We present a computational technique to model hydroacoustic waveforms from teleseismic earthquakes recorded by mid-column Mermaid floats deployed in the Pacific, taking into consideration bathymetric effects that modify seismo-acoustic conversions at the ocean bottom and acoustic wave propagation in the ocean layer, including reverberations. Our approach couples axisymmetric spectral-element simulations performed for moment-tensor earthquakes in a one-dimensional solid Earth to a two-dimensional Cartesian fluid-solid coupled spectral-element simulation that captures the conversion from displacement to acoustic pressure at an ocean-bottom interface with accurate bathymetry. We applied our workflow to 1,129 seismograms for 682 earthquakes from 16 Mermaids owned by Princeton University that were deployed in the Southern Pacific as part of the South Pacific Plume Imaging and Modeling (SPPIM) project. We compare the modeled synthetic waveforms to the observed records in individually selected frequency bands aimed at reducing local noise levels while maximizing earthquake-generated signal content. The modeled waveforms match the observations very well, with a median correlation coefficient of 0.72, and some as high as 0.95. We compare our correlation-based travel-time measurements to measurements made on the same data sets determined by automated arrival-time picking and ray-traced travel-time predictions, with the aim of opening up the use of Mermaid records for global seismic tomography via full-waveform inversion.
{"title":"Waveform modeling of hydroacoustic teleseismic earthquake records from autonomous Mermaid floats","authors":"Sirawich Pipatprathanporn, Frederik J Simons","doi":"10.1093/gji/ggae238","DOIUrl":"https://doi.org/10.1093/gji/ggae238","url":null,"abstract":"\u0000 We present a computational technique to model hydroacoustic waveforms from teleseismic earthquakes recorded by mid-column Mermaid floats deployed in the Pacific, taking into consideration bathymetric effects that modify seismo-acoustic conversions at the ocean bottom and acoustic wave propagation in the ocean layer, including reverberations. Our approach couples axisymmetric spectral-element simulations performed for moment-tensor earthquakes in a one-dimensional solid Earth to a two-dimensional Cartesian fluid-solid coupled spectral-element simulation that captures the conversion from displacement to acoustic pressure at an ocean-bottom interface with accurate bathymetry. We applied our workflow to 1,129 seismograms for 682 earthquakes from 16 Mermaids owned by Princeton University that were deployed in the Southern Pacific as part of the South Pacific Plume Imaging and Modeling (SPPIM) project. We compare the modeled synthetic waveforms to the observed records in individually selected frequency bands aimed at reducing local noise levels while maximizing earthquake-generated signal content. The modeled waveforms match the observations very well, with a median correlation coefficient of 0.72, and some as high as 0.95. We compare our correlation-based travel-time measurements to measurements made on the same data sets determined by automated arrival-time picking and ray-traced travel-time predictions, with the aim of opening up the use of Mermaid records for global seismic tomography via full-waveform inversion.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141641035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jiyan Xue, Qinghua Huang, Sihong Wu, Li Zhao, Bowen Ma
Ground penetrating radar (GPR) is becoming an increasingly important tool for understanding the shallow electrical structures of the earth and planets due to its adaptability to harsh detection environments, efficient data acquisition and accurate detection results. GPR full-waveform can simultaneously constrain the permittivity and resistivity of the medium, providing more comprehensive geophysical information and reducing the non-uniqueness of inversion. However, given the highly non-linear inverse problem and the massive data resulted from high temporal and spatial samplings, traditional full-waveform inversion algorithms are prohibitively costly. Inspired by Google's vision semantic segmentation system, we develop a robust deep learning-guided network that integrates geology and geophysics knowledge to support the real-time translation of zero-offset GPR data into dual-parameter electrical structures. We test our proposed network using synthetic data, which demonstrates that the algorithm can provide an accurate dual-parameter electrical model from a GPR sounding in milliseconds on a common laptop PC, exhibiting high robustness and adaptability to noise interference and extreme values of model parameters. We also apply our network to field data gathered for pollutant investigation in the US. The resulting dual-parameter structure provides a more comprehensive and realistic depiction of subsurface electrical properties and reveals the migration and aging of pollutants. Our algorithm's real-time and accurate advantages are expected to further unleash the potential of GPR technology and enable it to play a more significant role in earth and planetary exploration.
{"title":"Real-Time Dual-Parameter Full-Waveform Inversion of GPR Data Based on Robust Deep Learning","authors":"Jiyan Xue, Qinghua Huang, Sihong Wu, Li Zhao, Bowen Ma","doi":"10.1093/gji/ggae243","DOIUrl":"https://doi.org/10.1093/gji/ggae243","url":null,"abstract":"\u0000 Ground penetrating radar (GPR) is becoming an increasingly important tool for understanding the shallow electrical structures of the earth and planets due to its adaptability to harsh detection environments, efficient data acquisition and accurate detection results. GPR full-waveform can simultaneously constrain the permittivity and resistivity of the medium, providing more comprehensive geophysical information and reducing the non-uniqueness of inversion. However, given the highly non-linear inverse problem and the massive data resulted from high temporal and spatial samplings, traditional full-waveform inversion algorithms are prohibitively costly. Inspired by Google's vision semantic segmentation system, we develop a robust deep learning-guided network that integrates geology and geophysics knowledge to support the real-time translation of zero-offset GPR data into dual-parameter electrical structures. We test our proposed network using synthetic data, which demonstrates that the algorithm can provide an accurate dual-parameter electrical model from a GPR sounding in milliseconds on a common laptop PC, exhibiting high robustness and adaptability to noise interference and extreme values of model parameters. We also apply our network to field data gathered for pollutant investigation in the US. The resulting dual-parameter structure provides a more comprehensive and realistic depiction of subsurface electrical properties and reveals the migration and aging of pollutants. Our algorithm's real-time and accurate advantages are expected to further unleash the potential of GPR technology and enable it to play a more significant role in earth and planetary exploration.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141647585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The resolution of velocity models obtained by tomography varies due to multiple factors and variables, such as the inversion approach, ray coverage, data quality, etc. Combining velocity models with different resolutions can enable more accurate ground motion simulations (e.g., Yeh and Olsen, 2023). Toward this goal, we present a novel methodology to fuse multiresolution seismic velocity maps with probabilistic graphical models (PGMs). The PGMs provide segmentation results, corresponding to various velocity intervals, in seismic velocity models with different resolutions. Further, by considering physical information (such as ray-path density), we introduce physics-informed probabilistic graphical models (PIPGMs). These models provide data-driven relations between subdomains with low (LR) and high (HR) resolutions. Transferring (segmented) distribution information from the HR regions enhances the details in the LR regions by solving a maximum likelihood problem with prior knowledge from HR models. When updating areas bordering HR and LR regions, a patch-scanning policy is adopted to consider local patterns and avoid sharp boundaries. To evaluate the efficacy of the proposed PGM fusion method, we tested the fusion approach on both a synthetic checkerboard model and a fault zone structure imaged from the 2019 Ridgecrest, CA, earthquake sequence. The Ridgecrest fault zone image consists of a shallow (top 1 km) high-resolution shear-wave velocity model obtained from ambient noise tomography, which is embedded into the coarser Statewide California Earthquake Center Community Velocity Model version S4.26-M01. The model efficacy is underscored by the deviation between observed and calculated travel times along the boundaries between HR and LR regions, 38 per cent less than obtained by conventional Gaussian interpolation. The proposed PGM fusion method can merge any gridded multiresolution velocity model, a valuable tool for computational seismology and ground motion estimation.
{"title":"Graph-learning approach to combine multiresolution seismic velocity models","authors":"Zheng Zhou, Peter Gerstoft, K. Olsen","doi":"10.1093/gji/ggae212","DOIUrl":"https://doi.org/10.1093/gji/ggae212","url":null,"abstract":"\u0000 The resolution of velocity models obtained by tomography varies due to multiple factors and variables, such as the inversion approach, ray coverage, data quality, etc. Combining velocity models with different resolutions can enable more accurate ground motion simulations (e.g., Yeh and Olsen, 2023). Toward this goal, we present a novel methodology to fuse multiresolution seismic velocity maps with probabilistic graphical models (PGMs). The PGMs provide segmentation results, corresponding to various velocity intervals, in seismic velocity models with different resolutions. Further, by considering physical information (such as ray-path density), we introduce physics-informed probabilistic graphical models (PIPGMs). These models provide data-driven relations between subdomains with low (LR) and high (HR) resolutions. Transferring (segmented) distribution information from the HR regions enhances the details in the LR regions by solving a maximum likelihood problem with prior knowledge from HR models. When updating areas bordering HR and LR regions, a patch-scanning policy is adopted to consider local patterns and avoid sharp boundaries. To evaluate the efficacy of the proposed PGM fusion method, we tested the fusion approach on both a synthetic checkerboard model and a fault zone structure imaged from the 2019 Ridgecrest, CA, earthquake sequence. The Ridgecrest fault zone image consists of a shallow (top 1 km) high-resolution shear-wave velocity model obtained from ambient noise tomography, which is embedded into the coarser Statewide California Earthquake Center Community Velocity Model version S4.26-M01. The model efficacy is underscored by the deviation between observed and calculated travel times along the boundaries between HR and LR regions, 38 per cent less than obtained by conventional Gaussian interpolation. The proposed PGM fusion method can merge any gridded multiresolution velocity model, a valuable tool for computational seismology and ground motion estimation.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141338388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The harmonic variation of the P-to-S converted phases (i.e. Pms) observed from receiver functions (RFs) includes information on crustal azimuthal anisotropy. However, this harmonic analysis is easily influenced by low-quality RF traces, and the measurements may be misleading. Here, we propose an improved method, named the Iterative Weighted Least-Square method (IWLS), to extract the splitting parameters of the crust and simultaneously retrieve the two-lobed and four-lobed components of back-azimuthal variation. The quality and weights of different RF traces are estimated properly in the IWLS method. The weight function is related to the sharpness of the Pms phase and the smearing of other signals. We conduct many synthetic tests, and the IWLS method provides stable measurements for poor back-azimuthal coverage, strong noise, weak P-wave azimuthal anisotropy, and multiple anisotropic layers. We apply the IWLS method to observational data from two temporary stations on the southeastern Tibetan Plateau and North China Craton, respectively. The measurements are comparable to previous results and provide insight into crustal deformation.
{"title":"An iterative weighted least square fitting method for crustal anisotropy using receiver functions","authors":"Cong Ji, Zhouchuan Huang","doi":"10.1093/gji/ggae206","DOIUrl":"https://doi.org/10.1093/gji/ggae206","url":null,"abstract":"\u0000 The harmonic variation of the P-to-S converted phases (i.e. Pms) observed from receiver functions (RFs) includes information on crustal azimuthal anisotropy. However, this harmonic analysis is easily influenced by low-quality RF traces, and the measurements may be misleading. Here, we propose an improved method, named the Iterative Weighted Least-Square method (IWLS), to extract the splitting parameters of the crust and simultaneously retrieve the two-lobed and four-lobed components of back-azimuthal variation. The quality and weights of different RF traces are estimated properly in the IWLS method. The weight function is related to the sharpness of the Pms phase and the smearing of other signals. We conduct many synthetic tests, and the IWLS method provides stable measurements for poor back-azimuthal coverage, strong noise, weak P-wave azimuthal anisotropy, and multiple anisotropic layers. We apply the IWLS method to observational data from two temporary stations on the southeastern Tibetan Plateau and North China Craton, respectively. The measurements are comparable to previous results and provide insight into crustal deformation.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141338851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the first three-dimensional (3-D) upper-mantle conductivity models obtained by an inversion of the satellite-derived tidally-induced magnetic fields (TIMFs). We primarily use the M2 period, but the potential benefit of the O1 period is also inspected. The inverse-problem solution is found using the recently developed frequency-domain, spherical harmonic-finite element method based on the adjoint approach. We tested two different TIMF data sets derived from the satellite measurements of the Swarm mission and two different regularizations; the solution is either required to be sufficiently smooth or reasonably close to the a-priori 3-D conductivity model WINTERC-e Wd-emax. The reconstructed conductivity models are locally compared with the 1-D conductivity profiles from other studies. If we use one of the available TIMF data sets, the smooth reconstructed model gravitates towards Wd-emax and the TIMF-adjusted Wd-emax model is closer to the reference conductivity profiles than the original Wd-emax model. Finally, we use the obtained 3-D conductivity distributions to calculate the corresponding 3-D water distribution in the upper mantle using thermodynamical and compositional models coupled to the electrical-conductivity laboratory measurement of individual mantle constituents.
{"title":"Electrical conductivity of the suboceanic upper mantle constrained by satellite-derived tidal magnetic fields: 3-D inversion, validation and interpretation","authors":"L. Šachl, O. Knopp, J. Velímský","doi":"10.1093/gji/ggae209","DOIUrl":"https://doi.org/10.1093/gji/ggae209","url":null,"abstract":"\u0000 We present the first three-dimensional (3-D) upper-mantle conductivity models obtained by an inversion of the satellite-derived tidally-induced magnetic fields (TIMFs). We primarily use the M2 period, but the potential benefit of the O1 period is also inspected. The inverse-problem solution is found using the recently developed frequency-domain, spherical harmonic-finite element method based on the adjoint approach. We tested two different TIMF data sets derived from the satellite measurements of the Swarm mission and two different regularizations; the solution is either required to be sufficiently smooth or reasonably close to the a-priori 3-D conductivity model WINTERC-e Wd-emax. The reconstructed conductivity models are locally compared with the 1-D conductivity profiles from other studies. If we use one of the available TIMF data sets, the smooth reconstructed model gravitates towards Wd-emax and the TIMF-adjusted Wd-emax model is closer to the reference conductivity profiles than the original Wd-emax model. Finally, we use the obtained 3-D conductivity distributions to calculate the corresponding 3-D water distribution in the upper mantle using thermodynamical and compositional models coupled to the electrical-conductivity laboratory measurement of individual mantle constituents.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141342204","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yue Liu, J. Zhuang, Yicun Guo, Changsheng Jiang, Qinjian Tian, Yongxian Zhang, Feng Long
This study analyzed seismicity in southwestern China (1 January 2008 to 30 June 2021) using the earthquake catalog compiled by the China Earthquake Network Center and four different space–time Epidemic-Type Aftershock Sequence models: the 2D point-source (PS) model, the 2D finite-source (FS) model, the 3D PS model, and the 3D FS model. Our objective was to understand the features of the background seismicity and the patterns of earthquake clusters to better evaluate the regional seismic hazard. We carefully investigated the aftershock sequences that followed 7 of the 10 MS≥6.0 earthquakes that have struck this region since the occurrence of the 2008 Wenchuan MS8.0 earthquake (i.e., the Panzhihua (31 August 2008; MS6.0), Yaoan (9 July 2009; MS6.0), Lushan (20 April 2013; MS7.0), Ludian (3 August 2014; MS6.5), Jinggu (7 October 2014; MS6.6), Kangding (11 November 2014; MS6.3), and Yangbi (21 May 2021; MS6.4) earthquakes). Our results revealed the following. (1) The background seismicity level for natural earthquakes is usually stable but can experience sudden change due to major events, such as the 2014 Ludian MS6.5, and the 2014 Jinggu MS6.6 events. Such changes in the background rate can reach 50%. (2) Reservoir-induced earthquakes substantially increase the level of regional seismicity, indicating that they cannot be ignored when analyzing natural seismicity and evaluating regional earthquake hazards. (3) Events triggered directly by the mainshock occur mostly in regions adjacent to areas with large coseismic slip, showing a pattern complementary to the mainshock ruptures.
{"title":"Background and Clustering Characteristics of Recent Seismicity in Southwestern China","authors":"Yue Liu, J. Zhuang, Yicun Guo, Changsheng Jiang, Qinjian Tian, Yongxian Zhang, Feng Long","doi":"10.1093/gji/ggae211","DOIUrl":"https://doi.org/10.1093/gji/ggae211","url":null,"abstract":"\u0000 This study analyzed seismicity in southwestern China (1 January 2008 to 30 June 2021) using the earthquake catalog compiled by the China Earthquake Network Center and four different space–time Epidemic-Type Aftershock Sequence models: the 2D point-source (PS) model, the 2D finite-source (FS) model, the 3D PS model, and the 3D FS model. Our objective was to understand the features of the background seismicity and the patterns of earthquake clusters to better evaluate the regional seismic hazard. We carefully investigated the aftershock sequences that followed 7 of the 10 MS≥6.0 earthquakes that have struck this region since the occurrence of the 2008 Wenchuan MS8.0 earthquake (i.e., the Panzhihua (31 August 2008; MS6.0), Yaoan (9 July 2009; MS6.0), Lushan (20 April 2013; MS7.0), Ludian (3 August 2014; MS6.5), Jinggu (7 October 2014; MS6.6), Kangding (11 November 2014; MS6.3), and Yangbi (21 May 2021; MS6.4) earthquakes). Our results revealed the following. (1) The background seismicity level for natural earthquakes is usually stable but can experience sudden change due to major events, such as the 2014 Ludian MS6.5, and the 2014 Jinggu MS6.6 events. Such changes in the background rate can reach 50%. (2) Reservoir-induced earthquakes substantially increase the level of regional seismicity, indicating that they cannot be ignored when analyzing natural seismicity and evaluating regional earthquake hazards. (3) Events triggered directly by the mainshock occur mostly in regions adjacent to areas with large coseismic slip, showing a pattern complementary to the mainshock ruptures.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141347752","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Morison, S. Labrosse, R. Deguen, T. Alboussière
Thermal convection in planetary solid (rocky or icy) mantles sometimes occurs adjacent to liquid layers with a phase equilibrium at the boundary. The possibility of a solid-liquid phase change at the boundary has been shown to greatly help convection in the solid layer in spheres and plane layers and a similar study is performed here for a spherical shell with a radius-independent central gravity subject to a destabilising temperature difference. The solid-liquid phase change is considered as a mechanical boundary condition and applies at either or both horizontal boundaries. The boundary condition is controlled by a phase change number, Φ, that compares the time-scale for latent heat exchange in the liquid side to that necessary to build a topography at the boundary. We introduce a numerical tool, available at https://github.com/amorison/stablinrb, to carry out the linear stability analysis of the studied setup as well as other similar situations (cartesian geometry, arbitrary temperature and viscosity depth-dependent profiles). Decreasing Φ makes the phase change more efficient, which reduces the importance of viscous resistance associated to the boundary and makes the critical Rayleigh number for the onset of convection smaller and the wavelength of the critical mode larger, for all values of the radii ratio, γ. In particular, for a phase change boundary condition at the top or at both boundaries, the mode with a spherical harmonics degree of 1 is always favoured for Φ ≲ 10−1. Such a mode is also favoured for a phase change at the bottom boundary for small (γ ≲ 0.45) or large (γ ≳ 0.75) radii ratio. Such dynamics could help explaining the hemispherical dichotomy observed in the structure of many planetary objects.
{"title":"Onset of thermal convection in a solid spherical shell with melting at either or both boundaries","authors":"A. Morison, S. Labrosse, R. Deguen, T. Alboussière","doi":"10.1093/gji/ggae208","DOIUrl":"https://doi.org/10.1093/gji/ggae208","url":null,"abstract":"\u0000 Thermal convection in planetary solid (rocky or icy) mantles sometimes occurs adjacent to liquid layers with a phase equilibrium at the boundary. The possibility of a solid-liquid phase change at the boundary has been shown to greatly help convection in the solid layer in spheres and plane layers and a similar study is performed here for a spherical shell with a radius-independent central gravity subject to a destabilising temperature difference. The solid-liquid phase change is considered as a mechanical boundary condition and applies at either or both horizontal boundaries. The boundary condition is controlled by a phase change number, Φ, that compares the time-scale for latent heat exchange in the liquid side to that necessary to build a topography at the boundary. We introduce a numerical tool, available at https://github.com/amorison/stablinrb, to carry out the linear stability analysis of the studied setup as well as other similar situations (cartesian geometry, arbitrary temperature and viscosity depth-dependent profiles). Decreasing Φ makes the phase change more efficient, which reduces the importance of viscous resistance associated to the boundary and makes the critical Rayleigh number for the onset of convection smaller and the wavelength of the critical mode larger, for all values of the radii ratio, γ. In particular, for a phase change boundary condition at the top or at both boundaries, the mode with a spherical harmonics degree of 1 is always favoured for Φ ≲ 10−1. Such a mode is also favoured for a phase change at the bottom boundary for small (γ ≲ 0.45) or large (γ ≳ 0.75) radii ratio. Such dynamics could help explaining the hemispherical dichotomy observed in the structure of many planetary objects.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141350551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Karen Williams, D. S. Stamps, Jaqueline Austermann, Scott King, Emmanuel A. Njinju
Dynamic topography is defined as the deflection of Earth's surface due to the convecting mantle. ASPECT (Advanced Solver for Planetary Evolution, Convection, and Tectonics) is a continually evolving, finite element code that uses modern numerical methods to investigate problems in mantle convection. With ASPECT version 2.0.0 a consistent boundary flux (CBF) algorithm, used to calculate radial stresses at the model boundaries, was implemented into the release version of ASPECT. It has been shown that the CBF algorithm improves the accuracy of dynamic topography calculations by approximately one order of magnitude. We aim to evaluate the influence of the CBF algorithm and explore the geophysical implications of these improved estimates of dynamic topography changes along the East Coast of the United States. We constrain our initial temperature conditions using the tomography models SAVANI, S40RTS, and TX2008 and combine them with a corresponding radial viscosity profile (2 for TX2008), and 2 different boundary conditions for a total of 8 experiments. We perform simulations with and without the CBF method, which takes place during post-processing and does not affect the velocity solution. Our dynamic topography calculations are spatially consistent in both approaches, but generally indicate an increase in magnitude using the CBF method (an average ∼15 per cent and ∼76 per cent absolute change in present-day instantaneous and rate of change of dynamic topography, respectively). This enhanced accuracy in dynamic topography calculations can be used to better evaluate the effects of mantle convection on surface processes including vertical land motions, sea-level changes, and sedimentation and erosion. We explore results along the US East Coast, where a Pliocene shoreline has been deformed by dynamic topography change. An increased accuracy in estimates of dynamic topography can improve Pleistocene and Pliocene sea-level reconstructions, which allow for a better understanding of past sea-level changes and ice sheet stability.
{"title":"Effects of using the consistent boundary flux method on dynamic topography estimates","authors":"Karen Williams, D. S. Stamps, Jaqueline Austermann, Scott King, Emmanuel A. Njinju","doi":"10.1093/gji/ggae203","DOIUrl":"https://doi.org/10.1093/gji/ggae203","url":null,"abstract":"\u0000 Dynamic topography is defined as the deflection of Earth's surface due to the convecting mantle. ASPECT (Advanced Solver for Planetary Evolution, Convection, and Tectonics) is a continually evolving, finite element code that uses modern numerical methods to investigate problems in mantle convection. With ASPECT version 2.0.0 a consistent boundary flux (CBF) algorithm, used to calculate radial stresses at the model boundaries, was implemented into the release version of ASPECT. It has been shown that the CBF algorithm improves the accuracy of dynamic topography calculations by approximately one order of magnitude. We aim to evaluate the influence of the CBF algorithm and explore the geophysical implications of these improved estimates of dynamic topography changes along the East Coast of the United States. We constrain our initial temperature conditions using the tomography models SAVANI, S40RTS, and TX2008 and combine them with a corresponding radial viscosity profile (2 for TX2008), and 2 different boundary conditions for a total of 8 experiments. We perform simulations with and without the CBF method, which takes place during post-processing and does not affect the velocity solution. Our dynamic topography calculations are spatially consistent in both approaches, but generally indicate an increase in magnitude using the CBF method (an average ∼15 per cent and ∼76 per cent absolute change in present-day instantaneous and rate of change of dynamic topography, respectively). This enhanced accuracy in dynamic topography calculations can be used to better evaluate the effects of mantle convection on surface processes including vertical land motions, sea-level changes, and sedimentation and erosion. We explore results along the US East Coast, where a Pliocene shoreline has been deformed by dynamic topography change. An increased accuracy in estimates of dynamic topography can improve Pleistocene and Pliocene sea-level reconstructions, which allow for a better understanding of past sea-level changes and ice sheet stability.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141352289","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shichuan Yuan, Lei Pan, Caiwang Shi, Xianhai Song, Xiaofei Chen
In this study, we propose a systematic and effective method, that is, an extended version of the generalized reflection/transmission (R/T) coefficient method, for computing the phase-velocity (${c}_r$) dispersion curves, attenuation coefficient ($alpha $) curves, and eigenfunctions of both Rayleigh and Love waves as well as the ellipticity of Rayleigh waves in layered viscoelastic-vertical transversely isotropic (VTI) media. The numerical scheme of combining the root-searching method with the local optimization method is designed for determining the complex-valued modal solutions (i.e., complex wavenumber $k = {omega / {{c_{r}} - ialpha }}$) of surface waves. The near-surface sedimentary geological environment is taken as the model example because it is typical viscoelastic-VTI media. Besides the anisotropic-viscoelastic (AV) media, our algorithm can also compute surface waves in isotropic-elastic (IE), isotropic-viscoelastic (IV), and anisotropic-elastic (AE) media by resetting the corresponding parameters. Using the six-layer half-space models and in these four media, we verify the correctness of our algorithm by benchmarking the modal solutions against those from other methods. In the four-layer half-space model, by comparing the results of IE, IV, AE, and AV media, we analyze the effects of velocity anisotropy, viscoelasticity and attenuation anisotropy on the dispersion and attenuation characteristics of both Rayleigh and Love waves in detail. Our study can provide a theoretical basis and useful tool for surface wave imaging considering the anisotropy and/or viscoelasticity of the medium, which has the potential to better investigate the solid Earth's internal structure.
{"title":"Computation and analysis of surface wave dispersion and attenuation in layered viscoelastic-vertical transversely isotropic media by the generalized R/T coefficient method","authors":"Shichuan Yuan, Lei Pan, Caiwang Shi, Xianhai Song, Xiaofei Chen","doi":"10.1093/gji/ggae207","DOIUrl":"https://doi.org/10.1093/gji/ggae207","url":null,"abstract":"\u0000 In this study, we propose a systematic and effective method, that is, an extended version of the generalized reflection/transmission (R/T) coefficient method, for computing the phase-velocity (${c}_r$) dispersion curves, attenuation coefficient ($alpha $) curves, and eigenfunctions of both Rayleigh and Love waves as well as the ellipticity of Rayleigh waves in layered viscoelastic-vertical transversely isotropic (VTI) media. The numerical scheme of combining the root-searching method with the local optimization method is designed for determining the complex-valued modal solutions (i.e., complex wavenumber $k = {omega / {{c_{r}} - ialpha }}$) of surface waves. The near-surface sedimentary geological environment is taken as the model example because it is typical viscoelastic-VTI media. Besides the anisotropic-viscoelastic (AV) media, our algorithm can also compute surface waves in isotropic-elastic (IE), isotropic-viscoelastic (IV), and anisotropic-elastic (AE) media by resetting the corresponding parameters. Using the six-layer half-space models and in these four media, we verify the correctness of our algorithm by benchmarking the modal solutions against those from other methods. In the four-layer half-space model, by comparing the results of IE, IV, AE, and AV media, we analyze the effects of velocity anisotropy, viscoelasticity and attenuation anisotropy on the dispersion and attenuation characteristics of both Rayleigh and Love waves in detail. Our study can provide a theoretical basis and useful tool for surface wave imaging considering the anisotropy and/or viscoelasticity of the medium, which has the potential to better investigate the solid Earth's internal structure.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141354477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Pischiutta, Lawrence M. Baker, Jon B. Fletcher, Francesco Salvini, A. Rovelli, Y. Ben‐Zion
The amplitude, frequency and polarization of ground motion at the surface can be affected by the local geology. While low-velocity sediments and fill can amplify ground motions in certain frequency ranges, the low velocities found in fault zones can also produce prominent wavelets. In this paper we provide further evidence that polarization of ground motion can be affected by the geologic fabric in fault zones that have sustained significant brittle deformation. Aside from the well-known effect of fault-trapped waves in the low-velocity zone with polarization azimuths parallel to the fault strike, the effect of stiffness anisotropy was recently recognized with polarization azimuths at high-angle to the fault strike and orthogonal to the locally predominant fracture field in the fault damage zone. To clarify further such features, we investigate directional amplification effects across the San Jacinto fault zone in Southern California using seismic data recorded by permanent seismic stations and dense across-fault arrays. We observe three main polarization trends. The first trend parallel to the fault strike is ascribed to fault-trapped waves along the low-velocity zone, in agreement with several studies in the last decade in the same region. The second and third trends are orthogonal to the orientation of R and T Riedel planes, respectively. They are related to the stiffness anisotropy in densely fractured rocks in the damage zone, which are more compliant orthogonal to their fractures. At some locations the two effects are superimposed, occurring in different and distinct frequency ranges. Directional amplification at rock sites can be important for expected ground motion and seismic hazard. However, in seismic engineering the current prescriptions of seismic codes do not account for amplification effects at rock sites at frequencies of engineering interest.
地表地面运动的振幅、频率和极化会受到当地地质的影响。低速沉积物和填充物会放大某些频率范围内的地表运动，而断层带中的低速也会产生明显的小波。在本文中，我们提供了进一步的证据，证明地表运动的极化可能会受到断层带地质结构的影响，因为断层带承受了巨大的脆性变形。除了众所周知的极化方位角与断层走向平行的低速区断层陷波效应之外，最近还发现了刚度各向异性效应，即极化方位角与断层走向呈高角度，并与断层破坏区局部主要断裂场呈正交。为了进一步阐明这些特征，我们利用永久地震台和密集的跨断层阵列记录的地震数据，研究了南加州圣哈辛托断层带的定向放大效应。我们观察到三种主要的极化趋势。第一种趋势与断层走向平行，归因于沿低速区的断层捕获波，这与过去十年在同一地区进行的几项研究结果一致。第二和第三种趋势分别与 R 和 T 里德尔平面的方向正交。它们与破坏区密集断裂岩石的刚度各向异性有关，这些岩石的顺应性更强，与断裂方向正交。在某些位置，这两种效应是叠加的，出现在不同的频率范围内。岩石部位的定向放大效应对预期地动和地震灾害非常重要。然而，在地震工程中，目前的地震规范并没有考虑到岩层在工程频率上的放大效应。
{"title":"Directional amplification across the San Jacinto fault zone, CA","authors":"M. Pischiutta, Lawrence M. Baker, Jon B. Fletcher, Francesco Salvini, A. Rovelli, Y. Ben‐Zion","doi":"10.1093/gji/ggae198","DOIUrl":"https://doi.org/10.1093/gji/ggae198","url":null,"abstract":"\u0000 The amplitude, frequency and polarization of ground motion at the surface can be affected by the local geology. While low-velocity sediments and fill can amplify ground motions in certain frequency ranges, the low velocities found in fault zones can also produce prominent wavelets. In this paper we provide further evidence that polarization of ground motion can be affected by the geologic fabric in fault zones that have sustained significant brittle deformation. Aside from the well-known effect of fault-trapped waves in the low-velocity zone with polarization azimuths parallel to the fault strike, the effect of stiffness anisotropy was recently recognized with polarization azimuths at high-angle to the fault strike and orthogonal to the locally predominant fracture field in the fault damage zone. To clarify further such features, we investigate directional amplification effects across the San Jacinto fault zone in Southern California using seismic data recorded by permanent seismic stations and dense across-fault arrays. We observe three main polarization trends. The first trend parallel to the fault strike is ascribed to fault-trapped waves along the low-velocity zone, in agreement with several studies in the last decade in the same region. The second and third trends are orthogonal to the orientation of R and T Riedel planes, respectively. They are related to the stiffness anisotropy in densely fractured rocks in the damage zone, which are more compliant orthogonal to their fractures. At some locations the two effects are superimposed, occurring in different and distinct frequency ranges. Directional amplification at rock sites can be important for expected ground motion and seismic hazard. However, in seismic engineering the current prescriptions of seismic codes do not account for amplification effects at rock sites at frequencies of engineering interest.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141358735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：