Strong Ground Motion Research Articles

The physics-based deterministic scenarios for earthquake hazards and losses of the Zhujiangkou fault in southern China

Dynamic rupture directivity significantly impacts earthquake hazard and loss assessments; yet, it is often overlooked, leading to uncertainties. We developed high-resolution, broadband, deterministic scenarios for earthquake hazards and losses of the Zhujiangkou Fault (ZF) in the Guangdong-Hong Kong-Macao Greater Bay Area of southern China. The calculations cover the entire physical process from fault dynamic rupture through strong ground motion propagation to quantitative loss estimations. We fully incorporate the real 3D physical fields, including fault structure, regional stress, friction conditions, inhomogeneous velocity, and topography. Results revealed higher earthquake hazards and losses triggered by the northwestern ZF segment, affecting Hong Kong, Shenzhen, Dongguan, Macao, and Guangzhou. The rupture directivity effect, driven by seismic wave interferences in forward propagation, leads to stark differences in hazards and losses across urban agglomerations, even under similar fault conditions. These findings help enhance the precision of earthquake risk assessments and provide practical approaches for disaster prevention.

Relationship Between Near-Fault Strong Ground Motion and Earthquake Magnitude of Crustal Earthquake Using Dynamic Rupture Simulation

Relationship Between Near-Fault Strong Ground Motion and Earthquake Magnitude of Crustal Earthquake Using Dynamic Rupture Simulation

Modeling the rupture dynamics of strong ground motion (> 1 g) in fault stepovers

Following the July 2019 Ridgecrest, California earthquakes, multiple field investigators noted that pebble- to boulder-sized rocks had been displaced from their position in the desert pavement within a stepover along the right-lateral strike-slip M7.1 rupture trace, without evidence of dragging or shearing. This implies localized ground motions in excess of 1 g, in contrast to the instrumentally recorded peak of 0.57 g. Similar rock displacement occurred in a stepover in the predominantly strike-slip 2010 M7.2 El Mayor-Cucapah earthquake. Together, these examples suggest that some aspect of how earthquake rupture negotiates a strike-slip fault stepover produces extremely localized strong ground acceleration. Here, we use the 3D finite element method to investigate how rupture through a variety of strike-slip stepover geometries influences strong ground acceleration. For subshear ruptures, we find that the presence of a stepover in general matters more than its dimensions; the strongest ground acceleration always occurs at the end of the first fault. For supershear ruptures, the stepover is effectively irrelevant, since the strongest particle acceleration occurs at the point of the supershear transition on the first fault. Our model subshear and supershear ruptures alike do produce horizontal particle acceleration above 1 g, but over a region so close to the fault (< 1 km) that a seismic network may not catch it. We suggest that the physics of rupture through a fault stepover could have been responsible for the displaced rocks in the Ridgecrest and El Mayor-Cucapah earthquakes, and that stepover regions may have particularly high ground motion hazard. Our study suggests that ground motion predictions and local hazard assessments should account for much stronger accelerations in the immediate near field of active faults, especially around stepovers and other geometrical discontinuities.

Dynamically triggered seismicity in Japan following the 2024 Mw7.5 Noto earthquake

Abstract On January 1st, 2024, a moment magnitude (M w ) 7.5 earthquake occurred on an active reverse fault in the northern part of Noto Peninsula, being one of the largest intraplate events recorded in Japan. In previous studies, the dynamic triggering of seismicity in Japan following some large remote earthquakes has been well documented, such as in the case of the 2011 M w 9.0 Tohoku–Oki earthquake, the 2016 M w 7.1 Kumamoto earthquake, and other large teleseismic events. In this study, we investigate the remote triggering of microearthquakes by the 2024 Noto earthquake and their characteristics. We analyze waveform data recorded at high-sensitivity seismic stations in Japan, before and after the occurrence of the Noto mainshock. Local earthquakes are detected on high-pass filtered three-component seismograms. Low-pass filtered waveforms are used for visualizing the mainshock surface waves and estimating dynamic stresses. Our results show a relatively widespread activation of small earthquakes—none of them listed in the Japan Meteorological Agency (JMA) earthquake catalog—that were triggered by the passage of the mainshock surface waves in many regions of Japan. These include Hokkaido and Tohoku in northeastern Japan, Kanto in central Japan, and Kyushu in southern Japan. The triggering is mostly observed in volcanic regions, supporting the hypothesis that such places are relatively easy to be activated dynamically, likely due to the excitation of fluids by the passage of mainshock surface waves. The calculated dynamic stress changes estimated from peak ground velocities, which triggered the earthquakes after the Noto mainshock, are in the range 12.8–102.6 kPa. We also report potential, less well-constrained dynamic triggering by the Mw 5.3 Noto foreshock, which occurred ~ 4 min before the mainshock, at levels of stress about 100 times smaller. The analysis of a longer-term (1 month) seismicity pattern, based on the JMA catalog, revealed a statistically significant increase of seismicity in the remote Akita–Yakeyama (Tohoku region) volcanic area, following the Noto earthquake. Graphical Abstract

Prediction of Synthetic Seismograms and Accelerograms for Two-Layer Basis Beddings

A method has been developed for predicting strong ground motion displacements and accelerations, assuming that an earthquake is an instantaneous mechanical rupture of the Earth’s crust. The method uses derived theoretical formulas to calculate all three parameters of the ground motion: displacements, velocities, and accelerations during strong (with a magnitude of M 6.0) earthquakes for any non-homogeneous (multilayer) ground beddings with various physical and mechanical characteristics – thicknesses, densities, and shear moduli – and at a certain distance from the expected earthquake’s rupture. The example provided involves the results obtained for a number of two-layer heterogeneous site variants in seismic categories I-IV at the magnitude of M=7.0 and distance of 15 km from the expected earthquake’s rupture. A comparison of the results obtained for actual heterogeneous foundation beddings with the equivalent homogeneous beddings showed divergences by 1.3-1.6 times, depending on the number of higher mode oscillations considered. Recommendations are provided for simplified calculation of seismograms and accelerograms for heterogeneous foundation beddings, with a certain correction of calculation results for equivalent homogeneous beddings.

Data‐Physical Fusion Deep Learning for Site Seismic Response Using KiK‐Net Records

ABSTRACTIn the realm of earthquake engineering, response spectra play a crucial role in characterizing the effects of site dynamic characteristics under seismic activity. Consequently, accurately predicting seismic response spectra is of paramount importance. We have developed a physics‐guided bidirectional long short‐term memory neural network model (Phy‐BiLSTM) that is proficient in predicting site seismic response based on bedrock records. The core principle of the Phy‐BiLSTM is to improve the alignment between the solution space and the ground truth by integrating physics knowledge obtained from the physical model. The model introduced in this study utilized the 5%‐damped response spectra, which were derived from strong ground motion records collected at the KiK‐net downhole array. The results substantiate the performance enhancement of Phy‐BiLSTM in comparison to the data‐driven BiLSTM model. Furthermore, we conduct a comparative analysis of the Phy‐BiLSTM model against traditional methods (EQ, SBSR) as well as other neural network architectures (CNN and LSTM). The result highlights the advantages of Phy‐BiLSTM in accurately predicting the site seismic response.

Seismic performance of round-end hollow RC tall bridge piers considering to higher-order vibration mode effect

Round-end hollow reinforced concrete (RC) tall piers have been widespreadly utilized for railway bridges in river valleys and mountainous regions. The post-earthquake damage state of such bridge piers differs significantly from that of traditional short-to-medium piers. To investigate the seismic performance and failure mode of RC round-end hollow tall piers, a finite element model was developed using the OpenSees platform and calibrated against previous test results. Subsequently, incremental dynamic analysis (IDA) and modal pushover analysis (MPA) were conducted to obtain bending moment and curvature distributions as well as damage ranges for piers subjected to different intensities of ground motion. The results indicate that: The RC round-end hollow tall piers subjected to strong ground motions can crack up to 75% and 80% of its height according to IDA and MPA, respectively. The MPA incorporating mode coupling up to the third order is capable of predicting crack distribution of the pier as demonstrated in this study. Furthermore, it is recommended that the damage range of the pier be considered as a primary control indicator in seismic design.

Predictive model for peak ground velocity using long short-term memory networks

Predictive model for peak ground velocity using long short-term memory networks

Analysis of characteristics of ground motion and typical bridge performance in the Baoshan earthquake

A Ms5.2 earthquake occurred in Longyang District, Baoshan City, Yunnan Province on 2 May 2023. The earthquake caused some degree of damage to power facilities and roads. Since then, small and medium sized earthquakes have occurred frequently in this region. In order to better analyze the characteristics of ground motion in this area and the coping strategies of related bridges, the response spectra, omnidirectional response spectra and omnidirectional representations of other indexes of intensity measure from records of strong ground motion were analyzed using the seismic records recorded by stations near the epicenter. Four typical bridges near the epicenter were selected for modeling and seismic response analysis to derive their damages under the action of ground motion, and structural displacements of the bridges with the strong ground motion were compared to analyze directional linkages. The Incremental Dynamic Analysis (IDA) method was used to analyze the fragility of the four bridges, and the seismic capacity of different bridges under the ground motion was compared. The omnidirectional displacement response spectra of the two stations and the omnidirectional representations of other indexes of intensity measure have obvious directionality, and the predominant direction is perpendicular to the direction of the fault, reflecting the rupture directionality of the earthquake. Comparing the corresponding period of the structural displacement response with seismic action with the omnidirectional displacement response spectra, it was found that the bridge structural displacement is correlated with the predominant cycle and predominant direction of the omnidirectional displacement response spectra. Under the same seismic action, the maximum moment of the deck arch bridge in the transverse direction is larger than that in the bridge direction; the larger the span of the deck arch bridge, the larger the maximum moment at the arch footing. According to the analysis of fragility, it can be seen that the seismic capacity of the continuous rigid frame bridge is much lower than that of the deck steel truss arch bridge under this ground motion. Compared to the deck-type concrete arch bridge, the deck steel truss arch bridge has greater seismic capacity. In this paper, based on the structural analysis and fragility analysis of these four bridges close to the fault, the structural damage and damage levels in the future earthquake are speculated, which provide suggestions for the follow-up maintenance and reinforcement work, and are also conducive to the resilience evaluation and rapid repair work after the real earthquake damage.

Seismic performance assessment of base isolation systems in five hospitals during the Mw7.8 and Mw7.6 2023 earthquakes in Southeast Turkey

The February 6, 2023, Kahramanmaraş earthquakes (Mw7.8 and Mw7.6) in Southeast Turkey ruptured a 300 km section of the East Anatolian Fault, resulting in severe ground motions. These two strong earthquakes occurred 9 hours apart and were followed by large-magnitude aftershocks. Strong ground motions from the Kahramanmaraş earthquakes were recorded by more than 280 strong motion stations. Nine base-isolated hospital buildings located at distances less than 50 km from the ruptured fault were subjected to strong ground shaking. This paper examines five of the nine hospitals for which seismic isolation designs were available to the authors. The ground motions acting on these hospital buildings were recorded by strong motion stations situated in close proximity. Consequently, the February 6 earthquakes have presented a unique opportunity to assess the seismic performance of base isolation systems during severe earthquakes. All five hospitals were equipped with double spherical sliding (friction pendulum) seismic isolation devices. Subsequently, the authors conducted site visits to the hospitals following the February 6 earthquakes and collected data on maximum and residual response displacements at their isolation levels, as well as on the seismic response of structural and nonstructural components. The maximum response displacements measured at the isolation levels are compared with the maximum displacements calculated by nonlinear response history analysis under the ground motions recorded at the strong motion stations in close proximity to the hospitals.

Capturing Broadband Spectral Characteristics of Moderate-Size Earthquakes Using Nearby Recordings: A Case Study of 42 Mw 4.0–5.4 Ridgecrest Earthquakes

ABSTRACT Characterizing the information in earthquake source spectra requires three measures: seismic moment M0, apparent stress σa, and stress parameter ΔσB. We estimate σa and ΔσB for 42 Ridgecrest, California, earthquakes (4.0≤Mw≤5.4), using three-component records within 50 km to minimize path effects. We analyze the data in both the time and frequency domains. We account for the depth dependence of source velocity and density and calibrate the results using observations at a rock site. Time-domain analysis for σa reveals significant apparent crustal attenuation (∝r−1.6, in which r is the centroid distance) and large site amplifications. In the frequency domain, we estimate near-surface impedance as a function of frequency at each station. We conduct a grid search with F-tests to constrain a frequency-dependent crustal Q model (Q(f)=q0fα) and site attenuation constant κ0 for each station, assuming a ω−2 model. The global best model has q0=60, α=0.675, with κ0 ranging from 0.01 to 0.05 s. σa and ΔσB were estimated using corrected observations. The σa values from both time- and frequency-domain analyses are in excellent agreement, ranging from 0.09 to 2.7 MPa with a geometric mean of 0.59 MPa. ΔσB ranges from 0.27 to 6.9 MPa with a geometric mean of 1.8 MPa. The ratio of ΔσB and σa (∼3.0) suggests the source spectrum in this magnitude range is close to a single-corner spectral model. We find both σa and ΔσB increase quickly with centroid depth that cannot be explained with depth-dependent crustal attenuation. Geometric mean values for σaF and ΔσB for earthquakes with centroid depths of ≥6 km are 0.92 and 2.91 MPa, respectively, approximately fourfold the values for earthquakes with centroid depths &amp;lt;6 km. Considering the significant impact to near-fault strong ground motion, the cause of this sharp transition deserves further investigation.

Earthquake Source Spectra Estimates Vary Widely for Two Ridgecrest Aftershocks Because of Differences in Attenuation Corrections

ABSTRACT Differences in stress-drop estimates among groups of scientists for the same earthquakes suggest disagreement in the shape of the source spectra that are used to measure corner frequency. A critical step in characterizing source spectra involves applying empirical corrections for site effects and the loss of high-frequency energy that occurs along the source–receiver path. As part of the Ridgecrest stress-drop validation study, we compare path-corrected source spectra among different methods for two nearly collocated M 3 earthquakes and investigate whether systematic differences in the applied path corrections are affecting corner-frequency estimates. We find substantial disagreements in the path corrections, which are well approximated with a simple exponential function related to the strong ground motion parameter κ. These κ differences are strongly correlated with corner-frequency estimates for path-corrected spectra, suggesting they are a large source of systematic differences in corner frequency (and inferred stress drop) among the methods, reflecting varying trade-offs between the source and path contributions to observed spectra. Because each method presumably fits the data it uses sufficiently well, these results indicate the limitations of existing purely empirical techniques to estimating path corrections and the need for new approaches.

Study on applicability of rocking piers to high-speed railway bridge-track system under strong ground motions

Rocking piers have significant advantages in limiting the residual post-earthquake displacement of the pier top and reducing thus the structural damage. However, the application and research of such kind of piers are mainly concentrated on highway bridges. To study the applicability of rocking pier in high-speed railway (HSR) bridge-track system under strong ground motions, a preliminary rocking seismic design method for HSR gravity piers is proposed. The HSR simply supported beam bridge-track-subgrade integrated finite element model of the conventional pier system and the rocking pier system are established. The seismic response of the two pier systems under strong ground motions is compared and analysed. Results show that under strong ground motions, in the HSR bridge-track system, rocking bridge piers can exhibit smaller bending moments at the pier bottom and residual displacement at the pier top concerning conventional piers. Hence, the piers can effectively be protected from damage during a seismic event, while the bearings and the sliding layer exhibit smaller residual post-earthquake deformation. Thereby, with this system, it is possible to significantly improve the geometric irregularities of the rails, and increase the safety and comfort of running after strong ground motions.

Effect of soil profile-related parameters on seismic performance of ductile reinforced concrete building frames in California

Strong ground motions with specific site characteristics can lead to structural damage. Comprehending the effects of site characteristics on the dynamic response of structures is crucial for evaluating seismic performance and thereby implementing design that can mitigate potential damage. This study explores how the site characteristics, including the average shear wave velocity, soil depth to rock, and site period, influence the seismic response of reinforced concrete buildings. Soil column models were created using 319 soil profiles located in California and were employed to perform the nonlinear site response analysis of 80 rock motions to generate surface motions. Subsequently, low-to high-rise reinforced concrete moment-resisting frames with four, eight, twelve, and twenty stories that are representative of California were modeled to conduct nonlinear structural analyses. In this process, the influence of the three site characteristics on the response of the surface motions and structures was investigated. This investigation revealed that structural responses tend to increase when the average shear wave velocity ranges from 180 to 360 m/s or when the depth exceeds 135 m. Additionally, structures with a natural period exceeding 1 s were found to be more vulnerable as the number of stories increased. The outcomes will promote the development of seismic design methods based on different site characteristics.

The strong ground motion and structural response analysis of 06 February 2023 Pazarcık and Elbistan earthquakes (Mw 7.7 and 7.6): a Case study for Malatya-Türkiye, Eastern Anatolia

The strong ground motion and structural response analysis of 06 February 2023 Pazarcık and Elbistan earthquakes (Mw 7.7 and 7.6): a Case study for Malatya-Türkiye, Eastern Anatolia

Effects of ground motion characteristics on liquefaction response of earth dams using a non-Darcy hydro-mechanical model

During earthquake-induced excitations, significant pore pressure gradients can develop in earth dams, limiting the applicability of Darcy’s law for fluid flow. This study investigates the behavior of a liquefied earth dam subjected to various seismic excitations with differing frequency content, aiming to enhance insights into the effects of dynamic loading on fluid–structure interactions. To accurately capture the soil’s response, the Pastor-Zienkiewicz generalized plasticity model is employed to represent realistic soil behavior. Additionally, a modified Forchheimer equation is used to address varying permeability through a non-Darcy flow law. Numerical simulations, performed using a finite element code developed in Fortran, are validated through comparative analyses with previous studies. The results show that in low-permeability regions, changes in earthquake frequency content have minimal impact on discrepancies between the predicted results of Darcy and non-Darcy models. However, the non-Darcy model generally estimates horizontal displacements to be around 4% higher on average in these regions. This difference increases as earthquake frequency content decreases, reaching up to 6%. In contrast, in permeable regions, the non-Darcy model predicts significantly higher horizontal displacements, with an average increase of approximately 20% for high-frequency seismic events and 8% for low-frequency ones. Additionally, in high-permeability regions, the non-Darcy model deviates notably from the Darcy model as peak ground velocity increases, particularly affecting the upstream shell and clay core of the dam. This disparity becomes more pronounced as the input motion’s frequency content decreases, resulting in elevated pore pressures and slightly reduced vertical displacements in these regions.

A new approach for assessing the contribution of Ground Motions Frequency Content and Soil-Structure Interaction to the Seismic Response of Reinforced Concrete Moment Frames

One of the key steps in the seismic resilience assessment of buildings is gaining insight into their seismic response. The frequency content of ground motions and the dynamic characteristics of the building contribute mutually to the seismic response of the entire system (soil + structure). This study aims to present a new approach to assess the effects of the soil structure interaction (SSI) and of the frequency content of the ground motion. A case study of reinforced concrete moment frames (RCMFs) is herein presented by applying 280 ground motion time history records, which were registered on site classes A and B (based on ASCE 7–16). To this end, initially the characteristics of the input motions (e.g. amplitude and frequency content) were calculated, and then the time histories were partitioned into three clusters based on two optimal clustering features, namely Peak Ground Acceleration to Peak Ground Velocity ratio (PGA/PGV) and F5 (representing the frequency associated with 5% of total power in cumulative power spectral density, PSD). The clustering were done by implementing an unsupervised machine learning (ML) algorithm (i.e. K-means clustering), also the number of clusters was achieved using a well-known method in ML literature. Several time histories from each of the clusters were randomly selected to perform incremental dynamic analysis (IDA) on a 6- and a 10-story RCMF. Two different base conditions were considered: fixed-based (SSI neglected) and flexible-base (considering SSI effects). The findings demonstrate the contribution of frequency content and SSI to the seismic response of RCMFs, and also present an approach for considering frequency content in seismic analysis.

Seismogenic model of the 2023 MW5.5 Pingyuan earthquake in North China Plain and its tectonic implications

The 6 August 2023 MW5.5 Pingyuan earthquake is the largest earthquake in the central North China Plain (NCP) over the past two decades. Due to the thick sedimentary cover, no corresponding active faults have been reported yet in the epicenter area. Thus, this earthquake presents a unique opportunity to delve into the buried active faults beneath the NCP. By integrating strong ground motion records, high-precision aftershock sequence relocation, and focal mechanism solutions, we gain insights into the seismotectonics of the Pingyuan earthquake. The aftershocks are clustered at depths ranging from 15 to 20 km and delineate a NE-SW trend, consistent with the distribution of ground motion records. A NE-SW nodal plane (226°) of the focal mechanism solutions is also derived from regional waveform inversion, suggesting that the mainshock was dominated by strike-slip motion with minor normal faulting component. Integrating regional geological data, we propose that an unrecognized fault between the NE-SW trending Gaotang and Lingxian-Yangxin faults is the seismogenic fault of this event. Based on the S-wave velocity structure beneath the NCP, this fault probably extends into the lower crust with a high angle. Considering the tectonic regime and stress state, we speculate that the interplay of shear strain between the Amurian and South China blocks and the hot upwelling magma from the subducted paleo Pacific flat slab significantly contributed to the generation of the Pingyuan earthquake.

Seismic hazard mapping for peak ground velocity: microzonation of Novi Sad, Serbia—a case study in a low-seismicity region exposed to large and distant earthquakes

Seismic hazard mapping for peak ground velocity: microzonation of Novi Sad, Serbia—a case study in a low-seismicity region exposed to large and distant earthquakes

Investigation of the effects of mainshock-aftershock sequences on the dynamic responses of pipeline considering soil-pipeline interaction

Pipelines are important structural elements that are frequently used today to meet many infrastructures needs such as drainage, natural gas or water transmission. In this context, the usability of such structures, which are important elements of infrastructure systems, especially after disasters such as earthquakes, is of great importance. For this reason, within the scope of this study, a parametric investigation of the seismic behaviors of a natural gas pipeline system under mainshock-aftershock sequences have been carried out, specifically taking into account the soil-natural gas pipeline interaction (SNGPI) in the help of finite element model (FEM) proposed. Before developing the model of SNGPI system proposed using solid element, the fundamental mode frequencies of the pipeline system modeled using the solid element for the verification have been compared with those of obtained from the pipeline system modeled using the beam element and the analytical solutions. After verification of proposed model is demonstrated, SNGPI system has been modeled and its fundamental modes have been compared with mode frequencies of soil stratum obtained from well-known simple analytic solutions. After this stage, the dynamic analyses of natural gas pipeline (NGP) system in the time domain have been carried out using four different soil systems and four different mainshock-aftershock sequences. The results of the nonlinear time-history analyses have been investigated in terms of the stress and the displacement responses. Parametric evaluations show that the greatest displacements and the stresses occurring at the considered nodes of NGP system may be importantly affected from mainshock-aftershock sequences and soil stiffness changes. As the soil stiffness decreases, both the peak stresses and displacements increased significantly. On the other hand, the same responses obtained under mainshock loadings, which have relatively lower peak ground acceleration (PGA)/peak ground velocity (PGV) ratio compared to aftershock loadings, are generally larger than those obtained under aftershock loadings.