Yanqiang Wu, Guangli Su, Jianliang Nie, Changyun Chen, Zhaohui Chen, Huazhi Yu, Haiquan Yin, Liu Chang, Zheng Tang, Yajin Pang, Hongbao Liang, Wanju Bo
Summary A high-precision and high-resolution vertical velocity for the Chinese mainland is obtained by integrating precise leveling and GNSS data, using a Helmert joint adjustment method. The results show that the surface vertical rates range between -3.0 and 3.9 mm/yr with continuous deformation in most areas, except the obvious subsidence at the rates of -15.0 to -94.2 mm/yr induced by groundwater exploitation in the North China Plain. Particularly, the central and southern Tibet, Tien Shan, Alashan, Ordos, eastern Cathaysia, and Northeast China uplift at the rates of 0.5 – 3.9 mm/yr; the southeastern Tibetan Plateau, Sichuan basin, and Yangtze block are dominated by surface subsidence at the rates of -3.3 to -0.5 mm/yr. Furthermore, the vertical rates vary little between the eastern and western regions of the Chinese mainland despite their pronounced differences in horizontal deformations. The effects of gravity isostasy and non-tectonic factors, including the environmental mass loads, Glacier Isostatic Adjustment (GIA), poroelastic expansion/compression, and mining operations have partially contributed to the vertical deformation of the Chinese mainland. Overall, this velocity reflects the complicated deformation features induced by the multiple geodynamic processes of the Chinese mainland. These geodynamic processes include isostasy, orogenic processes, and geothermal anomalies associated with slab subduction/plate collision.
{"title":"High-Precision Vertical Deformation of the Chinese Mainland Constrained by Leveling and GNSS data","authors":"Yanqiang Wu, Guangli Su, Jianliang Nie, Changyun Chen, Zhaohui Chen, Huazhi Yu, Haiquan Yin, Liu Chang, Zheng Tang, Yajin Pang, Hongbao Liang, Wanju Bo","doi":"10.1093/gji/ggae303","DOIUrl":"https://doi.org/10.1093/gji/ggae303","url":null,"abstract":"Summary A high-precision and high-resolution vertical velocity for the Chinese mainland is obtained by integrating precise leveling and GNSS data, using a Helmert joint adjustment method. The results show that the surface vertical rates range between -3.0 and 3.9 mm/yr with continuous deformation in most areas, except the obvious subsidence at the rates of -15.0 to -94.2 mm/yr induced by groundwater exploitation in the North China Plain. Particularly, the central and southern Tibet, Tien Shan, Alashan, Ordos, eastern Cathaysia, and Northeast China uplift at the rates of 0.5 – 3.9 mm/yr; the southeastern Tibetan Plateau, Sichuan basin, and Yangtze block are dominated by surface subsidence at the rates of -3.3 to -0.5 mm/yr. Furthermore, the vertical rates vary little between the eastern and western regions of the Chinese mainland despite their pronounced differences in horizontal deformations. The effects of gravity isostasy and non-tectonic factors, including the environmental mass loads, Glacier Isostatic Adjustment (GIA), poroelastic expansion/compression, and mining operations have partially contributed to the vertical deformation of the Chinese mainland. Overall, this velocity reflects the complicated deformation features induced by the multiple geodynamic processes of the Chinese mainland. These geodynamic processes include isostasy, orogenic processes, and geothermal anomalies associated with slab subduction/plate collision.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"151 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177425","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}
Xiao Jiang, Jinyun Guo, Miao Lin, Heping Sun, Tao Jiang
Summary The gravity-geologic method (GGM) is an approach that utilizes marine gravity anomalies and shipborne bathymetric data to invert seafloor topography by resolving short-wavelength gravity anomalies through the Bouguer plate approximation. Such an approximation ignores the nonlinear effects caused by surrounding seafloor topographical undulations that actually exist in short-wavelength gravity anomalies, and thus leaving the space for further modification of GGM. This study thoroughly derives the relationship between seafloor topography and gravity anomaly (GA), as well as the formula of GGM. Then, we propose a self-adaptive method to improve the accuracy of the inversion significantly: the enhanced gravity-geologic method (EGGM). The method employs the equivalent mass line method to approximate the nonlinear gravitational effects of the surrounding seafloor topography to correct the short-wavelength gravity anomalies. By introducing two optimal density contrast parameters, EGGM has been designed to effectively integrate the combined effects of various nonlinear factors to a certain extent. The accuracy of the seafloor topography models, produced with a spatial resolution of 1'×1', was evaluated over the study area (132 °E-136 °E, 36 °N-40 °N) located in the Sea of Japan. The results indicate that the accuracy of EGGM has a relative improvement of 13.73% compared to that of GGM in the overall study area, while the accuracy of both models is higher than that of the SIO_unadjusted model. The study further investigated the feasibility and stability of EGGM by examining the accuracy of both GGM and EGGM in various water depth ranges and areas with diverse terrain characteristics.
{"title":"Enhanced Gravity-Geologic Method by Considering Nonlinear Effects of Surrounding Seafloor Topography: A Case of Bathymetric Prediction in the Sea of Japan","authors":"Xiao Jiang, Jinyun Guo, Miao Lin, Heping Sun, Tao Jiang","doi":"10.1093/gji/ggae301","DOIUrl":"https://doi.org/10.1093/gji/ggae301","url":null,"abstract":"Summary The gravity-geologic method (GGM) is an approach that utilizes marine gravity anomalies and shipborne bathymetric data to invert seafloor topography by resolving short-wavelength gravity anomalies through the Bouguer plate approximation. Such an approximation ignores the nonlinear effects caused by surrounding seafloor topographical undulations that actually exist in short-wavelength gravity anomalies, and thus leaving the space for further modification of GGM. This study thoroughly derives the relationship between seafloor topography and gravity anomaly (GA), as well as the formula of GGM. Then, we propose a self-adaptive method to improve the accuracy of the inversion significantly: the enhanced gravity-geologic method (EGGM). The method employs the equivalent mass line method to approximate the nonlinear gravitational effects of the surrounding seafloor topography to correct the short-wavelength gravity anomalies. By introducing two optimal density contrast parameters, EGGM has been designed to effectively integrate the combined effects of various nonlinear factors to a certain extent. The accuracy of the seafloor topography models, produced with a spatial resolution of 1'×1', was evaluated over the study area (132 °E-136 °E, 36 °N-40 °N) located in the Sea of Japan. The results indicate that the accuracy of EGGM has a relative improvement of 13.73% compared to that of GGM in the overall study area, while the accuracy of both models is higher than that of the SIO_unadjusted model. The study further investigated the feasibility and stability of EGGM by examining the accuracy of both GGM and EGGM in various water depth ranges and areas with diverse terrain characteristics.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"27 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177426","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 Downward flow of surface-derived water deep into the upper crust is investigated using two dimensional coupled hydrothermal numerical models. In the models, downward flow is driven by either topographic gradients or seismic pumping, while it is facilitated by large episodic variations in fault permeability, intended to mimic fracturing and healing on a fault over repeated seismic cycles. The models show that both forcing scenarios are equally capable of driving surface-derived fluid to the base of faults at 10 km depth in several tens of thousands of years under certain conditions. Downward flow of cold fluid occurs almost exclusively during and shortly after earthquakes, while during the remaining portion of the seismic cycle fluids remain relatively stationary while they undergo thermal relaxation (i.e., heating). Rapid downward flow is favoured by a large coseismic permeability, long permeability healing time scale, and large coseismic dilatancy or high topographic relief above the fault at the surface. However, downward fluid flow is completely inhibited if fluid pressures exceeds the hydrostatic gradient, even by modest amounts, which suggests that deep fluid infiltration is unlikely to occur in every region.
{"title":"Model constraints on infiltration of surface-derived fluids deep into the brittle crust","authors":"Guy Simpson","doi":"10.1093/gji/ggae295","DOIUrl":"https://doi.org/10.1093/gji/ggae295","url":null,"abstract":"Summary Downward flow of surface-derived water deep into the upper crust is investigated using two dimensional coupled hydrothermal numerical models. In the models, downward flow is driven by either topographic gradients or seismic pumping, while it is facilitated by large episodic variations in fault permeability, intended to mimic fracturing and healing on a fault over repeated seismic cycles. The models show that both forcing scenarios are equally capable of driving surface-derived fluid to the base of faults at 10 km depth in several tens of thousands of years under certain conditions. Downward flow of cold fluid occurs almost exclusively during and shortly after earthquakes, while during the remaining portion of the seismic cycle fluids remain relatively stationary while they undergo thermal relaxation (i.e., heating). Rapid downward flow is favoured by a large coseismic permeability, long permeability healing time scale, and large coseismic dilatancy or high topographic relief above the fault at the surface. However, downward fluid flow is completely inhibited if fluid pressures exceeds the hydrostatic gradient, even by modest amounts, which suggests that deep fluid infiltration is unlikely to occur in every region.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"32 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177448","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 Seismic phase detection and classification using deep learning is so far poorly investigated for regional events since most studies focus on local events and short time windows as the input to the detection models. To evaluate deep learning on regional seismic records, we create a dataset of events in Northern Europe and the European Arctic. This dataset consists of about 151,000 three component event waveforms and corresponding phase arrival picks at stations in mainland Norway, Finland, and Svalbard. We train several state-of-the-art and one newly-developed deep learning model on this dataset to pick P and S wave arrivals. The new method modifies the popular PhaseNet model with new convolutional blocks including transformers. This yields more accurate predictions on the long input time windows associated with regional events. Evaluated on event records not used for training, our new method improves the performance of the current state-of-the-art methods when it comes to recall, precision and pick time residuals. Finally, we test our new model for continuous mode processing on four days of single-station data from the ARCES array. Results show that our new method outperforms the existing array detector at ARCES. This opens up new opportunities to improve automatic array processing with deep learning detectors.
摘要 到目前为止，使用深度学习对区域事件进行地震相位检测和分类的研究还很少，因为大多数研究都集中在局部事件和作为检测模型输入的短时间窗口上。为了评估区域地震记录的深度学习，我们创建了一个北欧和欧洲北极地区的事件数据集。该数据集包括约 151,000 个三分量事件波形以及挪威大陆、芬兰和斯瓦尔巴群岛台站的相应相位到达采样。我们在该数据集上训练了几个最先进的模型和一个新开发的深度学习模型，以挑选 P 波和 S 波到达。新方法利用包括变压器在内的新卷积块修改了流行的 PhaseNet 模型。这样就能对与区域事件相关的长输入时间窗进行更准确的预测。通过对未用于训练的事件记录进行评估，我们的新方法在召回率、精确度和采样时间残差方面提高了当前最先进方法的性能。最后，我们在 ARCES 阵列的四天单站数据上测试了新模型的连续模式处理能力。结果表明，我们的新方法优于 ARCES 现有的阵列探测器。这为利用深度学习探测器改进阵列自动处理带来了新的机遇。
{"title":"Deep learning models for regional phase detection on seismic stations in Northern Europe and the European Arctic","authors":"Erik B Myklebust, Andreas Köhler","doi":"10.1093/gji/ggae298","DOIUrl":"https://doi.org/10.1093/gji/ggae298","url":null,"abstract":"Summary Seismic phase detection and classification using deep learning is so far poorly investigated for regional events since most studies focus on local events and short time windows as the input to the detection models. To evaluate deep learning on regional seismic records, we create a dataset of events in Northern Europe and the European Arctic. This dataset consists of about 151,000 three component event waveforms and corresponding phase arrival picks at stations in mainland Norway, Finland, and Svalbard. We train several state-of-the-art and one newly-developed deep learning model on this dataset to pick P and S wave arrivals. The new method modifies the popular PhaseNet model with new convolutional blocks including transformers. This yields more accurate predictions on the long input time windows associated with regional events. Evaluated on event records not used for training, our new method improves the performance of the current state-of-the-art methods when it comes to recall, precision and pick time residuals. Finally, we test our new model for continuous mode processing on four days of single-station data from the ARCES array. Results show that our new method outperforms the existing array detector at ARCES. This opens up new opportunities to improve automatic array processing with deep learning detectors.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"32 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177429","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}
Ziyi Xi, Min Chen, Songqiao Shawn Wei, Jiaqi Li, Tong Zhou, Baoshan Wang, YoungHee Kim
Summary We present a new 3-D radially anisotropic seismic velocity model EARA2024 of the crust and mantle beneath East Asia and the northwestern Pacific using adjoint full-waveform inversion tomography. We construct the EARA2024 model by iteratively minimizing the waveform similarity misfit between the synthetic and observed waveforms from 142 earthquakes recorded by about 2,000 broadband stations in East Asia. Compared to previous studies, this new model renders significantly improved images of the subducted oceanic plate in the upper mantle, mantle transition zone, and uppermost lower mantle along the Kuril, Japan, Izu-Bonin, and Ryukyu Trenches. Complex slab deformation and break-offs are observed at different depths. Moreover, our model provides new insights into the origins of intraplate volcanoes in East Asia, including the Changbaishan, Datong-Fengzhen, Tengchong, and Hainan volcanic fields.
{"title":"EARA2024: A New Radially Anisotropic Seismic Velocity Model for the Crust and Upper Mantle beneath East Asia and Northwestern Pacific Subduction Zones","authors":"Ziyi Xi, Min Chen, Songqiao Shawn Wei, Jiaqi Li, Tong Zhou, Baoshan Wang, YoungHee Kim","doi":"10.1093/gji/ggae302","DOIUrl":"https://doi.org/10.1093/gji/ggae302","url":null,"abstract":"Summary We present a new 3-D radially anisotropic seismic velocity model EARA2024 of the crust and mantle beneath East Asia and the northwestern Pacific using adjoint full-waveform inversion tomography. We construct the EARA2024 model by iteratively minimizing the waveform similarity misfit between the synthetic and observed waveforms from 142 earthquakes recorded by about 2,000 broadband stations in East Asia. Compared to previous studies, this new model renders significantly improved images of the subducted oceanic plate in the upper mantle, mantle transition zone, and uppermost lower mantle along the Kuril, Japan, Izu-Bonin, and Ryukyu Trenches. Complex slab deformation and break-offs are observed at different depths. Moreover, our model provides new insights into the origins of intraplate volcanoes in East Asia, including the Changbaishan, Datong-Fengzhen, Tengchong, and Hainan volcanic fields.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"386 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177427","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}
Thystere Matondo Bantidi, Takeo Ishibe, Georges Mavonga Tuluka, Bogdan Enescu
Summary The Epidemic-Type Aftershock Sequence (ETAS) model is currently the most powerful statistical seismicity model that reproduces the general characteristics of earthquake clustering in space and time. However, its application can be hampered by biased parameter estimations related to earthquake catalog deficiencies, particularly in regions where the spatial coverage of local recording networks is relatively poor. Here, we systematically investigate the possible influences of the effect introduced by data truncation through the choice of the cutoff magnitude (${m}_{cut})$ and missing events due to heterogeneity of the seismic network on ETAS parameter estimates along the East African Rift System (EARS). After dividing the region into six source zones based on rheological and mechanical behaviors, the ETAS model is fitted to the earthquakes within each zone using the Davidon-Fletcher-Powell optimization algorithm. The fits and variations in parameter estimates are compared for each zone to the others and the seismological implications are discussed. We found that some parameters vary as a function of ${m}_{cut}$ primarily driven by changes in catalog size. Additionally, a systematic regional dependency of ETAS parameters is found across source zones. Furthermore, a median heat flow value for each analyzed source zone in the EARS is calculated. In contrast to previous findings in other tectonic settings, the results reveal no significant correlations between the crustal heat flows and the ETAS parameters describing earthquake productivity (${K}_0$) and the relative efficiency of an earthquake with magnitude M to produce aftershocks ($alpha $). Our findings have significant implications for understanding the mechanisms of earthquake interaction and, therefore, provide tight constraints on the model's parameters that may serve as a testbed for existing earthquake forecasting models in this region where the vulnerability of local buildings and structures exacerbate seismic risk.
{"title":"Estimating spatio-temporal variable parameters of Epidemic Type Aftershock Sequence model in a region with limited seismic network coverage: a case study of the East African Rift System","authors":"Thystere Matondo Bantidi, Takeo Ishibe, Georges Mavonga Tuluka, Bogdan Enescu","doi":"10.1093/gji/ggae299","DOIUrl":"https://doi.org/10.1093/gji/ggae299","url":null,"abstract":"Summary The Epidemic-Type Aftershock Sequence (ETAS) model is currently the most powerful statistical seismicity model that reproduces the general characteristics of earthquake clustering in space and time. However, its application can be hampered by biased parameter estimations related to earthquake catalog deficiencies, particularly in regions where the spatial coverage of local recording networks is relatively poor. Here, we systematically investigate the possible influences of the effect introduced by data truncation through the choice of the cutoff magnitude (${m}_{cut})$ and missing events due to heterogeneity of the seismic network on ETAS parameter estimates along the East African Rift System (EARS). After dividing the region into six source zones based on rheological and mechanical behaviors, the ETAS model is fitted to the earthquakes within each zone using the Davidon-Fletcher-Powell optimization algorithm. The fits and variations in parameter estimates are compared for each zone to the others and the seismological implications are discussed. We found that some parameters vary as a function of ${m}_{cut}$ primarily driven by changes in catalog size. Additionally, a systematic regional dependency of ETAS parameters is found across source zones. Furthermore, a median heat flow value for each analyzed source zone in the EARS is calculated. In contrast to previous findings in other tectonic settings, the results reveal no significant correlations between the crustal heat flows and the ETAS parameters describing earthquake productivity (${K}_0$) and the relative efficiency of an earthquake with magnitude M to produce aftershocks ($alpha $). Our findings have significant implications for understanding the mechanisms of earthquake interaction and, therefore, provide tight constraints on the model's parameters that may serve as a testbed for existing earthquake forecasting models in this region where the vulnerability of local buildings and structures exacerbate seismic risk.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"151 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177449","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 The Mw 7.8 Kaikoura earthquake, which occurred on November 13, 2016, ruptured a complex system of strike-slip and reverse faults in northeastern South Island, New Zealand. However, the postseismic afterslip behavior and its relationship to the coseismic slip remain incompletely understood. This study investigates the spatiotemporal characteristics of afterslip following the mainshock by using four years of position data from 58 continuous GPS (cGPS) stations, considering the viscoelastic relaxation. Meanwhile, this study considers the contributions of crustal and the interface faults when exploring the combined effect of afterslip and viscoelastic relaxation. Results reveal substantial coseismic deformation northeastern of the epicenter, and postseismic displacements exhibit a continuation of the northeastward evolution. The primary coseismic slip occurred along the Kekerengu and Jordan Thrust faults, while secondary slip was accommodated by the Humps fault and the shallow subduction interface. Two primary afterslip zones are identified: one extending downdip from the secondary coseismic slip areas, and the other adjacent to shallow primary coseismic slip areas near the seismogenic Needles and Hope faults. The afterslip distribution exhibits a spatially complementary pattern to the coseismic slip areas, suggesting that velocity-strengthening zones may have hindered coseismic rupture propagation. The total seismic moment released by afterslip is estimated at ∼2.51×1020 N·m (Mw ∼7.53), approximately 30% of the coseismic moment. Meanwhile, about 80% of the postseismic seismic moment is ascribed to the slip along the southern subduction interface, suggesting the subduction fault plays an important role during postseismic slip. Temporal evolution modeling highlights that roughly 55% of the total afterslip moment was released within the initial three months. Postseismic afterslip dominated during the first month following the earthquake, with a slip rate of ∼10 mm/day. This rate subsequently decreased to ∼5 mm/day over the following two to three months, indicating that the majority of postseismic afterslip occurred shortly after the mainshock. In contrast to the earlier afterslip stages, the latter stages show continued movement along the Needles fault and the subduction interface. Cumulative peak slips have reached 2 cm since mid-2018, with fault slip rates decreasing to approximately 0.6-1.0 mm/day. This indicates ongoing afterslip at shallow faults and the subduction interface, with a steady slip rate over time. Importantly, the cumulative Coulomb stress changes induced by both coseismic slip and afterslip have increased the earthquake hazards potential near the Wellington fault, a densely populated region warranting further investigation.
{"title":"The Spatiotemporal properties of afterslip following the 2016 Kaikoura earthquake in New Zealand from GPS observations: Its complementary and inherited patterns with coseismic slip","authors":"Lupeng Zhang, Guojie Meng, Yawen She","doi":"10.1093/gji/ggae293","DOIUrl":"https://doi.org/10.1093/gji/ggae293","url":null,"abstract":"Summary The Mw 7.8 Kaikoura earthquake, which occurred on November 13, 2016, ruptured a complex system of strike-slip and reverse faults in northeastern South Island, New Zealand. However, the postseismic afterslip behavior and its relationship to the coseismic slip remain incompletely understood. This study investigates the spatiotemporal characteristics of afterslip following the mainshock by using four years of position data from 58 continuous GPS (cGPS) stations, considering the viscoelastic relaxation. Meanwhile, this study considers the contributions of crustal and the interface faults when exploring the combined effect of afterslip and viscoelastic relaxation. Results reveal substantial coseismic deformation northeastern of the epicenter, and postseismic displacements exhibit a continuation of the northeastward evolution. The primary coseismic slip occurred along the Kekerengu and Jordan Thrust faults, while secondary slip was accommodated by the Humps fault and the shallow subduction interface. Two primary afterslip zones are identified: one extending downdip from the secondary coseismic slip areas, and the other adjacent to shallow primary coseismic slip areas near the seismogenic Needles and Hope faults. The afterslip distribution exhibits a spatially complementary pattern to the coseismic slip areas, suggesting that velocity-strengthening zones may have hindered coseismic rupture propagation. The total seismic moment released by afterslip is estimated at ∼2.51×1020 N·m (Mw ∼7.53), approximately 30% of the coseismic moment. Meanwhile, about 80% of the postseismic seismic moment is ascribed to the slip along the southern subduction interface, suggesting the subduction fault plays an important role during postseismic slip. Temporal evolution modeling highlights that roughly 55% of the total afterslip moment was released within the initial three months. Postseismic afterslip dominated during the first month following the earthquake, with a slip rate of ∼10 mm/day. This rate subsequently decreased to ∼5 mm/day over the following two to three months, indicating that the majority of postseismic afterslip occurred shortly after the mainshock. In contrast to the earlier afterslip stages, the latter stages show continued movement along the Needles fault and the subduction interface. Cumulative peak slips have reached 2 cm since mid-2018, with fault slip rates decreasing to approximately 0.6-1.0 mm/day. This indicates ongoing afterslip at shallow faults and the subduction interface, with a steady slip rate over time. Importantly, the cumulative Coulomb stress changes induced by both coseismic slip and afterslip have increased the earthquake hazards potential near the Wellington fault, a densely populated region warranting further investigation.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"66 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177446","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}
Manuel Calvo-Rathert, Eva Vernet, Josep M Parés, Vicente Soler, Elisa-María Sánchez-Moreno, María-Felicidad Bógalo, Ángel Carrancho, Yuhji Yamamoto, Lidia Rodríguez-Méndez
Summary A basaltic lava flow erupted from the Tajogaite volcano on December 4th, 2021, in La Palma (Canary Islands, Spain) was sampled to find out to what extent reliable and correct information on both intensity and direction of the Earth's magnetic field can be obtained from the paleomagnetic signal recorded in a lava flow which erupted under known conditions. Samples were taken every few centimetres across a flow up to a total of 27 oriented cores. Paleomagnetic experiments showed a strong viscous overprint in many samples. Nevertheless, the mean paleomagnetic direction obtained agrees well with the actual value from IGRF-13. Rock magnetic experiments were performed to obtain additional information about the quality and reliability of the results and the reasons for unsuccessful determinations. Analysis of mostly irreversible thermomagnetic curves showed that the carriers of remanence were magnetite and titanomagnetite of low and/or intermediate Curie-temperature. Hysteresis parameter ratios showed a pronounced variability across the flow. Analyses of frequency dependent susceptibility, IRM acquisition coercivity spectra and FORCs showed a noticeably presence of very low coercivity grains (multidomain and superparamagnetic-single domain boundary). Multimethod paleointensity experiments were performed with the Thellier-Coe, multispecimen and Tsunakawa-Shaw methods. Only three of 25 cores from the flow yielded successful Thellier-Coe determinations, in agreement with the expected field value of 38.7μT (IGRF-13). However, paleointensities of 60% of the specimens agree with the expected value performing an informal analysis without considering criteria thresholds. Four of six Tsunakawa-Shaw determinations performed on samples from the flow yielded correct results, but three multispecimen determinations providing apparently successful determinations largely underestimate the expected field intensity. Combination of three Thellier-Coe and four Tsunakawa-Shaw successful determinations yields a multimethod paleointensity result B = (36.9 ± 2.0) μT in good agreement with the expected field intensity.
{"title":"Reliability of the paleomagnetic signal recorded in a lava flow erupted on 4 December 2021 in La Palma (Canary Islands, Spain)","authors":"Manuel Calvo-Rathert, Eva Vernet, Josep M Parés, Vicente Soler, Elisa-María Sánchez-Moreno, María-Felicidad Bógalo, Ángel Carrancho, Yuhji Yamamoto, Lidia Rodríguez-Méndez","doi":"10.1093/gji/ggae297","DOIUrl":"https://doi.org/10.1093/gji/ggae297","url":null,"abstract":"Summary A basaltic lava flow erupted from the Tajogaite volcano on December 4th, 2021, in La Palma (Canary Islands, Spain) was sampled to find out to what extent reliable and correct information on both intensity and direction of the Earth's magnetic field can be obtained from the paleomagnetic signal recorded in a lava flow which erupted under known conditions. Samples were taken every few centimetres across a flow up to a total of 27 oriented cores. Paleomagnetic experiments showed a strong viscous overprint in many samples. Nevertheless, the mean paleomagnetic direction obtained agrees well with the actual value from IGRF-13. Rock magnetic experiments were performed to obtain additional information about the quality and reliability of the results and the reasons for unsuccessful determinations. Analysis of mostly irreversible thermomagnetic curves showed that the carriers of remanence were magnetite and titanomagnetite of low and/or intermediate Curie-temperature. Hysteresis parameter ratios showed a pronounced variability across the flow. Analyses of frequency dependent susceptibility, IRM acquisition coercivity spectra and FORCs showed a noticeably presence of very low coercivity grains (multidomain and superparamagnetic-single domain boundary). Multimethod paleointensity experiments were performed with the Thellier-Coe, multispecimen and Tsunakawa-Shaw methods. Only three of 25 cores from the flow yielded successful Thellier-Coe determinations, in agreement with the expected field value of 38.7μT (IGRF-13). However, paleointensities of 60% of the specimens agree with the expected value performing an informal analysis without considering criteria thresholds. Four of six Tsunakawa-Shaw determinations performed on samples from the flow yielded correct results, but three multispecimen determinations providing apparently successful determinations largely underestimate the expected field intensity. Combination of three Thellier-Coe and four Tsunakawa-Shaw successful determinations yields a multimethod paleointensity result B = (36.9 ± 2.0) μT in good agreement with the expected field intensity.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"11 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177428","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}
Dunyu Liu, Simone Puel, Thorsten W Becker, Louis Moresi
Summary To what extent mechanical anisotropy is required to explain the dynamics of the lithosphere is an important yet unresolved question. If anisotropy affects stress and deformation, and hence processes such as fault loading, how can we quantify its role from observations? Here, we derive analytical solutions and build a theoretical framework to explore how a shear zone with linear anisotropic viscosity can lead to deviatoric stress heterogeneity, strain-rate enhancement, as well as non-coaxial principal stress and strain rate. We develop an open-source finite-element software based on FEniCS for more complicated scenarios in both 2-D and 3-D. Mechanics of shear zones with transversely isotropic and orthorhombic anisotropy subjected to misoriented shortening and simple shearing are explored. A simple regional example for potential non-coaxiality for the Leech River Schist above the Cascadia subduction zone is presented. Our findings and these tools may help to better understand, detect, and evaluate mechanical anisotropy in natural settings, with potential implications including the transfer of lithospheric stress and deformation through fault loading.
{"title":"Analytical and numerical models of viscous anisotropy: A toolset to constrain the role of mechanical anisotropy for regional tectonics and fault loading","authors":"Dunyu Liu, Simone Puel, Thorsten W Becker, Louis Moresi","doi":"10.1093/gji/ggae296","DOIUrl":"https://doi.org/10.1093/gji/ggae296","url":null,"abstract":"Summary To what extent mechanical anisotropy is required to explain the dynamics of the lithosphere is an important yet unresolved question. If anisotropy affects stress and deformation, and hence processes such as fault loading, how can we quantify its role from observations? Here, we derive analytical solutions and build a theoretical framework to explore how a shear zone with linear anisotropic viscosity can lead to deviatoric stress heterogeneity, strain-rate enhancement, as well as non-coaxial principal stress and strain rate. We develop an open-source finite-element software based on FEniCS for more complicated scenarios in both 2-D and 3-D. Mechanics of shear zones with transversely isotropic and orthorhombic anisotropy subjected to misoriented shortening and simple shearing are explored. A simple regional example for potential non-coaxiality for the Leech River Schist above the Cascadia subduction zone is presented. Our findings and these tools may help to better understand, detect, and evaluate mechanical anisotropy in natural settings, with potential implications including the transfer of lithospheric stress and deformation through fault loading.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"16 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177444","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}
Stefano Maffei, Andrew Jackson, Philip W Livermore
Summary The columnar-flow approximation allows the development of computationally efficient numerical models tailored to the study of the rapidly rotating dynamics of Earth’s fluid outer core. In this paper we extend a novel columnar-flow formulation, called Plesio-Geostrophy (PG) by including thermal effects and viscous boundary conditions. The effect of both no-slip and stress-free boundaries, the latter being a novelty for columnar-flow models, are included. We obtain a set of fully 2D evolution equations for fluid flows and temperature where no assumption is made regarding the geometry of the latter, except in the derivation of an approximate thermal diffusion operator. To test the new PG implementation, we calculated the critical parameters for onset of thermal convection in a spherical domain. We found that the PG model prediction is in better agreement with unapproximated, 3D calculations in rapidly rotating regimes, compared to another state-of-the-art columnar-flow model.
{"title":"Plesio-geostrophy for Earth’s core: II. Thermal equation and onset of convection","authors":"Stefano Maffei, Andrew Jackson, Philip W Livermore","doi":"10.1093/gji/ggae294","DOIUrl":"https://doi.org/10.1093/gji/ggae294","url":null,"abstract":"Summary The columnar-flow approximation allows the development of computationally efficient numerical models tailored to the study of the rapidly rotating dynamics of Earth’s fluid outer core. In this paper we extend a novel columnar-flow formulation, called Plesio-Geostrophy (PG) by including thermal effects and viscous boundary conditions. The effect of both no-slip and stress-free boundaries, the latter being a novelty for columnar-flow models, are included. We obtain a set of fully 2D evolution equations for fluid flows and temperature where no assumption is made regarding the geometry of the latter, except in the derivation of an approximate thermal diffusion operator. To test the new PG implementation, we calculated the critical parameters for onset of thermal convection in a spherical domain. We found that the PG model prediction is in better agreement with unapproximated, 3D calculations in rapidly rotating regimes, compared to another state-of-the-art columnar-flow model.","PeriodicalId":12519,"journal":{"name":"Geophysical Journal International","volume":"11 suppl_1 1","pages":""},"PeriodicalIF":2.8,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142177445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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