Summary For the analysis of spectral induced polarization (SIP) measurements and for the description of frequency-dependent electrical relaxation responses, so-called Cole-Cole models (CCMs) are widely used. Typically, CCM formulations in terms of complex electrical conductivity or complex electrical resistivity are used in geophysical applications. The differences between these model descriptions, in particular between the respective time constants, and their conversion have been studied. A third variant of the model is formulated in terms of complex permittivity, commonly used in materials science. In general, all these model formulations can be used equivalently for fitting SIP data, which, however, results in differing values for some of the model parameters. For a meaningful comparison of CCM parameters of different samples or measurements, it is necessary that they are based on the same model formulation. In this work, the relationships between the Debye model (DM) and CCM parameters in the formulation for complex permittivity and complex conductivity are studied. A direct analytical conversion is possible for generalized DM formulations, both in single- and multi-term model formulations, resulting in relationships between the respective relaxation time distributions (RTDs). Such a direct conversion for CCM formulations is not possible. We however derived an approximate relationship between log -normal RTD and CCM formulations and respective permittivity and conductivity parameter values. Our study also highlights the significance of using consistent model formulations when experimental data are compared in terms of DM or CCM parameters, as parameters used to predict ice temperature are incorrect if the conductivity time constant is used to predict the temperature from interpolation of a permittivity time constant-temperature relationship.
{"title":"Relationship between Cole-Cole model parameters in permittivity and conductivity formulation","authors":"Jonas K Limbrock, Andreas Kemna","doi":"10.1093/gji/ggae300","DOIUrl":"https://doi.org/10.1093/gji/ggae300","url":null,"abstract":"Summary For the analysis of spectral induced polarization (SIP) measurements and for the description of frequency-dependent electrical relaxation responses, so-called Cole-Cole models (CCMs) are widely used. Typically, CCM formulations in terms of complex electrical conductivity or complex electrical resistivity are used in geophysical applications. The differences between these model descriptions, in particular between the respective time constants, and their conversion have been studied. A third variant of the model is formulated in terms of complex permittivity, commonly used in materials science. In general, all these model formulations can be used equivalently for fitting SIP data, which, however, results in differing values for some of the model parameters. For a meaningful comparison of CCM parameters of different samples or measurements, it is necessary that they are based on the same model formulation. In this work, the relationships between the Debye model (DM) and CCM parameters in the formulation for complex permittivity and complex conductivity are studied. A direct analytical conversion is possible for generalized DM formulations, both in single- and multi-term model formulations, resulting in relationships between the respective relaxation time distributions (RTDs). Such a direct conversion for CCM formulations is not possible. We however derived an approximate relationship between log -normal RTD and CCM formulations and respective permittivity and conductivity parameter values. Our study also highlights the significance of using consistent model formulations when experimental data are compared in terms of DM or CCM parameters, as parameters used to predict ice temperature are incorrect if the conductivity time constant is used to predict the temperature from interpolation of a permittivity time constant-temperature relationship.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177475","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 Detection and separation of the subtle postseismic deformation signals associated with moderate magnitude earthquakes from Interferometric Synthetic Aperture Radar (InSAR) time-series is often challenging. Singular Spectrum Analysis (SSA) is a statistical non-parametric technique used to decompose and reconstruct signals from complex time-series data. We show that the SSA analysis effectively distinguished the postseismic signal associated with the 2019 Mw 6 Mirpur earthquake from periodic and noise components. The SSA derived postseismic deformation signal is smoother and fits better to an exponential model with a decay time of 34 days. The postseismic deformation is confined to the southeast of the rupture area and lasted for ∼90 days following the mainshock. Inversion of the postseismic deformation suggests an afterslip mechanism with a maximum slip of ∼0.07 m on the shallow, up-dip portions of the Main Himalayan Thrust. The 2019 Mirpur earthquake and afterslip together released less than 12 per cent of the accumulated strain energy since the 1555 Kashmir earthquake and implies continued seismic hazard in the future.
{"title":"Application of Singular Spectrum Analysis to InSAR time-series for constraining the postseismic deformation due to moderate magnitude earthquakes: the case of 2019 Mw 6 Mirpur earthquake, NW Himalaya","authors":"M C M Jasir, K M Sreejith, R Agrawal, S K Begum","doi":"10.1093/gji/ggae287","DOIUrl":"https://doi.org/10.1093/gji/ggae287","url":null,"abstract":"Summary Detection and separation of the subtle postseismic deformation signals associated with moderate magnitude earthquakes from Interferometric Synthetic Aperture Radar (InSAR) time-series is often challenging. Singular Spectrum Analysis (SSA) is a statistical non-parametric technique used to decompose and reconstruct signals from complex time-series data. We show that the SSA analysis effectively distinguished the postseismic signal associated with the 2019 Mw 6 Mirpur earthquake from periodic and noise components. The SSA derived postseismic deformation signal is smoother and fits better to an exponential model with a decay time of 34 days. The postseismic deformation is confined to the southeast of the rupture area and lasted for ∼90 days following the mainshock. Inversion of the postseismic deformation suggests an afterslip mechanism with a maximum slip of ∼0.07 m on the shallow, up-dip portions of the Main Himalayan Thrust. The 2019 Mirpur earthquake and afterslip together released less than 12 per cent of the accumulated strain energy since the 1555 Kashmir earthquake and implies continued seismic hazard in the future.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177450","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 Grid point discretization of the model has a significant impact on the accuracy of finite-difference seismic waveform simulations. Discretizing the discontinuous velocity model using local point medium parameters can lead to artifact diffraction caused by the stair-step representation and inaccuracies in calculated waveforms due to interface errors, particularly evident when employing coarse grids. To accurately represent model interfaces and reduce interface errors in finite-difference calculations, various equivalent medium parametrization methods have been developed in recent years. Most of these methods require volume-integrated averaging calculations of the medium parameter values within grid cells. The simplest way to achieve this volume averaging is to apply numerical integration averaging to all grid cells. However, this approach demands considerable computational time. To address this computational challenge, we propose employing a set of auxiliary grids to identify which grid cells intersected by the welded interface and perform volume averaging only on these specific cells, thereby reducing unnecessary computational overhead. Additionally, we present a three-dimensional tilted transversely isotropic equivalent medium parameterization method, which effectively suppresses interface errors and artefact diffraction under the application of coarse grids. We also provide an approach for computing the normal direction of the interface, which is essential for the tilted transversely isotropic equivalent medium parameterization. Numerical tests validate the accuracy of the tilted transversely isotropic equivalent medium parameterization method and demonstrate the practicality of the implementation proposed in this paper for complex models.
{"title":"Efficient implementation of equivalent medium parameterization in finite-difference seismic wave simulation methods","authors":"Luqian Jiang, Wei Zhang","doi":"10.1093/gji/ggae286","DOIUrl":"https://doi.org/10.1093/gji/ggae286","url":null,"abstract":"Summary Grid point discretization of the model has a significant impact on the accuracy of finite-difference seismic waveform simulations. Discretizing the discontinuous velocity model using local point medium parameters can lead to artifact diffraction caused by the stair-step representation and inaccuracies in calculated waveforms due to interface errors, particularly evident when employing coarse grids. To accurately represent model interfaces and reduce interface errors in finite-difference calculations, various equivalent medium parametrization methods have been developed in recent years. Most of these methods require volume-integrated averaging calculations of the medium parameter values within grid cells. The simplest way to achieve this volume averaging is to apply numerical integration averaging to all grid cells. However, this approach demands considerable computational time. To address this computational challenge, we propose employing a set of auxiliary grids to identify which grid cells intersected by the welded interface and perform volume averaging only on these specific cells, thereby reducing unnecessary computational overhead. Additionally, we present a three-dimensional tilted transversely isotropic equivalent medium parameterization method, which effectively suppresses interface errors and artefact diffraction under the application of coarse grids. We also provide an approach for computing the normal direction of the interface, which is essential for the tilted transversely isotropic equivalent medium parameterization. Numerical tests validate the accuracy of the tilted transversely isotropic equivalent medium parameterization method and demonstrate the practicality of the implementation proposed in this paper for complex models.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177452","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 Time-varying gravity fields play a crucial role in understanding and analyzing geodynamic processes, particularly the migration of matter across the Earth's surface. However, the current limitations in spatiotemporal resolution hinder their accurate representation. In this context, the use of a giant constellation of low-orbit satellites holds great potential for accurately recovering time-varying gravity fields with high spatiotemporal resolution. Based on the orbital parameters of 5199 satellites in 123 different orbital planes in the first phase configuration of the Starlink constellation and the orbital parameters of the Bender constellation in the next generation gravity mission, we conducted a closed-loop simulation to analyze the recovery ability of time-varying gravity field in 9 days using the short-arc integral method. The errors of aliasing AOHIS signal (Atmosphere, Ocean, Hydrology, Ice, and Solid Earth), ocean tide models, orbit positions, inter-satellite range rates, and accelerometer observations were considered in the numerical simulation. Compared with the Bender constellation, the Starlink-like constellation can effectively decrease the aliasing errors in the spatial- and frequency-domain when the observation noise is not considered. The Starlink-like constellation can also effectively improve the reliability of low-degree coefficients (below degree 15) of retrieved time-varying gravity field models and present higher time resolution (within 9 days) for the full degree spherical harmonic solutions than the Bender constellation when the observation noise is considered. The aliasing effect on the low-degree part of the Bender constellation can be significantly decreased by combining the Starlink-like and Bender constellations, and the accuracy of the recovered time-varying gravity field within degree 30 can be improved by about 0.5 ∼ 1 order of magnitude. Our results can provide a technical reference for the design of future gravity satellite mission.
{"title":"Simulation analysis of recovering time-varying gravity fields based on Starlink-like constellation","authors":"Youjian Liu, Jiancheng Li, Xinyu Xu, Hui Wei, Zhao Li, Yongqi Zhao","doi":"10.1093/gji/ggae273","DOIUrl":"https://doi.org/10.1093/gji/ggae273","url":null,"abstract":"Summary Time-varying gravity fields play a crucial role in understanding and analyzing geodynamic processes, particularly the migration of matter across the Earth's surface. However, the current limitations in spatiotemporal resolution hinder their accurate representation. In this context, the use of a giant constellation of low-orbit satellites holds great potential for accurately recovering time-varying gravity fields with high spatiotemporal resolution. Based on the orbital parameters of 5199 satellites in 123 different orbital planes in the first phase configuration of the Starlink constellation and the orbital parameters of the Bender constellation in the next generation gravity mission, we conducted a closed-loop simulation to analyze the recovery ability of time-varying gravity field in 9 days using the short-arc integral method. The errors of aliasing AOHIS signal (Atmosphere, Ocean, Hydrology, Ice, and Solid Earth), ocean tide models, orbit positions, inter-satellite range rates, and accelerometer observations were considered in the numerical simulation. Compared with the Bender constellation, the Starlink-like constellation can effectively decrease the aliasing errors in the spatial- and frequency-domain when the observation noise is not considered. The Starlink-like constellation can also effectively improve the reliability of low-degree coefficients (below degree 15) of retrieved time-varying gravity field models and present higher time resolution (within 9 days) for the full degree spherical harmonic solutions than the Bender constellation when the observation noise is considered. The aliasing effect on the low-degree part of the Bender constellation can be significantly decreased by combining the Starlink-like and Bender constellations, and the accuracy of the recovered time-varying gravity field within degree 30 can be improved by about 0.5 ∼ 1 order of magnitude. Our results can provide a technical reference for the design of future gravity satellite mission.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177451","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}
Li-Sheng Xu, Chang-Zai Wang, Zhe Zhang, Li-Hua Fang, Lei Yi, Xu Zhang, Xiang-Yun Guo, Chun-Lai Li
Summary The 2008 Mw7.9 Wenchuan earthquake ruptured the middle and northeastern segments of the Longmenshan Fault Zone (LMSFZ), and the 2013 Mw6.6 Lushan earthquake ruptured a 50km-long fault in the southwestern segment. Subsequently, an Mw5.8 earthquake occurred approximately 10 km distant from the Mw6.6 Lushan earthquake. Therefore, the potential risk for larger earthquakes (>Mw6.6)on the southwestern section must be considered. This study collects the latest seismological and GPS data to construct an integrated seismotectonic model for the two neighboring earthquake sequences. The model integrates the fault planes involved, the mainshock rupture processes, the mainshock-caused Coulomb stress perturbation, the aftershock distribution and the 3-D velocity structure of the source region, providing information for seismic risk evaluation. We find that three fault planes were involved, two of which were related to the mainshocks, and the third was generated by the aftershocks following the first mainshock. The mainshocks were caused by nearly pure thrust faulting on the two planes with dip angles of approximately 45° and almost opposite dipping directions, thereby forming a conjugate angle of around 90°. The third plane was located between the two mainshocks, approximately parallel to the second mainshock's fault plane. Each of the mainshocks primarily ruptured a single asperity, displaying simple time history. The Coulomb stress change of the first mainshock facilitated the generation of the second mainshock and the third fault plane, and the second mainshock increased the stress on the first mainshock's fault plane. The aftershocks were distributed within stratified materials by spatially varying interfaces and characterized by high Vp and Vs velocity and a low Vp/Vs ratio. The atypical dip angles of approximately 45° for thrust faults and the conjugate angle of approximately 90° are indicative of high stress state. The single asperity rupture implies simple stress accumulation. The mainshock-caused Coulomb stress change did not reduce the seismic risk in the source region. The varying interfaces are interpreted as a consequence of long-term horizontal compression. All of these characteristics suggest that the two earthquake sequences were generated by the breakage of three immature faults under strong compression by background stress, and the high stress state remains within the southwestern LMSFZ.
{"title":"Integrated seismotectonic model of the 2013 Mw6.6 and 2022 Mw5.8 earthquake sequences in the southwestern section of the longmenshan fault zone, China, and its implication","authors":"Li-Sheng Xu, Chang-Zai Wang, Zhe Zhang, Li-Hua Fang, Lei Yi, Xu Zhang, Xiang-Yun Guo, Chun-Lai Li","doi":"10.1093/gji/ggae274","DOIUrl":"https://doi.org/10.1093/gji/ggae274","url":null,"abstract":"Summary The 2008 Mw7.9 Wenchuan earthquake ruptured the middle and northeastern segments of the Longmenshan Fault Zone (LMSFZ), and the 2013 Mw6.6 Lushan earthquake ruptured a 50km-long fault in the southwestern segment. Subsequently, an Mw5.8 earthquake occurred approximately 10 km distant from the Mw6.6 Lushan earthquake. Therefore, the potential risk for larger earthquakes (>Mw6.6)on the southwestern section must be considered. This study collects the latest seismological and GPS data to construct an integrated seismotectonic model for the two neighboring earthquake sequences. The model integrates the fault planes involved, the mainshock rupture processes, the mainshock-caused Coulomb stress perturbation, the aftershock distribution and the 3-D velocity structure of the source region, providing information for seismic risk evaluation. We find that three fault planes were involved, two of which were related to the mainshocks, and the third was generated by the aftershocks following the first mainshock. The mainshocks were caused by nearly pure thrust faulting on the two planes with dip angles of approximately 45° and almost opposite dipping directions, thereby forming a conjugate angle of around 90°. The third plane was located between the two mainshocks, approximately parallel to the second mainshock's fault plane. Each of the mainshocks primarily ruptured a single asperity, displaying simple time history. The Coulomb stress change of the first mainshock facilitated the generation of the second mainshock and the third fault plane, and the second mainshock increased the stress on the first mainshock's fault plane. The aftershocks were distributed within stratified materials by spatially varying interfaces and characterized by high Vp and Vs velocity and a low Vp/Vs ratio. The atypical dip angles of approximately 45° for thrust faults and the conjugate angle of approximately 90° are indicative of high stress state. The single asperity rupture implies simple stress accumulation. The mainshock-caused Coulomb stress change did not reduce the seismic risk in the source region. The varying interfaces are interpreted as a consequence of long-term horizontal compression. All of these characteristics suggest that the two earthquake sequences were generated by the breakage of three immature faults under strong compression by background stress, and the high stress state remains within the southwestern LMSFZ.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177453","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 Ultra-low velocity zones (ULVZs) have been identified as regions of extremely low velocity anomalies in the Earth's lowermost mantle using seismic observations from reflected, refracted, and diffracted arrivals along the mantle side of the core-mantle boundary (CMB). Estimation of ULVZ geometrical (i.e., shape and size) and elastic (i.e., velocity and density) parameters with uncertainties is crucial in understanding the role of ULVZs in the ongoing dynamic processes within the Earth's mantle; however, these parameters are still poorly known due to uncertainties and tradeoffs of the seismically resolved ULVZ geometries and elastic parameters. Computation of synthetic waveforms for 2-D and 3-D ULVZs shapes is currently computationally feasible, but past studies utilize higher dimensional waveform modeling of mostly only low-frequency diffracted waves. Most studies focusing on high-frequency core-reflected waveforms (e.g., ScP) still use 1-D modeling approaches to determine ULVZ properties. This approach might lead to wrong results if the imaged structures have inherently 3-D geometries. This study investigates high-frequency synthetic ScP waveforms for various 2.5-D ULVZ geometries showing that additional seismic arrivals are generated even when the ScP geometrical ray path does not directly strike the location of the ULVZ. The largest amplitude additional phases in the 2.5-D models are post-cursor arrivals that are generated at the edges of the finite-length ULVZs. These newly identified ScP post-cursors can arrive within the ScsP post-cursor time window traditionally analyzed in 1-D ULVZ studies. These post-cursors might then be misidentified or constructively/destructively interfere with the ScsP postcursor, leading to incorrect estimation of ULVZ parameters. In this study we investigate the bias introduced by the 2.5-D morphologies on the 1D estimated ULVZ elastic properties in a Bayesian waveform inversion scheme. We further expand the Bayesian method by including the data noise covariance matrix in the inversion and compare it to an autoregressive noise model that was utilized in previous studies. From the application to the observed ScP data, we find that the new approach converges faster, particularly for the inversion of data from multiple events, and the new algorithm retrieves ULVZ parameters with more realistic uncertainties. The inversion of 2.5-D synthetic ScP waveforms suggests that the retrieved ULVZ parameters can be misleading with unrealistically high confidence if we do not consider the data noise covariance matrix in the inversion. Our new approach can also retrieve the shape of a multi-dimensional Gaussian ULVZ if its length is 12o or longer in the great circle arc direction. However, 2.5-D synthetic waveforms show additional waveform complexity which can constructively interfere with the ScP wavefield. Hence, in many cases the estimation of ULVZ properties using 1-D forward modeling can provide incorrect ULVZ paramet
{"title":"Examining the influence of 2.5-D ultra-low velocity zone morphology on ScP waveforms and estimated elastic parameters","authors":"Surya Pachhai, Michael S Thorne, Sebastian Rost","doi":"10.1093/gji/ggae285","DOIUrl":"https://doi.org/10.1093/gji/ggae285","url":null,"abstract":"Summary Ultra-low velocity zones (ULVZs) have been identified as regions of extremely low velocity anomalies in the Earth's lowermost mantle using seismic observations from reflected, refracted, and diffracted arrivals along the mantle side of the core-mantle boundary (CMB). Estimation of ULVZ geometrical (i.e., shape and size) and elastic (i.e., velocity and density) parameters with uncertainties is crucial in understanding the role of ULVZs in the ongoing dynamic processes within the Earth's mantle; however, these parameters are still poorly known due to uncertainties and tradeoffs of the seismically resolved ULVZ geometries and elastic parameters. Computation of synthetic waveforms for 2-D and 3-D ULVZs shapes is currently computationally feasible, but past studies utilize higher dimensional waveform modeling of mostly only low-frequency diffracted waves. Most studies focusing on high-frequency core-reflected waveforms (e.g., ScP) still use 1-D modeling approaches to determine ULVZ properties. This approach might lead to wrong results if the imaged structures have inherently 3-D geometries. This study investigates high-frequency synthetic ScP waveforms for various 2.5-D ULVZ geometries showing that additional seismic arrivals are generated even when the ScP geometrical ray path does not directly strike the location of the ULVZ. The largest amplitude additional phases in the 2.5-D models are post-cursor arrivals that are generated at the edges of the finite-length ULVZs. These newly identified ScP post-cursors can arrive within the ScsP post-cursor time window traditionally analyzed in 1-D ULVZ studies. These post-cursors might then be misidentified or constructively/destructively interfere with the ScsP postcursor, leading to incorrect estimation of ULVZ parameters. In this study we investigate the bias introduced by the 2.5-D morphologies on the 1D estimated ULVZ elastic properties in a Bayesian waveform inversion scheme. We further expand the Bayesian method by including the data noise covariance matrix in the inversion and compare it to an autoregressive noise model that was utilized in previous studies. From the application to the observed ScP data, we find that the new approach converges faster, particularly for the inversion of data from multiple events, and the new algorithm retrieves ULVZ parameters with more realistic uncertainties. The inversion of 2.5-D synthetic ScP waveforms suggests that the retrieved ULVZ parameters can be misleading with unrealistically high confidence if we do not consider the data noise covariance matrix in the inversion. Our new approach can also retrieve the shape of a multi-dimensional Gaussian ULVZ if its length is 12o or longer in the great circle arc direction. However, 2.5-D synthetic waveforms show additional waveform complexity which can constructively interfere with the ScP wavefield. Hence, in many cases the estimation of ULVZ properties using 1-D forward modeling can provide incorrect ULVZ paramet","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177477","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 Salt diapirs dominate the structure in many sedimentary basins and control the preservation and migration of hydrocarbon. The formation of salt diapirs generally falls into two endmember models: active (up-building) and passive (down-building) diapirism. In the active model, salt diapirs rise from salt buoyancy to pierce through the sedimentary overburden, whereas in the passive model, salt diapirs result from differential loading of sediments during deposition. These endmember models are mostly conceptual or kinematic, the mechanics of active and passive diapirism, and their relative roles and interactions in the formation of salt diapirs, remain uncertain. Here, we use two-dimensional high-resolution numerical models to investigate the primary factors and critical conditions for active and passive diapirism. Our results indicate that it is improper to use driving mechanisms to classify salt diapirs, because the buoyancy-driven active salt diapirism involves differential loading, while the passive diapirism requires salt buoyancy. The rise of salt diapirs is more sensitive to the effective viscosity of the overburden than to the salt viscosity. Stiff overburdens could prevent the rise of salt diapirs, but they could be pierced by salt diapirs if plastic yield of the overburden is allowed. During deposition, the coupled salt-sediment deformation, driven by both salt buoyancy and differential loading of sediments, can lead to various diapiric salt structures and minibasins. Regional tectonic stress generally promotes salt diapirism by enhancing strain weakening of salts and overburdens. We suggest that the classification of active and passive salt diapirism is an oversimplification in most cases. We propose a general model of the formation of salt diapirs that usually begins with dome initiation driven by salt buoyancy, followed by syndepositional down-building controlled by sedimentation and differential loading, and ends with canopy formation when sedimentation stops.
{"title":"Active and passive salt diapirs: a numerical study","authors":"Yiren Gou, Mian Liu","doi":"10.1093/gji/ggae284","DOIUrl":"https://doi.org/10.1093/gji/ggae284","url":null,"abstract":"Summary Salt diapirs dominate the structure in many sedimentary basins and control the preservation and migration of hydrocarbon. The formation of salt diapirs generally falls into two endmember models: active (up-building) and passive (down-building) diapirism. In the active model, salt diapirs rise from salt buoyancy to pierce through the sedimentary overburden, whereas in the passive model, salt diapirs result from differential loading of sediments during deposition. These endmember models are mostly conceptual or kinematic, the mechanics of active and passive diapirism, and their relative roles and interactions in the formation of salt diapirs, remain uncertain. Here, we use two-dimensional high-resolution numerical models to investigate the primary factors and critical conditions for active and passive diapirism. Our results indicate that it is improper to use driving mechanisms to classify salt diapirs, because the buoyancy-driven active salt diapirism involves differential loading, while the passive diapirism requires salt buoyancy. The rise of salt diapirs is more sensitive to the effective viscosity of the overburden than to the salt viscosity. Stiff overburdens could prevent the rise of salt diapirs, but they could be pierced by salt diapirs if plastic yield of the overburden is allowed. During deposition, the coupled salt-sediment deformation, driven by both salt buoyancy and differential loading of sediments, can lead to various diapiric salt structures and minibasins. Regional tectonic stress generally promotes salt diapirism by enhancing strain weakening of salts and overburdens. We suggest that the classification of active and passive salt diapirism is an oversimplification in most cases. We propose a general model of the formation of salt diapirs that usually begins with dome initiation driven by salt buoyancy, followed by syndepositional down-building controlled by sedimentation and differential loading, and ends with canopy formation when sedimentation stops.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177476","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}
Taiwan, one of the most active orogenic belts in the world, undergoes orogenic processes that can be elucidated by the doubly-vergent wedge model, explaining the extensive island-wide geological deformation. To provide a clearer depiction of its cross-island orogenic architecture, we apply ambient noise tomography across an east-west linear seismic array in central Taiwan, constructing the first high-resolution 2-D shear velocity model of the upper crust in the region. We observe robust fundamental- and higher-mode Rayleigh waves, with the latter being mainly present in the western Coastal Plain. We develop a multi-mode double beamforming method to determine local phase velocities across the array between 2 and 5-sec periods. For each location, we jointly invert all available fundamental- and higher-mode phase velocities using a Bayesian-based inversion method to obtain a 1-D model. All 1-D models are then combined to form a final 2-D model from the surface to ∼10 km depth. Our newly developed 2-D model clearly delineates major structural boundaries and fault geometries across central Taiwan, thereby corroborating the previously proposed pro-wedge and retro-wedge models while offering insight into regional seismic hazards.
{"title":"Multi-Mode Ambient Noise Double Beamforming Tomography with a Dense Linear Array: Revealing Accretionary Wedge Architecture across Central Taiwan","authors":"Cheng‐Nan Liu, Fan-Chi Lin, Hsin-Hua Huang, Yu Wang, Konstantinos Gkogkas","doi":"10.1093/gji/ggae283","DOIUrl":"https://doi.org/10.1093/gji/ggae283","url":null,"abstract":"\u0000 Taiwan, one of the most active orogenic belts in the world, undergoes orogenic processes that can be elucidated by the doubly-vergent wedge model, explaining the extensive island-wide geological deformation. To provide a clearer depiction of its cross-island orogenic architecture, we apply ambient noise tomography across an east-west linear seismic array in central Taiwan, constructing the first high-resolution 2-D shear velocity model of the upper crust in the region. We observe robust fundamental- and higher-mode Rayleigh waves, with the latter being mainly present in the western Coastal Plain. We develop a multi-mode double beamforming method to determine local phase velocities across the array between 2 and 5-sec periods. For each location, we jointly invert all available fundamental- and higher-mode phase velocities using a Bayesian-based inversion method to obtain a 1-D model. All 1-D models are then combined to form a final 2-D model from the surface to ∼10 km depth. Our newly developed 2-D model clearly delineates major structural boundaries and fault geometries across central Taiwan, thereby corroborating the previously proposed pro-wedge and retro-wedge models while offering insight into regional seismic hazards.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141921619","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}
Accurate absolute palaeointensity is essential for understanding dynamo processes on the Earth and other planetary bodies. Although great efforts have been made to propose techniques to obtain magnetic field strength from rock samples, such as Thellier-series methods, the amount of high-fidelity palaeointensities remains limited. One primary reason for this is the thermal alteration of samples that pervasively occurred during palaeointensity experiments. In this study, we developed a comprehensive rock magnetic experiment, termed thermal rock magnetic cycling (TRMC), that can utilize measurements of critical rock magnetic properties at elevated temperatures during multiple heating-cooling cycles to track thermal changes in bulk samples and individual magnetic components with different Curie temperatures in samples for palaeointensity interpretations. We demonstrate this method on a Galapagos lava sample, GA 84.6. The results for this specimen revealed that GA 84.6v underwent thermophysical alteration throughout the TRMC experiment, resulting in changes in its remanence carrying capacity. These findings were then used to interpret the palaeointensity results of specimen GA 84.6c, which revealed that the two-slope Arai plot yielded two linear segments with distinct palaeointensity values that were both biased by thermophysical alteration. To further test the TRMC method, we selected another historical lava sample (HS 2) from Mt. Lassen, detecting slight thermal-physical changes after heating the specimen HS 2–8C to a target temperature of 400° C. We also isolated a stable magnetic component with a Curie temperature below 400° C using the TRMC method, which may provide a more reliable palaeointensity estimate of 51 μT. By providing a method for tracking thermal alteration independent of palaeointensity experiments, the TRMC method can explore subtle, unrecognizable thermal alteration processes in less detailed palaeointensity measurements, which can help to assess the thermal stability of the measured samples and interpret the changes in the TRM unblocking spectrum and palaeointensity estimates, facilitating the acquisition of more reliable records for constrain the formation of the inner core and the evolution of Earth's magnetic field.
准确的绝对古磁场强度对于了解地球和其他行星体的动力过程至关重要。尽管人们已经做出巨大努力，提出了从岩石样本中获取磁场强度的技术，如 Thellier 系列方法，但高保真古强度的数量仍然有限。造成这种情况的一个主要原因是，在古强度实验过程中，样本普遍发生了热蚀变。在这项研究中，我们开发了一种称为热岩石磁循环（TRMC）的综合岩石磁性实验，可以利用多次加热-冷却循环过程中在高温下对关键岩石磁性的测量，来跟踪大块样品和样品中不同居里温度的单个磁性成分的热变化，从而进行古强度解释。我们在一个加拉帕戈斯熔岩样本 GA 84.6 上演示了这种方法。该样本的结果显示，GA 84.6v 在整个 TRMC 实验过程中经历了热物理变化，导致其剩磁承载能力发生变化。这些发现随后被用来解释 GA 84.6c 试样的古强度结果，结果显示双斜率 Arai 图产生了两个具有不同古强度值的线段，这两个线段都受到热物理变化的影响。为了进一步测试 TRMC 方法，我们选择了拉森山的另一个历史熔岩样本（HS 2），在将样本 HS 2-8C 加热到 400° C 的目标温度后，检测到了轻微的热物理变化。我们还使用 TRMC 方法分离出了居里温度低于 400° C 的稳定磁性成分，这可能会提供更可靠的 51 μT 古强度估计值。TRMC方法提供了一种独立于古强度实验的追踪热改变的方法，可以在不太详细的古强度测量中探索微妙的、无法识别的热改变过程，这有助于评估所测样品的热稳定性，解释TRM解锁谱和古强度估计值的变化，促进获得更可靠的记录，以制约内核的形成和地球磁场的演化。
{"title":"Thermal rock magnetic cycling (TRMC): a method to track Thermal alteration details for palaeointensity interpretations","authors":"Junxiang Miao, Huapei Wang","doi":"10.1093/gji/ggae268","DOIUrl":"https://doi.org/10.1093/gji/ggae268","url":null,"abstract":"\u0000 Accurate absolute palaeointensity is essential for understanding dynamo processes on the Earth and other planetary bodies. Although great efforts have been made to propose techniques to obtain magnetic field strength from rock samples, such as Thellier-series methods, the amount of high-fidelity palaeointensities remains limited. One primary reason for this is the thermal alteration of samples that pervasively occurred during palaeointensity experiments. In this study, we developed a comprehensive rock magnetic experiment, termed thermal rock magnetic cycling (TRMC), that can utilize measurements of critical rock magnetic properties at elevated temperatures during multiple heating-cooling cycles to track thermal changes in bulk samples and individual magnetic components with different Curie temperatures in samples for palaeointensity interpretations. We demonstrate this method on a Galapagos lava sample, GA 84.6. The results for this specimen revealed that GA 84.6v underwent thermophysical alteration throughout the TRMC experiment, resulting in changes in its remanence carrying capacity. These findings were then used to interpret the palaeointensity results of specimen GA 84.6c, which revealed that the two-slope Arai plot yielded two linear segments with distinct palaeointensity values that were both biased by thermophysical alteration. To further test the TRMC method, we selected another historical lava sample (HS 2) from Mt. Lassen, detecting slight thermal-physical changes after heating the specimen HS 2–8C to a target temperature of 400° C. We also isolated a stable magnetic component with a Curie temperature below 400° C using the TRMC method, which may provide a more reliable palaeointensity estimate of 51 μT. By providing a method for tracking thermal alteration independent of palaeointensity experiments, the TRMC method can explore subtle, unrecognizable thermal alteration processes in less detailed palaeointensity measurements, which can help to assess the thermal stability of the measured samples and interpret the changes in the TRM unblocking spectrum and palaeointensity estimates, facilitating the acquisition of more reliable records for constrain the formation of the inner core and the evolution of Earth's magnetic field.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141924078","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}
Junghyun Park, Stephen Arrowsmith, Il-Young Che, Chris Hayward, Brian Stump
Summary The Korean infrasound catalog (KIC) covers 1999 to 2022 and characterizes a rich variety of source types as well as document the effects of the time-varying atmosphere on event detection and location across the Korean Peninsula. The KIC is produced using data from six South Korean infrasound arrays that are cooperatively operated by Southern Methodist University and Korea Institute of Geoscience and Mineral Resources. Signal detection relies on an Adaptive F-Detector (Arrowsmith et al., 2009) that estimates arrival time and backazimuth, which draws a distinction between detection and parameter estimation. Detections and associated parameters are input into a Bayesian Infrasonic Source Location procedure (Modrak et al., 2010). The resulting KIC contains 38,455 infrasound events and documents repeated events from several locations. The catalog includes many anthropogenic sources such as an industrial chemical explosion, explosions at limestone open-pit mines and quarries, North Korean underground nuclear explosions, and other atmospheric or underwater events of unknown origin. Most events in the KIC occur during working hours and days, suggesting a dominance of human-related signals. The expansion of infrasound arrays over the years in South Korea and the inclusion of data from the International Monitoring System infrasound stations in Russia and Japan increase the number of infrasound events and improve location accuracy because of the increase in azimuthal station coverage. A review of selected events and associated signals at multiple arrays provides a location quality assessment. We quantify infrasound events that have accompanying seismic arrivals (seismoacoustic events) to support the source type assessment. Ray tracing using the Ground-to-Space (G2S) atmospheric model generally predicts observed arrivals when strong stratospheric winds exist, although the predicted arrival times have significant discrepancies. In some cases, local atmospheric data better captures small-scale variations in the wind velocity of the shallow atmosphere and can improve arrival time predictions that are not well matched by the G2S model. The analysis of selected events also illustrates the importance of topographic effects on tropospheric infrasound propagation at local distances. The KIC is the first infrasound catalog compiled in this region, and it can serve as a valuable dataset in developing more robust infrasound source localization and characterization methods.
{"title":"The Korean Infrasound Catalog (1999-2022)","authors":"Junghyun Park, Stephen Arrowsmith, Il-Young Che, Chris Hayward, Brian Stump","doi":"10.1093/gji/ggae277","DOIUrl":"https://doi.org/10.1093/gji/ggae277","url":null,"abstract":"Summary The Korean infrasound catalog (KIC) covers 1999 to 2022 and characterizes a rich variety of source types as well as document the effects of the time-varying atmosphere on event detection and location across the Korean Peninsula. The KIC is produced using data from six South Korean infrasound arrays that are cooperatively operated by Southern Methodist University and Korea Institute of Geoscience and Mineral Resources. Signal detection relies on an Adaptive F-Detector (Arrowsmith et al., 2009) that estimates arrival time and backazimuth, which draws a distinction between detection and parameter estimation. Detections and associated parameters are input into a Bayesian Infrasonic Source Location procedure (Modrak et al., 2010). The resulting KIC contains 38,455 infrasound events and documents repeated events from several locations. The catalog includes many anthropogenic sources such as an industrial chemical explosion, explosions at limestone open-pit mines and quarries, North Korean underground nuclear explosions, and other atmospheric or underwater events of unknown origin. Most events in the KIC occur during working hours and days, suggesting a dominance of human-related signals. The expansion of infrasound arrays over the years in South Korea and the inclusion of data from the International Monitoring System infrasound stations in Russia and Japan increase the number of infrasound events and improve location accuracy because of the increase in azimuthal station coverage. A review of selected events and associated signals at multiple arrays provides a location quality assessment. We quantify infrasound events that have accompanying seismic arrivals (seismoacoustic events) to support the source type assessment. Ray tracing using the Ground-to-Space (G2S) atmospheric model generally predicts observed arrivals when strong stratospheric winds exist, although the predicted arrival times have significant discrepancies. In some cases, local atmospheric data better captures small-scale variations in the wind velocity of the shallow atmosphere and can improve arrival time predictions that are not well matched by the G2S model. The analysis of selected events also illustrates the importance of topographic effects on tropospheric infrasound propagation at local distances. The KIC is the first infrasound catalog compiled in this region, and it can serve as a valuable dataset in developing more robust infrasound source localization and characterization methods.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141939660","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}
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：