Search

Upon heating, ultrastable glassy films transform into liquids via a propagating equilibration front, resembling the heterogeneous melting of crystals. A microscopic understanding of this robust phenomenology is, however, lacking because experimental resolution is limited. We simulate the heterogeneous transformation kinetics of ultrastable configurations prepared using the swap Monte Carlo algorithm, thus allowing a direct comparison with experiments. We resolve the liquid–glass interface both in space and in time as well as the underlying particle motion responsible for its propagation. We perform a detailed statistical analysis of the interface geometry and kinetics over a broad range of temperatures. We show that the dynamic heterogeneity of the bulk liquid is passed on to the front that propagates heterogeneously in space and intermittently in time. This observation allows us to relate the averaged front velocity to the equilibrium diffusion coefficient of the liquid. We suggest that an experimental characterization of the interface geometry during the heterogeneous devitrification of ultrastable glassy films could provide direct experimental access to the long-sought characteristic length scale of dynamic heterogeneity in bulk supercooled liquids. [ABSTRACT FROM AUTHOR]

An innovative concept of metabarrier is presented for seismic Rayleigh wave attenuation, which consists of a periodic array of cylindrical water tanks acting as resonant units above the soil surface. A pertinent theoretical framework is developed and implemented in COMSOL Multiphysics. The framework treats the dynamics of the water tank by a well-established three-dimensional linear, pressure-based model for fluid-structure interaction under earthquake excitation, accounting for the flexibility of the tank wall; furthermore, the soil is idealized as a homogeneous and isotropic medium. Floquet-Bloch dispersion analysis of the unit cell demonstrates the presence of relevant band gaps in the low-frequency range below 20 Hz and in the higher frequency range as well. The dispersion analysis is validated by comparison with the frequency-domain analysis of a soil domain with a finite array of water tanks. The band gaps are of interest to attenuate seismic Rayleigh waves and, more generally, Rayleigh waves caused by other ground vibration sources such as road or railway traffic. The water-tank resonant units are readily tunable by varying the water level, which allows changing opening frequencies/widths of the wave attenuation zones. This is a remarkable advantage over alternative seismic metamaterials that, in general, are not designed to be tunable. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

Recently, Egypt had seismic activity. These seismic events have affected the stability of minarets, especially historical ones. Weight is one of the minaret's main stability factors. The main objective of the current research is to perform a three-dimensional (3D) assessment of an existing minaret, determine its accurate spatial model, document its current condition, examine its stability in the event of earthquakes, and identify the requisite measures to safeguard the minaret from any potential damage. The masonry to construct the minaret was used by extracting and examining specimens of this substance to determine its physical characteristics. The current work created three-dimensional models of the Abou-Ghanam El-Bialy minaret using a terrestrial laser scanner (TLS) to document its current condition, as well as minaret was subjected to a free vibration analysis using 3D finite element modeling. Finally, the minaret's seismic behavior was assessed utilizing mode forms, base responses, and normal stresses. The surveying method effectively documented the Minarets' existing case. The 3D seismic analysis showed that the minaret responded dynamically to earthquake loading, with mode shapes, base reactions, and normal stresses being crucial characteristics. Based on these data, we may suggest procedures to protect the minaret during seismic events. [ABSTRACT FROM AUTHOR]

The warming climate in high-latitude permafrost regions is leading to permafrost degradation. Estimating seismic wave velocities in permafrost could help predict the geomechanical properties of permafrost and provide information to plan and design resilient civil infrastructure in cold regions. This paper evaluates the performance of seven models when predicting the seismic wave velocities of permafrost statistically; these models are the time-average, Zimmerman and King, Minshull et al., weighted equation, three-phase, Biot–Gassmann theory modified by Lee (BGTL), and Dou et al. models. The data used in the evaluation are from published laboratory and in situ data, which includes 369 data points for joint P and S wave velocities from nine publications and 943 unfrozen water content data points from 12 publications. The unfrozen water content that is used in these models is determined from a modified Dall'Amico's model that is proposed, which is evaluated against six existing unfrozen water content models based on soil temperature. This paper finds that saturated nonsaline permafrost generally shares similar linear trends between the P and S wave velocities, regardless of soil type, porosity, grain size, and temperature. Fitting all existing data, an empirical linear relationship is derived between the P and S wave velocities. Among the seven models evaluated, the Minshull et al. and BGTL models are the most accurate when predicting the seismic velocities of permafrost. Practical Applications: Unfrozen water content and seismic wave velocity models are valuable tools for quantitatively predicting permafrost dynamics and degradation, with practical applications in various engineering areas with permafrost environments. As permafrost thaws due to rising temperatures, these models could be used to guide the quantitative interpretation of geophysical changes in subsurface conditions, assess the potential for ground instability, and predict future permafrost degradation. Unfrozen water content models are used to predict the percentage of unfrozen water within permafrost, which links the changes with permafrost temperature. Unfrozen water content models of permafrost are essential when assessing permafrost thaw, thermal performance, heat transfer processes in permafrost, and the effect of civil infrastructure on permafrost (Chen et al.,). The seismic wave velocity models could help engineers assess the subsurface conditions in permafrost areas; this assessment is crucial for environmental and seismic monitoring, land use planning, infrastructure design and construction, and natural resources exploration. [ABSTRACT FROM AUTHOR]

Understanding the distribution of shear wave velocity (VS) in hydrocarbon reservoirs is a crucial concern in reservoir geophysics. This geophysical parameter is utilized for reservoir characterization, calculating elastic properties, assessing fractures, and evaluating reservoir quality. Unfortunately, not all wells have available VS data due to the expensive nature of its measurements. Hence, it is crucial to calculate this parameter using other relevant features. Therefore, over the past few decades, numerous techniques have been introduced to calculate the VS data using petrophysical logs in wells with limited information. Unfortunately, the majority of these methods have a drawback they only offer insight into the location of the wells and do not provide any details regarding the distribution of VS in the space between the wells. In this article, we employed three-dimensional post-stack seismic attributes and well-logging data integration to predict the distribution of VS in the Asmari formation in an Iranian oil field. To accomplish this objective, the model-based seismic inversion algorithm was utilized to convert the seismic section into the acoustic impedance (AI) section. Then, AI and seismic data were utilized in the cross-validation method to determine the relevant attributes for predicting the spatial distribution of VS throughout the entire reservoir area, using an artificial neural network. The proposed method was shown to provide 94% correlation and 109 m/s error between the actual and estimated VS. Also, the calculated VS section has a high correlation with the actual logs at the location of the wells. [ABSTRACT FROM AUTHOR]

Thermochemical inhomogeneities in the Earth's outer core that enhance our understanding of the geodynamo have been elusive. Seismic constraints on such inhomogeneities would provide clues on the amount and distribution of light elements in the core apart from iron and nickel. Here, we present evidence for a low-velocity volume within the outer core via the global coda correlation wavefield. Several key correlogram features with a unique sensitivity to the liquid core show variations with wave paths remarkably slower in the equatorial than polar planes. We constrain a torus structure at low latitudes with ~2% lower velocity than the surrounding liquid outer core via waveform modeling. We propose a thermochemical origin for such a low-velocity torus, providing important constraints on the dynamical processes of the Earth's outer core. [ABSTRACT FROM AUTHOR]

Severe storms produce ocean waves with periods of 18–26 s, corresponding to wavelengths 500–1,055 m. These waves radiate globally as swell, generating microseisms and affecting coastal areas. Despite their significance, long waves often elude detection by existing remote sensing systems when their height is below 0.2 m. The new Surface Water Ocean Topography (SWOT) satellite offers a breakthrough by resolving these waves in global sea level measurements. Here we show that SWOT can detect 25‐s waves with heights as low as 3 cm, and resolves period and direction better than in situ buoys. SWOT provides detailed maps of wave height, wavelength, and direction across ocean basins. These measurements unveil intricate spatial patterns, shedding light on wave generation in storms, currents that influence propagation, and refraction, diffraction and reflection in shallow regions. Notably, the magnitude of reflections exceeds previous expectations, illustrating SWOT's transformative impact. Plain Language Summary: Wind storms at sea make waves that increase in size with wind speed, and with the distance over which the high winds have been able to amplify the waves. Once generated these waves propagate as swell around the world ocean: in that stage the wave period remains constant while the wave height decay away from the source. Waves with periods longer than 18 s are relatively infrequent, but they are an important source of seismic waves and coastal impacts. However, current remote sensing techniques miss long waves under 0.2 m high. The Surface Water Ocean Topography (SWOT) satellite mission changes this, spotting 25‐s waves with heights as low as 3 cm. SWOT maps wave height, wavelength, and direction worldwide, revealing the influence of winds, currents and water depth. For example, We found stronger than expected coastal reflection, which will help revise wave forecasting models and their application in seismology. Key Points: Surface Water Ocean Topography (SWOT) data provide the first open ocean spatial measurements of phase‐resolved swells with wavelength 500–1,050 mSwells with heights as low as 3 cm are well detected by SWOT, allowing tracking across oceansSwell reflection off the coast can be separated from incident waves [ABSTRACT FROM AUTHOR]

As one of the main seismic imaging methods, conventional reverse time migration (RTM) may not produce high-quality images in areas with non-flat surfaces and anisotropy because the complex surfaces have a great impact on seismic wave simulation, resulting in strong scattering waves. In addition, in isotropic acoustic (ISO) RTM, the neglection of the anisotropic effects will lead to incorrect travel times during source and receiver wavefield extrapolation. To overcome these problems, we develop a topographic pseudo-acoustic vertical transverse isotropic (VTI) RTM algorithm based on the body-fitted grid. In this method, we first derive anisotropic pseudo-acoustic wave equations in the curvilinear coordinate system. Then, the Lebedev grid finite-difference scheme is used to update these equations to simulate wavefields. Finally, we use the source-normalized cross-correlation imaging condition to realize RTM. Numerical tests are performed to evaluate the feasibility and applicability of the proposed method. The imaging results show that the proposed method can remove the effect of surface topography and anisotropy on seismic wave propagation and improve migration imaging precision. [ABSTRACT FROM AUTHOR]

Earthquakes begin with abrupt shifts along the faults. These movements release seismic waves that propagate through the Earth, shaking the ground as a result of the stored “elastic strain” energy being released. Property loss and human deaths occur due to improper design of structures under the earthquake loading conditions. It is observed that Peninsular India witnessed steady-to-serious earthquakes in the last 50 years. Amaravati is the prospective capital city of Andhra Pradesh State, which is situated on the Coromandel Coast of Peninsular India. The upcoming capital city, Amaravati, requires an earthquake hazard analysis because important engineering structures and infrastructure systems will be constructed in the near future. In this study, a probabilistic approach is used to assess the earthquake hazard for Amaravati City (latitudes: 16∘24′36′′–16∘35′24′′N and longitudes: 80∘24′25′′–80∘36′18′′E), India. The seismic risks of Amaravati City presented in terms of the configuration of ground motion parameters, peak ground acceleration (PGA), and spectral response acceleration (Sa) at 0.05s and 1s for 2% and 10% Risks of Exceedance in 50 years, are produced. The uncertainties involved in seismic risk prediction are accounted for by selecting different attenuation relations developed for globally shallow crustal intraplate earthquakes with a logic tree approach. Additionally, the seismic risk values are disaggregated for Amaravati City (16∘31′37′′N and 80∘29′46′′E) to understand the individual contributions of seismic sources in terms of earthquake magnitude and site distance. The uniform hazard spectra are developed for the important places of the Amaravati Capital City and are compared with the Indian seismic code [IS 1893 (Part 1): Criteria for earthquake-resistant design of structures — Part 1: General provisions and buildings] for the rocky site. It is found that the estimated PGA values for Amaravati City are higher than the values recommended by IS 1893 (Part 1) for the rocky site. The results of this study will be very helpful for the composition of earthquake-resistant infrastructures in Amaravati City. [ABSTRACT FROM AUTHOR]

Seismic wave forward modelling is a crucial method for studying the propagation characteristics of seismic waves in subsurface media and is a key component of full waveform inversion. Compared to time‐domain forward modelling, frequency‐domain forward modelling offers advantages such as not being constrained by stability limits and reducing the dimension of the solution space. However, forward algorithms based on the rotation coordinate system in the frequency domain cannot adapt to situations with unequal spatial sampling intervals. To enhance the adaptability of the forward modelling algorithm in the frequency domain, we derived a 21‐point finite‐difference scheme based on the average derivative method and calculated the difference coefficients and dispersion conditions. Additionally, to address the significant computational cost in frequency domain forward modelling, we developed an improved 25‐point finite‐difference scheme. The improved 25‐point format is more accurate than the conventional 25‐point format. Building on this foundation, we applied the two derived differential schemes to full waveform inversion to synthesize the shot records of the inversion data. Additionally, we introduced a frequency compensation factor into the gradient processing, which effectively compensates for the deep layer while suppressing noise in the shallow gradient field. Finally, we demonstrated the effectiveness of our approach through a full waveform inversion application on the Marmousi model showcasing its capability in invertig fine subsurface structures. [ABSTRACT FROM AUTHOR]

In this study, the segment joint and ring joint of the lining of the straight‐jointed tunnel are simplified as an equivalent open cylindrical shell with a small central angle and an equivalent closed cylindrical shell with a small width, and the lining of the straight‐jointed tunnel is thus simplified as an equivalent continuous periodic shell (ECPS) described by the cylindrical shell theory. Since the ECPS lining is periodic along the longitudinal direction, the tunnel‐soil system can thus be treated as a periodic system, which is referred to as the periodic tunnel‐soil system (PTSS) in this study. Based on the proposed ECPS lining model, an analytical method for the tunnel with the ECPS lining (ECPS tunnel) under seismic waves is established in this study. By employing the periodicity condition for the PTSS as well as the wave function expansion method, the representation for the wave field in the soil is established. With the aforementioned cylindrical shell theory and Fourier series expansion method, the convolution type constitutive relation for the ECPS lining and the Fourier space equations of motion are derived. By using the soil‐lining continuity condition and aforementioned formulations for the ECPS lining and soil, the coupled Fourier space equations of motion for the PTSS are established, with which the response of the ECPS lining and scattered waves in the soil can be determined. [ABSTRACT FROM AUTHOR]

Second order accurate Cartesian grid methods have been well developed for interface problems in the literature. However, it is challenging to develop third or higher order accurate methods for problems with curved interfaces and internal boundaries. In this paper, alternative approaches are developed for some interface and internal layer problems based on non-matching grids, in which two mesh sizes are used to obtain comparable high order accuracy near and away from an interface or an internal layer. For one-dimensional, or two-dimensional problems with straight interfaces or boundary layers that are parallel to one of the axes, the discussion is relatively easy. One of the challenges is how to construct a fourth order compact finite difference scheme at border grid points that connect two meshes. The idea is to employ a second order discretization near the interface in the fine mesh and a fourth order discretization away from the interface in the coarse and border grid points. For two-dimensional problems with a curved interface or an internal layer, a level set representation is utilized for which we can build a fine mesh within a tube | φ (x) | ≤ δ h of the interface. A new super-third seven-point discretization that can guarantee the discrete maximum principle has been developed at hanging nodes. The coefficient matrices of the finite difference equations developed in this paper are M-matrices, which leads to the convergence of the finite difference schemes. Non-trivial numerical examples have confirmed the desired accuracy and convergence of the proposed method. [ABSTRACT FROM AUTHOR]

Determining the mechanisms responsible for intraplate volcanism ‐ such as slab devolatilization melting versus active mantle plumes ‐ remains a challenge. The greater South China Sea (SCS) region has experienced extensive intraplate Cenozoic volcanism across areas including Hainan, Southeast Indochina, northern Borneo, the northern SCS, and the post‐spreading SCS basin. The prevalence of volcanism distributed widely across this region prompts fundamental questions about the key geodynamic processes driving such diverse magmatic activities. In this study, we elucidate the mantle transition zone (MTZ) discontinuities in this region using SS precursors, which helps to overcome the sparse seismic coverage due to its predominantly oceanic setting. We collected over 16,000 high‐quality seismograms that sample the upper mantle and MTZ beneath this region from global earthquakes and stations. After correcting for the effects of shallow crustal variations and upper mantle heterogeneity on traveltimes of SS phases and their precursors, we unveil lateral variations in the MTZ boundaries (d410 and d660) and intricate features of the mid‐MTZ reflectors (S520S). Significant MTZ thinning and normal S520S waveforms beneath Hainan provide compelling evidence for mantle upwelling through the MTZ. Conversely, the evident splitting of S520S beneath the northern SCS, Southeast Indochina, and northern Borneo, all characterized by stagnant subducted slabs, indicates that the volcanism in these regions likely originated from a mechanism distinct from the active upwelling beneath Hainan. Dehydration melting attributed to devolatilizing stagnant slabs in the MTZ is a potential cause for Cenozoic volcanism in these regions. Plain Language Summary: Determining the causes of volcanic activity far from tectonic plate boundaries remains a challenge. The greater South China Sea region experienced widespread volcanism during the Cenozoic era, prompting questions about the driving geological processes behind this phenomenon. This study investigated the boundaries of the mantle transition zone (MTZ) beneath the region using seismic wave analysis of over 16,000 seismic recordings. By analyzing the travel times of signals reflected from the MTZ boundaries and internal reflectors, lateral variations in the structure of the MTZ boundaries and internal features were revealed. Beneath Hainan, thinning of the MTZ and normal waveforms of the internal MTZ reflector suggest upwelling of hot mantle material through the MTZ, likely causing the surface volcanism. In contrast, beneath the northern South China Sea, Southeast Indochina, and northern Borneo, the distorted waveforms of signals from the internal MTZ reflector indicate a different mechanism. These latter regions contain ancient, subducted slabs present in their MTZs. Dehydration melting, caused by the release of water from these stagnant slabs within the MTZ, is a potential cause of the Cenozoic volcanism in these areas, distinct from the mantle upwelling observed beneath Hainan. Key Points: SS precursors from the mantle transition zone (MTZ), notably the S520S, provide insights into mantle dynamics beneath the greater South China Sea (SCS) regionEvidence of MTZ thinning and normal S520S waveform beneath Hainan suggests active mantle upwelling through the MTZThe S520S splitting beneath areas with stagnant subducted slabs indicates a possible magmatic origin through flux melting [ABSTRACT FROM AUTHOR]

Groundwater level tidal analysis is a powerful technique to monitor aquifer's permeability and hence its change over time. Earthquakes are known to affect aquifer's properties, in their vicinity through static stress changes but also further away through dynamic stresses. Most often changes are in the form of permeability increases, but sometimes decreases; the changes can be either permanent or transient. These observations are relatively well documented but the physical processes behind these changes are not well understood. By combining solid‐earth and barometric tidal groundwater level responses in a borehole in a coherent poroelastic theoretical framework, and a bi‐layer hydrogeological model, we recover a 15 years‐long time series evolution of aquifer transmissivity and shear modulus. This study showcases the full potential of the tidal analysis method, coupling pore pressure diffusion and rock deformation, at the frontier of hydrogeology and rock physics. This unprecedented measurement of permeability and shear modulus evolution by tidal analysis reveals, during interseismic period, high sensitivity of this shallow aquifer to effective stress, and thus to pore pressure. Thanks to additional finite element simulation of seismic wave propagation, we explore the different mechanisms affecting permeability and shear modulus in the studied fractured andesite aquifer. This study confirms the predominant role of seismic dynamic stresses, and more precisely of dynamic shear stresses, in the change of permeability following an earthquake. Plain Language Summary: Tidal oscillations of groundwater level, observable in boreholes all around the world, are information‐rich signals for hydrogeologist to infer the properties of surrounding aquifers, and how they evolve over time. Most importantly, it allows to monitor aquifer permeability and how it evolves under the influence of earthquakes, especially through static stresses changes or seismic wave propagation. Here we push the limits of what tidal analysis can reveal by also retrieving the shear modulus of the studied aquifer. This new observable, combined with the computation of regional earthquakes stresses, allows us to understand better how aquifer properties are modified by earthquakes. The analysis reveals first that dynamic shear stresses are the most probable cause of permeability changes, and second that the sensitivity of our fractured aquifer permeability to pore pressure is high. Key Points: The 15‐years' time series of permeability and shear modulus of the aquifer is deduced from the analysis of solid earth and barometric tidesCo‐seismic irreversible changes of fractured aquifer permeability are induced by earthquakes dynamic shear stressesInterseismic permeability variations of the aquifer are controlled by pore pressure, that is, the hydraulic head [ABSTRACT FROM AUTHOR]

In recent decades, the application of seismic metamaterials to protect civil infrastructures being free of the damage of earthquakes has been attracting extensive attention. Specifically, the proposed locally resonant seismic metamaterials provide the probability of isolating the low-frequency seismic wave using a small-size isolation barrier. However, in previous studies, the energy absorption properties of locally resonant seismic metamaterials remain one of the least understood aspects of isolation. Benefit from the fascinating energy absorption characteristic of negative Poisson ratio (NPR) metamaterial, we creatively design a new seismic metamaterial structure by assembling the locally resonant seismic metamaterial and NPR metamaterial, to isolate seismic waves. The sound cone technique combining the transmission spectrum is employed to identify the surface wave from the hybrid waves. The generation mechanism of frequency bandgap and the isolation effectiveness of the proposed seismic metamaterial are discussed in detail. The results indicate that the generation of ultra-low and ultra-wide frequency bandgap with the range of 0.65 Hz–18.9 Hz is attributed to the locally resonant and energy absorption of the proposed seismic metamaterial structure and the excellent isolation effect is achieved by transforming the surface wave into the bulk wave. The frequency bandgap narrows as the distance increases between each resonator. In addition, the mechanical properties of the NPR bearing, such as the Poisson ratio, mass density, and elastic modulus, have remarkable impact on the frequency bandgap, especially on the upper bound frequency. In practical engineering, the NPR bearing with a low Poisson ratio, small mass density, and high elastic modulus is suggested for the design of the NPR locally resonant seismic metamaterial structures. Time domain analysis for the practical seismic wave verifies that the proposed seismic metamaterial has a promising application in isolating ultra-low and ultra-wide seismic waves, with the isolation effectiveness larger than 70%. This work contributes a new locally resonance seismic metamaterial design idea for isolating and adjusting the low-frequency seismic wave. [ABSTRACT FROM AUTHOR]

Dynamic analysis of problems with complex geometries requires utilization of numerical methods. To completely capture the effects of seismic wave propagation in a system, one must consider the structure or irregularity within its encompassing half-space. Correct consideration of half-space in a numerical model is important specially when it comes to cases where the half-space contains semi-infinite irregularities. In this study, a generalized numerical methodology is presented for dynamic analysis of a half-space with semi-infinite irregularities. The methodology is first verified through comparison with analytical solution of known problems. Then the method is employed to solve the dynamic analysis of an arbitrary-shaped existing valley within a half-space under propagating plane harmonic SH wave with different angles of incidence. Results indicate complete capability of the methodology in solving wave propagation problems for complex systems without the usual restrictions of common existing methods. [ABSTRACT FROM AUTHOR]

SUMMARY: We define double (S1S2) and triple (PS1S2) singularity points and their degeneracy classes in triclinic anisotropic media. We derive equations for the group velocity image for all these cases. The degeneracy classes are defined by factorization of quadratic (double singularity point) and cubic (triple singularity point) forms with three variables. [ABSTRACT FROM AUTHOR]

SUMMARY: Geophysics and Geotechnical Engineering commonly use 1-D wave propagation analysis, simplifying complex scenarios by assuming flat and homogeneous soil layers, vertical seismic wave propagation and negligible pore water pressure effects (total stress analysis). These assumptions are commonly used in practice, providing the basis for applications like analysing site responses to earthquakes and characterizing soil properties through inversion processes. These processes involve various in situ tests to estimate the subsurface soil's material profile, providing insights into its behaviour during seismic events. This study seeks to address the limitations inherent to 1-D analyses by using 3-D physics-based simulations to replicate in situ tests performed in the Argostoli basin, Greece. Active and passive source surveys are simulated, and their results are used to determine material properties at specific locations, using standard geophysical methods. Our findings underscore the potential of 3-D simulations to explore different scenarios, considering different survey configurations, source types and array sets. [ABSTRACT FROM AUTHOR]

Patchy saturation is a term used in the seismic prospecting literature to describe the state of a geological formation in which two immiscible pore fluids prevail in mesoscopic-scale clusters. If the pore fluids have contrasting compressibilities, wave-induced fluid pressure diffusion (FPD) processes may induce significant attenuation and velocity dispersion on seismic waves. Biot's monophasic poroelasticity theory is widely used to model the seismic response of rocks containing binary patches of two immiscible pore fluids. Even though effective fluid approximations may help to represent more realistic partially saturated patches using Biot's monophasic equations, the so inferred dissipation may not be representative of actual biphasic FPD phenomena. In this work, Biot's equations for mono- and biphasic fluids are combined to model FPD processes in porous media, comprising fully and partially saturated patches. An analytical solution for one-dimensional layered patchy-saturated media is presented which permits to explain some, as of yet enigmatic, experimentally observed characteristics such as increased seismic attenuation and stiffening effects occurring at low saturations. The results show that the existence of an additional diffusive wave mode within partially saturated patches may render conventional binary and effective fluid approaches incorrect and error prone. [ABSTRACT FROM AUTHOR]

When seismic waves propagate through the geological formation, there is a significant loss of energy and a decrease in imaging resolution, because of the viscoacoustic properties of subsurface medium. This profoundly impacts seismic wavefield propagation, imaging and interpretation. To accurately image the true structure of subsurface medium, the consensus among geophysicists is to no longer treat subsurface medium as ideal homogeneous medium, but rather to incorporate the viscoacoustic properties of subsurface medium. Based on the generalized screen propagator using conventional acoustic wave equation (acoustic GSP), our developed method introduces viscoacoustic compensation strategy, and derives a one-way wave generalized screen propagator based on time-fractional viscoacoustic wave equation (viscoacoustic GSP). In numerical experiments, we conducted tests on two-dimensional multi-layer model and the Marmousi model. When comparing with the acoustic GSP using the acoustic data, we found that the imaging results of the viscoacoustic GSP using the viscoacoustic data showed a significant attenuation compensation effect, and achieved imaging results for both algorithms were essentially consistent. However, the imaging results of acoustic GSP using viscoacoustic data showed significant attenuation effects, especially for deep subsurface imaging. This indicates that we have proposed an effective method to compensate the attenuated seismic wavefield. Our application on a set of real seismic data demonstrated that the imaging performance of our proposed method in local areas surpassed that of the conventional acoustic GSP. This suggests that our proposed method holds practical value and can more accurately image real subsurface structures while enhancing imaging resolution compared with the conventional acoustic GSP. Finally, with respect to computational efficiency, we gathered statistics on running time to compare our proposed method with conventional Q-RTM, and it is evident that our method exhibits higher computational efficiency. In summary, our proposed viscoacoustic GSP method takes into account the true properties of the medium, still achieves migration results comparable to conventional acoustic GSP. [ABSTRACT FROM AUTHOR]

This study quantitatively evaluated the level of conservatism or accuracy of four typical directions used to assess the maximum structural response over all nonredundant seismic input angles: fault-normal and fault-parallel (FN and FP), the direct maximum direction (MD), the maximum peak ground velocity (PGV) direction, and the principal axes directions. Two eight-story models of symmetric and asymmetric buildings were developed, and two ensembles of ground motion records were selected considering three varying ground motion intensities. Bidirectional nonlinear response-history analyses (RHAs) were performed by rotating each pair of ground motion horizontal components to 26 orientations, from 0° to 170° in increments of 10° as well as four critical and their orthogonal directions. The effect of rotating the ground motions on several engineering demand parameters (EDPs) was investigated and the seismic demands in four critical directions were compared and evaluated deterministically and probabilistically. The four critical directions were re-evaluated by considering the largest response between two orthogonal pairs. The results show that the response in the maximum PGV direction is very close or equal to the maximum value over all orientations, especially for high levels of ground motion intensities, and thus is recommended for ground motion selection in performance-based seismic design and assessment. In addition, the influence of rotation angle is effectively reduced when using the larger seismic response value of the two orthogonal pairs while maintaining the same number of RHAs. [ABSTRACT FROM AUTHOR]

A new damping control method for the adjacent liquid storage tanks (LSTs) based on vibration barrier (ViBa) is proposed. Considering liquid-solid-soil coupling and structure-soil-structure interaction, a three-dimensional numerical calculation model is established by ADINA. The seismic control effect of ViBa is investigated, and parametric analysis is carried out. The results show that ViBa has a significant control effect on seismic responses and wave height, and the reduction factor of base shear force reaches the maximum value of 49.26%. The larger the seismic intensity, the liquid storage height and the height-radius ratio, the larger the reduction factor of the ViBa. [ABSTRACT FROM AUTHOR]

Velocity response spectrum (SV) plays a critical role in the seismic design of structures equipped with velocity-dependent dampers. Often, the SV is approximated using the pseudo-velocity response spectrum (PSV), because of the lack of information on the SV in seismic codes. As indicated in the existing literature, the error of this approximation is significant for short and long periods, and therefore, researchers have started to develop PSV to SV conversion models for obtaining SV more accurately. Recent studies discovered that the relationship between the PSV and SV is affected not only by structural parameters, but also by magnitude, distance, and site class. However, models for converting PSV to SV including magnitude, distance, and site class as input parameters have not been developed. To this end, a PSV to SV conversion model including magnitude, distance, and site class is proposed in this study based on a large number of real ground motion records (16,660 horizontal acceleration time histories) selected from the Japan Strong Motion Network. Furthermore, since the magnitude and distance are not specified in the seismic design, a response-spectrum-shape factor, s, is discussed to reflect the influences of magnitude and distance. Accordingly, an SV/PSV model incorporating s is established. The proposed models show better accuracy than the existing models for cases with different magnitudes, distances, and site classes. [ABSTRACT FROM AUTHOR]

This paper presents a combined seismic metamaterial model based on the principle of local resonance to effectively shield Rayleigh waves at wide low-frequency bandgap in two-layered soil. In the proposed combined seismic metamaterial model, the unit-cell structure comprises two parts: a partially embedded underground concrete column and a multi-layer composite material structure enclosing the underground portion of the embedded concrete columns. By using the finite element method, the band structure and propagation characteristics of the proposed combined seismic metamaterial model are numerically investigated. Later the concrete column height effect is investigated, such as the combined seismic metamaterial model with positive gradient arrangement, negative gradient arrangement, concave arrangement, and convex arrangement. Then, the El-Centro seismic wave is considered and found that it can be considerably attenuated by the designed combined seismic metamaterial model. Additionally, this work does parameter analysis on items such as concrete density and column height. [ABSTRACT FROM AUTHOR]

The inversion of parameters characterizing reservoir property based on rock physics model is an important content in seismic exploration, while the strong nonlinearity between basic parameters and seismic attributes makes it challenging in practice or computationally expensive. This study focuses on the issue of wave propagation in porous media saturated with two immiscible fluids and proposes to utilize deep neural network (DNNs)-based surrogate model to conduct forward analysis and parameter inversion. First, three classical rock physics models were employed to generate the dataset for training DNNs. Among them, five basic parameters (the porosity, bulk modulus and shear modulus of rock matrix, the solid density, and the saturation) were sampled within each reasonable range, and then, the corresponding phase velocity and inverse quality factor of seismic wave were calculated based on the three models. Next, DNNs were trained as surrogate models of the three rock physics models for sensitivity analysis. Then, such approach was applied to parameter inversion and different scenarios with different provided information and unknown quantities were designed to investigate the feasibility. The results showed the sensitivity of different models to basic parameters determines the corresponding inversion accuracy. When providing the information on the compressional wave, the porosity can be well inferred in most cases, while the accuracies of inverting saturation based on different models vary. Furthermore, it was found that adding the information of the shear wave can improve the performance of parameter inversions to a high level. From the obtained results, it was concluded that the DNNs-based surrogate models can serve as efficient tools for forward and inverse problems. [ABSTRACT FROM AUTHOR]

Besides amplitude variation, phase variation of seismic wave is also an important carrier of geological information at the fault slip interface. To analyze the seismic propagation through the fault slip interface, which is assumed to be a flat, horizontal and imperfectly welded contact (nonwelded) interface between two different tilted anisotropic (TTI) media, we derived the analytical formulae for amplitude and phase variations of reflected and transmitted seismic waves with longitudinal wave (qP), the slow and fast waves (qS and SH) generated simultaneously. The derived formulae could satisfy the fracture model, in which the symmetry axis planes of the upper and lower media coincide. Also, we provided the exact and approximate methods for velocities and polarizations as well as the reflected and transmitted angles based on the slowness ellipsoid. Moreover, weakly anisotropic parameters are taken into consideration by the approximate amplitude (AVO) and phase formulae of qP and qS. The approximations also clearly show the effect of anisotropic parameters on the amplitude and phase change. The derived results show that the compliance parameters affect the phase change rather than amplitude, while anisotropic parameters affect both. The numerical model shows that with respect to the incident P-wave, the phase change of the reflected qP wave is more significant than the other generating waves due to the linear slip boundary; the coefficients could be used to determine the fracture dip and strike; the frequency hardly affects the real part of the coefficient, while the imaginary part of the coefficient. Moreover, the derived formulae for phase change will contribute to the seismic inversion with the formulae for amplitude variation simultaneously. [ABSTRACT FROM AUTHOR]

A buried utility tunnel can effectively protect internal pipes by preventing or mitigating corrosion, external damage, and facilitating maintenance. During an earthquake, the energy from seismic waves is transmitted through the soil to the utility tunnel, then to the support structure, and ultimately to the pipe, making the support's interaction with the pipe crucial. In this study, scaled utility tunnel system undergoes shaking table tests at a horizontally non-homogeneous site. Various supports within the tunnel are modeled dynamic elements to assess energy dissipation. The attenuated seismic waves are then applied directly to the pipe to evaluate its response and validate the results against the tests. The study reveals that greater sliding between the tunnel and pipe leads to more energy dissipation and reduces the likelihood of significant pipe deformation. Situations with increased sliding of the side-wall angle steel support exhibit smaller strain peaks. Longitudinal sliding becomes more pronounced only when peak ground acceleration exceeds 0.8 g in longitudinal loading. The transverse sliding response under longitudinal loading is not influenced by the input acceleration peak. Additionally, modeling the internal pipe's interaction with the support as a simplified dynamic element yields more accurate responses, offering a foundational calculation for the design of shock absorption and vibration isolation in utility tunnel supports. [ABSTRACT FROM AUTHOR]

Karst has an important impact on the safe construction and operation of tunnels in the intercity railway survey in limestone areas. Therefore targeted high-precision geological exploration is very important. In order to reduce the impact of complex urban environments and improve the accuracy and efficiency of intercity railway karst exploration, statistical analysis is conducted on the size of actual karst caves detected, and the karst detection effects of four methods including cross hole seismic CT, drilling, opposing coils transient electromagnetics method (OCTEM), and microtremor exploration in a 200 m long experimental area are compared and analyzed based on the comparison of theoretical and practical detection effects of a certain intercity railway. The detection effects of different hole spacing on cross hole seismic CT are studied, the resolution of cross hole seismic CT detecting karst caves, the principles for interpreting the velocity of cross hole seismic CT in specific areas, and the exploration effects of OCTEM and microtremor exploration in the absence of conditions for conducting cross hole seismic CT are studied. The research results indicate that in cross hole seismic CT work, the quality of the original data with a 15 m hole spacing is higher than that with a 30 m hole spacing, and the karst identification rate and resolution are higher. The determination of the scale and spatial location of karst development is more accurate, and the estimation of grouting and grouting dosage in later construction is more reliable. Cross hole seismic CT with a spacing of 15 m can accurately reveal karst caves above 2 m. In specific areas, the development of karst in limestone areas can be quantitatively explained as weathering layers, dissolution cracks, karst caves, and relatively complete limestone based on the magnitude of seismic wave velocity. When cross hole seismic CT working conditions are not available, conducting OCTEM and micro motion supplementary surveys can identify larger karst caves and qualitatively determine the degree of karst development in limestone areas. The survey method has the characteristics of high survey accuracy and is not easily affected by the environment along the intercity railway. And it is of great significance for karst survey of intercity railway engineering and can be promoted and used in other intercity railway karst surveys. [ABSTRACT FROM AUTHOR]

Seismic surface waves carry significant energy that poses a major threat to structures and may trigger damage to buildings. To address this issue, the implementation of periodic barriers around structures has proven effective in attenuating seismic waves and minimizing structural dynamic response. This paper introduces a framework for seismic surface wave barriers designed to generate multiple ultra-low-frequency band gaps. The framework employs the finite-element method to compute the frequency band gap of the barrier, enabling a deeper understanding of the generation mechanism of the frequency band gap based on vibrational modes. Subsequently, the transmission rates of elastic waves through a ten-period barrier were evaluated through frequency–domain analysis. The attentional effects of the barriers were investigated by the time history analysis using site seismic waves. Moreover, the influence of the soil damping and material damping are separately discussed, further enhancing the assessment. The results demonstrate the present barrier can generate low-frequency band gaps and effectively attenuate seismic surface waves. These band gaps cover the primary frequencies of seismic surface waves, showing notable attenuation capabilities. In addition, the soil damping significantly contributes to the attenuation of seismic surface waves, resulting in an attenuation rate of 50%. There is promising potential for the application of this novel isolation technology in seismic engineering practice. [ABSTRACT FROM AUTHOR]

Accurate seismic ground response analysis is crucial for the design and safety of civil infrastructure and establishing effective mitigation measures against seismic risks and hazards. This is a complex process due to the nonlinear soil properties and complicated underground geometries. As a simplified approach, the one-dimensional wave propagation model, which assumes that seismic waves travel vertically through a horizontally layered medium, is widely adopted for its reasonable performance in many practical applications. This study explores the potential of sequence deep learning models, specifically 1D convolutional neural networks (1D-CNNs), long short-term memory (LSTM) networks, and transformers, as an alternative for seismic ground response modeling. Utilizing ground motion data from the Kiban Kyoshin Network (KiK-net), we train these models to predict ground surface acceleration response spectra based on bedrock motions. The performance of the data-driven models is compared with the conventional equivalent-linear analysis model, SHAKE2000. The results demonstrate that the deep learning models outperform the physics-based model across various sites, with the transformer model exhibiting the smallest average prediction error due to its ability to capture long-range dependencies. The 1D-CNN model also shows a promising performance, albeit with occasional higher errors than the other models. All the data-driven models exhibit efficient computation times of less than 0.4 s for estimation. These findings highlight the potential of sequence deep learning approaches for seismic ground response modeling. [ABSTRACT FROM AUTHOR]

We estimate depth‐dependent azimuthal anisotropy and shear wave velocity structure beneath the Alaska subduction zone by the inversion of a new Rayleigh wave dispersion dataset from 8 to 85 s period. We present a layered azimuthal anisotropy model from the forearc region offshore to the subduction zone onshore. In the forearc crust, we find a trench‐parallel pattern in the Semidi and Kodiak segments, while a trench‐oblique pattern is observed in the Shumagins segment. These fast directions agree well with the orientations of local faults. Within the subducted slab, a dichotomous pattern of anisotropy fast axes is observed along the trench, which is consistent with the orientation of fossil anisotropy generated at the mid‐ocean ridges of the Pacific‐Vancouver and Kula‐Pacific plates that is preserved during subduction. Beneath the subducted slab, a trench‐parallel pattern is observed near the trench, which may indicate the direction of mantle flow. Plain Language Summary: The azimuthal anisotropy of seismic waves refers to the directional dependence of the seismic wave propagation speed. We present a comprehensive azimuthal anisotropy model of the Alaska subduction zone to a depth of 200 km, revealing anisotropy caused by local faults and fractures, fossil anisotropy inherited from the oceanic plate within the subducted slab, and sub‐slab mantle flow. The along‐strike variation of crustal anisotropy indicates variations in the stress regime in the forearc region. The along‐strike variation of anisotropy within the subducted slab identifies different origins of the subducted slab. Our model contributes to the understanding of the anisotropic structure and the sources of anisotropy in subduction zones. Key Points: A new model of depth‐dependent azimuthal anisotropy of the Alaska subduction zone is built based on a new surface wave datasetThe along‐strike variation in the azimuthal anisotropy of the forearc crust is caused by faults and fracturesAzimuthal anisotropy within the subducted slab is controlled by fossil anisotropy produced at different mid‐ocean ridges [ABSTRACT FROM AUTHOR]

When the drilling and blasting method is used to excavate urban subway tunnels, the blasting seismic waves will inevitably produce vibration effects on the pile foundations under the surface buildings, which will seriously threaten the safety of surrounding buildings and the environment. Based on the transmission and reflection laws of stress waves at the interface between soil medium and pile medium and the displacement–stress continuous assumption, the wave function expansion method is used to analyze the whole process mechanism of vibration effect of hollow pipe piles under the action of incident P waves. In addition, the theoretical model of safety criterion for hollow pipe piles under blasting vibration is proposed and the reliability of the model is verified. Furthermore, the impacts of the elastic modulus, density, and pile section parameters of soil and piles on the safety criterion for the blasting vibration effect of hollow pipe piles are analyzed. The results show that as the elastic modulus and density of the soil increase, the critical peak particle velocity (PPV) curves of hollow pipe piles move to the high-frequency and low-frequency bands, respectively, resulting in a decrease in the overall safety of piles. This indicates that hollow pipe piles should not be buried in soil layers with high elastic modulus and density. It is also shown that the larger the hollow area of hollow pipe piles, the lower their safety. Compared to solid circular piles, hollow pipe piles have a higher overall seismic safety reserve. The study results have guidance and reference value for effectively evaluating and controlling the harm of blasting vibration effects of hollow pipe piles. [ABSTRACT FROM AUTHOR]

One‐dimensional site response analysis (1D SRA) remains the standard practice in considering the effect of local soil deposits and predicting site‐specific ground motions, although its range of applicability to realistic seismic wavefields is still in question. In this 1D approach, horizontal and vertical ground shaking are assumed to be induced by vertically propagating shear and compressional waves, respectively. A recent study based on analytical two‐dimensional (2D) plane waves and simple point source earthquake simulations has shown two mechanistic limitations in this 1D modelling technique for general inclined seismic waves, that is, systematic over‐prediction of the vertical motion and wave trapping in the 1D soil column. In this article, we evaluate in detail the applicability of this 1D modelling approach to realistic three‐dimensional (3D) simulated seismic wavefields in shallow sedimentary basins. Linear‐viscoelastic 1D SRA predictions using two types of input motions that are commonly used in practice—rock outcrop and in‐column motions, are compared with the reference true site response results from 3D earthquake simulations in terms of various measures in the frequency and time domain. It is shown that the horizontal motion in the 3D seismic wavefield exhibits dominant shear wave propagation phenomenon, while the vertical motion is a combined effect of compressional and shear waves and can be over‐predicted by the 1D approach when the incident seismic waves are inclined. Direct evidence of the wave refraction process that leads to the vertical motion over‐prediction is provided. 1D SRA with in‐column inputs can yield motions that have significantly longer duration compared to the true 3D site response solution due to trapped waves, casting in doubt the frequent need for increased soil damping in existing site studies to compensate for wave attenuation due to scattering alone. Sensitivity investigation on the increase of soil profile damping by a multiplier Dmul shows Dmul values compatible with those found in the literature for both horizontal and vertical motions. It is shown that the level of Dmul optimized for a best match of the spectral acceleration is dependent on the characteristic of the input motion and a larger Dmul is typically required for the vertical component. In contrast, 1D SRA with outcrop motions predicts motions with shorter significant duration due to its inability to capture the basin‐edge generated surface waves. A suite of ground motion simulations was performed to assess the sensitivity of the observations to the basin geologic structure including the velocity gradient, rock‐basin impedance contrast and basin depth. The analysis results show that the accuracy of the simplified 1D procedure is dependent on the wavefield composition of both the input motions and the true 3D site response solution. While the horizontal motions in shallow sedimentary basins can, to the first order, be reasonably captured by the simplified 1D approach, 1D SRA for the vertical component is in general not reliable and contributions from inclined shear waves should be accounted for in site‐specific evaluation of the vertical design ground motion. [ABSTRACT FROM AUTHOR]

This study established a numerical model that considers elevation conditions and slope shape factors by the modified Sadovsky formula to analyze the vibration attenuation law of open-pit slopes under blasting vibration conditions. The blasting excavation of a slope in a certain open-pit mine in Yunfu, Guangdong, is selected as an example. Using a numerical model that considers elevation conditions and slope shape factors by the modified Sadovsky formula, a triangular pulse load was utilized to approximate the time-history characteristics of explosion vibration with FLAC[sup 3D] software. The simulation results showed the radiation range of the blasting vibration seismic wave. By comparison with field monitoring data, the numerical model that considers the slope shape factor had a relative error of ~10%, while the numerical model that disregards the slope shape factor had a relative error of ~15%. The relative accuracy of the calculation results of the new numerical model is higher and closer to the actual attenuation law of blasting particle vibration speed, providing more reliable results for slope stability assessment. The peak particle velocities obtained from the numerical simulation results were generally higher than the field monitoring data. These discrepancies might be attributed to the use of simplified models that disregard the discontinuous structural planes within the rock mass. This study provides an important reference for the stability assessment of open-pit slopes under blasting vibration conditions, offering guidance for improving slope stability assessment and related engineering practices. [ABSTRACT FROM AUTHOR]

The firn layer covers 98% of Antarctica's ice sheets, protecting underlying glacial ice from the external environment. Accurate measurement of firn properties is essential for assessing cryosphere mass balance and climate change impacts. Characterizing firn structure through core sampling is expensive and logistically challenging. Seismic surveys, which translate seismic velocities into firn densities, offer an efficient alternative. This study employs Distributed Acoustic Sensing technology to transform an existing fiber‐optic cable near the South Pole into a multichannel, low‐maintenance, continuously interrogated seismic array. The data resolve 16 seismic wave propagation modes at frequencies up to 100 Hz that constrain P and S wave velocities as functions of depth. Using co‐located geophones for ambient noise interferometry, we resolve very weak radial anisotropy. Leveraging nearby SPICEcore firn density data, we find prior empirical density‐velocity relationships underestimate firn air content by over 15%. We present a new empirical relationship for the South Pole region. Plain Language Summary: Firn, the layer of compacted snow merging into glacial ice covering Antarctica, acts as an insulating blanket that mitigates environmental perturbations to the polar ice sheet. Understanding the density and seismic characteristics of the firn layer helps scientists better infer its properties and variation, including factors relevant to glacial stability and sea level change. Firn density is the major uncertainty source for measuring ice sheet mass changes via satellite and airborne sensing. Traditional methods of assessing firn density involve drilling or snow pit analyses and are expensive and time‐consuming. We utilize the rapidly developing technology of Distributed Acoustic Sensing to transform a data communication cable near the South Pole into a dense array of seismic sensors, allowing us to noninvasively estimate firn properties by studying seismic waves propagating in the firn to assess its physical properties. Our findings suggest that previous parameterizations overestimate firn density by over 5% and underestimate its air content by over 15% and highlight the value of seismology for advancing glaciological and polar region's climate research. Key Points: Distributed Acoustic Sensing repurposes an 8 km fiber‐optic cable at the South Pole into a dense seismic arrayGathered data resolve 16 dispersion modes at frequencies up to 100 Hz that constrain P‐ and S‐wave velocities in the firn layerPrevious density‐velocity empirical relations overestimate the dry firn density at South Pole [ABSTRACT FROM AUTHOR]

The asthenosphere is commonly defined as an upper mantle zone with low velocities and high attenuation of seismic waves, and high electrical conductivity. These observations are usually explained by the presence of partial melt, or by a sharp contrast in the water content of the upper mantle. Low viscosity asthenosphere is an essential ingredient of functioning plate tectonics. We argue that a substantial component of asthenospheric weakening is dynamic, caused by dislocation creep at the base of tectonic plates. Numerical simulations of subduction show that dynamic weakening scales with the surface velocity both below the subducting and the overriding plate, and that the viscosity decrease reaches up to two orders of magnitude. The resulting scaling law is employed in an apriori estimate of the lateral viscosity variations (LVV) below Earth's oceans. The obtained LVV help in explaining some of the long‐standing as well as recent problems in mantle viscosity inversions. Plain Language Summary: The motion of lithospheric plates at the Earth's surface is enabled by a weak underlying layer—the asthenosphere. The origin of this low viscosity layer is still subject of discussion. Presence of water or partial melt were proposed as possible reasons of its reduced viscosity. Another mechanism that may lead to weakening is non‐linear deformation. Rheological description of asthenospheric material includes dislocation creep, a deformation mechanism that depends on the velocity contrast between the lithospheric plate and underlying mantle—the faster the plates are, the weaker the underlying layer becomes and vice versa. Here we argue that a substantial component of asthenospheric weakening is dynamic, caused by this deformation mechanism. We evaluate numerical models of subduction including dislocation creep and derive a relation between the surface velocity of oceanic plates and the magnitude of the underlying asthenospheric viscosity. This allows us to estimate how the viscosity varies under different oceanic plates on Earth, which is otherwise hard to constrain. Our results indicate that the asthenosphere below the Pacific plate should be particularly weak. Key Points: Substantial component of asthenospheric weakening is dynamic, caused by dislocation creep at the base of tectonic platesDynamic weakening scales with the surface velocity both below the subducting and the overriding plateThe resulting scaling law is employed in an apriori estimate of the lateral viscosity variations below Earth's oceans [ABSTRACT FROM AUTHOR]

The seismic‐electromagnetic phenomenon entails the generation of transient electromagnetic signals, which can be observed both simultaneously (co‐seismic) and preceding (pre‐seismic) a seismic wave arrival. Following the most accredited hypothesis, these signals are mainly due to electrokinetic effects, generated on microscopic scale in porous media containing electrolytic fluids. Thus, the seismic‐electromagnetic signals are expected to be suitable for the detection and tracking of crustal fluids. Despite the growing interest in this phenomenon, there is a lack of freely available observational database of earthquake‐related electromagnetic signals recorded at co‐located seismic and magnetotelluric stations. To fill this gap, we set up two multicomponent monitoring stations in two seismically active areas of Southern Italy: the Gargano Promontory and the High Agri Valley. This work is both aimed to systematically analyse earthquake‐generated seismic‐electromagnetic recordings and to make the collected database accessible to the scientific community. [ABSTRACT FROM AUTHOR]

During strong earthquakes, pounding may occur on large-span bridges and their approach bridges. The effect and mitigation measures of such pounding have rarely been explored in previous studies. This paper primarily uses finite element models to investigate the pounding effects at the expansion joints between the main cable-stayed bridge and its approach bridge. Friction pendulum bearings (FPBs) and fluid viscous dampers (FVDs) are used to alleviate poundings. Furthermore, a detailed analysis is conducted on how the pounding effect of the isolated main bridge with FPBs and FVDs is affected by the wave passage effect, ground motion type, and soil type. This study reveals that FPBs and FVDs can effectively reduce pounding effects and the associated risks. Even with the installation of FPBs and FVDs, lower seismic wave velocities and near-fault seismic motions with pulse effects can significantly increase the pounding effects between the cable-stayed bridge and its approach bridge. [ABSTRACT FROM AUTHOR]

This paper established a numerical model for the structure system in a soil–structure interaction using MATLAB 23.2 and ANSYS 24.1 software and validated the effectiveness and accuracy of a simplified nonlinear calculation model for soil–structure interaction through the numerical simulation results. Meanwhile, a list of key parameters was identified according to their influence on the simplified model, including the free field area, site soil parameters, equivalent soil area, superstructure size and number of stories, and input seismic waves. On this basis, a series of parametric investigations were carried out with the validated simplified model, by varying the selected key parameters. The research findings demonstrated that the simplified calculation model exhibited excellent accuracy and efficiency, and was capable of reflecting the nonlinear response of the structural system. It is applicable to the field of dynamic response analysis of the superstructure, considering soil–structure interaction. [ABSTRACT FROM AUTHOR]

Based on the domain reduction method, this study employs an SEM-FEM hybrid workflow which integrates the advantages of the spectral element method (SEM) for flexible and highly efficient simulation of seismic wave propagation in a three-dimensional (3D) regional-scale geophysics model and the finite element method (FEM) for fine simulation of structural response including soil-structure interaction, and performs a physics-based simulation from initial fault rupture on an ancient wood structure. After verification of the hybrid workflow, a large-scale model of an ancient wood structure in the Beijing area, The Tower of Buddhist Incense, is established and its responses under the 1665 Tongxian earthquake and the 1730 Yiheyuan earthquake are simulated. The results from the simulated ground motion and seismic response of the wood structure under the two earthquakes demonstrate that this hybrid workflow can be employed to efficiently provide insight into the relationships between geophysical parameters and the structural response, and is of great significance toward accurate input for seismic simulation of structures under specific site and fault conditions. [ABSTRACT FROM AUTHOR]

Based on the arctangent function, this work proposes a parametric model to predict the mechanical behavior of a shear thickening fluid damper. The parameters of this model are a function of the maximum operating velocity of the damper. The validity and accuracy of the model's damping force and displacement relationship under different sinusoidal loads and various seismic wave excitations are verified based on experimental data. On this basis, compared to a viscous damper, the finite element models of a stay-cable and shear thickening fluid damper system are established to evaluate the vibration reduction performance and mechanical advantages of the shear thickening fluid damper. The research shows that a shear thickening fluid damper can significantly reduce the amplitude of the stay-cable's primary resonance and main parametric vibration, with displacement reduction rates of 72.5 and 81.9%, respectively. Importantly, compared to viscous dampers, under the premise that both have the same damping force, the vibration reduction effect of shear thickening fluid dampers is more significant, 1.3 times and 1.15 times that of viscous dampers, and the stroke is only 55.2 and 59.7% of that of viscous dampers. These data indicate that shear thickening fluid dampers can provide a more significant damping force for stay-cable in limited space. [ABSTRACT FROM AUTHOR]

The seismic data recorded at 48 broadband stations on an 1,800‐km‐long linear array have been used to image the deep structure and deformation in the intra‐continental collision between the Tarim Basin and the Northern Tibetan Plateau (NTP). Common Conversion Point (CCP) stacking imaging along the linear array and joint inversion of receiver function and surface wave dispersion defined the crustal and upper mantle structure, indicating that the Tarim block underthrusts the Altyn Tagh Range–Qaidam Basin. Whereas Moho is flattened, the lithospheric mantle beneath the Qaidam Basin has unusually low velocity, which is thought to be the consequence of the delamination in the lower crust and mantle lithosphere. Strong positive phase occurring at depths of 150–200 km on the CCP stacking imaging is likely to be associated to the remnant subducted oceanic lithospheric slab or the underthrusting Tianshan lithospheric slab beneath the collision zone. The removal of the Altyn Tagh Range–Qaidam Basin orogenic root may be due to convection‐driven delamination underneath it and subsequent underthrusting of the Tarim block. The spatial variation of the SKS splitting is manifested as the large‐scale pattern of lithospheric deformation and local abrupt changes, transitioning from pure shear on the NTP to simple shear in the Altyn Tagh Range. A comprehensive analysis of SKS splitting and GPS data reveals a simple shear pattern of vertical coherent deformation in the Altyn Tagh Range and its adjacent areas, which is evidence of the lithospheric shear zones. Plain Language Summary: The seismic wave data received by 48 broadband stations on the newly 1,800 km long linear array were used to determine the deep structure and deformation of the crust and upper mantle caused by the intra‐continental collision between the Tarim block and the Northern Tibetan Plateau by the joint inversion of the receiver function and the surface wave dispersion method. The results of this study reveal that the Tarim block underthrusts the Altyn Tagh Range–Qaidam Basin, and the Moho discontinuity below it appears nearly flat, indicating that the underlying orogenic roots have been removed. The mantle lithosphere below the Qaidam Basin is a low‐velocity anomaly zone which is thought to be evidence of the delamination of the lower crust and upper mantle. Convection‐driven delamination underneath the Qaidam Basin and subsequent underthrusting of the Tarim block resulted in the removal of the orogenic roots below the Altyn Tagh Range–Qaidam Basin. The delamination and uplift resulted in the shortening and thickening of the Altyn Tagh Range–Qaidam Basin. A comprehensive analysis of SKS splitting and GPS data reveals the vertical coherent deformation of the Altyn Tagh Range. The consistency between the coherent SKS fast direction and the strike of the crustal faults is considered evidence of simple shear of the Altyn Tagh Range. Key Points: Flat Moho and anomalous low‐velocity lithospheric mantle beneath the Qaidam Basin are thought to be the consequence of delaminationStrong positive phases of receiver function at depth of 150–200 km may be related to the remnant subducted Tarim oceanic lithospheric slabSimple shear pattern of vertical coherent deformation resulting from SKS splitting suggests that the Altyn Tagh Range is a lithospheric shear zone [ABSTRACT FROM AUTHOR]

Shallow sediments can respond non‐linearly to large dynamic strains and undergo a subsequent healing phase as the material gradually recovers following the passing of seismic waves. This study focuses on the physical changes in the subsurface caused by the shaking from a buried chemical explosion detonated in a borehole in Nevada, USA, as a part of the Source Physics Experiment Phase II. The explosion damaged the shallow subsurface and modified the frequency content recorded by 491 geophones and 2240 Distributed Acoustic Sensing (DAS) channels within 2.5 km from surface ground zero. We observe a gradual shift of resonance frequencies in the 10–25 Hz frequency band in the hours following the explosion and develop a method to characterize the related logarithm‐type healing process of the shallow (i.e., upper ∼25 m) subsurface. We find that stronger levels of ground motion increase the relative degree of damage and duration of the subsurface healing; with the spall region exhibiting the largest degree of damage and longest healing recovery time. We observe coherent spatial patterns of damage with the region located to the southeast of the explosion exhibiting more damage than the southwest region. This study demonstrates that both DAS and co‐located geophones capture similar temporal changes associated with the physical processes occurring in the subsurface, with the high‐density sampling of DAS measurements enabling a new capability to monitor the fine‐scale changes of the Earth's shallow subsurface following the detonation of a buried explosion. Plain Language Summary: Strong seismic waves can damage the soft sediments that compose the shallow layers of the ground. A healing phase of the sediments generally follows the passing of the seismic waves as the medium gradually recovers with time. We study the spatio‐temporal response of the subsurface in the vicinity of a large buried chemical explosion that was detonated in a borehole at the Nevada National Security Site, USA. The explosion, which was part of the Source Physics Experiment Phase II, was well instrumented along a surface fiber‐optic cable with Distributed Acoustic Sensing (DAS) and hundreds of geophones. We find that the explosion, which generated a spallation of the shallow Earth, primarily damaged the upper ∼25 m of the subsurface. We characterize the healing of the sediments and find a correlation between the duration of the healing phase and the level of maximum shaking. The high density of sensors also allows us to study spatial variations in the response of the shallow subsurface. This study demonstrates that both DAS and geophone continuous data similarly capture the spatio‐temporal variations of the Earth's physical properties following strong ground motions, with DAS enabling meter‐scale measurements of the subsurface changes. Key Points: Shallow subsurface damage and subsequent healing caused by a buried chemical explosion are constrained with DAS and geophone dataThe explosion caused a relative drop of the average S‐wave velocity in the Earth's shallow layers of a few percentsThe logarithm‐type healing process of the subsurface exhibit a longer duration within the spall region [ABSTRACT FROM AUTHOR]

When applying the three-dimensional discontinuous deformation analysis (3D-DDA) method to simulate the dynamic response of rock mass in an earthquake, appropriate artificial boundaries and input methods should be considered. In this study, the 3D-DDA method was modified by introducing the viscoelastic artificial boundary and the seismic motion input method based on the wave field decomposition method and with the consideration of the lateral free-field wave. Subsequently, the correctness of the boundary and the input method was verified through numerical examples. The results of the numerical examples were almost consistent with the theoretical solution. The introduced viscoelastic artificial boundary and seismic motion input method improved the applicability of the 3D-DDA method and can be further applied to simulate actual engineering cases. Highlights: Viscoelastic artificial boundary is applied and validated in 3D-DDA. The differences between viscoelastic boundary and existing boundaries are compared. Modified 3D-DDA can consider wave field decomposition and lateral free-field wave for seismic motion input. Feasibility of modified 3D-DDA to study the dynamic response of rock mass in an earthquake is studied. [ABSTRACT FROM AUTHOR]

In this paper, symmetric Pearcey Gaussian beams (SPGBs) are studied in a Kerr medium. By varying the initial input power, the autofocusing ability of the beams is investigated, to find a clear restrictive relationship between the breath‐like structure and the initial input power. The critical collapse power is investigated when SPGBs change from discrete beams to regular breath‐like structure. Finally, the transmission of SPGBs is discussed under different phase modulation when SPGBs are affected by astigmatic, the whole beam is rotated and the angle of rotation can be controlled. [ABSTRACT FROM AUTHOR]

Modelling seismic wavefields in complex 3-D elastic media is the key in many fields of Earth Science: seismology, seismic imaging, seismic hazard assessment and earthquake source mechanism reconstruction. This modelling operation can incur significant computational cost, and its accuracy depends on the ability to take into account the scales of the subsurface heterogeneities varying. The theory of homogenization describes how the small-scale heterogeneities interact with the seismic waves and allows to upscale elastic media consistently with the wave equation. In this study, an efficient and scalable numerical homogenization tool is developed, relying on the similarity between the equations describing the propagation of elastic waves and the homogenization process. By exploiting the optimized implementation of an elastic modelling kernel based on a spectral-element discretization and domain decomposition, a fully scalable homogenization process, working directly on the spectral-element mesh, is presented. Numerical experiments on the entire SEAM II foothill model and a 3-D version of the Marmousi II model illustrate the efficiency and flexibility of this approach. A reduction of two orders of magnitude in terms of absolute computational cost is observed on the elastic wave modelling of the entire SEAM II model at a controlled accuracy. [ABSTRACT FROM AUTHOR]

Earthquakes with moment magnitude (M w) ranging from 6.5 to 7.0 have been observed to generate sufficiently strong acoustic waves (AWs) in the upper atmosphere. These AWs are detectable in Global Navigation Satellite System satellite signals-based total electron content (TEC) observations in the ionosphere at altitudes ∼250–300 km. However, the specific earthquake source parameters that influence the detectability and characteristics of AWs are not comprehensively understood. Here, we extend our approach of coupled earthquake-atmosphere dynamics modelling by combing dynamic rupture and seismic wave propagation simulations with 2-D and 3-D atmospheric numerical models, to investigate how the characteristics of earthquakes impact the generation and propagation of AWs. We developed a set of idealized dynamic rupture models varying faulting types and fault sizes, hypocentral depths and stress drops. We focus on earthquakes of M w 6.0–6.5, which are considered the smallest detectable with TEC, and find that the resulting AWs undergo non-linear evolution and form acoustic shock N waves reaching thermosphere at ∼90–140 km. The results reveal that the magnitude of the earthquakes is not the sole or primary factor determining the amplitudes of AWs in the upper atmosphere. Instead, various earthquake source characteristics, including the direction of rupture propagation, the polarity of seismic wave imprints on the surface, earthquake mechanism, stress drop and radiated energy, significantly influence the amplitudes and periods of AWs. The simulation results are also compared with observed TEC fluctuations from AWs generated by the 2023 M w 6.2 Suzu (Japan) earthquake, finding preliminary agreement in terms of model-predicted signal periods and amplitudes. Understanding these nuanced relationships between earthquake source parameters and AW characteristics is essential for refining our ability to detect and interpret AW signals in the ionosphere. [ABSTRACT FROM AUTHOR]

High-frequency non-physical oscillations may occur due to shock waves in seismic wavefield and dynamic rupture simulation. In this study, we introduced the alternative flux finite-difference weighted essentially non-oscillatory scheme to address potential shock wave issues in computational seismology effectively. The wavefield of the body-fitted curvilinear domain was accurately computed through conservative grid mapping, ensuring accurate implementation of free surface boundary conditions on irregular surfaces using characteristic boundary conditions and minimizing artificial boundary reflections with exponential decay absorbing layers. Finally, we compared our scheme with the GRTM for flat surfaces and the CGFDM3D-EQR for irregular surfaces to demonstrate its correctness and accuracy, and validated its non-oscillatory characteristics. The aforementioned scheme is anticipated to assume a significant function in simulating more intricate seismic wavefields or dynamic ruptures. [ABSTRACT FROM AUTHOR]

In this work, the propagation and attenuation of vertically polarized surface waves when interacting with terraced slopes is studied experimentally and numerically. To validate the devised simulation, a laboratory-scale physical model is tested in order to examine the attenuation properties of this well-known artificial landform. The experiment involves formation of a terraced slope, in a laboratory setup, via use of an unconsolidated granular medium made of silica microbeads. This granular medium exhibits a gravity-induced power-law stiffness profile, resulting in a depth-dependent velocity profile. A piezoelectric actuator was used to excite vertically polarized surface acoustic modes localized near the surface of the medium. The three components of the particle velocity field of these modes were measured by means of a 3-D laser Doppler vibrometer. In accordance with the terraced slope, a simple inclined plane was further tested to investigate and highlight the differences in terms of wave propagation along these two different ground formations. The results of this research provide significant experimental evidence that the terraced slopes form mechanisms which attenuate low-frequency surface waves, thus acting as metasurfaces. This work suggests the use of laboratory-scale physical models to investigate the wave propagation in different landforms, which extend beyond typical horizontal ground morphologies, and which could be linked to atypical wave propagation properties, possibly even influencing propagation of seismic waves. [ABSTRACT FROM AUTHOR]

Shear wave velocity (Vs) is a fundamental property of elastic media whose estimation from PS converted waves is challenging and requires modelling the boundary where P to S conversion occurs. This paper presents a PS tomography where seismic wave conversion/reflection points correspond to reflectors modelled with the level-set function set to zero [ ϕ (x, z) = 0]. The proposed method aims for stable Vs inversion in a seismic acquisition setting using multicomponent receivers. Synthetic models simulating true Vs , Vp and the location of the geological reflector are used in the study. The inversion starts by locating a flat reflector, ϕ (x, z) = 0, which defines the zone Ω1 between the surface and the reflector, where the initial Vs and Vp fields are also set. To calculate the traveltimes of incident PT (P wave that propagates in Ω1 from source to the reflector), converted PS and reflected PP waves, for both observed and modelled data (forward problem), the methodology proposed by Rawlinson and Sambridge is adopted. This method uses the arrival times of the P waves, Tpt , from the seismic source at each reflector point as secondary sources generating the times Tps and Tpp. These times are calculated as a solution to the eikonal equation by using the Fast Marching method. The PS and PP residual times are minimized by updating Vs , Vp and ϕ (x, z) = 0 through adjoint variables designed from a formulation using Lagrange Multipliers in a variational context. The performance of the algorithm is evaluated for models with synclinal, sinusoidal and monoclinal reflector geometries using numerical tests considering the inversion of: (1) ϕ , given the true values of Vs and Vp ; (2) ϕ and Vs , given the true value of Vp ; (3) ϕ and Vp , given the true value of Vs and (4) the three parameters ϕ, Vs and Vp , simultaneously. Good results are obtained by inverting Vs and ϕ , given the true value of Vp. The simultaneous inversion of the three parameters exhibits promising results, despite the illumination problems caused by the different distribution of the PS, PP and PT time gradients due to the geometry of the reflectors and the acquisition setting (sources–receivers in the same plane). The proposed tomography estimates Vs and reflector positions which could help in statics corrections and improve the lithological characterization of near surface. [ABSTRACT FROM AUTHOR]