Simulation Of Earthquake Ground Motions Research Articles

Evaluation of directionality in physics-based ground motion simulations of strike-slip earthquakes

Recent advances in engineering seismology and computing power have led to the development of realistic physics-based ground motion simulations. The use of these simulations for engineering applications requires that the ground motions exhibit characteristics consistent with those of recorded ground motions. While several studies have evaluated the intensity, frequency content, duration, and other characteristics of ground motion simulations for their possible use in engineering applications, few have focused on directionality. This article evaluates directionality in the response of single-degree-of-freedom oscillators when subjected to CyberShake Study 15.12 simulated ground motions from strike-slip earthquakes, by carefully comparing it to the directionality in recorded ground motions having the same style of faulting. Physics-based ground motion simulations at 334 stations from 5 different rupture variations in two large-magnitude earthquake scenarios on the Elsinore fault are evaluated. The orientation of maximum oscillator response and its spatial distribution are studied for each rupture. The orientation of maximum oscillator response is found to occur systematically close to the epicentral transverse orientation at all rupture distances, consistent with recent findings for ground motions recorded during strike-slip earthquakes. In addition, the orientation-specific spectral accelerations, when computed as a function of angular distance from the epicentral transverse orientation, are found to exhibit a variation consistent with the overall trend observed in records from the next-generation attenuation (NGA)-West2 database. However, the level of polarization at short periods in the simulated hybrid broadband waveforms used in this study is larger than that in recorded ground motions.

Evaluation of the Inter-frequency Correlation of New Zealand CyberShake Crustal Earthquake Simulations

The inter-frequency correlation of ground-motion residuals is related to the width of peaks and troughs in the ground-motion spectra (either response spectra or Fourier amplitude spectra; FAS) and is therefore an essential component of ground-motion simulations for representing the variability of structural response. As such, this component of the simulations requires evaluation and validation when the intended application is seismic fragility and seismic risk. This article evaluates the CyberShake NZ [1] crustal earthquake ground-motion simulations for their inter-frequency correlation, including comparisons with an empirical model developed from a global catalogue of shallow crustal earthquakes in active tectonic regions, and with results from similar simulations (SCEC CyberShake; [2]). Compared with the empirical model, the CyberShake NZ simulations have a satisfactory level of total inter-frequency correlation between the frequencies 0.1 – 0.25 Hz. At frequencies above 0.25 Hz, the simulations have lower (statistically significant at 95% confidence level) total inter-frequency correlation than the empirical model and therefore require calibration. To calibrate the total correlation, it is useful to focus on the correlation of the residual components. The between-event residual correlations, physically related to source effects (e.g., stress drop) which drive ground motions over a broad frequency range, are low at frequencies greater than about 0.25 Hz. Modifications to the cross-correlation between source parameters in the kinematic rupture generator can improve the inter-frequency correlations in this range [3]. The between-site residual correlations, which represents the correlation between frequencies of the systematic site amplification deviations, are larger (statistically significant at 95% confidence level) than the empirical model for frequencies less than about 0.5 Hz. We postulate that this relates to the relative simplicity of site amplification methods in the simulations, which feature less variability than the amplification observed in the data. Additional insight would be gained from future evaluations accounting for repeatable path and basin effects, using simulations with refined or alternative seismic velocity models, and using simulations with a higher crossover frequency to deterministic methods (e.g., 1 Hz or higher).

Stochastic simulation of earthquake ground motions based on improved finite-fault model

In the seismic reliability analysis of engineering structures, it is often necessary to adopt stochastic ground motions as inputs. However, the current methods used to generate stochastic samples, such as the spectral representation method, the spectral transfer method, the dynamic source method, the physical source method, and the comprehensive method, etc., are not very convincing since they do not contain the complete information of seismic occurrence and propagation. In this study, an improved finite-fault model for stochastic simulation of ground motions is proposed. Compared to existing stochastic finite-fault model, the improved model considers the propagation law of phase spectrum, local site effect, and the impact of wave velocity on the arrival time of seismic waves. Besides, identification and statistics of model parameters are carried out based on ground motion records. Reasonable samples of stochastic ground motions are then obtained. In addition, parameter sensitivity analysis is conducted to determine critical random variables, which reduces the complexity of stochastic simulation. Simulation results are compared with recorded accelerograms from the 1999 Chi-Chi earthquake. It is shown that the improved stochastic finite-fault model is reliable, and the acceleration response spectra of simulated samples are consistent with those of station records collected at various site classes and the design spectra.

Estimation of model parameters and simulation of earthquake ground motion by stochastic finite-fault modelling based on a modified slip-related corner frequency

Estimation of model parameters and simulation of earthquake ground motion by stochastic finite-fault modelling based on a modified slip-related corner frequency

Stochastic simulation of earthquake ground motions for the seismic assessment of monumental masonry structures: Source‐based vs site‐based approaches

AbstractEarthquakes are among the most destructive natural disasters and have resulted in a massive number of fatalities and economic losses all over the world. Simulated ground motion records are valuable, particularly for regions lacking seismic stations or with a limited history of large‐magnitude earthquakes. Notably, a significant percentage of monumental masonry buildings are located in regions with limited access to real records; hence, simulated records play a paramount role in their seismic protection. However, few studies have investigated the structural response of heritage buildings via response history analyses to assess the performance of simulated earthquakes against real ones. To accomplish this, this study simulates the recorded time‐series of the 9th of July 1998 Faial earthquake in the Azores (Mw = 6.2) at four available stations, using two different simulation approaches, that is, a source‐based stochastic finite‐fault method and a site‐based broadband stochastic method. First, two masonry facades with sidewalls characterized by different slenderness levels are adopted to conduct this research. Moreover, the proposed approach is also applied to an existing monumental structure, that is, São Francisco Church, located at Horta, which was affected by damage during the Faial earthquake. Results demonstrate that both simulation approaches provide similar results in terms of structural response prediction. The proposed framework also demonstrates that a small mismatch in terms of predicted damage patterns can result in a significant relative error in terms of displacement predictions.

Simulation of Ground Motion From Finite‐Fault Modeling Incorporating the Influence of Duration

AbstractOn 21 May 2021 (local time), an Mw 6.1 earthquake struck the Yangbi County, Yunnan Province, China. The finite fault stochastic simulation approach is usually used to simulate ground motions in high‐frequency band (f > 1 Hz). Model parameters needed for earthquake ground motion simulation mainly include source, path, and site. In the high‐frequency ground motion simulation program widely used in earthquake engineering, the reciprocal of corner frequency is typically used to define the source rise time; however, the complete step‐wise derivation process is unavailable. In deriving the static corner frequency f0, source rise time is typically estimated to be the time required for the rupture to reach 50% of the final location, and the source rise time then can be obtained as 0.27/f0, which is consistent with the hypothesis of corner frequency and rupture velocity, and the correlation and integrity between parameters are established. This study also focuses on the influence of different source rise times and path durations on the simulation results, such as Fourier acceleration spectrum, pseudo‐spectral acceleration, and peak ground acceleration. The results show that the source rise time recommended in this simulation can improve the accuracy of near‐fault ground motion simulations. This study provides suggestions for a reasonable selection of path duration in different engineering applications.

Ground motion simulations of historical earthquakes: the case study of the Fabriano (1741, Mw = 6.1) and Camerino (1799, Mw = 6.1) earthquakes in central Italy

Ground motion simulations of historical earthquakes: the case study of the Fabriano (1741, Mw = 6.1) and Camerino (1799, Mw = 6.1) earthquakes in central Italy

3-D shallow shear velocity structure of the Jakarta Basin from transdimensional ambient noise tomography.

Situated on the northern coast of the Indonesian island of Java, Jakarta and its metropolitan area (Greater Jakarta) are subject to significant earthquake hazards from a subduction zone south of Java and nearby active crustal faults. The seismic risk may be even higher because Greater Jakarta resides on a sedimentary basin filled with thick Pliocene-Pleistocene sediments. A comprehensive study of Jakarta Basin's properties and geometry is important for creating robust seismic hazard and risk assessments. The main objective of this study is to develop a 3-D model of Jakarta Basin's shallow shear-wave velocity (VS ) structure and improve on previous models that did not cover the basin edge due to the extent of data coverage. Between April and October 2018, we deployed a new temporary seismic network to extend the spatial coverage beyond that of a previous deployment in 2013, and sampled 143 locations through sequential deployments of 30 broad-band sensors covering Jakarta and its adjacent areas. We conducted a 2-stage transdimensional Bayesian inversion of Rayleigh wave phase velocity dispersion curves derived from seismic noise. To begin, we applied tomography and constructed 2-D phase velocity maps for periods 1-5s. Then, at each point in a regular grid defined on these maps, we invert each dispersion curve into 1-D depth profiles of VS . Finally, these profiles at gridpoints with ∼2km spacing are interpolated to form a pseudo-3-D VS model. Our results reveal the edge of the Pliocene-Pleistocene sediments along the south. Also, we resolve a basement offset across south Jakarta that we suggest may be related to the western extension of the Baribis Fault (alternatively, the West Java Backarc Thrust). We recommend using this 3-D model of the Jakarta Basin for scenario earthquake ground motion simulations. Such simulations would help establish how important it might be to re-assess seismic hazard and risk in Greater Jakarta so that basin resonance and amplification are considered.

Simulation of earthquake ground motion via stochastic finite-fault modeling considering the effect of rupture velocity

Simulation of earthquake ground motion via stochastic finite-fault modeling considering the effect of rupture velocity

A suite of broadband physics‐based ground motion simulations for the Istanbul region

AbstractPhysics‐based earthquake ground motion simulations (GMS) have acquired significant growth over the last two decades, mainly due to the explosive developments of high‐performance computing techniques and resources. These techniques benefit high/medium seismicity regions such as the city of Istanbul, which presents insufficient historical ground motion data to properly estimate seismic hazard and risk. We circumvent this reality with the aid of the Texas Advanced Computing Center (TACC) facilities to perform a suite of 57 high‐fidelity broadband (8–12 Hz) large‐scale physics‐based GMS for a region in Istanbul, Turkey. This paper focuses on the details of simulated GMS: (i) validation of the GMS approach against recorded ground motions produced by the 2019 Silivri earthquake; (ii) characteristics of 57 different source models, which aim to consider the uncertainties of many fault rupture features, including the length and width, dip, strike, and rake angles of considered fault planes, as well as hypocenter locations and earthquake magnitudes ranging between 6.5 and 7.2; (iii) high‐resolution topography and bathymetry and seismic data that are incorporated into all GMS; (iv) simulation results, such as PGAs and PGVs versus and distances to fault ruptures (), of 2912 surface stations for all 57 GMS. More importantly, this research provides a massive database of displacement, velocity and acceleration time histories in all three directions over more than 20,000 stations at both surface and bedrock levels. Such site‐specific high‐density and ‐frequency simulated ground motions can notably contribute to the seismic risk assessment of this region and many other applications.

Regional-Scale 3D Ground-Motion Simulations of Mw 7 Earthquakes on the Hayward Fault, Northern California Resolving Frequencies 0–10 Hz and Including Site-Response Corrections

ABSTRACTLarge earthquake ground-motion simulations in 3D Earth models provide constraints on site-specific shaking intensities but have suffered from limited frequency resolution and ignored site response in soft soils. We report new regional-scale 3D simulations for moment magnitude 7.0 scenario earthquakes on the Hayward Fault, northern California with SW4. Simulations resolved significantly broader band frequencies (0–10 Hz) than previous studies and represent the highest resolution simulations for any such earthquake to date. Seismic waves were excited by a kinematic rupture following Graves and Pitarka (2016) and obeyed wave propagation in a 3D Earth model with topography from the U.S. Geological Survey (USGS) assuming a minimum shear wavespeed, VSmin, of 500 m/s. We corrected motions for linear and nonlinear site response for the shear wavespeed, VS, from the USGS 3D model, using a recently developed ground-motion model (GMM) for Fourier amplitude spectra (Bayless and Abrahamson, 2018, 2019a). At soft soil locations subjected to strong shaking, the site-corrected intensities reflect the competing effects of linear amplification by low VS material, reduction of stiffness during nonlinear deformation, and damping of high frequencies. Sites with near-surface VS of 500 m/s or greater require no linear site correction but can experience amplitude reduction due to nonlinear response. Averaged over all sites, we obtained reasonable agreement with empirical ergodic median GMMs currently used for seismic hazard and design ground motions (epsilon less than 1), with marked improvement at soft sedimentary sites. At specific locations, the simulated shaking intensities show systematic differences from the GMMs that reveal path and site effects not captured in these ergodic models. Results suggest how next generation regional-scale earthquake simulations can provide higher spatial and frequency resolution while including effects of soft soils that are commonly ignored in scenario earthquake ground-motion simulations.

Analysis of Intensity Attenuation Characteristics Using Physics-based Earthquake Ground-motion Simulation with Site Effect in the Southern Korean Peninsula

Analysis of Intensity Attenuation Characteristics Using Physics-based Earthquake Ground-motion Simulation with Site Effect in the Southern Korean Peninsula

Earthquake risk assessment of underground railway station by fragility analysis based on numerical simulation

Korean society experienced successive earthquakes exceeding 5.0 magnitude in the past three years resulting in an increasing concern about earthquake stability of urban infrastructures. This study focuses on the significant aspects of earthquake risk assessment for the cut-and-cover underground railway station based on two-dimensional dynamic numerical analysis. Presented are features from a case study performed for the railway station in Seoul, South Korea. The PLAXIS2D was employed for numerical simulation and input of the earthquake ground motion was chosen from Pohang earthquake records (M5.4). The paper shows key aspects of earthquake risk for soil-structure system varying important parameters including embedded depth, supported ground information, and applied seismicity level, and then draws several meaningful conclusions from the analysis results such as seismic risk assessment.

Three-dimensional physics-based earthquake ground motion simulations for seismic risk assessment in densely populated urban areas

In this paper we describe a mathematical and numerical approach that combines physics-based simulated ground motion caused by earthquakes with fragility functions to model the structural damages induced to buildings. To simulate earthquake ground motion we use the discontinuous Galerkin spectral element method to solve a three-dimensional differential model at regional scale describing the propagation of seismic waves through the earth layers up to the surface. Selected intensity measures, retrieved from the synthetic time histories, are then employed as input for a vulnerability model based on fragility functions, in order to predict building damage scenarios at urban scale. The main features and effectiveness of the proposed numerical approach are tested on the Beijing metropolitan area.

Ground motion simulations of Hope fault earthquakes

This paper examines ground motions for a major potential Mw7.51 rupture of the Hope Fault using a physics based simulation methodology and a 3D crustal velocity model of New Zealand. The simulation methodology was validated for use in the region through comparison with observations for a suite of historic small magnitude earthquakes located proximal to the Hope Fault. Simulations are compared with conventionally utilised empirical ground motion models, with simulated peak ground velocities being notably higher in regions with modelled sedimentary basins. A sensitivity analysis was undertaken where the source characteristics of magnitude, stress parameter, hypocentre location and kinematic slip distribution were varied and an analysis of their effect on ground motion intensities is presented. It was found that the magnitude and stress parameter strongly influenced long and short period ground motion amplitudes, respectively. Ground motion intensities for the Hope Fault scenario are compared with the 2016 Kaik¯oura Mw7.8 earthquake, it was found that the Kaikoura earthquake produced stronger motions along the eastern South Island, while the Hope Fault scenario resulted in stronger motions immediately West of the near-fault region and similar levels of ground motion in Canterbury. The simulated ground motions for this scenario complement prior empirically-based estimates and are informative for mitigation and emergency planning purposes.

Quantification of the Influence of Deep Basin Effects on Structural Collapse Using SCEC CyberShake Earthquake Ground Motion Simulations

This paper examines the effects of earthquake ground motions in deep sedimentary basins on structural collapse risk using physics-based earthquake simulations of the Los Angeles basin developed through the Southern California Earthquake Center's CyberShake project. Distinctive waveform characteristics of deep basin seismograms are used to classify the ground motions into several archetype groups, and the damaging influence of the basin effects are evaluated by comparing nonlinear structural responses under spectrum and significant duration equivalent basin and nonbasin ground motions. The deep basin ground motions are observed to have longer period-dependent durations and larger sustained spectral intensities than nonbasin motions for vibration periods longer than about 1.5 s, which can increase structural collapse risk by up to 20% in ground motions with otherwise comparable peak spectral accelerations and significant durations. Two new metrics are proposed to quantify period-dependent duration effects that are not otherwise captured by conventional ground motion intensity measures. The proposed sustained amplitude response spectra and significant duration spectra show promise for characterizing the damaging effects of long duration features of basin ground motions on buildings and other structures.

ER3D: a structural and geophysical 3-D model of central Emilia-Romagna (northern Italy) for numerical simulation of earthquake ground motion

Abstract. During the 2012 seismic sequence of the Emilia region (northern Italy), the earthquake ground motion in the epicentral area featured longer duration and higher velocity than those estimated by empirical-based prediction equations typically adopted in Italy. In order to explain these anomalies, we (1) build up a structural and geophysical 3-D digital model of the crustal sector involved in the sequence, (2) reproduce the earthquake ground motion at some seismological stations through physics-based numerical simulations and (3) compare the observed recordings with the simulated ones. In this way, we investigate how the earthquake ground motion in the epicentral area is influenced by local stratigraphy and geological structure buried under the Po Plain alluvium. Our study area covers approximately 5000 km2 and extends from the right Po River bank to the Northern Apennine morphological margin in the N–S direction, and between the two chief towns of Reggio Emilia and Ferrara in the W–E direction, involving a crustal volume of 20 km thickness. We set up the 3-D model by using already-published geological and geophysical data, with details corresponding to a map at scale of 1:250 000. The model depicts the stratigraphic and tectonic relationships of the main geological formations, the known faults and the spatial pattern of the seismic properties. Being a digital vector structure, the 3-D model can be easily modified or refined locally for future improvements or applications. We exploit high-performance computing to perform numerical simulations of the seismic wave propagation in the frequency range up to 2 Hz. In order to get rid of the finite source effects and validate the model response, we choose to reproduce the ground motion related to two moderate-size aftershocks of the 2012 Emilia sequence that were recorded by a large number of stations. The obtained solutions compare very well to the recordings available at about 30 stations in terms of peak ground velocity and signal duration. Snapshots of the simulated wavefield allow us to attribute the exceptional length of the observed ground motion to surface wave overtones that are excited in the alluvial basin by the buried ridge of the Mirandola anticline. Physics-based simulations using realistic 3-D geomodels show eventually to be effective for assessing the local seismic response and the seismic hazard in geologically complex areas.

Numerical Simulation of M9 Megathrust Earthquakes in the Cascadia Subduction Zone

We estimate ground motions in the Pacific Northwest urban areas during M9 subduction scenario earthquakes on the Cascadia megathrust by simulating wave propagation from an ensemble of kinematic source descriptions. Velocities and densities in our computational mesh are defined by integrating the regional Cascadia Community Velocity Model (CVM) v1.6 (Stephenson et al. P-and S-wave velocity models incorporating the Cascadia subduction zone for 3D earthquake ground motion simulations—update for open-file report 2007–1348, US Geological Survey, 2017) including the ocean water layer with a local velocity model of the Georgia basin (Molnar, Predicting earthquake ground shaking due to 1D soil layering and 3D basin structure in SW British Columbia, Canada, 2011), including additional near-surface velocity information. We generate six source realizations, each consisting of a background slip distribution with correlation lengths, rise times and rupture velocities consistent with data from previous megathrust earthquakes (e.g., 2011 M 9 Tohoku or 2010 M 8.8 Maule). We then superimpose M ~ 8 subevents, characterized by short rise times and high stress drops on the background slip model to mimic high-frequency strong ground motion generation areas in the deeper portion of the rupture (Frankel, Bull Seismol Soc Am 107(1):372–386, 2017). The wave propagation is simulated using the discontinuous mesh (DM) version of the AWP finite difference code. We simulate frequencies up to 1.25 Hz, using a spatial discretization of 100 m in the fine grid, resulting in surface grid dimensions of 6540 × 10,728 mesh points. At depths below 8 km, the grid step increases to 300 m. We obtain stable and accurate results for the DM method throughout the simulation time of 7.5 min as verified against a solution obtained with a uniform 100 m grid spacing. Peak ground velocities (PGVs) range between 0.57 and 1.0 m/s in downtown Seattle and between 0.25 and 0.54 m/s in downtown Vancouver, while spectral accelerations at 2 s range between 1.7 and 3.6 m/s2 and 1.0 and 1.3 m/s2, respectively. These long-period ground motions are not significantly reduced if plastic Drucker-Prager yielding in shallow cohesionless sediments is taken into account. Effects of rupture directivity are significant at periods of ~ 10 s, but almost absent at shorter periods. We find that increasing the depth extent of the subducting slab from the truncation at 60 km in the Cascadia CVM version 1.6 to ~ 100 km increases the PGVs by 15% in Seattle and by 40% in Vancouver.

Simulation of multi-support depth-varying earthquake ground motions within heterogeneous onshore and offshore sites

This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions (MDSMs) within heterogeneous offshore and onshore sites. Based on 1D wave propagation theory, the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves. Moreover, the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation. Using the obtained transfer functions at any locations within a site, the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method (SRM). The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites. The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values, which fully validates the effectiveness of the proposed simulation method. The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.

Cluster Analysis of Long-Period Ground-Motion Simulation Data with Application to Nankai Trough Megathrust Earthquake Scenarios

We developed a clustering method combining principal component analysis and the k-means algorithm, which classifies earthquake scenarios based on the similarity of the spatial distribution of earthquake ground-motion simulation data generated for many earthquake scenarios, and applied it to long-period ground-motion simulation data for Nankai Trough megathrust earthquake scenarios. Values for peak ground velocity and relative velocity response at approximately 80,000 locations in 369 earthquake scenarios were represented by 15 principal components each, and earthquake scenarios were categorized into 30 clusters. In addition, based on clustering results, we determined that extracting relationships between principal components and scenario parameters is possible. Furthermore, by utilizing these relationships, it may be possible to easily estimate the approximate ground-motion distribution from the principal components of arbitrary sets of scenario parameters.