Simon Rebeyrol, Stéphan Ker, Laurent Duval, Wayne C Crawford
Summary This study focuses on improving the seafloor compliance noise removal method, which relies on estimates of the compliance transfer function frequency response (the deformation of the seafloor under long-period pressure waves). We first propose a new multi-scale deviation analysis of broadband ocean bottom seismometer data to evaluate stationarity properties that are key to the subsequent analysis. We then propose a new approach to removing the compliance noise from the vertical channel data, by stacking daily estimated transfer function frequency responses over a period of time. We also propose an automated transient event detection and data selection method based on a cross-correlation criterion. As an example, we apply the method to data from the Cascadia Initiative (network 7D2011). We find that the spectral extent of long-period forcing waves varies significantly over time so that standard daily transfer function calculation techniques poorly estimate the transfer function frequency response at the lowest frequencies, resulting in poor denoising performance. The proposed method more accurately removes noise at these lower frequencies, especially where coherence is low, reducing the mean deviation of the signal in our test case by 27 % or more. We also show that our calculated transfer functions can be transfered across time periods. The method should allow better estimates of seafloor compliance and help to remove compliance noise at stations with low pressure-acceleration coherence. Our results can be reproduced using the BRUIT-FM Python toolbox, available at https://gitlab.ifremer.fr/anr-bruitfm/bruit-fm-toolbox.
{"title":"Revisiting the OBS seafloor compliance signal removal with a stationarity and stacking-based approach: the BRUIT-FM toolbox","authors":"Simon Rebeyrol, Stéphan Ker, Laurent Duval, Wayne C Crawford","doi":"10.1093/gji/ggae265","DOIUrl":"https://doi.org/10.1093/gji/ggae265","url":null,"abstract":"Summary This study focuses on improving the seafloor compliance noise removal method, which relies on estimates of the compliance transfer function frequency response (the deformation of the seafloor under long-period pressure waves). We first propose a new multi-scale deviation analysis of broadband ocean bottom seismometer data to evaluate stationarity properties that are key to the subsequent analysis. We then propose a new approach to removing the compliance noise from the vertical channel data, by stacking daily estimated transfer function frequency responses over a period of time. We also propose an automated transient event detection and data selection method based on a cross-correlation criterion. As an example, we apply the method to data from the Cascadia Initiative (network 7D2011). We find that the spectral extent of long-period forcing waves varies significantly over time so that standard daily transfer function calculation techniques poorly estimate the transfer function frequency response at the lowest frequencies, resulting in poor denoising performance. The proposed method more accurately removes noise at these lower frequencies, especially where coherence is low, reducing the mean deviation of the signal in our test case by 27 % or more. We also show that our calculated transfer functions can be transfered across time periods. The method should allow better estimates of seafloor compliance and help to remove compliance noise at stations with low pressure-acceleration coherence. Our results can be reproduced using the BRUIT-FM Python toolbox, available at https://gitlab.ifremer.fr/anr-bruitfm/bruit-fm-toolbox.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"25 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141939663","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}
Ran Xu, Zhengyan Wang, Ying Xu, Peng Dong, Kaiwen Xia
Summary Fault rupture dynamics is expected to be significantly affected by the geometry of fault system, especially for orthogonal faults. However, the rupture behaviors of orthogonal faults especially the coseismic interactions are far from fully understood. Here, we present experimental results from a series of laboratory earthquakes to elucidate the effect of the stress state and initiation location on the rupture behaviors of orthogonal faults. Our results reveal a phase diagram of rupture behaviors of orthogonal faults, which is collectively controlled by stress state and rupture initiation location. For events initiating from the main fault, the rupture cannot jump to the branch, which may be due to the clamping effect or the inhibited shear stress accumulation on the branch. On the contrary, events initiating from the branch can persistently trigger ruptures of the main fault. This difference highlights the directional effect associated with the rupture of orthogonal faults. Further, the rupture length of triggered ruptures on the main fault is controlled by the stress state of the fault system. With the increase of the ratio between the shear stress and normal stress, the rupture length of the main fault increases. Our results reproduce the rupture behaviors of orthogonal faults, which may provide insights into the rupture characteristics of natural earthquakes.
{"title":"Experimental study on the rupture behaviors of orthogonal faults: effects of stress state and rupture initiation location","authors":"Ran Xu, Zhengyan Wang, Ying Xu, Peng Dong, Kaiwen Xia","doi":"10.1093/gji/ggae271","DOIUrl":"https://doi.org/10.1093/gji/ggae271","url":null,"abstract":"Summary Fault rupture dynamics is expected to be significantly affected by the geometry of fault system, especially for orthogonal faults. However, the rupture behaviors of orthogonal faults especially the coseismic interactions are far from fully understood. Here, we present experimental results from a series of laboratory earthquakes to elucidate the effect of the stress state and initiation location on the rupture behaviors of orthogonal faults. Our results reveal a phase diagram of rupture behaviors of orthogonal faults, which is collectively controlled by stress state and rupture initiation location. For events initiating from the main fault, the rupture cannot jump to the branch, which may be due to the clamping effect or the inhibited shear stress accumulation on the branch. On the contrary, events initiating from the branch can persistently trigger ruptures of the main fault. This difference highlights the directional effect associated with the rupture of orthogonal faults. Further, the rupture length of triggered ruptures on the main fault is controlled by the stress state of the fault system. With the increase of the ratio between the shear stress and normal stress, the rupture length of the main fault increases. Our results reproduce the rupture behaviors of orthogonal faults, which may provide insights into the rupture characteristics of natural earthquakes.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"12 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141969209","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}
Parviz Ajourlou, Fiona Darbyshire, Pascal Audet, Glenn A Milne
Summary Seismic velocity models provide important constraints on Greenland’s deep structure, which, in turn, has profound implications for our understanding of the tectonic history of this region. However, the resolution of seismic models has been limited by a sparse network, particularly in northern and central Greenland. We address these limitations by generating new high-resolution Rayleigh-wave phase velocity maps encompassing Greenland and northeastern Canada by processing over three decades of teleseismic earthquake records and incorporating recently added stations in Greenland and Arctic Canada. These phase velocity maps are sensitive to structure from the lower crust down to the sub-lithospheric mantle (25-185 s period). We find significant heterogeneity and a strong correlation between isotropic and anisotropic seismic velocities with inferred geological structure. High seismic velocities associated with cratonic lithosphere are broadly divided into two regions, with a belt of reduced velocity spanning central Greenland, which we interpret as lithospheric erosion resulting from interaction between the Greenland continental keel and the Iceland plume. Within each region, we identify tectonic subdivisions that suggest fundamental differences between the blocks that make up Precambrian Greenland. In the south, the North Atlantic craton (NAC) has a high-velocity keel exhibiting anisotropic stratification. Between the NAC and the cratonic lithosphere further north, the Proterozoic Nagssugtoqidian orogenic belt shows a distinct signature of reduced seismic velocity to ∼75 s period, but then appears to pinch out at depth. The northern Greenland lithosphere exhibits significant isotropic heterogeneity, with a distinct core of high velocities in the northwest (∼55-75 s period) giving way to a set of distinct east-west trending high-velocity belts at longer periods. At all periods sensitive to the lithospheric mantle in this region, anisotropic fast orientations are E-W, consistent with a north-south Precambrian assembly of the Greenland shield. In contrast to the NAC, there is no evidence of anisotropic stratification in the northern part of the cratonic keel. Based on both isotropic and anisotropic phase-velocity anomalies, we suggest that the Phanerozoic Caledonian and Ellesmerian-Franklinian fold belts are relatively thin-skinned features onshore Greenland, though the Caledonian belt may have a stronger signature off the east coast. At the longest periods, a prominent low-velocity anomaly initially centred on Iceland migrates northwards and spreads beneath central-eastern Greenland. Coupled with NW-SE trending anisotropy, this feature is interpreted as the effect of mantle flow radiating outward from the Iceland plume and interacting with the eroded Greenland lithosphere.
{"title":"Structure of the crust and upper mantle in Greenland and northeastern Canada: Insights from anisotropic rayleigh-wave tomography","authors":"Parviz Ajourlou, Fiona Darbyshire, Pascal Audet, Glenn A Milne","doi":"10.1093/gji/ggae269","DOIUrl":"https://doi.org/10.1093/gji/ggae269","url":null,"abstract":"Summary Seismic velocity models provide important constraints on Greenland’s deep structure, which, in turn, has profound implications for our understanding of the tectonic history of this region. However, the resolution of seismic models has been limited by a sparse network, particularly in northern and central Greenland. We address these limitations by generating new high-resolution Rayleigh-wave phase velocity maps encompassing Greenland and northeastern Canada by processing over three decades of teleseismic earthquake records and incorporating recently added stations in Greenland and Arctic Canada. These phase velocity maps are sensitive to structure from the lower crust down to the sub-lithospheric mantle (25-185 s period). We find significant heterogeneity and a strong correlation between isotropic and anisotropic seismic velocities with inferred geological structure. High seismic velocities associated with cratonic lithosphere are broadly divided into two regions, with a belt of reduced velocity spanning central Greenland, which we interpret as lithospheric erosion resulting from interaction between the Greenland continental keel and the Iceland plume. Within each region, we identify tectonic subdivisions that suggest fundamental differences between the blocks that make up Precambrian Greenland. In the south, the North Atlantic craton (NAC) has a high-velocity keel exhibiting anisotropic stratification. Between the NAC and the cratonic lithosphere further north, the Proterozoic Nagssugtoqidian orogenic belt shows a distinct signature of reduced seismic velocity to ∼75 s period, but then appears to pinch out at depth. The northern Greenland lithosphere exhibits significant isotropic heterogeneity, with a distinct core of high velocities in the northwest (∼55-75 s period) giving way to a set of distinct east-west trending high-velocity belts at longer periods. At all periods sensitive to the lithospheric mantle in this region, anisotropic fast orientations are E-W, consistent with a north-south Precambrian assembly of the Greenland shield. In contrast to the NAC, there is no evidence of anisotropic stratification in the northern part of the cratonic keel. Based on both isotropic and anisotropic phase-velocity anomalies, we suggest that the Phanerozoic Caledonian and Ellesmerian-Franklinian fold belts are relatively thin-skinned features onshore Greenland, though the Caledonian belt may have a stronger signature off the east coast. At the longest periods, a prominent low-velocity anomaly initially centred on Iceland migrates northwards and spreads beneath central-eastern Greenland. Coupled with NW-SE trending anisotropy, this feature is interpreted as the effect of mantle flow radiating outward from the Iceland plume and interacting with the eroded Greenland lithosphere.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"78 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141939665","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}
Mei Feng, Meijian An, Hulin Zang, Marcelo S Assumpção, Marcelo B Bianchi, George S França, Marcelo P Rocha, Leda S Bettucci, Carlos A Chaves
Summary The amalgamation and breakup of the West Gondwana shaped the South American platform. The dynamics during the processes can be reflected by crust anisotropy of the platform, but there are no specialized crustal anisotropic measurements yet. Splitting analysis of Moho-converted shear waves in P-wave receiver functions (Pms) can reveal crustal-scale anisotropy, which is important for understanding the dynamic evolution of the crust and for the interpretation of mantle anisotropy from splitting analysis of core–mantle refracted shear waves (XKS phases). This study measured crustal anisotropy for the old and stable South American platform by Pms splitting analysis. The splitting times vary mainly in the range of 0–0.5 s, with a regional mean of 0.2 s, slightly lower than that observed in tectonically active regions. The detected crustal anisotropy shows distinct characteristics and spatial zoning, providing insights into tectonic processes. (1) Fast polarization directions at stations close to the Transbrasiliano Lineament (TBL) are oriented NNE–SSW, generally consistent with the strike of the TBL but inconsistent with the maximum horizontal compressive stress, implying that they might be formed by dynamic metamorphism during the formation of the TBL. (2) Crustal anisotropy along the passive continental margin in the east and northeast is weak. Still, the fast polarization directions tend to be oriented along the margin, implying the existence of fossil extensional crustal fabrics formed during the continental rifting of West Gondwana. (3) The Paraná Basin, one of the world's largest Large Igneous Provinces (LIP) covered by continental flood basalts, shows distinctively strong anisotropy, with fast polarization directions highly aligned with mantle anisotropy, implying that synchronous crust–mantle deformation occurred in these regions as a result of magmatism during the breakup of West Gondwana.
{"title":"Dynamic evolution of West Gondwana inferred from crustal anisotropy of the South American platform","authors":"Mei Feng, Meijian An, Hulin Zang, Marcelo S Assumpção, Marcelo B Bianchi, George S França, Marcelo P Rocha, Leda S Bettucci, Carlos A Chaves","doi":"10.1093/gji/ggae267","DOIUrl":"https://doi.org/10.1093/gji/ggae267","url":null,"abstract":"Summary The amalgamation and breakup of the West Gondwana shaped the South American platform. The dynamics during the processes can be reflected by crust anisotropy of the platform, but there are no specialized crustal anisotropic measurements yet. Splitting analysis of Moho-converted shear waves in P-wave receiver functions (Pms) can reveal crustal-scale anisotropy, which is important for understanding the dynamic evolution of the crust and for the interpretation of mantle anisotropy from splitting analysis of core–mantle refracted shear waves (XKS phases). This study measured crustal anisotropy for the old and stable South American platform by Pms splitting analysis. The splitting times vary mainly in the range of 0–0.5 s, with a regional mean of 0.2 s, slightly lower than that observed in tectonically active regions. The detected crustal anisotropy shows distinct characteristics and spatial zoning, providing insights into tectonic processes. (1) Fast polarization directions at stations close to the Transbrasiliano Lineament (TBL) are oriented NNE–SSW, generally consistent with the strike of the TBL but inconsistent with the maximum horizontal compressive stress, implying that they might be formed by dynamic metamorphism during the formation of the TBL. (2) Crustal anisotropy along the passive continental margin in the east and northeast is weak. Still, the fast polarization directions tend to be oriented along the margin, implying the existence of fossil extensional crustal fabrics formed during the continental rifting of West Gondwana. (3) The Paraná Basin, one of the world's largest Large Igneous Provinces (LIP) covered by continental flood basalts, shows distinctively strong anisotropy, with fast polarization directions highly aligned with mantle anisotropy, implying that synchronous crust–mantle deformation occurred in these regions as a result of magmatism during the breakup of West Gondwana.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"20 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141884061","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}
Summary Geomagnetic field data from six magnetic observatories in and adjacent to the South Atlantic Anomaly were individually analysed to detect abrupt secular variation changes occurring on time scales of less than a year and to explore any correlation with the evolution of the South Atlantic Anomaly. After applying external field corrections by means of the CHAOS-7 model, twelve-month differences of the respective observatory monthly mean of the eastward component Y revealed evidence of several geomagnetic jerks with varying amplitudes during the period 2000-2020. These observations were compared to the CHAOS-7 spherical harmonic model and previous studies of the South Atlantic Anomaly’s evolution. It emerged from this study that global field models like CHAOS are not very effective in identifying rapid localised changes in the geomagnetic field, highlighting the importance of using observatory data in conjunction with satellite data when studying geomagnetic jerks.
{"title":"A comparative investigation of geomagnetic jerks across the SAA during the period 2000-2020","authors":"A E Nel, P B Kotzé","doi":"10.1093/gji/ggae264","DOIUrl":"https://doi.org/10.1093/gji/ggae264","url":null,"abstract":"Summary Geomagnetic field data from six magnetic observatories in and adjacent to the South Atlantic Anomaly were individually analysed to detect abrupt secular variation changes occurring on time scales of less than a year and to explore any correlation with the evolution of the South Atlantic Anomaly. After applying external field corrections by means of the CHAOS-7 model, twelve-month differences of the respective observatory monthly mean of the eastward component Y revealed evidence of several geomagnetic jerks with varying amplitudes during the period 2000-2020. These observations were compared to the CHAOS-7 spherical harmonic model and previous studies of the South Atlantic Anomaly’s evolution. It emerged from this study that global field models like CHAOS are not very effective in identifying rapid localised changes in the geomagnetic field, highlighting the importance of using observatory data in conjunction with satellite data when studying geomagnetic jerks.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"57 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141887284","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}
Congyue Cui, Wenjie Lei, Qiancheng Liu, Daniel Peter, Ebru Bozdağ, Jeroen Tromp, Judith Hill, Norbert Podhorszki, David Pugmire
Summary We present our third and final generation joint P and S global adjoint tomography (GLAD) model, GLAD-M35, and quantify its uncertainty based on a low-rank approximation of the inverse Hessian. Starting from our second-generation model, GLAD-M25, we added 680 new earthquakes to the database for a total of 2,160 events. New P-wave categories are included to compensate for the imbalance between P- and S-wave measurements, and we enhanced the window selection algorithm to include more major-arc phases, providing better constraints on the structure of the deep mantle and more than doubling the number of measurement windows to 40 million. Two stages of a Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton inversion were performed, each comprising five iterations. With this BFGS update history, we determine the model’s standard deviation and resolution length through randomized singular value decomposition.
摘要 我们介绍了第三代也是最后一代 P 和 S 联合全球邻接层析成像（GLAD）模型 GLAD-M35，并根据逆赫西方的低秩近似值对其不确定性进行了量化。从第二代模型 GLAD-M25 开始，我们在数据库中新增了 680 次地震，共计 2,160 次地震。我们增加了新的 P 波类别，以弥补 P 波和 S 波测量之间的不平衡。我们还增强了窗口选择算法，以包括更多的主弧相，从而为深地幔结构提供更好的约束，并将测量窗口数量增加了一倍多，达到 4000 万个。进行了两个阶段的布洛伊登-弗莱彻-戈德法布-山诺（BFGS）准牛顿反演，每个阶段包括五次迭代。根据 BFGS 更新历史，我们通过随机奇异值分解确定了模型的标准偏差和分辨率长度。
{"title":"GLAD-M35: A joint P and S global tomographic model with uncertainty quantification","authors":"Congyue Cui, Wenjie Lei, Qiancheng Liu, Daniel Peter, Ebru Bozdağ, Jeroen Tromp, Judith Hill, Norbert Podhorszki, David Pugmire","doi":"10.1093/gji/ggae270","DOIUrl":"https://doi.org/10.1093/gji/ggae270","url":null,"abstract":"Summary We present our third and final generation joint P and S global adjoint tomography (GLAD) model, GLAD-M35, and quantify its uncertainty based on a low-rank approximation of the inverse Hessian. Starting from our second-generation model, GLAD-M25, we added 680 new earthquakes to the database for a total of 2,160 events. New P-wave categories are included to compensate for the imbalance between P- and S-wave measurements, and we enhanced the window selection algorithm to include more major-arc phases, providing better constraints on the structure of the deep mantle and more than doubling the number of measurement windows to 40 million. Two stages of a Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton inversion were performed, each comprising five iterations. With this BFGS update history, we determine the model’s standard deviation and resolution length through randomized singular value decomposition.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"197 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141939664","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}
Yi-Wun Mika Liao, Bill Fry, Andrew Howell, Charles Williams, Andrew Nicol, Chris Rollins
Summary Seismic and tsunami hazard modelling and preparedness are challenged by uncertainties in the earthquake source process. Important parameters such as the recurrence interval of earthquakes of a given magnitude at a particular location, the probability of multi-fault rupture, earthquake clustering, rupture directivity and slip distribution are often poorly constrained. Physics-based earthquake simulators, such as RSQSim, offer a means of probing uncertainties in these parameters by generating long-term catalogues of earthquake ruptures on a system of known faults. The fault initial stress state in these simulations is typically prescribed as a single uniform value, which can promote characteristic earthquake behaviours and reduce variability in modelled events. Here, we test the role of spatial heterogeneity in the distribution of the initial stresses and frictional properties on earthquake cycle simulations. We focus on the Hikurangi-Kermadec subduction zone, which may produce Mw > 9.0 earthquakes and likely poses a major hazard and risk to Aotearoa New Zealand. We explore RSQSim simulations of Hikurangi-Kermadec subduction earthquake cycles in which we vary the rate and state coefficients (a and b). The results are compared with the magnitude-frequency distribution (MFD) of the instrumental earthquake catalogue and with empirical slip scaling laws from global earthquakes. Our results suggest stress heterogeneity produces more realistic and less characteristic synthetic catalogues, making them particularly well suited for hazard and risk assessment. We further find that the initial stress effects are dominated by the initial effective normal stresses, since the normal stresses evolve more slowly than the shear stresses. A heterogeneous stress model with a constant pore-fluid pressure ratio and a constant state coefficient (b) of 0.003 produces the best fit to MFDs and empirical scaling laws, while the model with variable frictional properties produces the best fit to earthquake depth distribution and empirical scaling laws. This model is our preferred initial stress state and frictional property settings for earthquake modelling of the Hikurangi-Kermadec subduction interface. Introducing heterogeneity of other parameters within RSQSim (e.g. friction coefficient, reference slip rate, characteristic distance, initial state variable, etc) could further improve the applicability of the synthetic earthquake catalogues to seismic hazard problems and form the focus of future research.
{"title":"The role of heterogeneous stress in earthquake cycle models of the Hikurangi-Kermadec subduction zone","authors":"Yi-Wun Mika Liao, Bill Fry, Andrew Howell, Charles Williams, Andrew Nicol, Chris Rollins","doi":"10.1093/gji/ggae266","DOIUrl":"https://doi.org/10.1093/gji/ggae266","url":null,"abstract":"Summary Seismic and tsunami hazard modelling and preparedness are challenged by uncertainties in the earthquake source process. Important parameters such as the recurrence interval of earthquakes of a given magnitude at a particular location, the probability of multi-fault rupture, earthquake clustering, rupture directivity and slip distribution are often poorly constrained. Physics-based earthquake simulators, such as RSQSim, offer a means of probing uncertainties in these parameters by generating long-term catalogues of earthquake ruptures on a system of known faults. The fault initial stress state in these simulations is typically prescribed as a single uniform value, which can promote characteristic earthquake behaviours and reduce variability in modelled events. Here, we test the role of spatial heterogeneity in the distribution of the initial stresses and frictional properties on earthquake cycle simulations. We focus on the Hikurangi-Kermadec subduction zone, which may produce Mw > 9.0 earthquakes and likely poses a major hazard and risk to Aotearoa New Zealand. We explore RSQSim simulations of Hikurangi-Kermadec subduction earthquake cycles in which we vary the rate and state coefficients (a and b). The results are compared with the magnitude-frequency distribution (MFD) of the instrumental earthquake catalogue and with empirical slip scaling laws from global earthquakes. Our results suggest stress heterogeneity produces more realistic and less characteristic synthetic catalogues, making them particularly well suited for hazard and risk assessment. We further find that the initial stress effects are dominated by the initial effective normal stresses, since the normal stresses evolve more slowly than the shear stresses. A heterogeneous stress model with a constant pore-fluid pressure ratio and a constant state coefficient (b) of 0.003 produces the best fit to MFDs and empirical scaling laws, while the model with variable frictional properties produces the best fit to earthquake depth distribution and empirical scaling laws. This model is our preferred initial stress state and frictional property settings for earthquake modelling of the Hikurangi-Kermadec subduction interface. Introducing heterogeneity of other parameters within RSQSim (e.g. friction coefficient, reference slip rate, characteristic distance, initial state variable, etc) could further improve the applicability of the synthetic earthquake catalogues to seismic hazard problems and form the focus of future research.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"22 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141939666","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}
U Kakhkhorov, W W Weibul, E B Raknes, S Kodaira, G Fujie, B Arntsen
SUMMARY The geometrical and seismic structure of the Pacific oceanic Plate of the Japan Trench is essential for the understanding of earthquake activity in the area. Ocean Bottom Seismometer (OBS) data can be used, via ray-based tomography, to obtain estimates of properties such as crust thickness and structure, hydration and depth to the Moho boundary. The spatial resolution of these properties can be substantially improved by using the full waveform inversion (FWI) method. Most OBS data in this area are acquired with a sparse receiver spacing of 5–6 km, whereas FWI is assumed to work best with denser (1–2 km) receiver spacing. We show that FWI can be adapted to sparsely sampled data with better resolution than traveltime tomography. Using a 500 km long OBS longitudinal profile from the Japan Trench we obtain a detailed velocity structure of the crust, a better definition of the Moho boundary, a well-defined low-velocity layer in the lower crust and a clear spatial definition of areas with velocity inversions.
{"title":"Full waveform inversion of ocean bottom seismometer data from the oceanic Pacific Plate of the Japan trench","authors":"U Kakhkhorov, W W Weibul, E B Raknes, S Kodaira, G Fujie, B Arntsen","doi":"10.1093/gji/ggae246","DOIUrl":"https://doi.org/10.1093/gji/ggae246","url":null,"abstract":"SUMMARY The geometrical and seismic structure of the Pacific oceanic Plate of the Japan Trench is essential for the understanding of earthquake activity in the area. Ocean Bottom Seismometer (OBS) data can be used, via ray-based tomography, to obtain estimates of properties such as crust thickness and structure, hydration and depth to the Moho boundary. The spatial resolution of these properties can be substantially improved by using the full waveform inversion (FWI) method. Most OBS data in this area are acquired with a sparse receiver spacing of 5–6 km, whereas FWI is assumed to work best with denser (1–2 km) receiver spacing. We show that FWI can be adapted to sparsely sampled data with better resolution than traveltime tomography. Using a 500 km long OBS longitudinal profile from the Japan Trench we obtain a detailed velocity structure of the crust, a better definition of the Moho boundary, a well-defined low-velocity layer in the lower crust and a clear spatial definition of areas with velocity inversions.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"46 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141884062","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}
Youlin Chen, Xiwei Xu, Jiakang Xie, Hafidh A A Ghalib, Shanshan Liang
Summary Utilizing over 31,000 Lg waveforms from 136 crustal earthquakes recorded at 346 regional stations, we conduct detailed tomographic mappings of the Lg Q structure across Eastern Asia in a frequency range from 0.5 to 4.0Hz. By improving the standard two-station (TS) method, we effectively correct non-unity site response ratios using site responses estimated at individual stations. This innovative approach combines the flexible recording geometry of the TS method with the precision of reversed two-station (RTS) and reversed two-event (RTE) methods, producing a comprehensive dataset devoid of source and site effects for Q tomography. To address unsolvable 3D structural effects in the Lg spectral amplitude modeling, we justify these as modeling errors with a Gaussian distribution. This approach supports our SVD-based tomographic method, allowing for effective inversion of attenuation parameters and quantitative assessment of model resolution and errors. Our results reveal a complex relationship between Lg Q and the tectonic characteristics of Eastern Asia. In well-resolved regions, low Qo (1-Hz Q) values correspond to areas with high heat flow, partial melt, thick sediment, and recent tectonic-thermal activities, in contrast to high Qo values in stable, ancient crusts lacking recent tectonic activity. Rift basins are characterized by low Lg Qo, whereas flexural basins generally have high Qo basements. We also note that post-formation factors, such as sedimentation and crustal flow intrusion, significantly impact Qo values. Furthermore, Lg Q shows a complex frequency relationship, though the power-law approximation with positive power η remains useful. The frequency dependence power η is inversely related to Qo: the regions with low Qo typically have high η and vice versa. This study provides reliable attenuation tomographic and relative site response models for Lg waves in Eastern Asia, pertinent for relative geophysical studies.
摘要 利用在 346 个区域台站记录的 136 次地壳地震的 31,000 多条 Lg 波形，我们在 0.5 至 4.0Hz 的频率范围内对整个东亚地区的 Lg Q 结构进行了详细的层析成像制图。通过改进标准的双台站（TS）方法，我们利用单个台站估算的台站响应有效地修正了非统一台站响应比。这种创新方法将 TS 方法灵活的记录几何形状与反向双站 (RTS) 和反向双事件 (RTE) 方法的精确性结合在一起，为 Q 层析成像提供了一个没有声源和站点效应的综合数据集。为了解决 Lg 频谱振幅建模中无法解决的三维结构效应问题，我们将其视为高斯分布的建模误差。这种方法支持我们基于 SVD 的层析成像方法，可以有效地反演衰减参数，并对模型分辨率和误差进行定量评估。我们的结果揭示了 Lg Q 与东亚构造特征之间的复杂关系。在分辨率较高的地区，低Qo（1-Hz Q）值对应于热流较高、部分熔融、沉积物较厚以及近期有构造热活动的地区，而在稳定、古老、缺乏近期构造活动的地壳中，Qo值较高。裂谷盆地的特点是低 Lg Qo 值，而褶皱盆地一般具有高 Qo 值的基底。我们还注意到，沉积和地壳流侵入等形成后因素对 Qo 值有重大影响。此外，尽管具有正幂次η的幂律近似仍然有用，但 Lg Q 显示出复杂的频率关系。频率相关功率 η 与 Qo 成反比：Qo 值低的区域通常 η 值高，反之亦然。这项研究为东亚地区的 Lg 波提供了可靠的衰减层析成像和相对场地响应模型，对相关地球物理研究很有意义。
{"title":"Two-Station Lg Wave Attenuation Tomography in Eastern Asia","authors":"Youlin Chen, Xiwei Xu, Jiakang Xie, Hafidh A A Ghalib, Shanshan Liang","doi":"10.1093/gji/ggae255","DOIUrl":"https://doi.org/10.1093/gji/ggae255","url":null,"abstract":"Summary Utilizing over 31,000 Lg waveforms from 136 crustal earthquakes recorded at 346 regional stations, we conduct detailed tomographic mappings of the Lg Q structure across Eastern Asia in a frequency range from 0.5 to 4.0Hz. By improving the standard two-station (TS) method, we effectively correct non-unity site response ratios using site responses estimated at individual stations. This innovative approach combines the flexible recording geometry of the TS method with the precision of reversed two-station (RTS) and reversed two-event (RTE) methods, producing a comprehensive dataset devoid of source and site effects for Q tomography. To address unsolvable 3D structural effects in the Lg spectral amplitude modeling, we justify these as modeling errors with a Gaussian distribution. This approach supports our SVD-based tomographic method, allowing for effective inversion of attenuation parameters and quantitative assessment of model resolution and errors. Our results reveal a complex relationship between Lg Q and the tectonic characteristics of Eastern Asia. In well-resolved regions, low Qo (1-Hz Q) values correspond to areas with high heat flow, partial melt, thick sediment, and recent tectonic-thermal activities, in contrast to high Qo values in stable, ancient crusts lacking recent tectonic activity. Rift basins are characterized by low Lg Qo, whereas flexural basins generally have high Qo basements. We also note that post-formation factors, such as sedimentation and crustal flow intrusion, significantly impact Qo values. Furthermore, Lg Q shows a complex frequency relationship, though the power-law approximation with positive power η remains useful. The frequency dependence power η is inversely related to Qo: the regions with low Qo typically have high η and vice versa. This study provides reliable attenuation tomographic and relative site response models for Lg waves in Eastern Asia, pertinent for relative geophysical studies.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"184 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141884063","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}
Rossella Fonzetti, Aladino Govoni, Pasquale De Gori, Claudio Chiarabba
Summary Moderate magnitude earthquakes and seismic sequences frequently develop on fault systems, but whether they are linked to future major ruptures is always ambiguous. In this study, we investigated a seismic sequence that has developed within a portion of the stretching region of the Apennines in Italy where moderate to large earthquakes are likely to occur. We captured a total of 2 039 aftershocks of the September 18, 2023, Mw4.9 earthquake occurred during the first week, by using ML-based algorithms. Aftershocks align on two 5-7 km long parallel faults, from a length that exceeds what is expected from the mainshock magnitude. The segments are ramping at about 6 km depth on closely spaced N100 striking 70 N dipping planes, at a distance of some kilometers from the mainshock hypocenter. Our results indicate that even moderate magnitude events trigger seismicity on a spread set of fault segments around the mainshock hypocenter, revealing processes of interaction within the crustal layer. The possibility that larger earthquakes develop during seismicity spread is favored by pore pressure diffusion, in relation with the closeness to criticality of fault segments. Based on the very rapid activation of seismicity on the entire system and a back-front signal from the hypocenter of the main event, we infer that fluid pressure, initially high within the crustal layer, rapidly dropped after the mainshock. Our study reinforces the importance of timely extracting information on fault geometry and seismicity distribution on faults. ML-based methods represent a viable tool for semi-real-time application, yielding constraints on short-time forecasts.
摘要 断层系统上经常发生中等震级地震和地震序列，但它们是否与未来的大断裂有关却总是模棱两可。在本研究中，我们调查了在意大利亚平宁山脉延伸区域内发生的地震序列，在该区域内可能会发生中到大型地震。我们使用基于 ML 的算法，捕捉了 2023 年 9 月 18 日发生的 Mw4.9 级地震第一周的 2 039 次余震。余震发生在两条 5-7 千米长的平行断层上，长度超过了主震震级的预期。余震段在距离主震震中约 6 千米深的地方，在间隔紧密的 N100 冲向 70 N 的倾角平面上急剧上升。我们的研究结果表明，即使是中等震级的事件也会在主震次中心周围的断层段上引发地震，揭示了地壳层内的相互作用过程。在地震扩散过程中，由于孔隙压力扩散与断层段临界程度的关系，可能会发生更大的地震。根据整个系统地震活动的快速启动和来自主震下中心的后前信号，我们推断地壳层内最初较高的流体压力在主震后迅速下降。我们的研究加强了及时提取断层几何和地震分布信息的重要性。基于 ML 的方法是半实时应用的可行工具，可为短时预报提供约束。
{"title":"A rapid analysis of aftershock processes after a moderate magnitude earthquake with ML-methods","authors":"Rossella Fonzetti, Aladino Govoni, Pasquale De Gori, Claudio Chiarabba","doi":"10.1093/gji/ggae262","DOIUrl":"https://doi.org/10.1093/gji/ggae262","url":null,"abstract":"Summary Moderate magnitude earthquakes and seismic sequences frequently develop on fault systems, but whether they are linked to future major ruptures is always ambiguous. In this study, we investigated a seismic sequence that has developed within a portion of the stretching region of the Apennines in Italy where moderate to large earthquakes are likely to occur. We captured a total of 2 039 aftershocks of the September 18, 2023, Mw4.9 earthquake occurred during the first week, by using ML-based algorithms. Aftershocks align on two 5-7 km long parallel faults, from a length that exceeds what is expected from the mainshock magnitude. The segments are ramping at about 6 km depth on closely spaced N100 striking 70 N dipping planes, at a distance of some kilometers from the mainshock hypocenter. Our results indicate that even moderate magnitude events trigger seismicity on a spread set of fault segments around the mainshock hypocenter, revealing processes of interaction within the crustal layer. The possibility that larger earthquakes develop during seismicity spread is favored by pore pressure diffusion, in relation with the closeness to criticality of fault segments. Based on the very rapid activation of seismicity on the entire system and a back-front signal from the hypocenter of the main event, we infer that fluid pressure, initially high within the crustal layer, rapidly dropped after the mainshock. Our study reinforces the importance of timely extracting information on fault geometry and seismicity distribution on faults. ML-based methods represent a viable tool for semi-real-time application, yielding constraints on short-time forecasts.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"31 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141784286","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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