Reference velocity profiles for ground-motion models (GMMs) provide more information about the site condition represented by the GMM than the simple site parameters used in the GMMs, such as VS30 (time-averaged S-wave velocity of top 30 m strata from the surface). A reference velocity profile for generic soft-rock site conditions is developed for Taiwan using multiple data sets to span the depth range from 0 to 16 km. The measured VS profiles from PS-logging at strong-motion stations with VS30 between 610 and 930 m/s (i.e., 760 m/s ± 20%) were selected to define the top 30 m of the profile. The velocity profiles obtained from multiple existing geophysical studies were then used to extend the VS profile to seismic bedrock (VS of 3.5 km/s). A corresponding generic rock P-wave velocity (VP) profile was developed using VP from PS-logging measurements and an empirical relationship between VP and VS for the deeper part of the profile. The proposed Taiwan Generic Rock (TWGR) model has VS30 of 754 m/s, Z1.0 (thickness of sediments with VS<1.0 km/s) of 29 m, Z2.5 (thickness of sediments with VS<2.5 km/s) of 2.1 km, and κ0 (spectral decay slope) of 0.052 s. The VS values of the TWGR profile at depths of 50 m–8 km are smaller than from the generic rock profile with VS30=760 m/s for California, which lead to different site amplifications between soft-rock sites in Taiwan and California. The TWGR provides information on the applicability of the large empirical data set of strong-motion recordings from Taiwan to other regions.
{"title":"Development of the Taiwan Generic Rock Seismic Velocity Profile","authors":"Chun-Hsiang Kuo, Norman Abrahamson","doi":"10.1785/0220230007","DOIUrl":"https://doi.org/10.1785/0220230007","url":null,"abstract":"\u0000 Reference velocity profiles for ground-motion models (GMMs) provide more information about the site condition represented by the GMM than the simple site parameters used in the GMMs, such as VS30 (time-averaged S-wave velocity of top 30 m strata from the surface). A reference velocity profile for generic soft-rock site conditions is developed for Taiwan using multiple data sets to span the depth range from 0 to 16 km. The measured VS profiles from PS-logging at strong-motion stations with VS30 between 610 and 930 m/s (i.e., 760 m/s ± 20%) were selected to define the top 30 m of the profile. The velocity profiles obtained from multiple existing geophysical studies were then used to extend the VS profile to seismic bedrock (VS of 3.5 km/s). A corresponding generic rock P-wave velocity (VP) profile was developed using VP from PS-logging measurements and an empirical relationship between VP and VS for the deeper part of the profile. The proposed Taiwan Generic Rock (TWGR) model has VS30 of 754 m/s, Z1.0 (thickness of sediments with VS<1.0 km/s) of 29 m, Z2.5 (thickness of sediments with VS<2.5 km/s) of 2.1 km, and κ0 (spectral decay slope) of 0.052 s. The VS values of the TWGR profile at depths of 50 m–8 km are smaller than from the generic rock profile with VS30=760 m/s for California, which lead to different site amplifications between soft-rock sites in Taiwan and California. The TWGR provides information on the applicability of the large empirical data set of strong-motion recordings from Taiwan to other regions.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47065995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
I. Oliveti, L. Faenza, Andrea Antonucci, M. Locati, A. Rovida, A. Michelini
Italy has a long tradition of studies on the seismic history of the country and the neighboring areas. Several archives and databases dealing with historical earthquake data—primarily intensity data points—have been published and are constantly updated. Macroseismic fields of significant events are of foremost importance in assessing earthquake effects and for the evaluation of seismic hazards. Here, we adopt the U.S. Geological Survey (USGS)-ShakeMap software to calculate the maps of strong ground shaking (shakemaps) of 79 historical earthquakes with magnitude ≥6 that have occurred in Italy between 1117 and 1968 C.E. We use the macroseismic data published in the Italian Macroseismic Database (DBMI15). The shakemaps have been determined using two different configurations. The first adopts the virtual intensity prediction equations approach (VIPE; i.e., a combination of ground-motion models [GMMs] and ground-motion intensity conversion equations [GMICEs]; Bindi, Pacor, et al., 2011; Oliveti et al., 2022b). The second exploits the intensity prediction equations (IPE; Pasolini, Albarello, et al., 2008; Lolli et al., 2019). The VIPE configuration has been found to provide more accurate results after appraisal through a cross-validation analysis and has been applied for the generation of the ShakeMap Atlas. The resulting maps are published in the Istituto Nazionale di Geofisica e Vulcanologia (INGV) ShakeMap (see Data and Resources; Oliveti et al., 2023), and in the Italian Archive of Historical Earthquake Data (ASMI; see Data and Resources; Rovida et al., 2017) platforms.
{"title":"The ShakeMap Atlas of Historical Earthquakes in Italy: Configuration and Validation","authors":"I. Oliveti, L. Faenza, Andrea Antonucci, M. Locati, A. Rovida, A. Michelini","doi":"10.1785/0220230138","DOIUrl":"https://doi.org/10.1785/0220230138","url":null,"abstract":"\u0000 Italy has a long tradition of studies on the seismic history of the country and the neighboring areas. Several archives and databases dealing with historical earthquake data—primarily intensity data points—have been published and are constantly updated. Macroseismic fields of significant events are of foremost importance in assessing earthquake effects and for the evaluation of seismic hazards. Here, we adopt the U.S. Geological Survey (USGS)-ShakeMap software to calculate the maps of strong ground shaking (shakemaps) of 79 historical earthquakes with magnitude ≥6 that have occurred in Italy between 1117 and 1968 C.E. We use the macroseismic data published in the Italian Macroseismic Database (DBMI15). The shakemaps have been determined using two different configurations. The first adopts the virtual intensity prediction equations approach (VIPE; i.e., a combination of ground-motion models [GMMs] and ground-motion intensity conversion equations [GMICEs]; Bindi, Pacor, et al., 2011; Oliveti et al., 2022b). The second exploits the intensity prediction equations (IPE; Pasolini, Albarello, et al., 2008; Lolli et al., 2019). The VIPE configuration has been found to provide more accurate results after appraisal through a cross-validation analysis and has been applied for the generation of the ShakeMap Atlas. The resulting maps are published in the Istituto Nazionale di Geofisica e Vulcanologia (INGV) ShakeMap (see Data and Resources; Oliveti et al., 2023), and in the Italian Archive of Historical Earthquake Data (ASMI; see Data and Resources; Rovida et al., 2017) platforms.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44956452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sylvert Paul, Tony Monfret, F. Courboulex, J. Chèze, Eric Calais, Steeve Julien Symithe, Anne Deschamps, F. Peix, Davis Ambrois, Xavier Martin, S. St Fleur, Dominique Boisson
Seismic monitoring in Haiti is currently provided by a mixed network of low-cost Raspberry Shake (RS) seismic stations hosted by citizens, and short-period and broadband stations located mainly in neighboring countries. The level of earthquake detection is constantly improving for a better spatio-temporal distribution of seismicity as the number of RS increases. In this article, we analyze the impact of the quality of the signals recorded by the RS—low-cost seismometers with the smallest magnitude that the network can detect by studying the ambient noise level at these stations. Because the RS stations are installed as part of a citizen-science project, their ambient noise estimated by the power spectral density (PSD) method often shows a high-noise level at frequencies above 1 Hz. In the near field (<50 km), we show that the network detects seismic events of local magnitude on the order of 2.2 with signal-to-noise ratios (SNRs) greater than 4. Improving the network detection threshold requires densifying the network with more RS stations in locations that are less noisy, if possible. In spite of these limitations, this mixed network has provided near-field data essential to rapidly understand the mechanism of the mainshock of the 14 August 2021 Mw 7.2 earthquake, to monitor its sequence of aftershocks in near-real time, and to monitor background seismicity in Haiti on a routine basis.
{"title":"Monitoring of Local Earthquakes in Haiti Using Low-Cost, Citizen-Hosted Seismometers and Regional Broadband Stations","authors":"Sylvert Paul, Tony Monfret, F. Courboulex, J. Chèze, Eric Calais, Steeve Julien Symithe, Anne Deschamps, F. Peix, Davis Ambrois, Xavier Martin, S. St Fleur, Dominique Boisson","doi":"10.1785/0220230059","DOIUrl":"https://doi.org/10.1785/0220230059","url":null,"abstract":"\u0000 Seismic monitoring in Haiti is currently provided by a mixed network of low-cost Raspberry Shake (RS) seismic stations hosted by citizens, and short-period and broadband stations located mainly in neighboring countries. The level of earthquake detection is constantly improving for a better spatio-temporal distribution of seismicity as the number of RS increases. In this article, we analyze the impact of the quality of the signals recorded by the RS—low-cost seismometers with the smallest magnitude that the network can detect by studying the ambient noise level at these stations. Because the RS stations are installed as part of a citizen-science project, their ambient noise estimated by the power spectral density (PSD) method often shows a high-noise level at frequencies above 1 Hz. In the near field (<50 km), we show that the network detects seismic events of local magnitude on the order of 2.2 with signal-to-noise ratios (SNRs) greater than 4. Improving the network detection threshold requires densifying the network with more RS stations in locations that are less noisy, if possible. In spite of these limitations, this mixed network has provided near-field data essential to rapidly understand the mechanism of the mainshock of the 14 August 2021 Mw 7.2 earthquake, to monitor its sequence of aftershocks in near-real time, and to monitor background seismicity in Haiti on a routine basis.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42094038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yuhao Gu, Zhenguo Zhang, Wenqiang Wang, Zhongqiu He
The 2022 Mw 6.6 Luding earthquake occurred on the Xianshuihe fault, one of China’s most active faults. Revealing the rupture process of the Luding earthquake and exploring the distribution of high intensities is important for earthquake hazard reduction around the active Xianshuihe fault in the future. Therefore, we modeled the dynamic rupture and ground motions of the Luding earthquake. The dynamic rupture modeling demonstrates that the maximum slip of the fault plane is ∼1.34 m, and the ground-motion simulations show the highest intensity attained is IX. In addition, we conducted a comparative analysis between synthetic data and station observation records, illustrating that our simulation results are compatible with the seismic station observations. We investigated the influence of geometric complexities on the Xianshuihe fault rupture and found that varying the dip angle of the southern segment may lead to premature rupture termination and constrain the rupture propagation. Our study provides insights into the complex geometry’s effect on the physical process of large earthquakes on the Xianshuihe fault.
{"title":"Dynamic Rupture Modeling and Ground-Motion Simulations of the 2022 Mw 6.6 Luding Earthquake","authors":"Yuhao Gu, Zhenguo Zhang, Wenqiang Wang, Zhongqiu He","doi":"10.1785/0220230110","DOIUrl":"https://doi.org/10.1785/0220230110","url":null,"abstract":"\u0000 The 2022 Mw 6.6 Luding earthquake occurred on the Xianshuihe fault, one of China’s most active faults. Revealing the rupture process of the Luding earthquake and exploring the distribution of high intensities is important for earthquake hazard reduction around the active Xianshuihe fault in the future. Therefore, we modeled the dynamic rupture and ground motions of the Luding earthquake. The dynamic rupture modeling demonstrates that the maximum slip of the fault plane is ∼1.34 m, and the ground-motion simulations show the highest intensity attained is IX. In addition, we conducted a comparative analysis between synthetic data and station observation records, illustrating that our simulation results are compatible with the seismic station observations. We investigated the influence of geometric complexities on the Xianshuihe fault rupture and found that varying the dip angle of the southern segment may lead to premature rupture termination and constrain the rupture propagation. Our study provides insights into the complex geometry’s effect on the physical process of large earthquakes on the Xianshuihe fault.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47149417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Repeating earthquakes (repeaters) are events that recurrently rupture the same fault patch with nearly identical magnitudes. Although repeaters have been widely studied and utilized in many fields over the last four decades, there are no standard criteria for reliably identifying such events. The current criteria adopted in the geophysical research community are inconsistent and difficult to justify. Different criteria may inescapably incur inadequate hypotheses and lead to controversial interpretations, highlighting the urgent need for seeking a uniform approach to reliably identify repeaters. In this study, we address this long-standing issue by deriving the most logical criteria on the basis of theoretical calculation with simple yet reasonable assumptions. Quantitatively, we define a repeating pair if their interevent distance is ≤80% of the rupture area of the larger event and their magnitude difference is ≤0.3. We demonstrate the superiority of our proposed approach with challenging cases in California, and our results shed new insight into the hierarchical fault structures in the source areas. Although this study focuses on defining repeating earthquakes, the application to repeating seismic events in other planetary bodies such as moonquakes and marsquakes is straightforward, potentially help avoid misinterpretations of the physical processes in both Earth and planetary interiors.
{"title":"Identification of Repeating Earthquakes: Controversy and Rectification","authors":"Dawei Gao, H. Kao, Jianxin Liu","doi":"10.1785/0220230124","DOIUrl":"https://doi.org/10.1785/0220230124","url":null,"abstract":"\u0000 Repeating earthquakes (repeaters) are events that recurrently rupture the same fault patch with nearly identical magnitudes. Although repeaters have been widely studied and utilized in many fields over the last four decades, there are no standard criteria for reliably identifying such events. The current criteria adopted in the geophysical research community are inconsistent and difficult to justify. Different criteria may inescapably incur inadequate hypotheses and lead to controversial interpretations, highlighting the urgent need for seeking a uniform approach to reliably identify repeaters. In this study, we address this long-standing issue by deriving the most logical criteria on the basis of theoretical calculation with simple yet reasonable assumptions. Quantitatively, we define a repeating pair if their interevent distance is ≤80% of the rupture area of the larger event and their magnitude difference is ≤0.3. We demonstrate the superiority of our proposed approach with challenging cases in California, and our results shed new insight into the hierarchical fault structures in the source areas. Although this study focuses on defining repeating earthquakes, the application to repeating seismic events in other planetary bodies such as moonquakes and marsquakes is straightforward, potentially help avoid misinterpretations of the physical processes in both Earth and planetary interiors.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43572666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Moment tensor inversion plays a crucial role in determining earthquake types, magnitude, and source geometry. Compared to polarity and amplitude methods, full-waveform approaches provide more comprehensive constraints on the complex full moment tensor (FMT). In this study, we propose a novel FMT inversion method named neighborhood algorithm-generalized cut-and-paste (NA-GCAP) method. Similar to the “cut-and-paste” method, our approach divides seismograms into Pnl and surface-wave segments. To enhance inversion efficiency, we employ the NA in conjunction with a newly developed strategy for efficient Green’s functions computation based on the renewed fast generalized reflection and transmission method (GRTM). Our method requires only a single forward computation and stores ten Green’s functions, significantly improving computational efficiency. We validate the robustness of our approach through synthetic tests using a velocity model perturbed by 5% relative to the input model. Furthermore, we apply the NA-GCAP method to the 2019 Changning earthquake sequence comprising 16 earthquakes, where twelve events exhibit double-couple (DC) components larger than 0.95, indicating a simple dislocation source, and four events display significant non-DC components. Our results align well with the previous studies and demonstrate the potential for widespread application to other earthquake sequences in the future.
{"title":"NA-GCAP: A New Full Moment Tensor Inversion Method Based on the Renewed GRTM and NA Method","authors":"J. Wen, F. Hu, Xiaofei Chen","doi":"10.1785/0220220259","DOIUrl":"https://doi.org/10.1785/0220220259","url":null,"abstract":"\u0000 Moment tensor inversion plays a crucial role in determining earthquake types, magnitude, and source geometry. Compared to polarity and amplitude methods, full-waveform approaches provide more comprehensive constraints on the complex full moment tensor (FMT). In this study, we propose a novel FMT inversion method named neighborhood algorithm-generalized cut-and-paste (NA-GCAP) method. Similar to the “cut-and-paste” method, our approach divides seismograms into Pnl and surface-wave segments. To enhance inversion efficiency, we employ the NA in conjunction with a newly developed strategy for efficient Green’s functions computation based on the renewed fast generalized reflection and transmission method (GRTM). Our method requires only a single forward computation and stores ten Green’s functions, significantly improving computational efficiency. We validate the robustness of our approach through synthetic tests using a velocity model perturbed by 5% relative to the input model. Furthermore, we apply the NA-GCAP method to the 2019 Changning earthquake sequence comprising 16 earthquakes, where twelve events exhibit double-couple (DC) components larger than 0.95, indicating a simple dislocation source, and four events display significant non-DC components. Our results align well with the previous studies and demonstrate the potential for widespread application to other earthquake sequences in the future.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44796574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lang Xu, Y. Aoki, Jiaqing Wang, Yan Cui, Qiang Chen, Yinghui Yang, Zhibo Yao
On 6 February 2023, Mw 7.8 and 7.6 earthquakes struck southeast Türkiye and northwest Syria. They are the largest earthquakes in Türkiye in over 80 yr, causing significant damage and fatalities. We used Advanced Land Observation Satellite-2 and Sentinel-1 Synthetic Aperture Radar images to obtain near-field coseismic displacements by Differential Interferometric Synthetic Aperture Radar (DInSAR) and pixel offset tracking (POT). Discontinuities of the surface deformation suggest that the Mw 7.8 event ruptured ∼320 km along the East Anatolian fault, and the Mw 7.6 event ruptured ∼150 km near Elbistan, southern Türkiye. We inverted these earthquakes' fault geometry and slip distribution based on Global Navigation Satellite Systems, DInSAR, and POT displacements. The estimated fault slip model shows that the first Mw 7.8 event ruptured a steeply southeast-dipping fault, and the seismogenic fault of the second Mw 7.6 event is north-dipping with complex geometry. The dip angle of subfaults of the Mw 7.6 earthquake decreases from east to west. Faults responsible for the two earthquakes are dominated by left-lateral strike-slip motion, with the maximum slip of ∼9.1 m. Early postseismic deformation within two months exhibits displacement discontinuities in the Amanos and Pazarcık segments and the Çardak fault, suggesting that the afterslip partially compensated the coseismic slip deficit at the shallow depths. Furthermore, static Coulomb failure stress changes induced by the two earthquakes indicate that the southwestern Pütürge segment of the East Anatolian fault has a high risk of future rupture.
{"title":"The 2023 Mw 7.8 and 7.6 Earthquake Doublet in Southeast Türkiye: Coseismic and Early Postseismic Deformation, Faulting Model, and Potential Seismic Hazard","authors":"Lang Xu, Y. Aoki, Jiaqing Wang, Yan Cui, Qiang Chen, Yinghui Yang, Zhibo Yao","doi":"10.1785/0220230146","DOIUrl":"https://doi.org/10.1785/0220230146","url":null,"abstract":"\u0000 On 6 February 2023, Mw 7.8 and 7.6 earthquakes struck southeast Türkiye and northwest Syria. They are the largest earthquakes in Türkiye in over 80 yr, causing significant damage and fatalities. We used Advanced Land Observation Satellite-2 and Sentinel-1 Synthetic Aperture Radar images to obtain near-field coseismic displacements by Differential Interferometric Synthetic Aperture Radar (DInSAR) and pixel offset tracking (POT). Discontinuities of the surface deformation suggest that the Mw 7.8 event ruptured ∼320 km along the East Anatolian fault, and the Mw 7.6 event ruptured ∼150 km near Elbistan, southern Türkiye. We inverted these earthquakes' fault geometry and slip distribution based on Global Navigation Satellite Systems, DInSAR, and POT displacements. The estimated fault slip model shows that the first Mw 7.8 event ruptured a steeply southeast-dipping fault, and the seismogenic fault of the second Mw 7.6 event is north-dipping with complex geometry. The dip angle of subfaults of the Mw 7.6 earthquake decreases from east to west. Faults responsible for the two earthquakes are dominated by left-lateral strike-slip motion, with the maximum slip of ∼9.1 m. Early postseismic deformation within two months exhibits displacement discontinuities in the Amanos and Pazarcık segments and the Çardak fault, suggesting that the afterslip partially compensated the coseismic slip deficit at the shallow depths. Furthermore, static Coulomb failure stress changes induced by the two earthquakes indicate that the southwestern Pütürge segment of the East Anatolian fault has a high risk of future rupture.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45212092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Underground explosions are observed to produce fewer and smaller aftershocks than similar size earthquakes. The seismic magnitude difference Δmx between an explosion and its largest aftershock is an expression of Båth’s law for explosions. Based on an analysis of a compilation of aftershock studies from Soviet testing at the Semipalatinsk test site in Kazakhstan and observations from American testing at the Nevada National Security Site (NNSS), we find that the average magnitude difference for explosions Δmx‾ is about 2.5. Based on the NNSS data, two standard deviations of Δmx is about 1.5. In all the cases studied, from ton to megaton yield, from shallow to overburied depth, and chemical or nuclear source, no explosion aftershock has been larger than the explosion that preceded it. In fact, the two events at the NNSS with the largest aftershock magnitudes relative to the explosion are associated with the collapse of the cavity created by the explosion. This is similar to observations from North Korean testing at the Punggye-ri Test Site, where the largest seismic event following the test is attributed to the collapse after the 2017 explosion and is from 0.8 to 2 magnitude units less than the mainshock.
{"title":"The Observed Inefficiency of Explosions to Produce Large Aftershocks: Båth’s Law for Explosions is 2.5","authors":"S. Ford, W. Walter","doi":"10.1785/0220230183","DOIUrl":"https://doi.org/10.1785/0220230183","url":null,"abstract":"\u0000 Underground explosions are observed to produce fewer and smaller aftershocks than similar size earthquakes. The seismic magnitude difference Δmx between an explosion and its largest aftershock is an expression of Båth’s law for explosions. Based on an analysis of a compilation of aftershock studies from Soviet testing at the Semipalatinsk test site in Kazakhstan and observations from American testing at the Nevada National Security Site (NNSS), we find that the average magnitude difference for explosions Δmx‾ is about 2.5. Based on the NNSS data, two standard deviations of Δmx is about 1.5. In all the cases studied, from ton to megaton yield, from shallow to overburied depth, and chemical or nuclear source, no explosion aftershock has been larger than the explosion that preceded it. In fact, the two events at the NNSS with the largest aftershock magnitudes relative to the explosion are associated with the collapse of the cavity created by the explosion. This is similar to observations from North Korean testing at the Punggye-ri Test Site, where the largest seismic event following the test is attributed to the collapse after the 2017 explosion and is from 0.8 to 2 magnitude units less than the mainshock.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":" ","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41560764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The variability of earthquake ground motions has a strong control on probabilistic seismic hazard analysis (PSHA), particularly for the low frequencies of exceedance used for critical facilities. We use a crossed mixed-effects model to partition the variance components from simulated ground motions of Mw 7 earthquakes on the Salt Lake City segment of the Wasatch fault zone. Total variability of simulated ground motions is approximately equivalent to empirical models. The high contribution from rupture speed suggests an avenue to reducing variability through research on the causes and predictions of rupture speed on specific faults. Simulations show a strong spatial heterogeneity in the variability that manifests from directivity effects. We illustrate the impact of this spatial heterogeneity on hazard using a partially nonergodic PSHA framework. The results highlight the benefit of accounting for directivity effects in nonergodic PSHA, in which models that account for additional processes controlling ground motions are paired with reductions in the modeled ground-motion variability.
{"title":"Ground-Motion Variability from Kinematic Rupture Models and the Implications for Nonergodic Probabilistic Seismic Hazard Analysis","authors":"G. Parker, M. Moschetti, E. Thompson","doi":"10.1785/0220220380","DOIUrl":"https://doi.org/10.1785/0220220380","url":null,"abstract":"\u0000 The variability of earthquake ground motions has a strong control on probabilistic seismic hazard analysis (PSHA), particularly for the low frequencies of exceedance used for critical facilities. We use a crossed mixed-effects model to partition the variance components from simulated ground motions of Mw 7 earthquakes on the Salt Lake City segment of the Wasatch fault zone. Total variability of simulated ground motions is approximately equivalent to empirical models. The high contribution from rupture speed suggests an avenue to reducing variability through research on the causes and predictions of rupture speed on specific faults. Simulations show a strong spatial heterogeneity in the variability that manifests from directivity effects. We illustrate the impact of this spatial heterogeneity on hazard using a partially nonergodic PSHA framework. The results highlight the benefit of accounting for directivity effects in nonergodic PSHA, in which models that account for additional processes controlling ground motions are paired with reductions in the modeled ground-motion variability.","PeriodicalId":21687,"journal":{"name":"Seismological Research Letters","volume":"9 3","pages":""},"PeriodicalIF":3.3,"publicationDate":"2023-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41296124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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