Joint inversion of multitype datasets is an effective approach for high-precision subsurface imaging. We present a new deep learning-based method to jointly invert Rayleigh wave phase velocity and ellipticity into shear-wave velocity of the crust and uppermost mantle. A multimodal deep neural network (termed JointNet) is designed to analyze these two independent physical parameters and generate outputs, including velocity and layer thicknesses. JointNet is trained using random 1D models and corresponding synthetic phase velocity and ellipticity, resulting in a low cost for the training dataset. Evaluation using synthetic and observed data shows that JointNet produces highly comparable results compared to those from a Markov chain Monte Carlo-based method and significantly improves inversion speed. Training using synthetic data ensures its generalized application in various regions with different velocity structures. Moreover, JointNet can be easily extended to include additional datatypes and act as a joint inversion framework to further improve imaging resolution.
{"title":"JointNet: A Multimodal Deep Learning-Based Approach for Joint Inversion of Rayleigh Wave Dispersion and Ellipticity","authors":"Xiang Huang, Ziye Yu, Weitao Wang, Fang Wang","doi":"10.1785/0120230199","DOIUrl":"https://doi.org/10.1785/0120230199","url":null,"abstract":"\u0000 Joint inversion of multitype datasets is an effective approach for high-precision subsurface imaging. We present a new deep learning-based method to jointly invert Rayleigh wave phase velocity and ellipticity into shear-wave velocity of the crust and uppermost mantle. A multimodal deep neural network (termed JointNet) is designed to analyze these two independent physical parameters and generate outputs, including velocity and layer thicknesses. JointNet is trained using random 1D models and corresponding synthetic phase velocity and ellipticity, resulting in a low cost for the training dataset. Evaluation using synthetic and observed data shows that JointNet produces highly comparable results compared to those from a Markov chain Monte Carlo-based method and significantly improves inversion speed. Training using synthetic data ensures its generalized application in various regions with different velocity structures. Moreover, JointNet can be easily extended to include additional datatypes and act as a joint inversion framework to further improve imaging resolution.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"124 6","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138958966","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}
Fault roughness influences earthquake rupture dynamics, seismic energy radiation, and, hence, resulting ground motion and its variability. Using 3D dynamic rupture simulations considering a range of rough-fault realizations, we investigate the effects of rupture complexity caused by fault roughness on ground-motion variability, that is, the variability of peak ground acceleration (PGA) and velocity (PGV) as a function of distance. In our analysis, we vary hypocenter locations (leading to unilateral and bilateral ruptures) and fault roughness amplitude to generate a set of magnitude M ≈ 7 strike-slip dynamic rupture simulations. Synthetic seismic waveforms computed on a dense set of surface sites (maximum resolved frequency 5.75 Hz) form our database for detailed statistical analyses. For unilateral ruptures, our simulations reveal that ground-shaking variability (in terms of PGA and PGV) remains nearly constant with increasing distance from the fault. In contrast, bilateral ruptures lead to slowly decreasing ground-motion variability with increasing distance in the near field (less than 20 km). The variability becomes almost constant at large fault distances. We also find that low-amplitude fault roughness leads to ruptures that are likely to generate higher PGA variability than events on faults with high-amplitude roughness. Increasing fault roughness distorts the radiation pattern, thereby reducing directivity effects and, hence, potentially lowering ground-motion variability. The average PGV variability from our rough-fault rupture models is consistent with estimates from empirical ground-motion models (GMMs). However, the average PGA variability exceeds the variability encoded in empirical GMMs by nearly 20%. Hence, our findings have implications for near-source ground-motion prediction in seismic hazard studies, because ground-motion variability depends on details of the earthquake rupture process and is larger than GMM estimates.
{"title":"Ground-Motion Variability for Ruptures on Rough Faults","authors":"J. Vyas, M. Galis, P. M. Mai","doi":"10.1785/0120230117","DOIUrl":"https://doi.org/10.1785/0120230117","url":null,"abstract":"\u0000 Fault roughness influences earthquake rupture dynamics, seismic energy radiation, and, hence, resulting ground motion and its variability. Using 3D dynamic rupture simulations considering a range of rough-fault realizations, we investigate the effects of rupture complexity caused by fault roughness on ground-motion variability, that is, the variability of peak ground acceleration (PGA) and velocity (PGV) as a function of distance. In our analysis, we vary hypocenter locations (leading to unilateral and bilateral ruptures) and fault roughness amplitude to generate a set of magnitude M ≈ 7 strike-slip dynamic rupture simulations. Synthetic seismic waveforms computed on a dense set of surface sites (maximum resolved frequency 5.75 Hz) form our database for detailed statistical analyses. For unilateral ruptures, our simulations reveal that ground-shaking variability (in terms of PGA and PGV) remains nearly constant with increasing distance from the fault. In contrast, bilateral ruptures lead to slowly decreasing ground-motion variability with increasing distance in the near field (less than 20 km). The variability becomes almost constant at large fault distances. We also find that low-amplitude fault roughness leads to ruptures that are likely to generate higher PGA variability than events on faults with high-amplitude roughness. Increasing fault roughness distorts the radiation pattern, thereby reducing directivity effects and, hence, potentially lowering ground-motion variability. The average PGV variability from our rough-fault rupture models is consistent with estimates from empirical ground-motion models (GMMs). However, the average PGA variability exceeds the variability encoded in empirical GMMs by nearly 20%. Hence, our findings have implications for near-source ground-motion prediction in seismic hazard studies, because ground-motion variability depends on details of the earthquake rupture process and is larger than GMM estimates.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"253 2","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139002231","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 Delaware basin in Texas, one of the largest oil and gas production sites in the United States, has been impacted by widespread seismicity in recent years. The M 5.0 earthquake that occurred in March 2020 near the town of Mentone is one of the largest induced earthquakes recorded in this region. Characterizing the source parameters and triggering mechanism of this major event is imperative to assess and mitigate future hazard risk. A former study showed that this event may be attributed to the deep injection nearby. Interestingly, the earthquake is in proximity to shallow injection wells with much larger total injection volume. In this study, we investigate the role of these shallow injection wells in the triggering of the M 5.0 event despite their farther distance from the mainshock. We perform source-parameter inversion and earthquake relocation to determine the precise orientation of the south-facing normal-fault plane where the mainshock occurred, followed by fully coupled poroelastic stress modeling of the change of Coulomb failure stress (ΔCFS) on the fitted fault plane caused by shallow injection in the region. Results show that shallow wells caused up to 20 kPa of ΔCFS near the mainshock location, dominated by positive poroelastic stress change. Such perturbation surpasses the general triggering threshold of faults that are well aligned with the local stress field and suggests the nonnegligible role of these shallow wells in the triggering of the mainshock. We also discuss the complex effect of poroelastic stress perturbation in the subsurface and highlight the importance of detailed geomechanical evaluation of the reservoir when developing relevant operational and safety policies.
得克萨斯州的特拉华盆地是美国最大的石油和天然气产地之一，近年来受到大范围地震的影响。2020 年 3 月在 Mentone 镇附近发生的 M 5.0 地震是该地区有记录以来最大的诱发地震之一。要评估和减轻未来的灾害风险，就必须确定这一重大事件的震源参数和触发机制。之前的一项研究表明，这次地震可能与附近的深层注水有关。有趣的是，地震发生在总注入量大得多的浅层注入井附近。在本研究中，我们调查了这些浅层注水井在引发 M 5.0 事件中的作用，尽管它们距离主震较远。我们进行了震源参数反演和地震定位，确定了主震发生地南向法向断层面的精确方位，然后对该地区浅层注浆引起的拟合断层面上库仑破坏应力（ΔCFS）的变化进行了全耦合孔弹性应力建模。结果表明，浅井在主震位置附近造成了高达 20 千帕的ΔCFS，以正的孔弹性应力变化为主。这种扰动超过了与当地应力场完全一致的断层的一般触发阈值，表明这些浅井在触发主震中发挥了不可忽视的作用。我们还讨论了孔弹性应力扰动在地下的复杂影响，并强调了在制定相关运行和安全政策时对储层进行详细地质力学评估的重要性。
{"title":"Potential Poroelastic Triggering of the 2020 M 5.0 Mentone Earthquake in the Delaware Basin, Texas, by Shallow Injection Wells","authors":"Xinyu Tan, S. Y. Lui","doi":"10.1785/0120230142","DOIUrl":"https://doi.org/10.1785/0120230142","url":null,"abstract":"\u0000 The Delaware basin in Texas, one of the largest oil and gas production sites in the United States, has been impacted by widespread seismicity in recent years. The M 5.0 earthquake that occurred in March 2020 near the town of Mentone is one of the largest induced earthquakes recorded in this region. Characterizing the source parameters and triggering mechanism of this major event is imperative to assess and mitigate future hazard risk. A former study showed that this event may be attributed to the deep injection nearby. Interestingly, the earthquake is in proximity to shallow injection wells with much larger total injection volume. In this study, we investigate the role of these shallow injection wells in the triggering of the M 5.0 event despite their farther distance from the mainshock. We perform source-parameter inversion and earthquake relocation to determine the precise orientation of the south-facing normal-fault plane where the mainshock occurred, followed by fully coupled poroelastic stress modeling of the change of Coulomb failure stress (ΔCFS) on the fitted fault plane caused by shallow injection in the region. Results show that shallow wells caused up to 20 kPa of ΔCFS near the mainshock location, dominated by positive poroelastic stress change. Such perturbation surpasses the general triggering threshold of faults that are well aligned with the local stress field and suggests the nonnegligible role of these shallow wells in the triggering of the mainshock. We also discuss the complex effect of poroelastic stress perturbation in the subsurface and highlight the importance of detailed geomechanical evaluation of the reservoir when developing relevant operational and safety policies.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"6 9","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139008746","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}
Sanjay S. Bora, Brendon A. Bradley, E. Manea, Matthew C. Gerstenberger, Robin L. Lee, Peter J. Stafford, Gail M. Atkinson, Anna Kaiser, Christopher J. DiCaprio, R. V. Van Dissen
This article summarizes hazard sensitivities associated with the updated ground-motion characterization modeling (GMCM) scheme adopted in the recent revision of New Zealand National Seismic Hazard Model (NZ NSHM 2022). In terms of impact on ground-motion hazard, the current GMCM scheme (GMCM 2022) results in an overall, at times significant, increase in calculated mean hazard with respect to NZ NSHM 2010. With regard to relative impact, the update in GMCM accounts for the dominant change in high-hazard regions, whereas in low-hazard regions update in source characterization model dominate. Within GMCM 2022, the change in shallow crustal ground-motion models (GMMs) dominates the effect on calculated hazard, whereas change in subduction interface GMMs has a compounding effect for east coast of North Island and southwest of South Island. Impact of the two NZ-specific adjustments to some of the published GMMs is also discussed. The back-arc attenuation adjustment accounts for a 20%–30% reduction in calculated hazard for peak ground acceleration in northwest of North Island, whereas aleatory uncertainty adjustment accounts for 10%–20% reduction in high-hazard regions such as along the east coast of North Island and in the lower west of South Island.
{"title":"Hazard Sensitivities Associated with Ground-Motion Characterization Modeling for the New Zealand National Seismic Hazard Model Revision 2022","authors":"Sanjay S. Bora, Brendon A. Bradley, E. Manea, Matthew C. Gerstenberger, Robin L. Lee, Peter J. Stafford, Gail M. Atkinson, Anna Kaiser, Christopher J. DiCaprio, R. V. Van Dissen","doi":"10.1785/0120230167","DOIUrl":"https://doi.org/10.1785/0120230167","url":null,"abstract":"\u0000 This article summarizes hazard sensitivities associated with the updated ground-motion characterization modeling (GMCM) scheme adopted in the recent revision of New Zealand National Seismic Hazard Model (NZ NSHM 2022). In terms of impact on ground-motion hazard, the current GMCM scheme (GMCM 2022) results in an overall, at times significant, increase in calculated mean hazard with respect to NZ NSHM 2010. With regard to relative impact, the update in GMCM accounts for the dominant change in high-hazard regions, whereas in low-hazard regions update in source characterization model dominate. Within GMCM 2022, the change in shallow crustal ground-motion models (GMMs) dominates the effect on calculated hazard, whereas change in subduction interface GMMs has a compounding effect for east coast of North Island and southwest of South Island. Impact of the two NZ-specific adjustments to some of the published GMMs is also discussed. The back-arc attenuation adjustment accounts for a 20%–30% reduction in calculated hazard for peak ground acceleration in northwest of North Island, whereas aleatory uncertainty adjustment accounts for 10%–20% reduction in high-hazard regions such as along the east coast of North Island and in the lower west of South Island.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"33 5","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138596590","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 Redmond Salt Mine (RSM) Monitoring Experiment in Utah was designed to record seismoacoustic data at distances less than 50 km for algorithm testing and development. During the experiment from October 2017 to July 2019, six broadband seismic stations were operating at a time, with three of them having fixed locations for the duration, whereas the three other stations were moved to different locations every one-and-half to two-and-half months. RSM operations consist of nighttime underground blasting several times per week. The RSM is located in proximity to a belt of active seismicity, allowing direct comparison of natural and anthropogenic sources. Using the recorded data set, we built 1373 events with local magnitude (ML) of −2.4 and lower to 3.3. For 75 blasts (RMEs) from the Redmond Salt Mine and 206 tectonic earthquakes (EQs), both ML and the coda duration magnitude (MC) are well constrained. We used these events to test and design discriminants that separate the RMEs from the EQs and are effective at local distances. The discriminants consist of ML−MC, low-frequency Sg to high-frequency Sg, Pg/Sg phase-amplitude ratios, and Rg/Sg spectral amplitude ratios, as well as different combinations of two or more of these classifiers. The areas under the receiver operating characteristic curves (AUCs) of 0.92–1.0 for ML−MC, low-frequency Sg to high-frequency Sg, and Rg/Sg indicate that these discriminants are very effective. Conversely, the AUC of only 0.57 for Pg/Sg suggests that this discriminant is only slightly better than a random classifier. Among the effective classifiers, Rg/Sg, shows the lowest likelihood of misclassification (4.3%) for the populations. Results of joint discriminant analyses suggest that even the arguably ineffective single classifier, like Pg/Sg in this case, can provide some value when used in combination with others.
{"title":"Testing and Design of Discriminants for Local Seismic Events Recorded during the Redmond Salt Mine Monitoring Experiment","authors":"R. Tibi, Nathan Downey, R. Brogan","doi":"10.1785/0120230193","DOIUrl":"https://doi.org/10.1785/0120230193","url":null,"abstract":"\u0000 The Redmond Salt Mine (RSM) Monitoring Experiment in Utah was designed to record seismoacoustic data at distances less than 50 km for algorithm testing and development. During the experiment from October 2017 to July 2019, six broadband seismic stations were operating at a time, with three of them having fixed locations for the duration, whereas the three other stations were moved to different locations every one-and-half to two-and-half months. RSM operations consist of nighttime underground blasting several times per week. The RSM is located in proximity to a belt of active seismicity, allowing direct comparison of natural and anthropogenic sources. Using the recorded data set, we built 1373 events with local magnitude (ML) of −2.4 and lower to 3.3. For 75 blasts (RMEs) from the Redmond Salt Mine and 206 tectonic earthquakes (EQs), both ML and the coda duration magnitude (MC) are well constrained. We used these events to test and design discriminants that separate the RMEs from the EQs and are effective at local distances. The discriminants consist of ML−MC, low-frequency Sg to high-frequency Sg, Pg/Sg phase-amplitude ratios, and Rg/Sg spectral amplitude ratios, as well as different combinations of two or more of these classifiers. The areas under the receiver operating characteristic curves (AUCs) of 0.92–1.0 for ML−MC, low-frequency Sg to high-frequency Sg, and Rg/Sg indicate that these discriminants are very effective. Conversely, the AUC of only 0.57 for Pg/Sg suggests that this discriminant is only slightly better than a random classifier. Among the effective classifiers, Rg/Sg, shows the lowest likelihood of misclassification (4.3%) for the populations. Results of joint discriminant analyses suggest that even the arguably ineffective single classifier, like Pg/Sg in this case, can provide some value when used in combination with others.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"114 22","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599418","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}
Robin L. Lee, Brendon A. Bradley, E. Manea, Jesse A. Hutchinson, Sanjay S. Bora
This article presents an evaluation of empirical ground-motion models (GMMs) for active shallow crustal, subduction interface, and subduction slab earthquakes using a recently developed New Zealand (NZ) ground-motion database for the 2022 New Zealand National Seismic Hazard Model revision. This study considers both NZ-specific and global models, which require evaluation to inform of their applicability in an NZ context. A quantitative comparison between the models is conducted based on intensity measure residuals and a mixed-effects regression framework. The results are subsequently investigated to assess how the models are performing in terms of overall accuracy and precision, as well as to identify the presence of any biases in the model predictions when applied to NZ data. Many models showed reasonable performance and could be considered appropriate for inclusion within suites of models to properly represent ground-motion predictions and epistemic uncertainty. In general, the recent models that are NZ-specific or developed on large international databases performed the best. This evaluation of models helped inform suitable GMMs for the ground-motion characterization model logic tree. In addition, spatial trends in systematic site-to-site residuals to the west of the Taupō Volcanic Zone demonstrated the need for backarc attenuation modifications for slab earthquakes.
{"title":"Evaluation of Empirical Ground-Motion Models for the 2022 New Zealand National Seismic Hazard Model Revision","authors":"Robin L. Lee, Brendon A. Bradley, E. Manea, Jesse A. Hutchinson, Sanjay S. Bora","doi":"10.1785/0120230180","DOIUrl":"https://doi.org/10.1785/0120230180","url":null,"abstract":"\u0000 This article presents an evaluation of empirical ground-motion models (GMMs) for active shallow crustal, subduction interface, and subduction slab earthquakes using a recently developed New Zealand (NZ) ground-motion database for the 2022 New Zealand National Seismic Hazard Model revision. This study considers both NZ-specific and global models, which require evaluation to inform of their applicability in an NZ context. A quantitative comparison between the models is conducted based on intensity measure residuals and a mixed-effects regression framework. The results are subsequently investigated to assess how the models are performing in terms of overall accuracy and precision, as well as to identify the presence of any biases in the model predictions when applied to NZ data. Many models showed reasonable performance and could be considered appropriate for inclusion within suites of models to properly represent ground-motion predictions and epistemic uncertainty. In general, the recent models that are NZ-specific or developed on large international databases performed the best. This evaluation of models helped inform suitable GMMs for the ground-motion characterization model logic tree. In addition, spatial trends in systematic site-to-site residuals to the west of the Taupō Volcanic Zone demonstrated the need for backarc attenuation modifications for slab earthquakes.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"98 10","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599917","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}
Mark Stirling, Michelle Fitzgerald, Bruce Shaw, Clarissa Ross
We develop new magnitude–area scaling relations for application in the New Zealand National Seismic Hazard Model 2022 (NZ NSHM 2022) and future applications. A total of 18 published relations are selected, comprising the following tectonic and slip types: crustal strike-slip (seven relations), reverse (two relations), normal (two relations), subduction interface (five relations), and two dip-slip relations to augment the small number of available reverse and normal relations. The scaling relations are evaluated against an instrumental earthquake database flatfile, and scores are provided for each relation. Equations of the form Mw=logA+C are then used to develop mean and bounding relations for the suite of scaling relations. The final set of relations used in NZ NSHM 2022 is adjusted to be consistent with observations of major historical New Zealand earthquakes and U.S. Geological Survey practice. We also provide a second set of Mw=logA+C relations that are absent of these adjustments and so more directly reflect the results of our scoring of the published relations.
{"title":"New Magnitude–Area Scaling Relations for the New Zealand National Seismic Hazard Model 2022","authors":"Mark Stirling, Michelle Fitzgerald, Bruce Shaw, Clarissa Ross","doi":"10.1785/0120230114","DOIUrl":"https://doi.org/10.1785/0120230114","url":null,"abstract":"\u0000 We develop new magnitude–area scaling relations for application in the New Zealand National Seismic Hazard Model 2022 (NZ NSHM 2022) and future applications. A total of 18 published relations are selected, comprising the following tectonic and slip types: crustal strike-slip (seven relations), reverse (two relations), normal (two relations), subduction interface (five relations), and two dip-slip relations to augment the small number of available reverse and normal relations. The scaling relations are evaluated against an instrumental earthquake database flatfile, and scores are provided for each relation. Equations of the form Mw=logA+C are then used to develop mean and bounding relations for the suite of scaling relations. The final set of relations used in NZ NSHM 2022 is adjusted to be consistent with observations of major historical New Zealand earthquakes and U.S. Geological Survey practice. We also provide a second set of Mw=logA+C relations that are absent of these adjustments and so more directly reflect the results of our scoring of the published relations.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"116 s437","pages":""},"PeriodicalIF":3.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138622511","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}
István Bondár, Tea Godoladze, Eric Cowgill, Gurban Yetirmishli, Stephen C. Myers, Irakli Gunia, Albert Buzaladze, Barbara Czecze, Tuna Onur, Rengin Gök, Andrea Chiang
ABSTRACT Our objective is to improve the view of the seismicity in the Caucasus region using instrumental data between 1951 and 2019. To create a comprehensive catalog, we combine the bulletins of local agencies and the International Seismological Centre, and use an advanced single-event location algorithm, iLoc, to obtain better locations. We show that relocations with iLoc, using travel-time predictions from the 3D upper mantle velocity model, Regional Seismic Travel Time, improve the locations. Then, using the iLoc results as initial locations and the ground-truth events identified in the iLoc results as fix points, we apply Bayesloc, a multiple-event location algorithm, to simultaneously relocate the entire seismicity of the Caucasus region. We demonstrate that the simultaneous relocation of the seismicity with Bayesloc clarifies the location and geometry of major active structures accommodating ongoing convergence between the Arabian and Eurasian continents between the Black and Caspian Seas. Among our major findings is the confirmation of widespread seismicity in the mantle beneath the northern flank of the Greater Caucasus and central Caspian, resulting from north-dipping subduction of the Kura and South Caspian basins and the identification of a discrete band of crustal seismicity beneath the southern flank of the Greater Caucasus.
{"title":"Relocation of the Seismicity of the Caucasus Region","authors":"István Bondár, Tea Godoladze, Eric Cowgill, Gurban Yetirmishli, Stephen C. Myers, Irakli Gunia, Albert Buzaladze, Barbara Czecze, Tuna Onur, Rengin Gök, Andrea Chiang","doi":"10.1785/0120230155","DOIUrl":"https://doi.org/10.1785/0120230155","url":null,"abstract":"ABSTRACT Our objective is to improve the view of the seismicity in the Caucasus region using instrumental data between 1951 and 2019. To create a comprehensive catalog, we combine the bulletins of local agencies and the International Seismological Centre, and use an advanced single-event location algorithm, iLoc, to obtain better locations. We show that relocations with iLoc, using travel-time predictions from the 3D upper mantle velocity model, Regional Seismic Travel Time, improve the locations. Then, using the iLoc results as initial locations and the ground-truth events identified in the iLoc results as fix points, we apply Bayesloc, a multiple-event location algorithm, to simultaneously relocate the entire seismicity of the Caucasus region. We demonstrate that the simultaneous relocation of the seismicity with Bayesloc clarifies the location and geometry of major active structures accommodating ongoing convergence between the Arabian and Eurasian continents between the Black and Caspian Seas. Among our major findings is the confirmation of widespread seismicity in the mantle beneath the northern flank of the Greater Caucasus and central Caspian, resulting from north-dipping subduction of the Kura and South Caspian basins and the identification of a discrete band of crustal seismicity beneath the southern flank of the Greater Caucasus.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":" 7","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135241370","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}
Mark Stirling, Elena Manea, Matt Gerstenberger, Sanjay Bora
ABSTRACT We summarize the work that has been done within the New Zealand National Seismic Hazard Model 2022 (NZ NSHM 2022) to evaluate and test the updated hazard model and its components against observational data. We undertake a two-phase analysis to learn about the performance of the hazard model with respect to several limited databases. Phase 1 is the evaluation phase, involving multiple efforts to optimize various source rate model and ground-motion characterization model components against: (1) the New Zealand earthquake catalog for 1950–2020; (2) international catalogs (where relevant); and (3) New Zealand paleoseismic and geodetic data. Phase 2 involves testing the hazard results. We perform ground-motion-based testing of the NZ NSHM 2022 exceedance rates against the observed exceedance rates for strong-motion stations around New Zealand. To account for the modeled variability in rate, the comparisons are done by assuming a binomial distribution about the mean exceedance rate for 0.1g and 0.2g at each station location. We use a combined approach that considers the full epistemic uncertainty distribution for those exceedance rates by weighting the binomial for each branch in the logic tree. We find that, in general, the observed exceedance rates can be drawn from the NZ NSHM 2022 with probabilities greater than 0.05, and that the discrepancies are generally confined to areas close to major earthquake sequences (e.g., Christchurch). These sequences were not considered in the NZ NSHM 2022 forecast. This initial iteration of testing does not provide evidence to reject the NZ NSHM 2022 based on the New Zealand accelerograph record. Importantly, we can only draw limited conclusions from the testing due to the very short time frame of data available for testing.
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