing neighborhood associations is supposed to be the community organizer. From bridging aspect, information sharing among presidents of the neighborhood association in temporary housing was effective for the improvement of community management in the neighborhood associations. If this information sharing is run by an external organization, the external organization can be a bridging organization to make weak ties among neighborhood associations, which overcomes negative impacts of social capital. From linking aspect, particularly housing reconstruction is a big concern for residents in temporary housing and gives impact to community management, and therefore, linking information on housing reconstruction process to management of neighborhood associations in temporary housing is significant. To foster three categories of social capital in temporary housing, key is a bridging organization as an external organization, which functions to link among neighborhood associations and neighborhood associations to external resources. [ABSTRACT FROM AUTHOR]

Among the schemes for earthquake forecasting, the search for semi-periodicity during large earthquakes in a given seismogenic region plays an important role. When considering earthquake forecasts based on semi-periodic sequence identification, the Bayesian formalism is a useful tool for: (1) assessing how well a given earthquake satisfies a previously made forecast; (2) re-evaluating the semi-periodic sequence probability; and (3) testing other prior estimations of the sequence probability. A comparison of Bayesian estimates with updated estimates of semi-periodic sequences that incorporate new data not used in the original estimates shows extremely good agreement, indicating that: (1) the probability that a semi-periodic sequence is not due to chance is an appropriate estimate for the prior sequence probability estimate; and (2) the Bayesian formalism does a very good job of estimating corrected semi-periodicity probabilities, using slightly less data than that used for updated estimates. The Bayesian approach is exemplified explicitly by its application to the Parkfield semi-periodic forecast, and results are given for its application to other forecasts in Japan and Venezuela. [ABSTRACT FROM AUTHOR]

This paper reports results from the first-ever simultaneous measurements of the volumetric activities of radon and thoron in subsoil gas and in the near-surface air. These measurements were in progress during the precursory period and occurrence of the March 11, 2011 disastrous earthquake in Japan at a distance of 2000 km from the observation site. The earthquake was preceded by an anomalous increases in radon and thoron activity in the subsoil gas, and afterwards in the air, 44.7 days prior to the earthquake. The anomalous values persisted for 24.9 days. We discuss the features and causes of these increases. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the distribution of earthquake magnitudes for the period 1990-1998 in a broad area surrounding the epicenter of the 1995 Kobe earthquake. The frequency-magnitude distribution analysis is performed in a nonextensive statistical physics context. The nonextensive parameter q, which is related to the frequency-magnitude distribution, reflects the existence of long-range correlations and is used as an index of the physical state of the studied area. Examination of the possible variations of q values is performed during the period 1990-1998. A significant increase of q occurs some months before the strong earthquake on April 9, 1994 indicating the start of a preparation phase prior to the Kobe earthquake. It should be noted that this increase coincides with the occurrence of six seismic events. Each of these events had a magnitude M = 4.1. The evolution of seismicity along with the increase of q indicate the system's transition away from equilibrium and its preparation for energy release. It seems that the variations of q values reflect rather well the physical evolution towards the 1995 Kobe earthquake. [ABSTRACT FROM AUTHOR]

The seismic catastrophe in Japan was forecasted far ahead of time by scientists from the Russian Academy of Sciences. The most reliable forecast was made by A.A. Lyubushin, a leading researcher at the Schmidt Institute of Physics of the Earth. Over the 2008-2010 period, at a number of the most important international conferences, including that of the Seismological Society of Japan, Lyubushin warned that an earthquake with a magnitude of 8.5-9.0 could occur in Japan; it was published in English in leading scientific journals all over the world. On April 26, 2010, Lyubushin officially informed the Russian Advisory Council on Earthquake Prediction and Seismic Hazard Assessment of his forecast. One distinctive feature of this forecast is that it is based on large bodies of data on microseismic oscillations for the territory of Japan, which were mathematically treated using present-day methods. This forecast has a reliable physical justification and a visual interpretation. Brief information on the results of other Russian studies on the precursors of the main shock and aftershocks of the earthquake of March 11, 2011, in Japan is given. [ABSTRACT FROM AUTHOR]

Volcanic earthquakes provide essential information for evaluating volcanic activity. Because volcanic earthquakes are often characterized by swarm-like features, conventional methods using manual picking require considerable time to construct seismic catalogs. In this study, using a machine learning framework and a trained model from a volcanic earthquake catalog, we obtained a detailed picture of volcanic earthquakes during the past 12 years at the Kirishima volcano, southwestern Japan. We detected ~ 6.2 times as many earthquakes as a conventional seismic catalog and obtained a high-resolution hypocenter distribution through waveform correlation analysis. Earthquake clusters were estimated below the craters, where magmatic or phreatic eruptions occurred in recent years. Increases in seismic activities, b values, and the number low-frequency earthquakes were detected before the eruptions. The process can be conducted in real time, and monitoring volcanic earthquakes through machine learning methods contributes to understanding the changes in volcanic activity and improving eruption predictions. [ABSTRACT FROM AUTHOR]

We quantify the fiscal impacts of earthquakes in Japan. In contrast with earlier research which examined national level aggregate spending in several countries, we are able to provide a detailed examination of separate budget categories within the local governments' fiscal accounts. We do this using detailed line-budget expenditure data, and by comparing regions and towns affected and unaffected by the damage from earthquakes. Besides the obvious - that government spending increases in the short-term (one year) after a disaster event - we observe that the share of public spending on disaster relief, at the prefecture level, increases significantly, but with no corresponding change in the other budget lines. In contrast, at the lower administrative units, we observe a decrease in the share of spending going to finance other priorities. For the bigger cities, we observe a decrease in the share of spending targeting education, while for the smaller towns, we find that spending on construction and servicing public debt goes down. This evidence suggests that while at the prefecture level fiscal policy-making is robust enough to prevent presumably unwanted declines in public services, the same cannot be said for the city/town level. [ABSTRACT FROM AUTHOR]

We discuss the problem of the ambiguity of gravity inversion, i.e., finding the depth distribution of density and the depth and frequency dependences of the Q-factor from the entire set of the present-day seismic and astrometric data on the travel times of seismic waves, the periods and attenuation factors of the free oscillations of the Earth, as well as the amplitudes and phases of the forced nutations. In the first part of the paper, we present the new and more accurate determinations of the periods and Q-factors for the fundamental tones and overtones of the spheroidal and toroidal oscillations of the Earth, which have periods longer than 3 min. These determinations are based on analyzing the signals from the Sumatra, Tohoku, and Okhotsk earthquakes of magnitude 9, which were recorded by the stations of the Global Seismographic Network (GSN) in Obninsk and Kazakhstan. It is shown that, although the Okhotsk earthquake had a lower magnitude than the other quakes analyzed (since its seismic source was extremely deep (about 600 km)), the amplitudes of the overtones excited by this event are significantly higher than the amplitudes of the overtones caused by the Sumatra and Tohoku events of magnitude 9. Moreover, the amplitudes of the overtones from the Okhotsk earthquake exceed the amplitudes of the overtones of the free oscillations caused by the other seismic events of magnitude 9 that occurred in the second half of the 20th century. Due to this, the data on the Okhotsk Sea earthquake are of utmost importance for the solution of the inverse problems of reconstructing the vertical profiles of Q-factor in the ultra-low frequency (ULF) range and for reconstructing the vertical distribution of density. Based on the new empirical data, we obtained new and more accurate estimates for the periods and attenuation factors of the free oscillations of the Earth. [ABSTRACT FROM AUTHOR]

A large number of debris flows occurred in the Wenchuan earthquake zone after the 12 May 2008 earthquake. The risks posed by these debris flows were rather high. An appropriate model is required to predict the possible runout distance and impacted area. This paper describes a study on the runout characteristics of the debris flows that occurred in the Wenchuan earthquake zone over the past four years. A total of 120 debris flows are analyzed. Separate multivariate regression models are established for the runout distances of hill-slope debris flows and channelized debris flows. The control variables include type of debris flow, debris flow volume, and elevation difference. Comparison of the debris flows occurring before and after the earthquake shows that the runout distance increased after the earthquake due to sufficient material supply and increased mobility of the source materials. In addition, the runout distances of annual debris flow events in 2008, 2010 and 2011 are analyzed and compared. There is a tendency that the runout distance decreases over time due to the decreasing source material volume and possible changes of debris flow type. Comparison between the debris flows in the earthquake zone and the debris flows in Swiss Alps, Canada, Austria, and Japan shows that the former have a smaller mobility. [ABSTRACT FROM AUTHOR]

The question posed in this paper is whether the triple disaster of 3/11 constitutes a 'critical juncture' in Japan. We can point to minor discontinuities in Japanese policies, institutions, and identity caused by the earthquake, tsunami, and nuclear plant meltdown that eventuated on March 11, 2011, but in the year following the event there was no evidence of a critical change. The disaster and post-disaster situation in Japan are summarized, and an explanation for the lack of critical change in nuclear policy-an area where change might have been expected in view of the fact that European countries reacted to 3/11 with critical changes in nuclear energy policy-is sought by comparing the ability of mainstream theories of Japanese politics to explain the situation. [ABSTRACT FROM AUTHOR]

The idea of predicting earthquakes by continuously monitoring temporal variations in the tidal response of the medium was suggested by Beaumont and Berger in 1974. However, it became possible to implement the idea only recently. This possibility has arisen due to the deployment of Global Seismic Network (GSN), which collects the data on tidal tilts and gravity in the epicenters of strong earthquakes before and after the strongest events. In this paper, we present the results of model analytical and numerical calculations of the elastic displacements of the Earth's surface caused by the earthquakes and their preparatory processes. The analytical calculations are limited to the model of a uniform elastic halfspace; the numerical calculations, in addition to this model, also cover the models with radially heterogeneous distributions of elastic moduli in the crust and in the upper mantle, which are determined by the PREM model. We describe the results of modeling temporal variations in the tidal response of the medium in the vicinity of the source of a catastrophic earthquake. The model of seismic source is specified by the length and the orientations of the fault plane and by the value of the discontinuity in the tangential component of the displacement vector on the opposite sides of the fault. The model is based on the GPS data on the horizontal and vertical displacements of the Earth's surface. We suggest the method for determining temporal changes in the tidal response of the medium in the seismically active regions. This method improves the sensitivity and time resolution of the standard techniques of sliding-window analysis by more than an order of magnitude. The comparative analysis of temporal variations in the tidal response of the medium in the zones of the magnitude 9 earthquake in Japan (March 9, 2011) illustrates the described approach. [ABSTRACT FROM AUTHOR]

On March 11, 2011, a large earthquake and subsequent tsunami near the east coast of Japan destroyed the Fukushima Daiichi nuclear power plant (FD-NPP), causing a massive release of nuclear contaminants. In this paper, a Pacific basin-wide physical dispersion model is developed and used to investigate the transport of nuclear contaminants. The Pacific circulation model, based on the Regional Ocean Modeling System (ROMS), is forced with air-sea flux climatology derived from COADS (the Comprehensive Ocean-Atmosphere Data Set). It is shown that ocean current dominates nuclear contaminant transport. Following the Kuroshio Extension and North Pacific Current, nuclear contaminants at the surface will move eastward in the Pacific as far as 140°W, thereafter dividing into two branches. For the south branch, nuclear contaminants will be transported westward by the equatorial current, and can reach the Philippines after 10 years' time. In contrast, the north branch will arrive at the American west coast and then migrate to the Bering Sea. At 200 m water depth, part of the nuclear materials will move southwestward along with deep ocean circulation, which could potentially reach the east coast of Taiwan. The other part will move to the west coast of America and separate into two branches. One will move northward along the west coast of Alaska, while the other will travel southward to the Hawaiian Islands. The transport of radiation contaminants below 500 m is slow, and will primarily remain in the central Pacific. The physical dispersion model results show that high concentrations of the radioactive isotope cesium-137 (Cs) will move eastward and reach the central Pacific and west coast of North America in two and eight years, respectively. The sea areas influenced by the nuclear contaminants continue to expand, while peak concentrations decrease in the North Pacific. [ABSTRACT FROM AUTHOR]