Stochastic Finite-fault Model Research Articles

Ground-motion simulations using two-dimensional convolution condition adversarial neural network(2D-cGAN)

In this paper, an integrated framework based on conditional adversarial neural network (cGAN) is established to simulate ground motions for earthquake scenarios with different magnitude, distance, and local site conditions. A ground motion dataset is created for training the network, within which most data are observed accelerograms collected from PEER and gaps for certain magnitude-site conditions are filled with accelerograms simulated using stochastic finite-fault modeling. During the learning of cGAN, the dataset is classified first with multi-labels according to local site conditions, and the multi-labels are set to be the conditional information Y for the network. Effects of using one-dimensional convolution (Conv1D) and two-dimensional convolution (Conv2D) in cGAN are tested in terms of the time-domain and frequency-domain characteristics of the generated ground motion. The test proves the strengths of Conv2D in capturing high-dimensional temporal and spectral characteristics from one-dimensional time series of ground motion. Ground motions generated using 2D-cGAN network are compared to the measures predicted by widely-used ground motion prediction equations, through which the reliability of 2D-cGAN network on ground motion simulation is verified.

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.

Composite Source Model for Broadband Ground-Motion Simulations: 2021 Mw 7.4 Maduo, China, Earthquake Case Study

Abstract On 22 May 2021, at 2:40 a.m. (local time), an earthquake with a moment magnitude of 7.4 was reported to have occurred in Maduo County (34.59° N, 98.34° E), China. The focal depth was 17 km. After the earthquake, many scholars inverted the slip distribution of the Maduo earthquake based on ground-motion recordings, and the Global Positioning System and the Interferometric Synthetic Aperture Radar data. To verify the reliability of the fast estimation source model method adopted in this study, the hybrid slip model of the 2011 Mw 7.4 Maduo earthquake, in Qinghai Province, China, is synthetized based on the stochastic finite-fault model and the semiempirical relation between the earthquake magnitude (Mw) and source parameters. The truncated normal distribution and regional crustal structure are used to generate 30 sets of global source parameters, which describes that the deterministic characteristics of the source mainly include the size of the rupture fault, and the average slip, and the local source parameters. The local parameters include asperity and k2 model parameters. Finally, stochastic finite-fault modeling is adopted to synthetic the acceleration response spectra at four selected sites meeting different geological conditions and orientations, and the minimum residual principle is used to select the final slip model for the Maduo earthquake with the minimum residual of the average response spectra. The research results show that the width, maximum slip, and asperity body position of the source model estimated in this study are consistent with those of the inversion slip model, which verifies the reliability and applicability of this method. This work provides technical and theoretical support for rapid prediction of the source model of earthquakes with specific magnitudes.

Stochastic finite-fault modeling of Ms 6.8 Luding earthquake in 2022 and seismic hazard scenario of Moxi fault, southwestern China

Stochastic finite-fault modeling of Ms 6.8 Luding earthquake in 2022 and seismic hazard scenario of Moxi fault, southwestern China

Simulation of the 2022 Mw 6.6 Luding, China, earthquake by a stochastic finite-fault model with a nonstationary phase

We adopted stochastic finite-fault simulations considering the nonstationary frequency characteristics for the 2022 Mw 6.6 Luding, China, earthquake at 16 strong-motion stations using the stochastic finite-fault model based on a dynamic corner frequency (EXSIM) code. The average simulated response spectra of earthquake ground motions were obtained and then compared with response spectra of 5% damped single degree of freedom system under recorded ground motion excitation to verify whether the finite-fault model that considers the nonstationary frequency characteristics can reproduce the critical characteristics of ground motions and improve the simulation accuracy. The high-frequency spectral decay is calculated by the real recordings and the stress drop is determined by the trial-and-error method. In addition, the local site amplifications are estimated from the horizontal-vertical spectral ratio (H/V). An improved EXSIM that considers the slip-related corner frequency is also used in this study. The results indicate that the nonstationary phase can significantly improve the simulation accuracy of EXSIM in the short period and has little effect on the long-period simulation results. However, the effect of the nonstationary phase on the simulation results obtained from the improved EXSIM is not significant. Regarding the peak ground acceleration (PGA), the nonstationary phase can produce waveform characteristics that are more similar to the real waveform, and the synthetic PGA is closer to the observed ones.

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

Stochastic finite fault modeling of Mw 6.4 earthquake along Indo-Burmese arc and site classification of its seismic recording station

This study simulates the strong ground motion of an earthquake having magnitude 6.4 occurred on 4 February 2011 in Indo-Burmese Arc (IBA). This earthquake recorded on seven seismic recording stations namely Jowai, Jorhat, Sibsagar, Nagaon, Guwahati, Cooch Bihar and Kokhrajhar. Also, estimation of site class performed to observe the site effects of recording stations in this study. The simulation performed on the basis of revised stochastic finite fault model with dynamic corner frequency and site class for the seismic recording station where the earthquake recorded has been estimated by using Horizontal to Vertical Spectral Ratio (HVSR) technique because modeling and simulation of ground motion majorly depend upon the recorded ground motion as well as site effects, where earthquake has been recorded. The revised well known finite source simulation program (EXSIM) used in this study becomes efficient in providing the results for small magnitude earthquake occurred at large distance. The average HVSR curves plotted for all the recording stations, providing peak frequency for all 7 sites. It is observed from the present work that simulated time histories as far as primary attributes, for example, Fourier spectra, Peak ground acceleration (PGA), Response spectra, Predominant frequency are in close concurrence with the recorded ones. The predominant frequency (fpeak) obtained from HVSR technique has been validated from existing literature for the estimation of site class for seismic recording stations. The fpeak determines the average shear wave velocity (Vs30) at depth of 30 ​m of overburden thickness which varies from 200 ​m/s to 1600 ​m/s according to Program for Excellence in Strong Motion Studies (PESMOS). Whereas, National Earthquake Hazard Reduction Program (NEHRP) provision consider the site class for Vs30 below 180 ​m/s. Due its wide range of site characterization, it has been adopted globally. Therefore, in this study, the site class obtained has been compared with the site classification scheme recommended by PESMOS, NEHRP provisions and previous literature. However, the ground motion parameters and the soil classification of the earthquake recording stations for the IBA region has not been explored yet even after seeing its severity in the past decades. Productive representation of present earthquake gives the confidence to understand and evaluate seismic danger at various parts of Indo- Burmese region from tremors of various sizes. In this study it is proposed that PESMOS site classification data should be revised because it covers wide range of soil types just into three (A, B and C type) class.

An updated stochastic finite fault modeling: Application to the Mw 6.0 earthquake in Jiashi, China

On January 19, 2020 at 21:27 local time, the Jiashi County in China witnessed an Mw 6.0 earthquake. The earthquake event was recorded by 42 strong ground-motion observation stations and recorded a total of 126 sets of acceleration time history records. In this study, we simulated the Jiashi earthquake based on the updated finite-fault modeling. The zero-distance high-frequency attenuation parameter κ0 and local site amplification factor were calculated based on the recordings, and the other input parameters were obtained from the previous studies. Then the Fourier amplitude spectrum, 5%-damped pseudo-acceleration response spectrum, peak ground acceleration, and accelerograms at 12 selected stations were synthetized using an updated finite-fault modeling. The results indicated that the synthetic results had no evident differences at most of the selected stations, which showed that the updated approach can be adopted to predict the ground motion. In addition, the simulated accelerograms are similar to the observed records at most stations, which indicated that the updated modeling can be used to generate the seismic input records required for structural analysis. In the future research, we should more analyze the interconnection between each input parameter and establish the relationship between parameters. If so, even though we cannot obtain the detailed information of several parameters, we can still accurately estimate the seismic field of imminent earthquakes in the future, which will help to establish the disaster maps of the target region.

Slip-Correlated High-Frequency Scaling Factor for Stochastic Finite-Fault Modeling of Ground Motion

ABSTRACTTo eliminate the effect of the subfault dimension on the synthetic ground motion of the stochastic finite-fault technique, Motazedian and Atkinson developed the dynamic corner frequency. Furthermore, they derived a high-frequency scaling factor based on the velocity spectrum to compensate for the underestimation of the ground-motion source spectrum amplitude in the high-frequency range caused by the dynamic corner frequency. However, this high-frequency scaling factor was developed on the assumption that the slip amount, seismic moment, and the high-frequency received energy of each subfault on the rupture surface were the same. Considering the nonuniformity of the slip of each subfault and the large amount of received energy released on the asperity body, the received energy of the entire fault was distributed to each subfault according to the ratio of the slip of the subfault to the total slip. This could ensure not only that the high-frequency received energy radiated by the subfault with a large slip was greater but also that the total received energy was conserved. Finally, an example was used to discuss the effect of the improvement on the synthetic ground motion. The results showed that the proposed improved approach can further eliminate the dependence of the synthetic results on the dimension of the subfault.

Seismic zoning of Tabriz area by stochastic finite fault model considering site-specific soil effects

Abstract Tabriz, as one of the most earthquake-prone cities in the Iran plateau, has experienced enormous earthquakes that have even destroyed the city altogether. Considering this seismological background and the vicinity of Tabriz's northwestern fault, reducing the possible earthquake losses can be highly useful by scrutinizing the strong ground motion resulting from the fault activation. To this end, a stochastic finite-fault ground motion simulation (EXSIM) method was applied as an important means for predicting the ground motion near the epicenter of the earthquake. EXSIM is an open-source stochastic finite-fault simulation algorithm that generates the time-series of the earthquake's ground motion. Based on the findings, the peak horizontal acceleration reached 0.83 g in the northern parts by creating artificial accelerograms and Tabriz's seismic zonation. In comparison, it reduced by 0.48 g by departing from the fault in the city's southern parts. Additionally, providing a seismic zonation map in Tabriz revealed that stopping the construction in the north parts while extending the settlement construction to the south part of the city are considered vital and unavoidable. Also, by applying the magnification and effects of the soil layers above the bedrock, it was further found that the existence of the loose layer with low strength and compaction intensify the application of seismic acceleration on the near-surface structures in the central, west, and southwest parts of the target area.

Simulation of the MW = 7.9 Gulf of Alaska earthquake on January 23, 2018, by the stochastic finite fault model

On the premise of constraining the seismogenic fault structure of a future large earthquake, we proposed using empirical equations to determine the length, width, seismic moment and slip distribution of a large seismogenic fault plane and using the stochastic finite fault model to predict future large earthquakes. The ground motion time histories and response spectra recorded by 12 seismic stations on bedrock during the MW = 7.9 Gulf of Alaska earthquake on January 23, 2018, were simulated. The simulation error determined by the average ratio of the simulated spectrum amplitude to the recorded spectrum amplitude varied between 1.08 and 0.92 in the period range of 0–10 s, and the standard deviation of the simulation error at different frequencies did not exceed 1; the 95% confidence interval also did not change significantly with the period. The above analyses show that our simulation results reflect the mean ground motion. To further discuss the reliability of predicting future large earthquakes by the stochastic finite fault model, we redistributed the initial rupture point and slip distribution on the seismogenic fault plane by the quasi-random method, and the simulation errors and simulation results of the redistribution model were similar to those of the previous model. Further research confirmed that our method for obtaining the seismic source parameters is viable and that the stochastic finite fault model for the prediction of future large earthquakes is reliable, especially for large far-field earthquakes. The seismic stations that we used are all situated on bedrock on one side of the fault and do not involve rupture directivity, i.e., the seismic wave pathways may be similar, so the simulation results are ideal. However, if the rupture directivity, different site conditions, surface topography and basin effects are considered, it will be necessary to amend the proposed method.

Across-fault ground motions and their effects on some bridges in the 1999 Chi-Chi earthquake

Simply-supported bridges are vulnerable to surface fault rupture as evidenced by several fault-crossing bridges in the 1999 Chi-Chi earthquake. To investigate the seismic collapse mechanism of simply-supported bridges crossing the fault, across-fault ground motions are firstly simulated in the present study. In particular, based on a previously developed fault model of the 1999 Chi-Chi earthquake, broadband across-fault ground motions at six fault-crossing bridges are simulated using the hybrid deterministic-stochastic method, in which the low- and high-frequency components are computed using the deterministic Green’s function method and the stochastic finite-fault modeling method, respectively. The simulation results indicate that the hybrid deterministic-stochastic method can give reasonable predictions to the across-fault ground motions. Furthermore, utilizing the explicit dynamic finite element (FE) code LS-DYNA, behaviors of a three-span simply-supported bridge under a selected pair of across-fault ground motions are numerically simulated. Numerical results indicate that the structural responses and collapse mechanisms are dominated by the low-frequency ground motions. The large differential static offset across the fault is the main reason for the collapse of the simply-supported bridges. This study contributes understandings for the across-fault ground motions and the collapse mechanism of some bridges in the 1999 Chi-Chi earthquake.

Experimental and Numerical Investigation of Old Masonry Wall Using a Macro-Modeling Approach

Background: A 3-D finite element model of the internal masonry wall of a 103-year-Old Senate hall, Allahabad University, has been modeled using macro-modeling approaches. The masonry wall is an excellent example of Indo-Saracenic style architecture used by Britishers during the late 19th Century, which is a unification of the Mughal and Colonial architecture. Methods: Non-destructive Test (NDT) has been conducted to estimate is compressive strength and Young’s modulus of the wall. Compressive strength of the brick masonry and stone arch was estimated in the range of 10.5-12.5 MPa and 18.6-21.2 MPa, respectively, whereas Young’s Modulus was estimated in the range of 1800-5000 MPa and 5500-8000 MPa (outlier not considered). Finite Element model was prepared using the macro-modeling approach. Results: The gravity load analysis shows that the wall is stable, and its geometrical configuration is safe with maximum Von-Mises stress of 5.38 MPa and deformation of 2.27 mm. The results of the first six modes are presented. Further, in the absence of a recorded ground motion for the Prayag city, synthetic ground motion is simulated for 25th April 2015 Nepal earthquake (Mw) using a stochastic finite fault model. Conclusion: Evaluated behaviour of the internal masonry wall is shown in the form of acceleration, deformation and stress response.

Broad-band ground-motion simulation of 2016 Amatrice earthquake, Central Italy

SUMMARYOn 24 August 2016 at 01:36 UTC a ML6.0 earthquake struck several villages in central Italy, among which Accumoli, Amatrice and Arquata del Tronto. The earthquake was recorded by about 350 seismic stations, causing 299 fatalities and damage with macroseismic intensities up to 11. The maximum acceleration was observed at Amatrice station (AMT) reaching 916 cm s–2 on E–W component, with epicentral distance of 15 km and Joyner and Boore distance to the fault surface (RJB) of less than a kilometre. Motivated by the high levels of observed ground motion and damage, we generate broad-band seismograms for engineering purposes by adopting a hybrid method. To infer the low frequency seismograms, we considered the kinematic slip model by Tinti et al . The high frequency seismograms were produced using a stochastic finite-fault model approach based on dynamic corner-frequency. Broad-band synthetic time-series were therefore obtained by merging the low and high frequency seismograms. Simulated hybrid ground motions were compared both with the observed ground motions and the ground-motion prediction equations (GMPEs), to explore their performance and to retrieve the region-specific parameters endorsed for the simulations. In the near-fault area we observed that hybrid simulations have a higher capability to detect near source effects and to reproduce the source complexity than the use of GMPEs. Indeed, the general good consistency found between synthetic and observed ground motion (both in the time and frequency domain), suggests that the use of regional-specific source scaling and attenuation parameters together with the source complexity in hybrid simulations improves ground motion estimations. To include the site effect in stochastic simulations at selected stations, we tested the use of amplification curves derived from HVRSs (horizontal-to-vertical response spectra) and from HVSRs (horizontal-to-vertical spectral ratios) rather than the use of generic curves according to NTC18 Italian seismic design code. We generally found a further reduction of residuals between observed and simulated both in terms of time histories and spectra.

Simulation of strong ground motion for a potential Mw7.3 earthquake in Kopili fault zone, northeast India

In this study, we present the results of strong ground motion simulation carried out for a potential earthquake (Mw7.3) in the Kopili source zone of northeast India using the stochastic finite fault modeling technique. Prior to simulation of the potential event, the technique was validated by simulating a recorded earthquake Mw5.3, which was located close to the Nagaon district of Assam, India. The earthquake records (Mw5.3) of ten stations in the study region were analyzed, and average source parameters, namely corner frequency, seismic moment, stress drop and source radius, estimated to be 0.48 Hz, 1.44E + 24 dyne-cm, 103.4 bar and 2.7 km, respectively. While estimating the source parameters, the path attenuation parameters (Q and ko) also constrained at each seismic station. Using the constrained attenuation parameters, site amplification factors and source parameters, we simulated strong ground motion time histories for Mw5.3 event at individual sites and found them comparable with amplitude and frequency content of the respective observed records satisfactorily. The results, therefore, validated the technique used in the study. Further, the fault parameters, site amplification factors and average of the constrained attenuation parameters were used in simulation of the potential event (Mw7.3) and strong ground motion predicted for the entire northeast region (NER) at a grid interval of 0.5°. We used average values of constrained quality factor (Q) and Kappa parameter (ko) equivalent to 182f 0.95 and 0.038, respectively, in the simulation. It is apparent that the simulated PGA conditionally followed the attenuation curves of the region, and hence, we suggest developing an appropriate attenuation curve for the NER. The study reveals that the sites located up to 250 km distance away from the source zone may experience significant PGA ranging between 160 Gals and 360 Gals. The cities located within this zone, viz., Tezpur, Nagaon, Udalguri, Diphu and Bomdila, may witness strong to very strong ground shaking associated with substantial damage to buildings and other important structures in the region.

Stochastic Finite Fault Modeling and Simulation of Strong Ground Motion of Mosha Fault in Iran

This study aims at predicting large earthquakes caused by Mosha fault in Tehran, the capital of Iran with population of more than 13 million people which located alongside active faults. This study uses the EXSIM program to do the finite fault modeling of simulation. Using Geopsy software and programming in MATLAB we evaluated the site effect of 13 station. Using other required parameters of Mosha fault in EXSIM, we gained the artificial strong motions of the stations. Finally, using SeismoSignal and MATLAB software, we depicted the Acceleration -time graph and the semi-logarithm frequency spectrum with “Fourier transform” of each station. we compared the results of the finite fault simulation with Ambraseys attenuation relationship, semi-logarithm frequency spectrum with Fourier transform and spectrum-response graphs of 2009 earthquake in Shahr-e Rey measuring Mw = 4.2. In both cases of comparing meaningful results were found. Finally, in order to generalize the results to the city of Tehran, we evaluated the seismicity using Arc GIS software. The results show that if Mosha fault is activated, east of Tehran is influenced the most. Consequently, it is of high importance to study different ways to reduce the risk of the possible earthquake caused by Mosha fault.

Seismic Hazard Assessment of the Mid-Northern Segment of Xiaojiang Fault Zone in Southwestern China Using Scenario Earthquakes

ABSTRACTSeismic hazards in the vicinity of the mid-northern segment of the Xiaojiang fault zone were estimated from scenario earthquakes. Based on its history of earthquakes and activity data, the whole segment is considered capable of generating large earthquakes. The characteristics of previous ruptures and the geometric structures of the fault were used to establish seven scenario earthquakes with various strike and length properties. On the basis of focal mechanism parameters and the distribution of previous earthquakes, we determined the values of the source parameters for each scenario using empirical equations. We then used a stochastic finite-fault model to generate the ground motion from the targeted fault. The results show that the vicinity of the mid-northern segment of the Xiaojiang fault zone faces significant seismic hazards. The peak ground acceleration (PGA) values along the fault line are obviously larger than in other areas. Based on the recurrence interval theory, the Qiaojia–Menggu and Xiaoxinjie–Xujiadu areas have a high probability of being struck by large earthquakes in the near future. The results also show that the current design PGA for the near-fault area of the mid-northern segment of Xiaojiang fault zone might not be adequate.

The Simulation of Tangshan Earthquake Intensity Field Based on Stochastic Finite Fault Model

The random ground motion simulation method based on the finite fault model is one of the proven methods in the field of simulating high frequency ground motion. Taking the extreme earthquake zone of the Tangshan earthquake in 1976 as the research goal, by combing the research results of the predecessors, the calculation model of the target zone was established and the parameters of the source model were determined. The local site data and the site dynamics parameters of the target zone were utilized. The quarter-wavelength method is used to obtain the local field amplification effect parameters. The strong ground motion simulation results of Tangshan earthquake are given by using the stochastic finite-fault model. The reliability and applicability of the method is confirmed by comparing with the historical seismic macro-intensity. The results will help improve the seismic design accuracy of the project in areas lacking strong vibration observation records, and have certain reference value and engineering significance for the development of urban earthquake prevention and disaster prevention measures.

Seismic Behaviour of 17th Century Khusro Tomb due to Site-Specific Ground Motion

Introduction:Site Specific time history analysis is performed on a 17thcentury old Khusro Tomb built-in 1622 A.D. by Sultan Nisar Begum. It is a beautiful example of Mughal architecture.Methods:A 3-D finite element model is prepared on Ansys Workbench. Gravity analysis results show the behaviour of Tomb due to its geometry and stress variation is plotted in a form of contour. Modal analysis results show the first three frequencies of Khusro Tombviz., 21.62, 21.68 and 25.38 Hz. In the absence of earthquake record, the stochastic finite fault model is used to generate synthetic site-specific time history to assess the seismic behaviour of the tomb.Results and Conclusion:Time history analysis results shows that the Khusro Tomb's geometrical configuration is adequate to withstand the earthquake due to nearest Allahabad fault. The critical elements of the Tomb are highlighted based on analysis that can be effectively used for the maintenance of the Tomb.

ESTIMATION OF STATIC COULOMB STRESS CHANGE AND STRONG MOTION SIMULATION FOR JIUZHAIGOU 7.0 EARTHQUAKE BASE ON SENTINEL-1 INSAR DATA INVERSION

Abstract. On August 8, 2017, an earthquake of M 7.0 occurred at Jiuzhaigou. Based on the Sentinel-1 satellite InSAR data, we obtained coseismic deformation field and inverted the source slip model. Results show that this event is dominated by strike slip, and the total released seismic moment is 8.06 × 1018 Nm, equivalent to an earthquake of Mw ~ 6.57. We calculated static stress changes along strike and dip direction, and the static stress analysis show that the average stress drop are at low level, which may be responsible for the low level of ground motion during Jiuzhaigou earthquake. The coseismic Coulomb stress changes are calculated base on the inverted slip model, which revealed that 82.59 % of aftershocks are located in the Coulomb stress increasing area, 78.42 % of total aftershocks may be triggered by the mainshock aftershock, indicating that the mainshock has a significant triggering effect on the subsequent aftershocks. Based on stochastic finite fault model, we simulated regional peak ground acceleration (PGA), peak ground velocity (PGV) and the intensity, and results could capture basic features associated with the ground motion patterns. Moreover, the simulated results reflect the obvious rupture directivity effect.