Broadband Ground Motion Research Articles

A View of the Linkup Between the Neodeterministic and the Probabilistic Seismic Hazard Assessments

Abstract In this article, with a focus on improving the framework of seismic hazard assessment (SHA), we propose a link-up procedure between the neodeterministic seismic hazard assessment (NDSHA) and the widely adopted probabilistic seismic hazard assessment (PSHA). We discussed why NDSHA should be linked with PSHA if the former is to play a role in the framework of the existing multilevel fortification strategy against earthquake disasters. The link-up procedure was illustrated by a case study in which scenario earthquake (SE) was the bridge between the two SHAs. Some potential issues related to the proposed procedure, such as the determination of SE, modeling of finite-fault source, and synthesis method of broadband ground motion, were further discussed. The final result is a set of hazard maps with multiple parameters and multiple fortification levels, which is appropriate for application to the seismic design of engineering structures. The improved hazard map highlights the hazards from future large earthquakes near big cities.

Stochastic Green’s Function Method Considering Non-Uniform Rise Time Distribution to Simulate 3D Broadband Ground Motion

The stochastic Green’s function method has been widely used in the field of ground motion simulation in recent years. It is generally assumed that the rise time of each subfault is the same in this method. Since the rise time significantly influences the amplitude of simulation results in the intermediate frequency band, to improve the accuracy of stochastic Green’s function method for near-fault broadband ground motion simulation, referring to the numerical simulation results of Day, the rise time is assumed to be non-uniformly distributed on the fault, and an improved approximate expression of rise time on a rectangular fault considering that the rupture starting point may be at any position and the aspect ratio may be arbitrary is proposed. Additionally, the contributions of P, SV and SH wave are considered, respectively, and an improved stochastic Green’s function method is proposed for 3D broadband ground motion simulation. Taking the 1994 Northridge earthquake in America and 2013 Lushan earthquake in China as examples, under different subfault division numbers, the synthesized source spectra are compared with the omega-squared theoretical source spectra of the large earthquake, and the simulated ground motions at observation points are compared with observed records to verify the effectiveness of the improved method. The results show that when the Northridge earthquake fault and Lushan earthquake fault are divided into 9 × 10 subfaults and 11 × 7 subfaults, respectively, the simulation results obtained using the improved method are close to the observed records in the broadband frequency range. Therefore, the improved method can effectively simulate the 3D ground motion in near-fault regions.

Kinematic rupture modeling of broadband ground motion from the 2022 MS6.9 Menyuan earthquake

AbstractWe propose a novel kinematic rupture modeling procedure for synthesizing broadband ground motions derived from the frequency-wavenumber integration algorithm. This procedure addresses two key issues in characterizing the rupture processes relevant to broadband seismic radiation: an accurate Green's function and a well-constrained kinematic source model. For the first issue, we derive the theoretical Green's function based on an improved dynamic stiffness matrix approach that effectively handles wave propagation in a 1D crustal velocity structure across a broad frequency band. For the second issue, we generate the hybrid source model that combines asperity slip and random slip over the fault plane to effectively implement constraints on the radiated energy during the whole rupture process. The accuracy and effectiveness of the proposed methodology are verified by comparing with the surface acceleration traces and Fourier spectra calculated by spectral element method. With the hybrid source model and crustal velocity structure applicable to the target area, the broadband (0–10 Hz) ground motion of the 2022 MS6.9 Menyuan earthquake is synthesized. The amplitude, duration, and frequency content of the synthetic motions are systematically compared with those of the available observed records and ground motion attenuation relationships, as well as the spatial distribution characteristics of the near-field ground motions from the earthquake scenarios are presented. In conclusion, the case study of the Menyuan MS6.9 earthquake demonstrates that the presented modeling procedure can estimate broadband ground motions rapidly and reliably from a physics-based kinematic rupture perspective.

Improvements to EXSIM in Ground Motion Simulation for Earthquakes Explained by Double‐Corner‐Frequency Source Model

AbstractThe stochastic EXtended finite‐fault ground‐motion SIMulation algorithm (EXSIM) has been widely applied in simulating and predicting broadband strong ground‐motion. However, an increasingly number of researchers have found that EXSIM may overestimate ground‐motions at low frequencies for some large‐magnitude earthquakes and/or thrust earthquakes, for which the far‐field source model has been explained by a double‐corner‐frequency model. Despite controversy, the double‐corner‐frequency model is now being accepted as one of the main categories of the far‐field source model. This study demonstrated the limited applicability of EXSIM to earthquakes explained by the double‐corner‐frequency source model, by presenting the equivalence between motions generated by EXSIM and those generated by EXSIM's point‐source version, SMSIM, which adopts the ω‐square single‐corner‐frequency model. Furthermore, two improvements to EXSIM have been proposed: (a) the incorporation of the asperity‐distributed stress‐drop compound faults model and (b) the hybrid application of EXSIM with the proposed model. The effects of the two improvements have been verified by comparing EXSIM‐generating motions with recorded ground‐motions for the 2013 Mw 6.7 Lushan thrust earthquake. Significantly, consistent simulation accuracy has been achieved across high‐ and low‐frequency bands as well as in far‐ and near‐fields. The consistent accuracy of the improved EXSIM in simulating high‐ and low‐frequency ground motions enables its direct and independent application to broadband ground motion simulations. Moreover, the first validation of this consistent accuracy in both near‐ and far‐field scenarios further enhances its application in earthquake engineering practices.

Revisiting the 1934Mw 8.2 Bihar–Nepal earthquake—Simulation of broadband ground motions

SUMMARYThe 1934 Mw 8.2 Bihar–Nepal earthquake was one of the devastating earthquakes, which made seismologists realize the importance of proper seismic hazard analysis and design aspects in India. The event occurred way before proper seismic networks were implemented and hence there are no recorded ground motions available for this event. This study, thus aims to generate possible ground motions for the 1934 Mw 8.2 Bihar–Nepal event. The complex geographical features, ambiguous source information and lack of ground motion data make the simulation and validation of ground motions very difficult. In this regard, the broad-band (BB) ground motions are simulated and validated for the most recent well-documented Himalayan event, that is, the 2015 Mw 7.9 Nepal earthquake in order to calibrate the model and simulation methodology. For this purpose, the computational model is presented for a region of 1000 km × 670 km (longitude 80–89 °E and latitude 23–30 °N) in the Indo-Gangetic Basin to simulate the low-frequency (LF) ground motions using spectral element method. These deterministically simulated LF ground motions are combined with stochastically simulated high-frequency (HF) ground motions based on an improved seismological model . The seismic moment and dimensions of the rupture plane are used to generate ten samples for the finite fault source model having different slip distribution along the rupture plane as a random field. The BB ground motions (0.01–25 Hz) are obtained by merging LF and HF ground motions in the time domain by matching them at a frequency of ∼0.3 Hz. Such BB results are simulated at a grid of stations and at locations where modified Mercalli intensity (MMI) values are available. The estimated MMI values and the observed MMI values are compared to emphasize the efficacy of the model. The maximum PGA estimated from the simulated ground motions in horizontal and vertical directions are observed to be 0.48 g and 0.4 g. Further, 5 per cent damped response spectra and spectral amplification are analysed concerning the sediment depth of the Indo-Gangetic Basin. The results from the study can serve as inputs for dynamic analysis and the design of earthquake-resistant structures across different locations in the Indo-Gangetic Basin.

Spatial correlation assessment of multiple earthquake intensity measures using physics-based simulated ground motions

Predictive models for spatial correlation play an effective role in the assessment of seismic risk associated with distributed infrastructure and building portfolios. However, existing models often rely on simplified approaches, assuming isotropy and stationarity. This paper verifies these assumptions by presenting a comprehensive study using a database of 3D physics-based simulated broadband ground motions for Istanbul, generated by the SPEED software. The results reveal significant event-to-event variability and nonstationary and anisotropic characteristics of spatial correlation influenced by source, path, and site effects. The development of nonstationary correlation models requires exploring influential metrics beyond spatial proximity and gaining a deep understanding of their impact, which is the focus of this study. Analysis of the spatial correlations of peak ground displacement, peak ground velocity, peak ground acceleration, and response spectral accelerations at different periods, employing both stationary and nonstationary correlation modelling methods and considering the finite fault model, indicates that the slip distribution pattern, direction and distance of station pairs relative to earthquake rupture, soil softness, and homogeneity of soil properties significantly influence the spatial correlations of near-field earthquake ground motions. Implementation of the introduced parameters in predictive spatial correlation models enhances the precision of regional seismic hazard assessments.

Broadband Ground-Motion Simulations with Machine-Learning-Based High-Frequency Waves from Fourier Neural Operators

ABSTRACT Seismic hazards analysis relies on accurate estimation of expected ground motions for potential future earthquakes. However, obtaining realistic and robust ground-motion estimates for specific combinations of earthquake magnitudes, source-to-site distances, and site conditions is still challenging due to the limited empirical data. Seismic hazard analysis also benefits from the simulation of ground-motion time histories, whereby physics-based simulations provide reliable time histories but are restricted to a lower frequency for computational reasons and missing information on small-scale earthquake-source and Earth-structure properties that govern high-frequency (HF) seismic waves. In this study, we use densely recorded acceleration broadband (BB) waveforms to develop a machine-learning (ML) model for estimating HF ground-motion time histories from their low-frequency (LF) counterparts based on Fourier Neural Operators (FNOs) and Generative Adversarial Networks (GANs). Our approach involves two separate FNO models to estimate the time and frequency properties of ground motions. In the time domain, we establish a relationship between normalized low-pass filtered and BB waveforms, whereas in the frequency domain, the HF spectrum is trained based on the LF spectrum. These are then combined to generate BB ground motions. We also consider seismological and site-specific factors during the training process to enhance the accuracy of the predictions. We train and validate our models using ground-motion data recorded over a 20 yr period at 18 stations in the Ibaraki province, Japan, considering earthquakes in the magnitude range M 4–7. Based on goodness-of-fit measures, we demonstrate that our simulated time series closely matches recorded observations. To address the ground-motion variability, we employ a conditioned GAN approach. Finally, we compare our results with several alternative approaches for ground-motion simulation (stochastic, hybrid, and ML-based) to highlight the advantages and improvements of our method.

Prediction of Regional Broadband Strong Ground Motions Using a Teleseismic Source Model of the 18 April 2014 Mw 7.3 Papanoa, Mexico, Earthquake

ABSTRACT To estimate predicted ground motion from a teleseismic slip model, we use a low- and high-frequency hybrid method to simulate the regional, strong ground motions observed following the 18 April 2014 moment magnitude (Mw) 7.3 Papanoa, Mexico, earthquake. To generate the regional ground motion at low frequencies (<1 Hz), a teleseismically derived, finite-fault, kinematic model is used to define the earthquake source, taking into account slip-model variations identified with a parameter sampling approach that considers possible errors in the fault geometry, the hypocenter depth, and the rupture velocity. A 3D crustal model is used to calculate the low-frequency ground motions using a finite-element calculation that includes topography and considers variations in the source model to estimate the uncertainty in the calculations. High frequencies (>1 Hz) are added using a 1D full-wave propagation code that estimates uncertainties by considering multiple random distributions of slip with different spatial correlation lengths. The synthetic, broadband (0.05–10.0 Hz) ground motions are obtained by combining the low- and high-frequency portions match filtered at 1 Hz. These synthetic ground motions are compared with the regional observations using velocity records, peak ground acceleration, and medians of the orientation-independent response spectra of the horizontal components (RotD50) calculated at periods of 0.2, 0.3, 0.5, 1.0, 2.0, 3.0, 5.0, 7.5, and 10.0 s. The results indicate that ground motions estimated at these periods using our hybrid approach based primarily on a teleseismically derived source model are comparable to the values observed for the 2014 Papanoa earthquake at regional distances. The approach could be used to estimate strong-motion spectral levels expected for regions with limited local and regional recordings and could also fill in magnitude or distance gaps in ground-motion prediction relations utilized in the assessment of seismic hazard.

Predicting the seismic ground-motion parameters: 3D physics-based numerical simulations combined with artificial neural networks

Typically, it is challenging to incorporate near-surface soils into 3D physics-based numerical simulations (PBSs) for ground-motion prediction. The low shear wave speed of near-surface soils, coupled with the complexity of the soil seismic response, poses significant difficulties. To overcome these limitations, a hybrid approach was proposed in this study, combining PBSs with artificial neural networks (ANNs). The essence of the hybrid method can be summarized as follows: (1) development of ANN models, establishing a strong-motion database, training the ANNs on it to predict the ground-motion parameters for East–West (EW), North–South (NS), and Vertical (UD) directions afterward; (2) establishment of 3D PBS model, obtaining the ground-motion parameters of the bedrock face corresponding to a certain shear wave speed; (3) application of the trained ANNs to predict the ground-motion parameters on the ground surface, taking the simulated results and related site parameters as inputs, and the outputs are peak ground acceleration (PGA) and 5% damped spectral accelerations (Sa) at different periods on the ground surface. In this study, ANN models were trained on a strong-motion database based on Kiban–Kyoshin Network (KiK-net). After several verifications of the ANN predictions, a case study of the 21 October 2016 Mw6.2 Central Tottori earthquake was conducted. In addition to the comparison with observations, the broadband (0.1–10 Hz) results of the hybrid method were also compared with the results that obtained by transfer function based on recorded data and Next Generation Attenuation (NGA)-West2 ground-motion prediction equations (GMPEs) to demonstrate the effectiveness and applicability of the proposed method. In addition, the distribution of Sa for four periods in simulated area was presented. The performance of the hybrid method for predicting broadband ground-motion characteristics was generally satisfactory.

A future scenario earthquake and ground motion hazards for Kathmandu, Nepal

Since Nepal is an earthquake-prone country due to the collision of the Indian and Eurasian plates, it is crucial for its capital of Kathmandu to evaluate ground motion hazards from a future large earthquake. For this purpose, we constructed a realistic scenario earthquake with realistic rupture parameters in a likely location. To obtain the location, a new distribution of the rupture zones of large historical earthquakes along the Main Himalayan Thrust (MHT) was obtained by integrating the distribution from a previous study and the results of trench surveys. Global Navigation Satellite System observations indicated that the plate boundary is strongly coupled from the southern boundary of the MHT to a depth of approximately 10 km and there is almost no lateral change in the coupling. This implies that all regions along the MHT have similar rates of strain increase. Therefore, it is most probable that the rupture zone of the oldest previous event will rupture as a scenario earthquake. In the new distribution, the 1255 earthquake is the oldest. However, large earthquakes occurred in 1934 and 2015 within its rupture zone. Thus, we adopted the area obtained by removing the 1934 and 2015 rupture zones from the western part of the 1255 rupture zone. The relationship between the rupture area size and seismic moment of the 2015 earthquake lies between the scaling formulas for crustal earthquakes and plate-boundary earthquakes, but is closer to the former. Therefore, using this and the scheme for characterized source models, we determined realistic rupture parameters. We then simulated broadband ground motions in Kathmandu using these rupture parameters, our 3-D velocity structure models, and a hybrid method combining the finite-difference method and the stochastic Green’s function method. We obtained the peak ground accelerations (PGAs) of simulated ground motions, and calculated the seismic intensities in the Modified Mercalli intensity scale from the PGAs as indexes of hazards for Kathmandu. Intensities IX coincide with the center of the Kathmandu Valley, and intensities VIII and VII are found in the area surrounded by the sedimentary boundary and the southernmost part of the valley.Graphical abstract

Simulation of Broadband Ground Motions for the 2016 Mw 6.8 Chauk Earthquake

Simulation of Broadband Ground Motions for the 2016 Mw 6.8 Chauk Earthquake

Broadband Ground-Motion Synthesis via Generative Adversarial Neural Operators: Development and Validation

ABSTRACT We present a data-driven framework for ground-motion synthesis that generates three-component acceleration time histories conditioned on moment magnitude (M), rupture distance (Rrup), time-average shear-wave velocity at the top 30 m (VS30), and style of faulting. We use a Generative Adversarial Neural Operator (GANO)—a resolution invariant architecture that guarantees model training independent of the data sampling frequency. We first present the conditional ground-motion synthesis algorithm (cGM-GANO) and discuss its advantages compared to the previous work. We next train cGM-GANO on simulated ground motions generated by the Southern California Earthquake Center Broadband Platform (BBP) and on recorded the Kiban–Kyoshin network (KiK-net) data, and show that the model can learn the overall magnitude, distance, and VS30 scaling of effective amplitude spectra (EAS) ordinates and pseudospectral accelerations (PSA). Results specifically show that cGM-GANO produces consistent median scaling with the training data for the corresponding tectonic environments over a wide range of frequencies for scenarios with sufficient data coverage. For the BBP dataset, cGM-GANO cannot learn the ground-motion scaling of the stochastic frequency components (f > 1 Hz); for the KiK-net dataset, the largest misfit is observed at short distances (Rrup<50 km) and for soft-soil conditions (VS30<200 m/s) due to the scarcity of such data. Except for these conditions, the aleatory variability of EAS and PSA are captured reasonably well. Finally, cGM-GANO produces similar median scaling to traditional ground-motion models (GMMs) for frequencies greater than 1 Hz for both PSA and EAS but underestimates the aleatory variability of EAS. Discrepancies in the comparisons between the synthetic ground motions and GMMs are attributed to inconsistencies between the training dataset and the datasets used in GMM development. Our pilot study demonstrates GANO’s potential for efficient synthesis of broadband ground motions.

Erratum to The 3D Physics-Based Broadband Ground-Motion Simulation, including Topography Effects Causing Damage to Structures, for the 2022 Mw 6.6 Menyuan, China, Earthquake

<i>Erratum to</i> The 3D Physics-Based Broadband Ground-Motion Simulation, including Topography Effects Causing Damage to Structures, for the 2022 Mw 6.6 Menyuan, China, Earthquake

GA-BPNN Prediction Model of Broadband Ground Motion Parameters in Tianjin Area Driven by Synthetic Database Based on Hybrid Simulated Method

GA-BPNN Prediction Model of Broadband Ground Motion Parameters in Tianjin Area Driven by Synthetic Database Based on Hybrid Simulated Method

The 3D Physics-Based Broadband Ground-Motion Simulation, including Topography Effects Causing Damage to Structures, for the 2022 Mw 6.6 Menyuan, China, Earthquake

ABSTRACT On 8 January 2022, Menyuan County, China, was struck by an Mw 6.6 earthquake that caused surface rupture in the epicentral area and severe damage to an important railway bridge. The earthquake was recorded by only one strong-motion station, which presents a challenge for quantitatively estimating the extent of the ground-motion distribution caused by this event. In this study, the spectral element method (SPECFEM3D code), which solves the elastodynamic equations and can capture the full physics of seismic-wave propagation, is employed for broadband (0–10 Hz) ground-motion simulations of this earthquake. A hybrid kinematic source is developed in which the final slip distribution combines a prescribed asperity model based on Interferometric Synthetic Aperture Radar data (as a source for low-frequency radiation) and a stochastic part (as a source for high-frequency radiation), which introduces spatial heterogeneities to the prescribed asperity model. The numerical approach is first validated by modeling the well-recorded 1994 Northridge earthquake before modeling the Menyuan earthquake. The simulated ground motion is compared with the only observed strong-motion station record, as well as with empirical Next Generation Attenuation-West2 ground-motion models. Then, topography effect in Menyuan earthquake is studied in detail. The simulated ground motions with and without surface topography indicate that the topography tends to focus and scatter the seismic wavefield, resulting in amplification of the ground shaking. The results show a significant correlation between the peak ground velocity (PGV) and topography. The PGV amplification caused by topography effects is period dependent, and its peak amplification reaches up to 50% within a typical resonance period (1–2 s). It could be inferred that the railway bridge probably vibrated in resonance and suffered severe damage owing to the amplified long-period ground motion caused by the topography.

Comparing and evaluating alternative methods to account for shallow site effects in hybrid broadband ground-motion simulations

Comparing and evaluating alternative methods to account for shallow site effects in hybrid broadband ground-motion simulations

Pseudo-dynamic rupture implementation in 3D viscoelastic finite-difference code for physics based broadband ground motion synthetics

Pseudo-dynamic rupture implementation in 3D viscoelastic finite-difference code for physics based broadband ground motion synthetics

City-scale buildings damage estimation based on broadband physics-based ground motion simulation of 2021 Ms 6.4 Yangbi, China, earthquake

This article proposed a computational workflow for city-scale building damage estimation based on broadband physics-based ground motion simulation. The dynamic stiffness matrix method in frequency-wavenumber domain is employed for broadband physics-based ground motion simulation of finite fault along with site response correction using equivalent-linear site response analysis approach. With simulated ground motion, seismic response of buildings, using multi-degree of freedom model, is simulated using nonlinear time history analysis, and building damage is evaluated based on a trilinear backbone curve of story’s nonlinear force-drift model. Main advantage of the framework lies in the employed dynamic stiffness matrix method for ground motion simulation, which can efficiently generate broadband ground motions in perfect parallel and naturally capture the physics of finite fault source, propagation path, and spatial variability characteristics of ground motion. To demonstrate the salient features of proposed workflow, the 2021 Ms 6.4 Yangbi earthquake is simulated with frequency resolution up to 20 Hz, and seismic damage of buildings in Yangbi county are estimated. Results show that most traditional wood-adobe structures suffer moderate to severe damage, and engineered seismic buildings (mostly RC frame) in Yangbi county suffer minor damage, which agrees with field investigation results.

Uncertainties in Broadband Determination of the High-Frequency Spectral Decay, Kappa, in Eastern Canada

ABSTRACT Kappa (the high-frequency spectral decay slope at near-source distances; often referred to as κ0) is determined at 25 seismograph stations in Eastern Canada using broadband ground-motion modeling approaches. The database comprises Fourier spectra (effective amplitude spectrum for the horizontal component and the vertical component, 0.8–40 Hz) computed from 3318 earthquakes of moment magnitude M 1.5–5 recorded on stations within 150 km. Average kappa values for bedrock sites, having shear-wave velocities from 850 to 2400 m/s, are highly variable, ranging from −29 to +21 ms (horizontal) and −28 to +11 ms (vertical), but appear on average to be near-zero. The values obtained are sensitive to methodology, especially the necessary adjustments to the spectra to account for site amplification effects. Kappa values do not appear to correlate well with site parameters such as rock shear-wave velocity, average shear-wave velocity in the upper 30 m, primary wave velocity, site class, type and age of rock, or instrument housing. This lack of correlation may reflect the noted sensitivities to methodological factors. We conclude that kappa values in rock environments are not reliably estimated from such proxies and should be determined from recorded ground motions at a given location. On average, there is little evidence of significant high-frequency attenuation on rock sites beyond that already accounted for in ground-motion modeling by the empirical parameterization of regional Q-related path effects.

Broadband ground motion simulation using a hybrid approach of the May 21, 2021 M7.4 earthquake in Maduo, Qinghai, China

In this study, the broadband ground motions of the 2021 M7.4 Maduo earthquake were simulated to overcome the scarcity of ground motion recordings and the low resolution of macroseismic intensity map in sparsely populated high-altitude regions. The simulation was conducted with a hybrid methodology, combining a stochastic high-frequency simulation with a low-frequency ground motion simulation, from the regional 1-D velocity structure model and the Wang WM et al. (2022) source rupture model, respectively. We found that the three-component waveforms simulated for specific stations matched the waveforms recorded at those stations, in terms of amplitude, duration, and frequency content. The validation results demonstrate the ability of the hybrid simulation method to reproduce the main characteristics of the observed ground motions for the 2021 Maduo earthquake over a broad frequency range. Our simulations suggest that the official map of macroseismic intensity tends to overestimate shaking by one intensity unit. Comparisons of simulations with empirical ground motion models indicate generally good consistency between the simulated and empirically predicted intensity measures. The high-frequency components of ground motions were found to be more prominent, while the low-frequency components were not, which is unexpected for large earthquakes. Our simulations provide valuable insight into the effects of source complexity on the level and variability of the resulting ground motions. The acceleration and velocity time histories and corresponding response spectra were provided for selected representative sites where no records were available. The simulated results have important implications for evaluating the performance of engineering structures in the epicentral regions of this earthquake and for estimating seismic hazards in the Tibetan regions where no strong ground motion records are available for large earthquakes.