Nikolaos Vavlas, Ioannis Fountoulakis, Zafeiria Roumelioti, Christos P. Evangelidis, Anastasia Kiratzi
ABSTRACT In March 2021, a series of three moderate events with moment magnitudes Mw 6.3, 6.0, and 5.5 occurred within a span of 10 days in northern Thessaly, Greece, resulting in a stop–start pattern. The moment tensors (MTs) obtained from the events suggested normal faulting along distinct yet adjacent southeast–northwest-trending faults, indicating a sequential triggering process. We applied two methods to investigate the spatial and temporal characteristics of the source process of the triplet. This approach includes linear slip inversion of regional seismic waveforms and static Global Positioning System offsets, along with backprojection of regional waveforms using the Source-Scanning Algorithm technique. The detailed modeling suggests that three adjacent, subparallel (∼300°), and low-angle, detachment-type structures were responsible for the earthquakes. The stress axes orientation was determined by inverting a dataset of recomputed MTs combined with published solutions of the sequence. The results indicated a clockwise rotation of the local extensional axis by ∼25° compared to the regional ∼north–south extension. This rotation is consistent with the orientation of the modeled seismogenic structures. Inversions for both nodal planes and grid-searching fault geometry and orientation showed that for the first-two strongest events, the activated fault planes dipped to the northeast, whereas an antithetic (southwest dipping) fault was activated during the last weaker event. For the Mw 6.3 event, both the independent analyses indicated an overall rupture duration of ∼10 s, energy bursts above and near the hypocenter, up-dip (toward the southwest) rupture propagation in the early stages of the source process, and a bilateral rupture at later stages.
{"title":"Imaging the Sources of the March 2021 Seismic Sequence in Thessaly Basin (Central Greece) from Kinematic Slip Inversion and Backprojection of Waveform Envelopes","authors":"Nikolaos Vavlas, Ioannis Fountoulakis, Zafeiria Roumelioti, Christos P. Evangelidis, Anastasia Kiratzi","doi":"10.1785/0120230024","DOIUrl":"https://doi.org/10.1785/0120230024","url":null,"abstract":"ABSTRACT In March 2021, a series of three moderate events with moment magnitudes Mw 6.3, 6.0, and 5.5 occurred within a span of 10 days in northern Thessaly, Greece, resulting in a stop–start pattern. The moment tensors (MTs) obtained from the events suggested normal faulting along distinct yet adjacent southeast–northwest-trending faults, indicating a sequential triggering process. We applied two methods to investigate the spatial and temporal characteristics of the source process of the triplet. This approach includes linear slip inversion of regional seismic waveforms and static Global Positioning System offsets, along with backprojection of regional waveforms using the Source-Scanning Algorithm technique. The detailed modeling suggests that three adjacent, subparallel (∼300°), and low-angle, detachment-type structures were responsible for the earthquakes. The stress axes orientation was determined by inverting a dataset of recomputed MTs combined with published solutions of the sequence. The results indicated a clockwise rotation of the local extensional axis by ∼25° compared to the regional ∼north–south extension. This rotation is consistent with the orientation of the modeled seismogenic structures. Inversions for both nodal planes and grid-searching fault geometry and orientation showed that for the first-two strongest events, the activated fault planes dipped to the northeast, whereas an antithetic (southwest dipping) fault was activated during the last weaker event. For the Mw 6.3 event, both the independent analyses indicated an overall rupture duration of ∼10 s, energy bursts above and near the hypocenter, up-dip (toward the southwest) rupture propagation in the early stages of the source process, and a bilateral rupture at later stages.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135696499","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}
Neala Creasy, Ebru Bozdağ, Daniel A. Frost, Roel Snieder
ABSTRACT The Earth’s Coriolis force has been well-known to impact surface waves and normal modes, which is essential to accurately interpret these waves. However, the Coriolis force on body waves has been assumed to be negligible and mostly ignored. It has been previously shown that the Coriolis force impacts polarizations of shear waves, whereas the wavefronts remain unaffected. We expand on the potential influences of Earth’s Coriolis force on shear-wave polarization measurements by conducting 3D numerical simulations for elastic waves generated by earthquake and explosive sources in a radially symmetric, and 3D mantle and crustal models. The Coriolis force can produce polarization anomalies of mantle shear waves up to 7° and core phases, such as SKS and SKKS, up to 4°. Uncorrected shear-wave polarizations due to the Coriolis force can cause an additional source of error (5°–10° in fast direction, and 0.2–0.3 s delay time depending on the method and seismic phase), inaccurate interpretation of station misalignments, and imprecise estimates of the core–mantle boundary topography. We show how to correct for the Coriolis force on teleseismic shear waves using 1D ray tracing for well-isolated phases. We recommend the use of full waveform simulations to accurately account for earthquake sources parameters, poorly isolated phases that could include interfering phase arrivals within the measurement time window, and the effect of the Coriolis force on the polarizations of shear waves.
{"title":"<i>SKS</i> Polarization Anomalies Due to the Coriolis Force","authors":"Neala Creasy, Ebru Bozdağ, Daniel A. Frost, Roel Snieder","doi":"10.1785/0120230125","DOIUrl":"https://doi.org/10.1785/0120230125","url":null,"abstract":"ABSTRACT The Earth’s Coriolis force has been well-known to impact surface waves and normal modes, which is essential to accurately interpret these waves. However, the Coriolis force on body waves has been assumed to be negligible and mostly ignored. It has been previously shown that the Coriolis force impacts polarizations of shear waves, whereas the wavefronts remain unaffected. We expand on the potential influences of Earth’s Coriolis force on shear-wave polarization measurements by conducting 3D numerical simulations for elastic waves generated by earthquake and explosive sources in a radially symmetric, and 3D mantle and crustal models. The Coriolis force can produce polarization anomalies of mantle shear waves up to 7° and core phases, such as SKS and SKKS, up to 4°. Uncorrected shear-wave polarizations due to the Coriolis force can cause an additional source of error (5°–10° in fast direction, and 0.2–0.3 s delay time depending on the method and seismic phase), inaccurate interpretation of station misalignments, and imprecise estimates of the core–mantle boundary topography. We show how to correct for the Coriolis force on teleseismic shear waves using 1D ray tracing for well-isolated phases. We recommend the use of full waveform simulations to accurately account for earthquake sources parameters, poorly isolated phases that could include interfering phase arrivals within the measurement time window, and the effect of the Coriolis force on the polarizations of shear waves.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135689500","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}
Shao-Jinn Chin, Rupert Sutherland, Martha K. Savage, Julien Collot, Olivier Monge, John Townend
ABSTRACT An analysis of earthquakes recorded in southern New Caledonia (SNC) over 14 months during 2018–2019 reveals focal mechanisms consistent with a normal-faulting stress state. The minimum principal stress is perpendicular to the Vanuatu subduction zone (VSZ), which is 200 km away, and is highly oblique to the local topographic ridge of New Caledonia, which may induce additional tension. An Mw 7.5 earthquake occurred in VSZ on 5 December 2018, and focal mechanisms appear to be different to those before the big earthquake. Significant increase in seismicity rates in both VSZ and SNC are observed following this large earthquake. A strong correlation between local and subduction zone seismicity rates is confirmed by analyses of seismic records before and after large subduction zone earthquakes 200–350 km away during the period of 2000–2018. The local seismicity rate and seismic hazard in SNC is about four times higher immediately after a large subduction earthquake, and Omori decay returns it to background levels after about 30 days. The triggering mechanisms remains unclear, but our study provides the first observations and a framework for future work.
{"title":"Stress State and Earthquake Triggering on the Outer Rise of the Southern Vanuatu Subduction Zone, Southern New Caledonia","authors":"Shao-Jinn Chin, Rupert Sutherland, Martha K. Savage, Julien Collot, Olivier Monge, John Townend","doi":"10.1785/0120230107","DOIUrl":"https://doi.org/10.1785/0120230107","url":null,"abstract":"ABSTRACT An analysis of earthquakes recorded in southern New Caledonia (SNC) over 14 months during 2018–2019 reveals focal mechanisms consistent with a normal-faulting stress state. The minimum principal stress is perpendicular to the Vanuatu subduction zone (VSZ), which is 200 km away, and is highly oblique to the local topographic ridge of New Caledonia, which may induce additional tension. An Mw 7.5 earthquake occurred in VSZ on 5 December 2018, and focal mechanisms appear to be different to those before the big earthquake. Significant increase in seismicity rates in both VSZ and SNC are observed following this large earthquake. A strong correlation between local and subduction zone seismicity rates is confirmed by analyses of seismic records before and after large subduction zone earthquakes 200–350 km away during the period of 2000–2018. The local seismicity rate and seismic hazard in SNC is about four times higher immediately after a large subduction earthquake, and Omori decay returns it to background levels after about 30 days. The triggering mechanisms remains unclear, but our study provides the first observations and a framework for future work.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135689501","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}
Marco T. Herrera, Jorge G. F. Crempien, José Cembrano
ABSTRACT The Chilean subduction zone hosts Mw>8 earthquakes, which could trigger earthquakes on crustal faults located along the plate margin. Using synthetic earthquakes from a quasi-dynamic boundary element method model, we obtain traction fields and perform a slip tendency analysis to obtain synthetic faults, which we compare with existing potentially seismogenic crustal faults. With our results, we find geometric patterns of the highest slip tendency planes with deformations induced by synthetic subduction events, such that north of the rupture area of each event, correlate with normal N20°W–50°W/N60°SW fault planes, and to the south, correlate with normal N30°E–80°E/N60°NW faults planes. These observations agree with observed fault traces in central and northern Chile, and past observations of crustal fault reactivation.
{"title":"Complex Crustal Deformation Controlled by the 3D Geometry of the Chile Subduction Zone","authors":"Marco T. Herrera, Jorge G. F. Crempien, José Cembrano","doi":"10.1785/0120230062","DOIUrl":"https://doi.org/10.1785/0120230062","url":null,"abstract":"ABSTRACT The Chilean subduction zone hosts Mw&gt;8 earthquakes, which could trigger earthquakes on crustal faults located along the plate margin. Using synthetic earthquakes from a quasi-dynamic boundary element method model, we obtain traction fields and perform a slip tendency analysis to obtain synthetic faults, which we compare with existing potentially seismogenic crustal faults. With our results, we find geometric patterns of the highest slip tendency planes with deformations induced by synthetic subduction events, such that north of the rupture area of each event, correlate with normal N20°W–50°W/N60°SW fault planes, and to the south, correlate with normal N30°E–80°E/N60°NW faults planes. These observations agree with observed fault traces in central and northern Chile, and past observations of crustal fault reactivation.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135243677","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}
ABSTRACT China has relatively rich macroseismic isoseismal maps, which play an important role in seismic hazard analysis and the development of reliable earthquake loss models. The macroseismic intensity is assessed based on the Chinese Seismic Intensity Scale, which is constantly being revised as research progresses and the seismic defense capability is enhanced. To investigate whether intensity rating values show consistency across time in statistical significance, this study collected 543 isoseismal lines for 216 earthquakes on the Tibetan Plateau from 1960 to 2020. Taking intensity prediction equations (IPEs) as a reference, statistical tests of the residuals indicate that there is temporal variation in intensity rating values, which is inconsistent with the default assumption that intensity rating values are consistent for different time periods when developing IPEs. Therefore, we analyze the characteristics of intensity rating values by statistical tests and investigate the mechanism by which the temporal variation in intensity rating values affects IPEs by residual decomposition. The results show that despite the temporal variation in intensity rating values, they can still be used to develop IPEs, and that temporal variability can be reduced by adjustment. Finally, we obtain the regression process of IPEs based on the partially nonergodic assumption considering the temporal variation in intensity rating values, and perform a case study, using the Tibetan Plateau as an example.
{"title":"Analyzing the Temporal Variation in Macroseismic Intensity Rating Values and Predicting Macroseismic Intensity on the Tibetan Plateau","authors":"Zhenbiao Liu, Yanxiang Yu, Liang Xiao","doi":"10.1785/0120230102","DOIUrl":"https://doi.org/10.1785/0120230102","url":null,"abstract":"ABSTRACT China has relatively rich macroseismic isoseismal maps, which play an important role in seismic hazard analysis and the development of reliable earthquake loss models. The macroseismic intensity is assessed based on the Chinese Seismic Intensity Scale, which is constantly being revised as research progresses and the seismic defense capability is enhanced. To investigate whether intensity rating values show consistency across time in statistical significance, this study collected 543 isoseismal lines for 216 earthquakes on the Tibetan Plateau from 1960 to 2020. Taking intensity prediction equations (IPEs) as a reference, statistical tests of the residuals indicate that there is temporal variation in intensity rating values, which is inconsistent with the default assumption that intensity rating values are consistent for different time periods when developing IPEs. Therefore, we analyze the characteristics of intensity rating values by statistical tests and investigate the mechanism by which the temporal variation in intensity rating values affects IPEs by residual decomposition. The results show that despite the temporal variation in intensity rating values, they can still be used to develop IPEs, and that temporal variability can be reduced by adjustment. Finally, we obtain the regression process of IPEs based on the partially nonergodic assumption considering the temporal variation in intensity rating values, and perform a case study, using the Tibetan Plateau as an example.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135535549","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}
Alysha D. Armstrong, Zachary Claerhout, Ben Baker, Keith D. Koper
ABSTRACT Traditional seismic phase pickers perform poorly during periods of elevated seismicity due to inherent weakness when detecting overlapping earthquake waveforms. This weakness results in incomplete seismic catalogs, particularly deficient in earthquakes that are close in space and time. Supervised deep-learning (DL) pickers allow for improved detection performance and better handle the overlapping waveforms. Here, we present a DL phase-picking procedure specifically trained on Yellowstone seismicity and designed to fit within the University of Utah Seismograph Stations (UUSS) real-time system. We modify and combine existing DL models to label the seismic phases in continuous data and produce better phase arrival times. We use transfer learning to achieve consistency with UUSS analysts while maintaining robust models. To improve the performance during periods of enhanced seismicity, we develop a data augmentation strategy to synthesize waveforms with two nearly coincident P arrivals. We also incorporate a model uncertainty quantification method, Multiple Stochastic Weight Averaging-Gaussian (MultiSWAG), for arrival-time estimates and compare it to dropout—a more standard approach. We use an efficient, model-agnostic method of empirically calibrating the uncertainties to produce meaningful 90% credible intervals. The credible intervals are used downstream in association, location, and quality assessment. For an in-depth evaluation of our automated method, we apply it to continuous data recorded from 25 March to 3 April 2014, on 20 three-component stations and 14 vertical-component stations. This 10-day period contains an Mw 4.8 event, the largest earthquake in the Yellowstone region since 1980. A seismic analyst manually examined more than 1000 located events, including ∼855 previously unidentified, and concluded that only two were incorrect. Finally, we present an analyst-created, high-resolution arrival-time data set, including 651 new arrival times, for one hour of data from station WY.YNR for robust evaluation of missed detections before association. Our method identified 60% of the analyst P picks and 81% of the S picks.
{"title":"A Deep-Learning Phase Picker with Calibrated Bayesian-Derived Uncertainties for Earthquakes in the Yellowstone Volcanic Region","authors":"Alysha D. Armstrong, Zachary Claerhout, Ben Baker, Keith D. Koper","doi":"10.1785/0120230068","DOIUrl":"https://doi.org/10.1785/0120230068","url":null,"abstract":"ABSTRACT Traditional seismic phase pickers perform poorly during periods of elevated seismicity due to inherent weakness when detecting overlapping earthquake waveforms. This weakness results in incomplete seismic catalogs, particularly deficient in earthquakes that are close in space and time. Supervised deep-learning (DL) pickers allow for improved detection performance and better handle the overlapping waveforms. Here, we present a DL phase-picking procedure specifically trained on Yellowstone seismicity and designed to fit within the University of Utah Seismograph Stations (UUSS) real-time system. We modify and combine existing DL models to label the seismic phases in continuous data and produce better phase arrival times. We use transfer learning to achieve consistency with UUSS analysts while maintaining robust models. To improve the performance during periods of enhanced seismicity, we develop a data augmentation strategy to synthesize waveforms with two nearly coincident P arrivals. We also incorporate a model uncertainty quantification method, Multiple Stochastic Weight Averaging-Gaussian (MultiSWAG), for arrival-time estimates and compare it to dropout—a more standard approach. We use an efficient, model-agnostic method of empirically calibrating the uncertainties to produce meaningful 90% credible intervals. The credible intervals are used downstream in association, location, and quality assessment. For an in-depth evaluation of our automated method, we apply it to continuous data recorded from 25 March to 3 April 2014, on 20 three-component stations and 14 vertical-component stations. This 10-day period contains an Mw 4.8 event, the largest earthquake in the Yellowstone region since 1980. A seismic analyst manually examined more than 1000 located events, including ∼855 previously unidentified, and concluded that only two were incorrect. Finally, we present an analyst-created, high-resolution arrival-time data set, including 651 new arrival times, for one hour of data from station WY.YNR for robust evaluation of missed detections before association. Our method identified 60% of the analyst P picks and 81% of the S picks.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135815350","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}
ABSTRACT Widespread distributed fracturing during earthquakes threatens infrastructure and lifelines. We combine high-resolution rupture maps from the five major surface-rupturing strike-slip earthquakes in southern California and northern Mexico since 1992 to incorporate the displacements produced by distributed ruptures into a probabilistic displacement hazard analysis framework. Through analysis of the spatial distribution of mapped ruptures and displacements for each of these events, we develop a magnitude-dependent expression for the probability per unit area of finding a distributed rupture that accommodates a displacement that exceeds a displacement threshold at a given distance from the principal fault. Our model is best applied to estimating expected distributed displacements for strike-slip earthquakes, similar to those analyzed, with widespread ruptures across immature fault zones.
{"title":"Displacement Hazard from Distributed Ruptures in Strike-Slip Earthquakes","authors":"Alba Mar Rodriguez Padilla, Michael E. Oskin","doi":"10.1785/0120230044","DOIUrl":"https://doi.org/10.1785/0120230044","url":null,"abstract":"ABSTRACT Widespread distributed fracturing during earthquakes threatens infrastructure and lifelines. We combine high-resolution rupture maps from the five major surface-rupturing strike-slip earthquakes in southern California and northern Mexico since 1992 to incorporate the displacements produced by distributed ruptures into a probabilistic displacement hazard analysis framework. Through analysis of the spatial distribution of mapped ruptures and displacements for each of these events, we develop a magnitude-dependent expression for the probability per unit area of finding a distributed rupture that accommodates a displacement that exceeds a displacement threshold at a given distance from the principal fault. Our model is best applied to estimating expected distributed displacements for strike-slip earthquakes, similar to those analyzed, with widespread ruptures across immature fault zones.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136235206","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}
ABSTRACT This study simulates strong ground motions in the Tokyo metropolitan area during the 1923 Kanto earthquake using the stochastic Green’s function method. Source characteristics were modeled using seismic intensity inversion analysis, and path and site characteristics were modeled using inhomogeneous attenuation structure and empirical amplification factors. The results of these simulations were consistent with seismic intensities estimated based on the collapse rate of wooden houses. The distribution of pseudovelocity response spectra averaged at periods of 1–2 s was large: ∼200 cm/s in southern Kanagawa and southern Chiba prefectures, ∼100–200 cm/s in eastern Tokyo, and ∼50–100 cm/s in eastern Saitama prefecture despite its distance from strong-motion generation areas (SMGAs). The simulation results were regressed on site characteristics and fault distance, and the residuals were interpolated using the Kriging method to estimate detailed maps of seismic intensity and response spectra on an ∼250 m mesh reflecting site-specific characteristics. The following conclusions can be made: (1) all SMGAs, other than those in northern Tokyo Bay, were located near large slip areas based on coseismic geodetic and seismic waveform data. Although the SMGAs in the northern part of Tokyo Bay exerted little influence on the southern part of the Kanto region, their consideration was required to reproduce the seismic intensity at the northwest Tokyo and Saitama; (2) intense strong motion in central Tokyo occurred at the back marsh, delta, coastal lowlands, and filled lands, whereas low levels of strong motion were determined at terraces covered with volcanic ash soil. Combined with building distribution, this indicates areas of high seismic risk; (3) the seismic intensity and response spectra in the Tokyo metropolitan area obtained through this simulation were larger than those obtained from seismic records of the 2011 Tohoku earthquake—the most recent megathrust earthquake.
{"title":"Simulating Strong Ground Motion from the Great 1923 Kanto Earthquake in the Tokyo Metropolitan Area Based on Source Model Derived from Seismic Intensity Data","authors":"Fumino Suzuki, Kenichi Kato, Tetsushi Watanabe, Katsuhisa Kanda, Yusuke Tomozawa","doi":"10.1785/0120230071","DOIUrl":"https://doi.org/10.1785/0120230071","url":null,"abstract":"ABSTRACT This study simulates strong ground motions in the Tokyo metropolitan area during the 1923 Kanto earthquake using the stochastic Green’s function method. Source characteristics were modeled using seismic intensity inversion analysis, and path and site characteristics were modeled using inhomogeneous attenuation structure and empirical amplification factors. The results of these simulations were consistent with seismic intensities estimated based on the collapse rate of wooden houses. The distribution of pseudovelocity response spectra averaged at periods of 1–2 s was large: ∼200 cm/s in southern Kanagawa and southern Chiba prefectures, ∼100–200 cm/s in eastern Tokyo, and ∼50–100 cm/s in eastern Saitama prefecture despite its distance from strong-motion generation areas (SMGAs). The simulation results were regressed on site characteristics and fault distance, and the residuals were interpolated using the Kriging method to estimate detailed maps of seismic intensity and response spectra on an ∼250 m mesh reflecting site-specific characteristics. The following conclusions can be made: (1) all SMGAs, other than those in northern Tokyo Bay, were located near large slip areas based on coseismic geodetic and seismic waveform data. Although the SMGAs in the northern part of Tokyo Bay exerted little influence on the southern part of the Kanto region, their consideration was required to reproduce the seismic intensity at the northwest Tokyo and Saitama; (2) intense strong motion in central Tokyo occurred at the back marsh, delta, coastal lowlands, and filled lands, whereas low levels of strong motion were determined at terraces covered with volcanic ash soil. Combined with building distribution, this indicates areas of high seismic risk; (3) the seismic intensity and response spectra in the Tokyo metropolitan area obtained through this simulation were larger than those obtained from seismic records of the 2011 Tohoku earthquake—the most recent megathrust earthquake.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134989615","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}
Charles Scawthorn, Tomoaki Nishino, J. Charles Schencking, Janet Borland
ABSTRACT The 1923 Great Kantō earthquake is one of the most deadly and destructive natural disasters in history. As the name connotes, fire is less considered in examinations of this event even though fire was responsible for the vast majority of death and destruction. Moreover, destruction of Tokyo by fire following an earthquake was foreseen and foretold as early as 1905, yet no actions were taken to reduce the risk. We therefore focus on fire aspects of the 1 September event with special attention to the capital Tokyo. Shaking intensities varied significantly across central Tokyo, with ∼100 ignitions distributed in all parts of the city occurring within the first hour. These rapidly grew into large fires due to the prevailing flammable wood-framed construction, high winds, and lack of firefighting water caused by breaks in water mains. However, even with adequate water, firefighters would likely still have been overwhelmed given the adverse meteorological conditions. The large fires soon merged into very large conflagrations that created their own localized high winds, further feeding the fires to the extent that fire whirls were created. The worst of these occurred in an area where many people were sheltering, causing 40,000 deaths. Even without this particularly tragic occurrence, the deaths due to fires were still greater than due to building collapse and other causes. Why the prescient warning issued years earlier went unheeded, what the social and political impact of the disaster and its aftermath was, and how fire and seismic risk reduction awareness influenced postdisaster reconstruction, are all questions we address. Although Japan since 1923 has implemented many measures to improve earthquake and postearthquake fire preparedness, the risk of fire following an earthquake remains significant in Japan as well as elsewhere.
{"title":"Kantō Daikasai: The Great Kantō Fire Following the 1923 Earthquake","authors":"Charles Scawthorn, Tomoaki Nishino, J. Charles Schencking, Janet Borland","doi":"10.1785/0120230106","DOIUrl":"https://doi.org/10.1785/0120230106","url":null,"abstract":"ABSTRACT The 1923 Great Kantō earthquake is one of the most deadly and destructive natural disasters in history. As the name connotes, fire is less considered in examinations of this event even though fire was responsible for the vast majority of death and destruction. Moreover, destruction of Tokyo by fire following an earthquake was foreseen and foretold as early as 1905, yet no actions were taken to reduce the risk. We therefore focus on fire aspects of the 1 September event with special attention to the capital Tokyo. Shaking intensities varied significantly across central Tokyo, with ∼100 ignitions distributed in all parts of the city occurring within the first hour. These rapidly grew into large fires due to the prevailing flammable wood-framed construction, high winds, and lack of firefighting water caused by breaks in water mains. However, even with adequate water, firefighters would likely still have been overwhelmed given the adverse meteorological conditions. The large fires soon merged into very large conflagrations that created their own localized high winds, further feeding the fires to the extent that fire whirls were created. The worst of these occurred in an area where many people were sheltering, causing 40,000 deaths. Even without this particularly tragic occurrence, the deaths due to fires were still greater than due to building collapse and other causes. Why the prescient warning issued years earlier went unheeded, what the social and political impact of the disaster and its aftermath was, and how fire and seismic risk reduction awareness influenced postdisaster reconstruction, are all questions we address. Although Japan since 1923 has implemented many measures to improve earthquake and postearthquake fire preparedness, the risk of fire following an earthquake remains significant in Japan as well as elsewhere.","PeriodicalId":9444,"journal":{"name":"Bulletin of the Seismological Society of America","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135786286","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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