The East Anatolian Fault Zone (EAFZ) is a 700-km-long left-lateral transform fault system along the boundary between the Anatolian and Arabian plates. In the interseismic period, the eastern segments of the EAFZ display relatively uniform seismic activity, whereas the western segments exhibit seismic gaps, localized clusters, and extensive diffuse zones. Hence, our understanding of the geometry and kinematics of the western and northern segments remain limited. The occurrences of the 6 February 2023 Mw 7.8 Kahramanmaraş on the main branch and Mw 7.6 Elbistan earthquakes on the northern branch have led to complex aftershock activity shedding light on the nature of these relatively silent segments. In this study, to better understand the complexities of the fault, we constructed a comprehensive catalog of ∼32,000 earthquakes that occurred between 6 February 2023 and 30 March 2023, using a deep-neural-network-based picker. In addition, 170 earthquake source mechanisms with Mw 3.5+ were obtained from regional moment tensor inversion. The spatial distribution of the aftershocks shows that most of the activity clusters around the fault bends and major depressions. Previously unmapped and inactive secondary faults of varying lengths are identified within these geometrical complexities. The new seismological observations provide compelling evidence of extension along the Karasu valley, compression occurring along the Erkenek segment, reactivation of basin faults near the Narlı fault zone and the persistent shallow seismic creep of the Pütürge segment. The analysis of seismicity and earthquake source mechanisms along the northern branch reveals the structures of previously inactive faults, both near the extensional Göksun bend in the west and the compressional Nurhak fault complex in the east. In summary, we illustrate the intricacies of previously quiet segments of the EAFZ and aim to gain a deeper understanding of how secondary faults and geometrical discontinuities along the EAFZ played a role in shaping the 2023 Türkiye doublet earthquakes.
{"title":"2023 Earthquake Doublet in Türkiye Reveals the Complexities of the East Anatolian Fault Zone: Insights from Aftershock Patterns and Moment Tensor Solutions","authors":"Sezim Ezgi Güvercin","doi":"10.1785/0220230317","DOIUrl":"https://doi.org/10.1785/0220230317","url":null,"abstract":"\u0000 The East Anatolian Fault Zone (EAFZ) is a 700-km-long left-lateral transform fault system along the boundary between the Anatolian and Arabian plates. In the interseismic period, the eastern segments of the EAFZ display relatively uniform seismic activity, whereas the western segments exhibit seismic gaps, localized clusters, and extensive diffuse zones. Hence, our understanding of the geometry and kinematics of the western and northern segments remain limited. The occurrences of the 6 February 2023 Mw 7.8 Kahramanmaraş on the main branch and Mw 7.6 Elbistan earthquakes on the northern branch have led to complex aftershock activity shedding light on the nature of these relatively silent segments. In this study, to better understand the complexities of the fault, we constructed a comprehensive catalog of ∼32,000 earthquakes that occurred between 6 February 2023 and 30 March 2023, using a deep-neural-network-based picker. In addition, 170 earthquake source mechanisms with Mw 3.5+ were obtained from regional moment tensor inversion. The spatial distribution of the aftershocks shows that most of the activity clusters around the fault bends and major depressions. Previously unmapped and inactive secondary faults of varying lengths are identified within these geometrical complexities. The new seismological observations provide compelling evidence of extension along the Karasu valley, compression occurring along the Erkenek segment, reactivation of basin faults near the Narlı fault zone and the persistent shallow seismic creep of the Pütürge segment. The analysis of seismicity and earthquake source mechanisms along the northern branch reveals the structures of previously inactive faults, both near the extensional Göksun bend in the west and the compressional Nurhak fault complex in the east. In summary, we illustrate the intricacies of previously quiet segments of the EAFZ and aim to gain a deeper understanding of how secondary faults and geometrical discontinuities along the EAFZ played a role in shaping the 2023 Türkiye doublet earthquakes.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"40 25","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139608623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Arthur Cuvier, É. Beucler, Mickael Bonnin, R. F. Garcia
Degradation of the seismic signal quality sometimes occurs at permanent and temporary stations. Although the most likely cause is a high level of humidity, leading to corrosion of the connectors, environmental changes can also alter recording conditions in different frequency ranges and not necessarily for all three components in the same way. Assuming that the continuous seismic signal can be described by a normal distribution, we present a new approach to quantify the seismogram quality and to point out any time sample that deviates from this Gaussian assumption. We introduce the notion of background Gaussian signal (BGS) to characterize a set of samples that follows a normal distribution. The discrete function obtained by sorting the samples in ascending order of amplitudes is compared with a modified Probit function to retrieve the elements composing the BGS, and its statistical properties (mostly its standard deviation σG). As soon as there is any amplitude perturbation, σG deviates from the standard deviation of all samples composing the time window (σ). Hence, the parameter log(σσG) directly quantifies the alteration level. For a single day, a given frequency range and a given component, the median of all log(σσG) that can be computed using short-time windows, reflects the overall gaussianity of the continuous seismic signal. We demonstrate that it can be used to efficiently monitor the quality of seismic traces using this approach at four broadband permanent stations. We show that the daily log(σσG) is sensitive to both subtle changes on one or two components as well as the signal signature of a sensor’s degradation. Finally, we suggest that log(σσG) and other parameters that are computed from the BGS bring useful information for station monitoring in addition to existing methods.
{"title":"Seismic Station Monitoring Using Deviation from the Gaussianity","authors":"Arthur Cuvier, É. Beucler, Mickael Bonnin, R. F. Garcia","doi":"10.1785/0220230305","DOIUrl":"https://doi.org/10.1785/0220230305","url":null,"abstract":"\u0000 Degradation of the seismic signal quality sometimes occurs at permanent and temporary stations. Although the most likely cause is a high level of humidity, leading to corrosion of the connectors, environmental changes can also alter recording conditions in different frequency ranges and not necessarily for all three components in the same way. Assuming that the continuous seismic signal can be described by a normal distribution, we present a new approach to quantify the seismogram quality and to point out any time sample that deviates from this Gaussian assumption. We introduce the notion of background Gaussian signal (BGS) to characterize a set of samples that follows a normal distribution. The discrete function obtained by sorting the samples in ascending order of amplitudes is compared with a modified Probit function to retrieve the elements composing the BGS, and its statistical properties (mostly its standard deviation σG). As soon as there is any amplitude perturbation, σG deviates from the standard deviation of all samples composing the time window (σ). Hence, the parameter log(σσG) directly quantifies the alteration level. For a single day, a given frequency range and a given component, the median of all log(σσG) that can be computed using short-time windows, reflects the overall gaussianity of the continuous seismic signal. We demonstrate that it can be used to efficiently monitor the quality of seismic traces using this approach at four broadband permanent stations. We show that the daily log(σσG) is sensitive to both subtle changes on one or two components as well as the signal signature of a sensor’s degradation. Finally, we suggest that log(σσG) and other parameters that are computed from the BGS bring useful information for station monitoring in addition to existing methods.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"24 11","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139612612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Within a span of 9 hr on 6 February 2023, two significant earthquakes, with magnitudes of Mw 7.8 and 7.6, struck the southeastern part of Türkiye and the northern region of Syria, resulting in significant casualties and widespread economic losses. The occurrence of such intense earthquakes in rapid succession on adjacent faults, especially within a highly complex intraplate region with a multifault network, poses a rare phenomenon, presenting new challenges for seismic hazard analysis in such areas. To investigate whether the preparatory processes for the Mw 7.8–7.6 earthquake doublet could be identified on a large spatial scale prior to the seismic events, we employed a data-driven approach for b-value calculation. The difference in b-values from the background values (Δb) in a reference period were used as inputs, and the cumulative migration pattern (CMP) method, quantitatively describing the migration of seismic activity, was utilized to calculate the corresponding probability distributions. The results indicate a widespread phenomenon of decreasing b-values in the study area over a decade before the occurrence of the earthquake doublet, revealing a significant enhancement of differential crustal stress over a large region. In addition, despite not being the region with the most pronounced decrease in b-values, there is a distinct high probability distribution of CMP near the nucleation points of the earthquake doublet, indicating a spatial and temporal “focus” of increased crustal differential stress in the study area, unveiling the preparatory process of the earthquake doublet. This study reveals quantifiable migration patterns over a long time scale and a large spatial extent, providing new insights into the evolution and occurrence processes of the 2023 Mw 7.8–7.6 Kahramanmaraş earthquake doublet. Moreover, it offers potential clues for seismic hazard analysis in such intraplate regions with multiple fault systems.
2023 年 2 月 6 日，在短短 9 小时内，土耳其东南部和叙利亚北部地区分别发生了 7.8 级和 7.6 级大地震，造成了重大人员伤亡和广泛的经济损失。在相邻的断层上，尤其是在具有多断层网络的高度复杂的板块内部区域内，迅速连续发生如此强烈的地震是一种罕见的现象，给此类地区的地震灾害分析带来了新的挑战。为了研究是否能在地震发生前的大空间尺度上确定 Mw 7.8-7.6 双重地震的准备过程，我们采用了数据驱动的 b 值计算方法。将基准期 b 值与背景值的差值（Δb）作为输入，利用定量描述地震活动迁移的累积迁移模式（CMP）方法计算相应的概率分布。结果表明，在双联地震发生前的十多年里，研究区域内普遍存在 b 值下降的现象，揭示了大区域内地壳应力差异的显著增强。此外，尽管不是 b 值下降最明显的区域，但在地震双响成核点附近存在明显的 CMP 高概率分布，表明研究区域存在地壳差应力增强的时空 "焦点"，揭示了地震双响的准备过程。这项研究揭示了长时间尺度和大空间范围内可量化的迁移模式，为 2023 年 7.8-7.6 级卡赫拉曼马拉什双发地震的演变和发生过程提供了新的视角。此外，它还为此类板内地区多断层系统的地震灾害分析提供了潜在线索。
{"title":"Unraveling the Preparatory Processes of the 2023 Mw 7.8–7.6 Kahramanmaraş Earthquake Doublet","authors":"Fengling Yin, Changsheng Jiang","doi":"10.1785/0220230413","DOIUrl":"https://doi.org/10.1785/0220230413","url":null,"abstract":"\u0000 Within a span of 9 hr on 6 February 2023, two significant earthquakes, with magnitudes of Mw 7.8 and 7.6, struck the southeastern part of Türkiye and the northern region of Syria, resulting in significant casualties and widespread economic losses. The occurrence of such intense earthquakes in rapid succession on adjacent faults, especially within a highly complex intraplate region with a multifault network, poses a rare phenomenon, presenting new challenges for seismic hazard analysis in such areas. To investigate whether the preparatory processes for the Mw 7.8–7.6 earthquake doublet could be identified on a large spatial scale prior to the seismic events, we employed a data-driven approach for b-value calculation. The difference in b-values from the background values (Δb) in a reference period were used as inputs, and the cumulative migration pattern (CMP) method, quantitatively describing the migration of seismic activity, was utilized to calculate the corresponding probability distributions. The results indicate a widespread phenomenon of decreasing b-values in the study area over a decade before the occurrence of the earthquake doublet, revealing a significant enhancement of differential crustal stress over a large region. In addition, despite not being the region with the most pronounced decrease in b-values, there is a distinct high probability distribution of CMP near the nucleation points of the earthquake doublet, indicating a spatial and temporal “focus” of increased crustal differential stress in the study area, unveiling the preparatory process of the earthquake doublet. This study reveals quantifiable migration patterns over a long time scale and a large spatial extent, providing new insights into the evolution and occurrence processes of the 2023 Mw 7.8–7.6 Kahramanmaraş earthquake doublet. Moreover, it offers potential clues for seismic hazard analysis in such intraplate regions with multiple fault systems.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"95 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139612557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Earthquake clusters possess profound potential for discerning antecedent seismic cues. This study examines the self-similarity of earthquakes to characterize recent seismic patterns in the prolonged quiescent Eastern Anatolian fault zone (EAFZ). We thoroughly investigate the correlation fractal dimension (Dc) formulated upon the scale-invariant relative clustering in earthquake pattern identification. We provide a comprehensive examination of pre- and postseismicity patterns of the Mw 7.7 Nurdağı-Pazarcık, Mw 7.6 Ekinözü, and Mw 6.7 Elazığ earthquakes, each shattering different segments of the EAFZ. The spatiotemporal fluctuations of Dc suggest the commencement of the preparatory process observed around October 2021 to February 2022 for the 2023 dual catastrophe, whereas in the case of the Mw 6.7 Elazığ, this was witnessed from November 2018. Prior to the 2023 events, low-moderate Dc regions predominated on the Pazarcık segment and Cardak fault. The Pürtürge segment that ruptured with an Mw 6.7 event was within a low Dc area. We identified a consistent relationship between stress levels and Dc for the 2023 twin events and the Mw 6.7 earthquake, with low Dc indicative of high stress. Intriguingly, mainshocks and a substantial proportion of their aftershocks have occurred within areas characterized by low to moderate Dc. Various fault zones like Malatya, Amanos, and Adiyaman are situated in areas with low Dc. The southwestern area of the Amanos segment exhibits clustering, elevated stress levels, and low Dc, followed by the Mw 7.7. Therefore, it is imperative to maintain vigilant monitoring of this region to prevent another disaster.
{"title":"Tectonic Duets: Self-Similar Approach to Investigate Eastern Anatolian Fault’s Recent Seismicity, with Special Emphasis on the 6 February 2023 Earthquake Doublet","authors":"Haritha Chandriyan, Paresh Nath Singha Roy","doi":"10.1785/0220230341","DOIUrl":"https://doi.org/10.1785/0220230341","url":null,"abstract":"\u0000 Earthquake clusters possess profound potential for discerning antecedent seismic cues. This study examines the self-similarity of earthquakes to characterize recent seismic patterns in the prolonged quiescent Eastern Anatolian fault zone (EAFZ). We thoroughly investigate the correlation fractal dimension (Dc) formulated upon the scale-invariant relative clustering in earthquake pattern identification. We provide a comprehensive examination of pre- and postseismicity patterns of the Mw 7.7 Nurdağı-Pazarcık, Mw 7.6 Ekinözü, and Mw 6.7 Elazığ earthquakes, each shattering different segments of the EAFZ. The spatiotemporal fluctuations of Dc suggest the commencement of the preparatory process observed around October 2021 to February 2022 for the 2023 dual catastrophe, whereas in the case of the Mw 6.7 Elazığ, this was witnessed from November 2018. Prior to the 2023 events, low-moderate Dc regions predominated on the Pazarcık segment and Cardak fault. The Pürtürge segment that ruptured with an Mw 6.7 event was within a low Dc area. We identified a consistent relationship between stress levels and Dc for the 2023 twin events and the Mw 6.7 earthquake, with low Dc indicative of high stress. Intriguingly, mainshocks and a substantial proportion of their aftershocks have occurred within areas characterized by low to moderate Dc. Various fault zones like Malatya, Amanos, and Adiyaman are situated in areas with low Dc. The southwestern area of the Amanos segment exhibits clustering, elevated stress levels, and low Dc, followed by the Mw 7.7. Therefore, it is imperative to maintain vigilant monitoring of this region to prevent another disaster.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"40 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139613340","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Mojave section of the San Andreas fault is the closest section to the megacity of greater Los Angeles. A major issue for the population is that the life-threatening hazard estimate of a future rare, large earthquake on this fault section is highly uncertain and untested at timescales and ground motions beyond limited historical recordings. Of relevance to this issue is that the nearby precariously balanced rocks at Lovejoy Buttes have survived these ground motions, despite the past tens of thousands of years of San Andreas fault earthquakes. Therefore, the fragility and age of these precariously balanced rocks provide crucial ground-motion constraints over the timescales of rare, large San Andreas fault earthquakes. We rigorously validate and update an earthquake hazard model for the Mojave section of the San Andreas fault using the independent observational data of precariously balanced rock survival at Lovejoy Buttes. The joint probability of survival of all five studied precariously balanced rocks was used to validate the hazard estimates and reweight the estimates using new Bayesian updating methods to deliver an improved, precariously balanced rock-informed earthquake hazard estimate. At an annual frequency of exceedance of 1×10−4 yr−1, equivalent to a mean return period of 10,000 yr, the precariously balanced rock survival data significantly reduced the mean hazard ground-motion estimate by 65% and the 5th–95th fractile uncertainty range by 72%. The magnitude of this inconsistency provides striking evidence for the need to reevaluate both the source and ground-motion components of our earthquake hazard model for the southern San Andreas fault.
{"title":"San Andreas Fault Earthquake Hazard Model Validation Using Probabilistic Analysis of Precariously Balanced Rocks and Bayesian Updating","authors":"A. H. Rood, Peter J. Stafford, Dylan H. Rood","doi":"10.1785/0220220287","DOIUrl":"https://doi.org/10.1785/0220220287","url":null,"abstract":"\u0000 The Mojave section of the San Andreas fault is the closest section to the megacity of greater Los Angeles. A major issue for the population is that the life-threatening hazard estimate of a future rare, large earthquake on this fault section is highly uncertain and untested at timescales and ground motions beyond limited historical recordings. Of relevance to this issue is that the nearby precariously balanced rocks at Lovejoy Buttes have survived these ground motions, despite the past tens of thousands of years of San Andreas fault earthquakes. Therefore, the fragility and age of these precariously balanced rocks provide crucial ground-motion constraints over the timescales of rare, large San Andreas fault earthquakes. We rigorously validate and update an earthquake hazard model for the Mojave section of the San Andreas fault using the independent observational data of precariously balanced rock survival at Lovejoy Buttes. The joint probability of survival of all five studied precariously balanced rocks was used to validate the hazard estimates and reweight the estimates using new Bayesian updating methods to deliver an improved, precariously balanced rock-informed earthquake hazard estimate. At an annual frequency of exceedance of 1×10−4 yr−1, equivalent to a mean return period of 10,000 yr, the precariously balanced rock survival data significantly reduced the mean hazard ground-motion estimate by 65% and the 5th–95th fractile uncertainty range by 72%. The magnitude of this inconsistency provides striking evidence for the need to reevaluate both the source and ground-motion components of our earthquake hazard model for the southern San Andreas fault.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"11 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139616871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Two large-magnitude earthquakes hit southern Türkiye on February 2023. The first, Mw 7.8 strike-slip earthquake generated a rupture of 300 km section along the ∼600 km long East Anatolian fault (EAF). Here, we present an analytical solution using perturbation theory for the static stress field near the EAF induced by the fault geometry and the tectonic loading before these earthquakes. By applying the Coulomb failure criterion, we show that a large stress barrier is developed around the segment that ruptured in the first earthquake. Considering stress field conditions that are associated with left-lateral strike-slip on the fault, we demonstrate how the barrier location is mostly determined by the fault geometry, while its magnitude is sensitive to the background stress value and direction. We further show that the elastic energy around the fault increases to maximum values near the barrier region and decreases away from it. Therefore, we suggest that the high magnitude and the associated long rupture of the earthquake were strongly influenced by the static stress heterogeneity generated by the fault geometry.
{"title":"Can Geometrical Barrier Explain the Mw 7.8 Earthquake in Southern Türkiye on February 2023?","authors":"Amir Sagy, Doron Morad, V. Lyakhovsky","doi":"10.1785/0220230280","DOIUrl":"https://doi.org/10.1785/0220230280","url":null,"abstract":"\u0000 Two large-magnitude earthquakes hit southern Türkiye on February 2023. The first, Mw 7.8 strike-slip earthquake generated a rupture of 300 km section along the ∼600 km long East Anatolian fault (EAF). Here, we present an analytical solution using perturbation theory for the static stress field near the EAF induced by the fault geometry and the tectonic loading before these earthquakes. By applying the Coulomb failure criterion, we show that a large stress barrier is developed around the segment that ruptured in the first earthquake. Considering stress field conditions that are associated with left-lateral strike-slip on the fault, we demonstrate how the barrier location is mostly determined by the fault geometry, while its magnitude is sensitive to the background stress value and direction. We further show that the elastic energy around the fault increases to maximum values near the barrier region and decreases away from it. Therefore, we suggest that the high magnitude and the associated long rupture of the earthquake were strongly influenced by the static stress heterogeneity generated by the fault geometry.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":" 13","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139616843","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We probe the interaction of large earthquakes on the East Anatolian fault zone, site of four Mw ≥ 6.8 events since 2020. We find that the 2023 Mw 7.8 Pazarcık shock promoted the Mw 7.7 Elbistan earthquake 9 hr later, largely through unclamping of the epicentral patch of the future rupture. Epicentral unclamping is also documented in the 1987 Superstition Hills, 1997 Kagoshima, and 2019 Ridgecrest sequences, so this may be common. The Mw 7.7 Elbistan earthquake, in turn, is calculated to have reduced the shear stress on the central Pazarcık rupture, producing a decrease in the aftershock rate along that section of the rupture. Nevertheless, the Mw 7.7 event ruptured through a Çardak fault section on which the shear stress was decreased by the Mw 7.8 rupture, and so rupture propagation was not halted by the static stress decrease. The 2020 Mw 6.8 Doğanyol–Sivrice earthquake, located beyond the northeast tip of the Mw 7.8 Pazarcık rupture, locally dropped the stress by ∼10 bars. The 2023 Mw 7.8 earthquake then increased the stress there by 1–2 bar, leaving a net stress drop, resulting in a hole in the 2023 Pazarcık aftershocks. We find that many lobes of calculated stress increase caused by the 2020–2023 Mw 6.8–7.8 earthquakes are sites of aftershocks, and we calculate 5–10 faults in several locations off the ruptures brought closer to failure. The earthquakes also cast broad stress shadows in which most faults were brought farther from failure, and we observe the beginnings of seismicity rate decreases in some of the deepest stress shadows. Some 41 Mw ≥ 5 aftershocks have struck since the Mw 7.8 mainshock. But based on these Coulomb interactions and on the rapid Kahramanmaraş aftershock decay, we forecast only about 1–3 Mw ≥ 5 earthquakes during the 12–month period beginning 1 December 2023, which is fortunately quite low.
{"title":"The Role of Stress Transfer in Rupture Nucleation and Inhibition in the 2023 Kahramanmaraş, Türkiye, Sequence, and a One-Year Earthquake Forecast","authors":"Shinji Toda, Ross S. Stein","doi":"10.1785/0220230252","DOIUrl":"https://doi.org/10.1785/0220230252","url":null,"abstract":"\u0000 We probe the interaction of large earthquakes on the East Anatolian fault zone, site of four Mw ≥ 6.8 events since 2020. We find that the 2023 Mw 7.8 Pazarcık shock promoted the Mw 7.7 Elbistan earthquake 9 hr later, largely through unclamping of the epicentral patch of the future rupture. Epicentral unclamping is also documented in the 1987 Superstition Hills, 1997 Kagoshima, and 2019 Ridgecrest sequences, so this may be common. The Mw 7.7 Elbistan earthquake, in turn, is calculated to have reduced the shear stress on the central Pazarcık rupture, producing a decrease in the aftershock rate along that section of the rupture. Nevertheless, the Mw 7.7 event ruptured through a Çardak fault section on which the shear stress was decreased by the Mw 7.8 rupture, and so rupture propagation was not halted by the static stress decrease. The 2020 Mw 6.8 Doğanyol–Sivrice earthquake, located beyond the northeast tip of the Mw 7.8 Pazarcık rupture, locally dropped the stress by ∼10 bars. The 2023 Mw 7.8 earthquake then increased the stress there by 1–2 bar, leaving a net stress drop, resulting in a hole in the 2023 Pazarcık aftershocks. We find that many lobes of calculated stress increase caused by the 2020–2023 Mw 6.8–7.8 earthquakes are sites of aftershocks, and we calculate 5–10 faults in several locations off the ruptures brought closer to failure. The earthquakes also cast broad stress shadows in which most faults were brought farther from failure, and we observe the beginnings of seismicity rate decreases in some of the deepest stress shadows. Some 41 Mw ≥ 5 aftershocks have struck since the Mw 7.8 mainshock. But based on these Coulomb interactions and on the rapid Kahramanmaraş aftershock decay, we forecast only about 1–3 Mw ≥ 5 earthquakes during the 12–month period beginning 1 December 2023, which is fortunately quite low.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":" 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139620293","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Duan, Lianqing Zhou, Cuiping Zhao, Zhaofei Liu, Xiaodong Zhang
The eastern boundary of the Sichuan–Yunnan rhombic block (EB-SYRB) has complex structures and strong seismicity. Although multiple 3D high-resolution velocity models have been constructed for this region, its seismogenic environment has been controversial. Seismic wave attenuation (inversely proportional to Q) describes the anelastic properties of the Earth’s medium, and is more sensitive to changes in subsurface fluid and temperature than seismic wave velocity. Based on the data of a long-term dense array in downstream of the Jinsha River, this article uses local earthquake tomography to obtain 3D QP and QS models of the middle EB-SYRB with the highest resolution to date, improving the lateral resolution of the Q model from 100 km to 5–10 km and the depth resolution from 10 to 2 km. Combined with the existing high-resolution velocity and resistivity models and geochemical observation results, we can comprehensively understand the medium structure and the seismogenesis in the study area. The results show that the high-attenuation characteristics in the shallow layer of the Xiaojiang fault zone and the Zemuhe fault zone (within a depth of ∼5 km) are consistent with the topographic relief and the distribution of hot springs, which reveals the Quaternary sedimentary characteristics of the basins and the presence of shallow fluids in the fault zone. The columnar high-attenuation anomaly beneath Huize reveals the fluid channel created by deep melting. The Ludian earthquake sequence occurred in a prominent low-attenuation area, which is favorable for stress accumulation and has a seismogenic environment for strong earthquakes. The high attenuation near the southwest end of the Huize fault is closely related to the Huize earthquake cluster, which is driven by fluids in the upper crust.
{"title":"High-Resolution 3D QP and QS Models of the Middle Eastern Boundary of the Sichuan–Yunnan Rhombic Block: New Insight into Implication for Seismogenesis","authors":"M. Duan, Lianqing Zhou, Cuiping Zhao, Zhaofei Liu, Xiaodong Zhang","doi":"10.1785/0220230232","DOIUrl":"https://doi.org/10.1785/0220230232","url":null,"abstract":"\u0000 The eastern boundary of the Sichuan–Yunnan rhombic block (EB-SYRB) has complex structures and strong seismicity. Although multiple 3D high-resolution velocity models have been constructed for this region, its seismogenic environment has been controversial. Seismic wave attenuation (inversely proportional to Q) describes the anelastic properties of the Earth’s medium, and is more sensitive to changes in subsurface fluid and temperature than seismic wave velocity. Based on the data of a long-term dense array in downstream of the Jinsha River, this article uses local earthquake tomography to obtain 3D QP and QS models of the middle EB-SYRB with the highest resolution to date, improving the lateral resolution of the Q model from 100 km to 5–10 km and the depth resolution from 10 to 2 km. Combined with the existing high-resolution velocity and resistivity models and geochemical observation results, we can comprehensively understand the medium structure and the seismogenesis in the study area. The results show that the high-attenuation characteristics in the shallow layer of the Xiaojiang fault zone and the Zemuhe fault zone (within a depth of ∼5 km) are consistent with the topographic relief and the distribution of hot springs, which reveals the Quaternary sedimentary characteristics of the basins and the presence of shallow fluids in the fault zone. The columnar high-attenuation anomaly beneath Huize reveals the fluid channel created by deep melting. The Ludian earthquake sequence occurred in a prominent low-attenuation area, which is favorable for stress accumulation and has a seismogenic environment for strong earthquakes. The high attenuation near the southwest end of the Huize fault is closely related to the Huize earthquake cluster, which is driven by fluids in the upper crust.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"5 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139439580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Guangdong–Hong Kong–Macao Greater Bay Area (GBA), known as the fourth largest bay area in the world, is a world-class urban agglomeration located on the southeastern coast of China. Littoral fault zones that might trigger strong earthquakes are located offshore of the GBA, making it particularly crucial to pay attention to seismic disasters caused by the site-amplification effect of the strong earthquakes. Therefore, it is essential to determine the fine subsurface structure of the GBA urban agglomeration. In this study, we present the newly collected short-period dense array seismic data in the core urban area of the GBA, which covers a detection area of 60×60 km2 and consists of a backbone observation network and a basic observation network. The backbone observation network included 720 seismic stations spaced 2.25 km apart that recorded continuously for 30–35 days. The basic observation network has a total of 6214 seismic stations that were spaced 0.75 km apart and recorded continuously for 3–10 days. In addition, 63 excitation shots generated by methane detonation source were fired within the observation network. According to the preliminary analysis, the seismic stations recorded both clear active source signals and an abundance of passive source signals, indicating the high quality of the data. The high density of the seismic array and the high-quality seismic data provide important constraints for constructing the shallow fine crustal structure model and the 3D sedimentary thickness model.
{"title":"Shallow 3D Structure Investigation of Some Cities in the Guangdong–Hong Kong–Macao Greater Bay Area","authors":"Xiuwei Ye, Liwei Wang, Cheng Xiong, Xiaona Wang, Genggeng Wen, Dayong Yu, Zhen Guo, Weitao Wang, Zuoyong Lv, Huaping Wu, Yanxin Zhang","doi":"10.1785/0220230155","DOIUrl":"https://doi.org/10.1785/0220230155","url":null,"abstract":"\u0000 The Guangdong–Hong Kong–Macao Greater Bay Area (GBA), known as the fourth largest bay area in the world, is a world-class urban agglomeration located on the southeastern coast of China. Littoral fault zones that might trigger strong earthquakes are located offshore of the GBA, making it particularly crucial to pay attention to seismic disasters caused by the site-amplification effect of the strong earthquakes. Therefore, it is essential to determine the fine subsurface structure of the GBA urban agglomeration. In this study, we present the newly collected short-period dense array seismic data in the core urban area of the GBA, which covers a detection area of 60×60 km2 and consists of a backbone observation network and a basic observation network. The backbone observation network included 720 seismic stations spaced 2.25 km apart that recorded continuously for 30–35 days. The basic observation network has a total of 6214 seismic stations that were spaced 0.75 km apart and recorded continuously for 3–10 days. In addition, 63 excitation shots generated by methane detonation source were fired within the observation network. According to the preliminary analysis, the seismic stations recorded both clear active source signals and an abundance of passive source signals, indicating the high quality of the data. The high density of the seismic array and the high-quality seismic data provide important constraints for constructing the shallow fine crustal structure model and the 3D sedimentary thickness model.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"93 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139444578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xintao Chai, Zhiyuan Gu, Hang Long, Shaoyong Liu, Wenjun Cao, Xiaodong Sun
Physics-informed neural networks (PINNs) have been used by researchers to solve partial differential equation (PDE)-constrained problems. We evaluate PINNs to solve for frequency-domain acoustic wavefields. PINNs can solely use PDEs to define the loss function for optimization without the need for labels. Partial derivatives of PDEs are calculated by mesh-free automatic differentiations. Thus, PINNs are free of numerical dispersion artifacts. It has been applied to the scattered acoustic wave equation, which relied on boundary conditions (BCs) provided by the background analytical wavefield. For a more direct implementation, we solve the nonscattered acoustic wave equation, avoiding limitations related to relying on the background homogeneous medium for BCs. Experiments support our following insights. Although solving time-domain wave equations using PINNs does not require absorbing boundary conditions (ABCs), ABCs are required to ensure a unique solution for PINNs that solve frequency-domain wave equations, because the single-frequency wavefield is not localized and contains wavefield information over the full domain. However, it is not trivial to include the ABC in the PINN implementation, so we develop an adaptive amplitude-scaled and phase-shifted sine activation function, which performs better than the previous implementations. Because there are only two outputs for the fully connected neural network (FCNN), we validate a linearly shrinking FCNN that can achieve a comparable and even better accuracy with a cheaper computational cost. However, there is a spectral bias problem, that is, PINNs learn low-frequency wavefields far more easily than higher frequencies, and the accuracy of higher frequency wavefields is often poor. Because the shapes of multifrequency wavefields are similar, we initialize the FCNN for higher frequency wavefields by that of the lower frequencies, partly mitigating the spectral bias problem. We further incorporate multiscale positional encoding to alleviate the spectral bias problem. We share our codes, data, and results via a public repository.
{"title":"Practical Aspects of Physics-Informed Neural Networks Applied to Solve Frequency-Domain Acoustic Wave Forward Problem","authors":"Xintao Chai, Zhiyuan Gu, Hang Long, Shaoyong Liu, Wenjun Cao, Xiaodong Sun","doi":"10.1785/0220230297","DOIUrl":"https://doi.org/10.1785/0220230297","url":null,"abstract":"\u0000 Physics-informed neural networks (PINNs) have been used by researchers to solve partial differential equation (PDE)-constrained problems. We evaluate PINNs to solve for frequency-domain acoustic wavefields. PINNs can solely use PDEs to define the loss function for optimization without the need for labels. Partial derivatives of PDEs are calculated by mesh-free automatic differentiations. Thus, PINNs are free of numerical dispersion artifacts. It has been applied to the scattered acoustic wave equation, which relied on boundary conditions (BCs) provided by the background analytical wavefield. For a more direct implementation, we solve the nonscattered acoustic wave equation, avoiding limitations related to relying on the background homogeneous medium for BCs. Experiments support our following insights. Although solving time-domain wave equations using PINNs does not require absorbing boundary conditions (ABCs), ABCs are required to ensure a unique solution for PINNs that solve frequency-domain wave equations, because the single-frequency wavefield is not localized and contains wavefield information over the full domain. However, it is not trivial to include the ABC in the PINN implementation, so we develop an adaptive amplitude-scaled and phase-shifted sine activation function, which performs better than the previous implementations. Because there are only two outputs for the fully connected neural network (FCNN), we validate a linearly shrinking FCNN that can achieve a comparable and even better accuracy with a cheaper computational cost. However, there is a spectral bias problem, that is, PINNs learn low-frequency wavefields far more easily than higher frequencies, and the accuracy of higher frequency wavefields is often poor. Because the shapes of multifrequency wavefields are similar, we initialize the FCNN for higher frequency wavefields by that of the lower frequencies, partly mitigating the spectral bias problem. We further incorporate multiscale positional encoding to alleviate the spectral bias problem. We share our codes, data, and results via a public repository.","PeriodicalId":508466,"journal":{"name":"Seismological Research Letters","volume":"44 35","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139442420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：