Viacheslav Emelianov, Zeyu Zhang, A. Weller, Matthias Halisch, K. Titov
Clay minerals are extensively used in a wide range of applications. In particular, clay-bearing formations are considered as suitable radioactive waste repository. Electrical resistivity tomography is an appropriate tool to monitor the properties of clay-bearing locations. However, an inherent drawback of a conventional resistivity survey is its ambiguity in distinguishing between the effects of groundwater salinity, clay content, and porosity. A discrimination can be achieved on the basis of the induced polarization method that provides a complex conductivity. The main purpose of this study is the investigation of the complex conductivity of clay samples with a special focus on the contribution of surface conductivity produced by an excess of ions in the electrical double layer coating the solid particles. Six clay mixtures were selected that include an almost pure kaolinite sample, a sample consisting of a mixture of kaolinite, illite, and smectite, a crushed saponite breccia, a Ca-bentonite sample, and two illite clay samples. Besides the enriched kaolinite, the other samples are natural geomaterials that contain more than 40 weight per cent clay minerals. The mineralogical compositions of the samples were determined by quantitative X-ray diffraction analysis. The clay powder was mixed with a varying volume of sodium chloride solution to get plastic state clay samples with varying water content. The samples were investigated by the spectral induced polarization method in a frequency range between 1 mHz and 1 kHz. The resulting complex conductivity spectra indicate a decrease of the real part of the electrical conductivity with rising water content for the illite, bentonite and saponite breccia samples. The overall conductivity of these clay samples is dominated by their surface conductivity. In contrast, the electrical conductivity of kaolinite and kaolinite-illite mixture does not show any significant changes with the water content. For all samples, the imaginary part of electrical conductivity increases at low water content. The real part of the surface conductivity indicates a linear dependence on the volumetric clay content. The slope of this linear relationship can be used to distinguish the types of clay. The ratio between imaginary conductivity and surface conductivity, which decreases with increasing clay content, proves to be a suitable parameter that characterizes the connectivity of clay aggregates in the sample. The surface conductivity of the pure kaolinite sample has been determined in an additional multi-salinity experiment. The resulting surface conductivity is in good agreement with the experiment of varying water content. The multi-salinity experiment has shown that the resulting petrophysical parameters depend on the procedure of sample packing, which may lead to anisotropy. The effect of anisotropy is attributed to the alignment of the plate-like kaolinite particles in the course of the packing and consolidation procedure
粘土矿物被广泛应用于各种领域。特别是，含粘土地层被认为是合适的放射性废物储存库。电阻率层析成像技术是监测含粘土地层特性的合适工具。然而，传统电阻率勘测的一个固有缺点是难以区分地下水盐度、粘土含量和孔隙度的影响。通过提供复合电导率的诱导极化法可以实现区分。本研究的主要目的是调查粘土样本的复合电导率，特别关注由包裹固体颗粒的电双层中过量离子产生的表面电导率的贡献。研究选取了六种粘土混合物，包括一种几乎纯净的高岭石样品，一种由高岭石、伊利石和直闪石混合而成的样品，一种破碎的皂石角砾岩，一种钙膨润土样品，以及两种伊利石粘土样品。除富集高岭石外，其他样品均为天然地质材料，其中粘土矿物含量超过 40%。样品的矿物成分是通过定量 X 射线衍射分析确定的。将粘土粉末与不同体积的氯化钠溶液混合，得到不同含水量的可塑状态粘土样品。在 1 mHz 至 1 kHz 的频率范围内，采用光谱诱导极化法对样品进行了研究。得出的复电导率光谱表明，伊利石、膨润土和皂角砾岩样品的电导率实部随着含水量的增加而降低。这些粘土样品的整体电导率主要由其表面电导率决定。相比之下，高岭石和高岭石-伊利石混合物的电导率并没有随着含水量的增加而发生明显变化。对于所有样品，低含水量时电导率的虚部都会增加。表面电导率的实部与粘土的体积含量呈线性关系。这种线性关系的斜率可用于区分粘土类型。假想电导率和表面电导率之间的比率随着粘土含量的增加而减小，这被证明是表征样品中粘土聚集体连通性的合适参数。纯高岭石样品的表面电导率是在额外的多盐度实验中测定的。得出的表面电导率与不同含水量的实验结果十分吻合。多盐度实验表明，得出的岩石物理参数取决于样品堆积的程序，这可能导致各向异性。各向异性的影响归因于板状高岭石颗粒在堆积和固结过程中的排列。
{"title":"Surface conductivity of clays","authors":"Viacheslav Emelianov, Zeyu Zhang, A. Weller, Matthias Halisch, K. Titov","doi":"10.1093/gji/ggae201","DOIUrl":"https://doi.org/10.1093/gji/ggae201","url":null,"abstract":"\u0000 Clay minerals are extensively used in a wide range of applications. In particular, clay-bearing formations are considered as suitable radioactive waste repository. Electrical resistivity tomography is an appropriate tool to monitor the properties of clay-bearing locations. However, an inherent drawback of a conventional resistivity survey is its ambiguity in distinguishing between the effects of groundwater salinity, clay content, and porosity. A discrimination can be achieved on the basis of the induced polarization method that provides a complex conductivity. The main purpose of this study is the investigation of the complex conductivity of clay samples with a special focus on the contribution of surface conductivity produced by an excess of ions in the electrical double layer coating the solid particles. Six clay mixtures were selected that include an almost pure kaolinite sample, a sample consisting of a mixture of kaolinite, illite, and smectite, a crushed saponite breccia, a Ca-bentonite sample, and two illite clay samples. Besides the enriched kaolinite, the other samples are natural geomaterials that contain more than 40 weight per cent clay minerals. The mineralogical compositions of the samples were determined by quantitative X-ray diffraction analysis. The clay powder was mixed with a varying volume of sodium chloride solution to get plastic state clay samples with varying water content. The samples were investigated by the spectral induced polarization method in a frequency range between 1 mHz and 1 kHz. The resulting complex conductivity spectra indicate a decrease of the real part of the electrical conductivity with rising water content for the illite, bentonite and saponite breccia samples. The overall conductivity of these clay samples is dominated by their surface conductivity. In contrast, the electrical conductivity of kaolinite and kaolinite-illite mixture does not show any significant changes with the water content. For all samples, the imaginary part of electrical conductivity increases at low water content. The real part of the surface conductivity indicates a linear dependence on the volumetric clay content. The slope of this linear relationship can be used to distinguish the types of clay. The ratio between imaginary conductivity and surface conductivity, which decreases with increasing clay content, proves to be a suitable parameter that characterizes the connectivity of clay aggregates in the sample. The surface conductivity of the pure kaolinite sample has been determined in an additional multi-salinity experiment. The resulting surface conductivity is in good agreement with the experiment of varying water content. The multi-salinity experiment has shown that the resulting petrophysical parameters depend on the procedure of sample packing, which may lead to anisotropy. The effect of anisotropy is attributed to the alignment of the plate-like kaolinite particles in the course of the packing and consolidation procedure","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141374955","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 Pohang Basin sustained the most extensive seismic damage in the history of instrumental recording in Korea due to the 2017 Mw 5.5 earthquake. The pattern of damage shows marked differences from a radial distribution, suggesting important contributions by local site effects. Our understanding of these site effects and their role in generating seismic damage within the study area remains incomplete, which indicates the need for a thorough exploration of subsurface information, including the thickness of soil to bedrock and basin geometry, in the Pohang Basin. We measured the depth to bedrock in the Pohang Basin using dense ambient noise measurements conducted at 698 sites. We propose a model of basin geometry based on depths and dominant frequencies derived from the horizontal-to-vertical spectral ratio (HVSR) of microtremor at 698 sites. Most microseismic measurements exhibit one or more clear HVSR peak(s), implying one or more strong impedance contrast(s), which are presumed to represent the interface between the basement and overlying basin-fill sediments at each measurement site. The ambient seismic noise induces resonance at frequencies as low as 0.32 Hz. The relationship between resonance frequency and bedrock depth was derived using data from 27 boreholes to convert the dominant frequencies measured at stations adjacent to the boreholes into corresponding depths to the strong impedance contrast. The relationship was then applied to the dominant frequencies to estimate the depth to bedrock over the whole study area. Maps of resonance frequency and the corresponding depth to bedrock for the study area show that the greatest depths to bedrock are in the coastal area. The maps also reveal lower fundamental frequencies in the area west of the Gokgang Fault. The results indicate a more complex basin structure than previously proposed based on a limited number of direct borehole observations and surface geology. The maps and associated profiles across different parts of the study area show pronounced changes in bedrock depth near inferred blind faults proposed in previous studies, suggesting that maps of bedrock depth based on the HVSR method can be used to infer previously unknown features, including concealed or blind faults that are not observed at the surface.
{"title":"Mapping bedrock topography and detecting blind faults using the fundamental resonance of microtremor: a case study of the Pohang Basin, southeastern Korea","authors":"Su Young Kang","doi":"10.1093/gji/ggae194","DOIUrl":"https://doi.org/10.1093/gji/ggae194","url":null,"abstract":"\u0000 The Pohang Basin sustained the most extensive seismic damage in the history of instrumental recording in Korea due to the 2017 Mw 5.5 earthquake. The pattern of damage shows marked differences from a radial distribution, suggesting important contributions by local site effects. Our understanding of these site effects and their role in generating seismic damage within the study area remains incomplete, which indicates the need for a thorough exploration of subsurface information, including the thickness of soil to bedrock and basin geometry, in the Pohang Basin. We measured the depth to bedrock in the Pohang Basin using dense ambient noise measurements conducted at 698 sites. We propose a model of basin geometry based on depths and dominant frequencies derived from the horizontal-to-vertical spectral ratio (HVSR) of microtremor at 698 sites. Most microseismic measurements exhibit one or more clear HVSR peak(s), implying one or more strong impedance contrast(s), which are presumed to represent the interface between the basement and overlying basin-fill sediments at each measurement site. The ambient seismic noise induces resonance at frequencies as low as 0.32 Hz. The relationship between resonance frequency and bedrock depth was derived using data from 27 boreholes to convert the dominant frequencies measured at stations adjacent to the boreholes into corresponding depths to the strong impedance contrast. The relationship was then applied to the dominant frequencies to estimate the depth to bedrock over the whole study area. Maps of resonance frequency and the corresponding depth to bedrock for the study area show that the greatest depths to bedrock are in the coastal area. The maps also reveal lower fundamental frequencies in the area west of the Gokgang Fault. The results indicate a more complex basin structure than previously proposed based on a limited number of direct borehole observations and surface geology. The maps and associated profiles across different parts of the study area show pronounced changes in bedrock depth near inferred blind faults proposed in previous studies, suggesting that maps of bedrock depth based on the HVSR method can be used to infer previously unknown features, including concealed or blind faults that are not observed at the surface.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141373491","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}
Wei Xiong, Caijun Xu, Wei Chen, Bin Zhao, Yangmao Wen
The 2022 Har Lake earthquake sequence, which began in January 2022 and lasted for ∼70 days, jolted the Har Lake area, which is located in the western Qilian Shan, northeastern Tibetan Plateau. Two Mw>5.5 earthquakes occurred during the earthquake sequence, among which the March 25 Mw5.8 event is considered the largest event recorded in the area. However, determining the seismogenic faults of the earthquake sequence, as well as the detailed rupture features, is difficult due to the lack of geological data and near-field seismological observations. In this study, we use Sentinel-1 synthetic aperture radar (SAR) data to obtain the coseismic deformation field, identify possible ruptured faults and associated fault geometries, and further estimate detailed coseismic slip models of the two Mw>5.5 earthquakes. The results show that the January 23 Mw5.6 earthquake (Earthquake A) occurred on a N15°W-trending dextral-slip fault with a dip angle of ∼61°. For the March 25 Mw5.8 earthquake (Earthquake B), the interferometric synthetic aperture radar (InSAR) data can be described by either an ∼N–S-trending dextral-slip fault or an ∼E–W-trending sinistral-slip fault. The ∼N–S-trending fault better describes the aftershock distribution, while the ∼E–W-trending model is more consistent with the regional geological setting. We suggest that the complex coseismic ruptures in the multiple-fault system are driven by widespread NE–SW-trending compression in the western Qilian Shan. This study demonstrates the importance of integrating geodetic and seismological observations to capture the full complexity of moderate earthquakes and further suggests potential seismic hazards in the Har Lake area.
{"title":"The 2022 Har Lake earthquake sequence highlights a complex fault system in the western Qilian Shan, northeastern Tibetan Plateau","authors":"Wei Xiong, Caijun Xu, Wei Chen, Bin Zhao, Yangmao Wen","doi":"10.1093/gji/ggae190","DOIUrl":"https://doi.org/10.1093/gji/ggae190","url":null,"abstract":"\u0000 The 2022 Har Lake earthquake sequence, which began in January 2022 and lasted for ∼70 days, jolted the Har Lake area, which is located in the western Qilian Shan, northeastern Tibetan Plateau. Two Mw>5.5 earthquakes occurred during the earthquake sequence, among which the March 25 Mw5.8 event is considered the largest event recorded in the area. However, determining the seismogenic faults of the earthquake sequence, as well as the detailed rupture features, is difficult due to the lack of geological data and near-field seismological observations. In this study, we use Sentinel-1 synthetic aperture radar (SAR) data to obtain the coseismic deformation field, identify possible ruptured faults and associated fault geometries, and further estimate detailed coseismic slip models of the two Mw>5.5 earthquakes. The results show that the January 23 Mw5.6 earthquake (Earthquake A) occurred on a N15°W-trending dextral-slip fault with a dip angle of ∼61°. For the March 25 Mw5.8 earthquake (Earthquake B), the interferometric synthetic aperture radar (InSAR) data can be described by either an ∼N–S-trending dextral-slip fault or an ∼E–W-trending sinistral-slip fault. The ∼N–S-trending fault better describes the aftershock distribution, while the ∼E–W-trending model is more consistent with the regional geological setting. We suggest that the complex coseismic ruptures in the multiple-fault system are driven by widespread NE–SW-trending compression in the western Qilian Shan. This study demonstrates the importance of integrating geodetic and seismological observations to capture the full complexity of moderate earthquakes and further suggests potential seismic hazards in the Har Lake area.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141373311","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}
Ziyi Xi, S. S. Wei, Weiqiang Zhu, G. Beroza, Yaqi Jie, N. Saloor
Applications of machine learning in seismology have greatly improved our capability of detecting earthquakes in large seismic data archives. Most of these efforts have been focused on continental shallow earthquakes, but here we introduce an integrated deep-learning-based workflow to detect deep earthquakes recorded by a temporary array of ocean-bottom seismographs (OBSs) and land-based stations in the Tonga subduction zone. We develop a new phase picker, PhaseNet-TF, to detect and pick P- and S-wave arrivals in the time-frequency domain. The frequency-domain information is critical for analyzing OBS data, particularly the horizontal components, because they are contaminated by signals of ocean-bottom currents and other noise sources in certain frequency bands. PhaseNet-TF shows a much better performance in picking S waves at OBSs and land stations compared to its predecessor PhaseNet. The predicted phases are associated using an improved Gaussian Mixture Model Associator GaMMA-1D and then relocated with a double-difference package teletomoDD. We further enhance the model performance with a semi-supervised learning approach by iteratively refining labelled data and retraining PhaseNet-TF. This approach effectively suppresses false picks and significantly improves the detection of small earthquakes. The new catalogue of Tonga deep earthquakes contains more than 10 times more events compared to the reference catalogue that was analyzed manually. This deep-learning-enhanced catalogue reveals Tonga seismicity in unprecedented detail, and better defines the lateral extent of the double-seismic zone at intermediate depths and the location of 4 large deep-focus earthquakes relative to background seismicity. It also offers new potential for deciphering deep earthquake mechanisms, refining tomographic models, and understanding of subduction processes.
机器学习在地震学中的应用大大提高了我们在大型地震数据档案中探测地震的能力。这些工作大多集中在大陆浅层地震上，但在这里，我们介绍了一种基于深度学习的集成工作流程，用于探测汤加俯冲带的海洋底部地震仪（OBS）临时阵列和陆基台站记录的深层地震。我们开发了一种新的相位选取器 PhaseNet-TF，用于检测和选取时频域的 P 波和 S 波到达。频域信息对于分析 OBS 数据，尤其是水平分量至关重要，因为它们在某些频段受到洋底流信号和其他噪声源的污染。与前代 PhaseNet 相比，PhaseNet-TF 在拾取 OBS 和陆地站的 S 波方面表现出更好的性能。使用改进的高斯混合模型关联器 GaMMA-1D 对预测的相位进行关联，然后使用双差分软件包 teletomoDD 进行重定位。我们采用半监督学习方法，通过迭代完善标记数据和重新训练 PhaseNet-TF 来进一步提高模型性能。这种方法有效地抑制了误判，并显著提高了对小地震的检测能力。与人工分析的参考目录相比，新的汤加深层地震目录包含的地震事件多出 10 倍以上。这份经深度学习增强的地震目录以前所未有的细节揭示了汤加的地震活动，并更好地界定了中等深度双震带的横向范围以及 4 个大型深焦距地震相对于背景地震的位置。它还为破译深层地震机制、完善层析成像模型和了解俯冲过程提供了新的潜力。
{"title":"Deep Learning for Deep Earthquakes: Insights from OBS Observations of the Tonga Subduction Zone","authors":"Ziyi Xi, S. S. Wei, Weiqiang Zhu, G. Beroza, Yaqi Jie, N. Saloor","doi":"10.1093/gji/ggae200","DOIUrl":"https://doi.org/10.1093/gji/ggae200","url":null,"abstract":"\u0000 Applications of machine learning in seismology have greatly improved our capability of detecting earthquakes in large seismic data archives. Most of these efforts have been focused on continental shallow earthquakes, but here we introduce an integrated deep-learning-based workflow to detect deep earthquakes recorded by a temporary array of ocean-bottom seismographs (OBSs) and land-based stations in the Tonga subduction zone. We develop a new phase picker, PhaseNet-TF, to detect and pick P- and S-wave arrivals in the time-frequency domain. The frequency-domain information is critical for analyzing OBS data, particularly the horizontal components, because they are contaminated by signals of ocean-bottom currents and other noise sources in certain frequency bands. PhaseNet-TF shows a much better performance in picking S waves at OBSs and land stations compared to its predecessor PhaseNet. The predicted phases are associated using an improved Gaussian Mixture Model Associator GaMMA-1D and then relocated with a double-difference package teletomoDD. We further enhance the model performance with a semi-supervised learning approach by iteratively refining labelled data and retraining PhaseNet-TF. This approach effectively suppresses false picks and significantly improves the detection of small earthquakes. The new catalogue of Tonga deep earthquakes contains more than 10 times more events compared to the reference catalogue that was analyzed manually. This deep-learning-enhanced catalogue reveals Tonga seismicity in unprecedented detail, and better defines the lateral extent of the double-seismic zone at intermediate depths and the location of 4 large deep-focus earthquakes relative to background seismicity. It also offers new potential for deciphering deep earthquake mechanisms, refining tomographic models, and understanding of subduction processes.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141381196","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}
Atmospheric pressure changes on Earth’s surface can deform the solid Earth. Sorrells derived analytical formulas for displacement in a homogeneous, elastic half-space, generated by a moving surface pressure source with speed c. Ben-Menahem and Singh derived formulas when an atmospheric P-wave impinges on Earth’s surface. For a P-wave with an incident angle close to the grazing angle, which essentially meant a slow apparent velocity ca in comparison to P-wave (α′) and S-wave velocities (β′) in the Earth (ca ≪ β′ < α′), they showed that their formulas for solid-earth deformations become identical with Sorrells’ formulas if ca is replaced by c. But this agreement was only for the asymptotic cases (ca ≪ β′). The first point of this paper is that the agreement of the two solutions extends to non-asymptotic cases, or when ca/β′ is not small. The second point is that the angle of incidence in Ben-Menahem and Singh’s problem does not have to be the grazing angle. As long as the incident angle exceeds the critical angle of refraction from the P-wave in the atmosphere to the S-wave in the solid Earth, the formulas for Ben-Menahem and Singh’s solution become identical to Sorrell’s formulas. The third point is that this solution has two different domains depending on the speed c (or ca) on the surface. When c/β′ is small, deformations consist of the evanescent waves. When c approaches Rayleigh-wave phase velocity, the driven oscillation in the solid Earth turns into a free oscillation due to resonance and dominates the wave field. The non-asymptotic analytical solutions may be useful for the initial modeling of seismic deformations by fast-moving sources, such as those generated by shock waves from meteoroids and volcanic eruptions because the condition c/β′ ≪ 1 may be violated for such fast-moving sources.
地球表面的大气压力变化会使固体地球变形。本-梅纳海姆和辛格推导出了大气 P 波撞击地球表面时的公式。对于入射角接近掠过角的 P 波，这基本上意味着与地球上的 P 波（α′）和 S 波速度（β′）（ca ≪ β′ < α′）相比，表观速度 ca 较慢（ca ≪ β′ < α′）。但这种一致仅适用于渐近情况（ca ≪ β′）。本文的第一点是，两种解法的一致性扩展到了非渐近情况，或者当 ca/β′ 不小时。第二点是 Ben-Menahem 和 Singh 问题中的入射角不一定是掠过角。只要入射角超过从大气中的 P 波到固体地球中的 S 波的临界折射角，Ben-Menahem 和 Singh 的解法公式就与 Sorrell 的公式相同。第三点是，根据地表速度 c（或 ca）的不同，该解法有两个不同的域。当 c/β′ 较小时，变形由蒸发波组成。当 c 接近雷利波相位速度时，固体地球中的驱动振荡会因共振而变成自由振荡，并主导波场。由于 c/β′≪ 1 这一条件可能会被这类快速移动源所违反，因此非渐近分析解可能有助于对快速移动源（如流星体和火山喷发产生的冲击波）引起的地震形变进行初始建模。
{"title":"Deformation of solid earth by surface pressure: Equivalence between Ben-Menahem and Singh’s formula and Sorrells’ formula","authors":"Toshiro Tanimoto","doi":"10.1093/gji/ggae185","DOIUrl":"https://doi.org/10.1093/gji/ggae185","url":null,"abstract":"\u0000 Atmospheric pressure changes on Earth’s surface can deform the solid Earth. Sorrells derived analytical formulas for displacement in a homogeneous, elastic half-space, generated by a moving surface pressure source with speed c. Ben-Menahem and Singh derived formulas when an atmospheric P-wave impinges on Earth’s surface. For a P-wave with an incident angle close to the grazing angle, which essentially meant a slow apparent velocity ca in comparison to P-wave (α′) and S-wave velocities (β′) in the Earth (ca ≪ β′ < α′), they showed that their formulas for solid-earth deformations become identical with Sorrells’ formulas if ca is replaced by c. But this agreement was only for the asymptotic cases (ca ≪ β′). The first point of this paper is that the agreement of the two solutions extends to non-asymptotic cases, or when ca/β′ is not small. The second point is that the angle of incidence in Ben-Menahem and Singh’s problem does not have to be the grazing angle. As long as the incident angle exceeds the critical angle of refraction from the P-wave in the atmosphere to the S-wave in the solid Earth, the formulas for Ben-Menahem and Singh’s solution become identical to Sorrell’s formulas. The third point is that this solution has two different domains depending on the speed c (or ca) on the surface. When c/β′ is small, deformations consist of the evanescent waves. When c approaches Rayleigh-wave phase velocity, the driven oscillation in the solid Earth turns into a free oscillation due to resonance and dominates the wave field. The non-asymptotic analytical solutions may be useful for the initial modeling of seismic deformations by fast-moving sources, such as those generated by shock waves from meteoroids and volcanic eruptions because the condition c/β′ ≪ 1 may be violated for such fast-moving sources.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141376308","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}
Y. Usui, M. Uyeshima, S. Sakanaka, Tasuku Hashimoto, M. Ichiki, Toshiki Kaida, Yusuke Yamaya, Yasuo Ogawa, Masataka Masuda, Takahiro Akiyama
The solution of the remote reference method, a frequently used technique in magnetotelluric data processing, can be viewed as a product of the two-input-multiple-output relationship between the local electromagnetic field and the reference field at a remote station. By applying a robust estimator to the two-input-multiple-output system, one can suppress the influence of outliers in the local magnetic field as well as those in the local electric field based on regression residuals. Therefore, this study develops a new robust remote reference estimator with the aid of robust multivariate linear regression. By applying the robust multivariate regression S-estimator to the multiple-output system, the present work derives a set of equations for robust estimates of the transfer function, noise variances, and the scale of the Mahalanobis distance simultaneously. The noise variances are necessary for the multivariate analysis to normalize the residuals of dependent variables. The Mahalanobis distance, a distance measure for multivariate data, is a commonly-used indicator of outliers in multivariate statistics. By updating those robust estimates iteratively, the new robust remote reference estimator seeks the transfer function that minimizes the robust scale estimate of the Mahalanobis distance. The developed estimator can avoid bias in the magnetotelluric transfer function even if there are significant noises in the reference magnetic field and handle outlying data more robustly than previously proposed robust remote reference estimators. The authors applied the developed method to a synthetic dataset and real-world data. The test results demonstrate that the developed method downweights outliers in the local electric and magnetic fields and gives an unbiased transfer function.
{"title":"New robust remote reference estimator using robust multivariate linear regression","authors":"Y. Usui, M. Uyeshima, S. Sakanaka, Tasuku Hashimoto, M. Ichiki, Toshiki Kaida, Yusuke Yamaya, Yasuo Ogawa, Masataka Masuda, Takahiro Akiyama","doi":"10.1093/gji/ggae199","DOIUrl":"https://doi.org/10.1093/gji/ggae199","url":null,"abstract":"\u0000 The solution of the remote reference method, a frequently used technique in magnetotelluric data processing, can be viewed as a product of the two-input-multiple-output relationship between the local electromagnetic field and the reference field at a remote station. By applying a robust estimator to the two-input-multiple-output system, one can suppress the influence of outliers in the local magnetic field as well as those in the local electric field based on regression residuals. Therefore, this study develops a new robust remote reference estimator with the aid of robust multivariate linear regression. By applying the robust multivariate regression S-estimator to the multiple-output system, the present work derives a set of equations for robust estimates of the transfer function, noise variances, and the scale of the Mahalanobis distance simultaneously. The noise variances are necessary for the multivariate analysis to normalize the residuals of dependent variables. The Mahalanobis distance, a distance measure for multivariate data, is a commonly-used indicator of outliers in multivariate statistics. By updating those robust estimates iteratively, the new robust remote reference estimator seeks the transfer function that minimizes the robust scale estimate of the Mahalanobis distance. The developed estimator can avoid bias in the magnetotelluric transfer function even if there are significant noises in the reference magnetic field and handle outlying data more robustly than previously proposed robust remote reference estimators. The authors applied the developed method to a synthetic dataset and real-world data. The test results demonstrate that the developed method downweights outliers in the local electric and magnetic fields and gives an unbiased transfer function.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141378469","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 aim of this study is to investigate the aftershock sequence data recorded by a dense temporary seismological network deployed in the epicentral area of the 2013 April 9 Shonbeh (Kaki) earthquake, located in the south of the Simply Folded Belt of the Zagros (Iran). For a comprehensive understanding, coseismic displacements of the Shonbeh earthquake have been investigated using Interferometric Synthetic Aperture Radar (InSAR) data. The epicentral distribution of high-resolution relocated aftershocks shows NW-SE and N-S trending of seismicity. The aftershocks are confined between ∼3 and ∼14 km depth, which implies that the rupture occurred mostly within the sedimentary cover beside the fault parameters retrieved from InSAR modeling. Projection of precisely located aftershocks on NE-oriented section and InSAR ground displacement data are consistent with both NW-trending NE- and SW-dipping fault segments. We observe a NNW-SSE right-lateral strike-slip motions that accommodate oblique convergence and differential motion between the North and Central Zagros. The spatial pattern and focal mechanisms of aftershocks are consistent with a distributed deformation between NW-SE trending reverse and N-S trending right-lateral strike-slip fault segments in the south of the Kazerun transition zone that accommodates a wide shear zone.
{"title":"The 2013 Mw 6.2 Shonbeh (Kaki) earthquake (Zagros-Iran): seismo-tectonic implications for the Kazerun shear transition zone from high-resolution aftershock and InSAR data analysis","authors":"F. Yaminifard, M. Tatar, A. Fathian","doi":"10.1093/gji/ggae193","DOIUrl":"https://doi.org/10.1093/gji/ggae193","url":null,"abstract":"\u0000 The aim of this study is to investigate the aftershock sequence data recorded by a dense temporary seismological network deployed in the epicentral area of the 2013 April 9 Shonbeh (Kaki) earthquake, located in the south of the Simply Folded Belt of the Zagros (Iran). For a comprehensive understanding, coseismic displacements of the Shonbeh earthquake have been investigated using Interferometric Synthetic Aperture Radar (InSAR) data. The epicentral distribution of high-resolution relocated aftershocks shows NW-SE and N-S trending of seismicity. The aftershocks are confined between ∼3 and ∼14 km depth, which implies that the rupture occurred mostly within the sedimentary cover beside the fault parameters retrieved from InSAR modeling. Projection of precisely located aftershocks on NE-oriented section and InSAR ground displacement data are consistent with both NW-trending NE- and SW-dipping fault segments. We observe a NNW-SSE right-lateral strike-slip motions that accommodate oblique convergence and differential motion between the North and Central Zagros. The spatial pattern and focal mechanisms of aftershocks are consistent with a distributed deformation between NW-SE trending reverse and N-S trending right-lateral strike-slip fault segments in the south of the Kazerun transition zone that accommodates a wide shear zone.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141377192","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}
Taking advantage of the simultaneous recording during 471 days between 2019 and 2021 by two superconducting gravimeters installed at the surface and 520 m under the surface at the Low Noise Underground Laboratory (LSBB) in Rustrel, France, we investigate whether a difference between the tidal gravity signals at the two locations can be detected. First, we model the periodical variations of the Earth’s gravity owing to the tidal influence from the Sun and Moon, at the Earth’s surface and at shallow depths. We provide analytical formulas for the Love numbers, gravimetric factor and gravity variation of simple spherical planetary models. We also numerically compute those parameters and function for a realistic spherical Earth model. We find that the fractional difference between the semi-diurnal tidal gravity variations at the surface and 520 m below is as small as 8.5 10−5. We next evaluate the effect on the amplitude of the recorded gravity signal due to the calibration factors of the two superconducting gravimeters at LSBB. Finally, we compute the spectra of the difference between the gravity variations measured on and under the surface in the semi-diurnal band of the M2 tidal wave. We find that the uncertainties associated to the calibration factors are larger than the theoretical or observational difference between the tidal gravity variations on the surface and at a 520-m depth.
{"title":"Subsurface tidal gravity variation and gravimetric factor","authors":"Y. Rogister, J. Hinderer, U. Riccardi, S. Rosat","doi":"10.1093/gji/ggae196","DOIUrl":"https://doi.org/10.1093/gji/ggae196","url":null,"abstract":"\u0000 Taking advantage of the simultaneous recording during 471 days between 2019 and 2021 by two superconducting gravimeters installed at the surface and 520 m under the surface at the Low Noise Underground Laboratory (LSBB) in Rustrel, France, we investigate whether a difference between the tidal gravity signals at the two locations can be detected. First, we model the periodical variations of the Earth’s gravity owing to the tidal influence from the Sun and Moon, at the Earth’s surface and at shallow depths. We provide analytical formulas for the Love numbers, gravimetric factor and gravity variation of simple spherical planetary models. We also numerically compute those parameters and function for a realistic spherical Earth model. We find that the fractional difference between the semi-diurnal tidal gravity variations at the surface and 520 m below is as small as 8.5 10−5. We next evaluate the effect on the amplitude of the recorded gravity signal due to the calibration factors of the two superconducting gravimeters at LSBB. Finally, we compute the spectra of the difference between the gravity variations measured on and under the surface in the semi-diurnal band of the M2 tidal wave. We find that the uncertainties associated to the calibration factors are larger than the theoretical or observational difference between the tidal gravity variations on the surface and at a 520-m depth.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141384991","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}
Magnetic susceptibility behaviour around the Verwey transition of magnetite (≈ 125 K) is known to be sensitive to stress, composition and oxidation. From the isotropic point (≈ 130 K) to room temperature, decreasing magnetic susceptibility indicates an increase in magnetocrystalline anisotropy. In this study, we present a model which numerically analyses low-temperature magnetic susceptibility curves (80 to 280 K) of an experimentally shocked (up to 30 GPa) and later heated (973 K) magnetite ore. To quantify variations of the transition shape caused by both shock and heating, the model statistically describes local variations in the Verwey transition temperature within bulk magnetite. For the description, Voigt profiles are used, which indicate variations between a Gaussian and a Lorentzian character. These changes are generally interpreted as variations in the degree of correlation between observed events, i.e. between local transition temperatures in the model. Shock pressures exceeding the Hugoniot elastic limit of magnetite ($ ge $ 5 GPa) cause an increase in transition width and Verwey transition temperature, which is partially recovered by heat treatment. Above the Verwey transition temperature, susceptibility variations related to the magnetocrystalline anisotropy are described with an exponential approach. The room temperature magnetic susceptibility relative to the maximum near the isotropic point is reduced after shock, which is related to grain size reduction. Since significant oxidation and cation substitution can be excluded for the studied samples, variations are only attributed to changes in elastic strain associated with shock-induced deformation and annealing due to heat treatment. The shocked magnetite shows a high correlation between local transition temperatures which is reduced by heat treatment. The model allows a quantitative description of low-temperature magnetic susceptibility curves of experimentally shocked and subsequently heat-treated polycrystalline magnetite around the Verwey transition temperature. The curves are accurately reproduced within the experimental uncertainties. Further applications for analysing magnetite-bearing rocks seem possible if model parameters, such as for oxidation are included into the model.
{"title":"Stress-induced changes in magnetite: Insights from a numerical analysis of the verwey transition","authors":"H. Fuchs, Agnes Kontny, Frank R Schilling","doi":"10.1093/gji/ggae189","DOIUrl":"https://doi.org/10.1093/gji/ggae189","url":null,"abstract":"\u0000 Magnetic susceptibility behaviour around the Verwey transition of magnetite (≈ 125 K) is known to be sensitive to stress, composition and oxidation. From the isotropic point (≈ 130 K) to room temperature, decreasing magnetic susceptibility indicates an increase in magnetocrystalline anisotropy. In this study, we present a model which numerically analyses low-temperature magnetic susceptibility curves (80 to 280 K) of an experimentally shocked (up to 30 GPa) and later heated (973 K) magnetite ore. To quantify variations of the transition shape caused by both shock and heating, the model statistically describes local variations in the Verwey transition temperature within bulk magnetite. For the description, Voigt profiles are used, which indicate variations between a Gaussian and a Lorentzian character. These changes are generally interpreted as variations in the degree of correlation between observed events, i.e. between local transition temperatures in the model. Shock pressures exceeding the Hugoniot elastic limit of magnetite ($ ge $ 5 GPa) cause an increase in transition width and Verwey transition temperature, which is partially recovered by heat treatment. Above the Verwey transition temperature, susceptibility variations related to the magnetocrystalline anisotropy are described with an exponential approach. The room temperature magnetic susceptibility relative to the maximum near the isotropic point is reduced after shock, which is related to grain size reduction. Since significant oxidation and cation substitution can be excluded for the studied samples, variations are only attributed to changes in elastic strain associated with shock-induced deformation and annealing due to heat treatment. The shocked magnetite shows a high correlation between local transition temperatures which is reduced by heat treatment. The model allows a quantitative description of low-temperature magnetic susceptibility curves of experimentally shocked and subsequently heat-treated polycrystalline magnetite around the Verwey transition temperature. The curves are accurately reproduced within the experimental uncertainties. Further applications for analysing magnetite-bearing rocks seem possible if model parameters, such as for oxidation are included into the model.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141382526","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}
Y-X He, S. X. Wang, G. Y. Tang, C. H. Dong, C. Sun, S. Y. Yuan, P. D. Shi
Based on both forced oscillation and ultrasonic pulse transmission methods, we investigated solid pore infill influences on rock elastic moduli in a broad frequency range $[ {1 - 3000, {{10}}^6} ]$ Hz for different differential pressures. For a Berea sandstone sample, filled sequentially by solid (${22}^{rm{o}}{rm{C}}$), quasi-solid (${26}^{rm{o}}{rm{C}}$) and liquid (${34}^{rm{o}}{rm{C}}$) octadecane, a frequency-dependence was found for the Poisson's ratio, Young's modulus and bulk modulus, nevertheless, these elastic parameters were strongly suppressed by increasing pressures. Experimental measurements showed that shear wave velocity and modulus of solid-octadecane-filled samples are significantly larger than those of the dry and liquid-octadecane-filled ones, implying the potential stiffening effects related to solid infill in compliant pores. A three porosity structure model, which describes the solid stiffening effects related to equant, compliant and the intermediate pores with aspect ratios larger than those of compliant pores but much less than those of stiff pores, was used to compare against the experimentally measured elastic properties for octadecane pore infill, together with several other fluid/solid substitution theories. The agreement between experimental measurements and theoretical predictions is reasonably good for the sandstone tested, providing that the three porosity model can be applied for pressure- and frequency-dependent elastic moduli estimations for a viscoelastic pore-infill-saturated sandstone. Evaluating the combined squirt flow mechanism responsible for the observed moduli dispersion and attenuation is of great importance to reduce potential errors in seismic AVO inversion and 4D seismic monitoring of gas-hydrate or bitumen-saturated reservoir, especially for reservoir rocks with complex microstructures and heterogeneous pore types.
{"title":"Experimental investigation of pore-filling substitution effect on frequency-dependent elastic moduli of Berea sandstone","authors":"Y-X He, S. X. Wang, G. Y. Tang, C. H. Dong, C. Sun, S. Y. Yuan, P. D. Shi","doi":"10.1093/gji/ggae195","DOIUrl":"https://doi.org/10.1093/gji/ggae195","url":null,"abstract":"\u0000 Based on both forced oscillation and ultrasonic pulse transmission methods, we investigated solid pore infill influences on rock elastic moduli in a broad frequency range $[ {1 - 3000, {{10}}^6} ]$ Hz for different differential pressures. For a Berea sandstone sample, filled sequentially by solid (${22}^{rm{o}}{rm{C}}$), quasi-solid (${26}^{rm{o}}{rm{C}}$) and liquid (${34}^{rm{o}}{rm{C}}$) octadecane, a frequency-dependence was found for the Poisson's ratio, Young's modulus and bulk modulus, nevertheless, these elastic parameters were strongly suppressed by increasing pressures. Experimental measurements showed that shear wave velocity and modulus of solid-octadecane-filled samples are significantly larger than those of the dry and liquid-octadecane-filled ones, implying the potential stiffening effects related to solid infill in compliant pores. A three porosity structure model, which describes the solid stiffening effects related to equant, compliant and the intermediate pores with aspect ratios larger than those of compliant pores but much less than those of stiff pores, was used to compare against the experimentally measured elastic properties for octadecane pore infill, together with several other fluid/solid substitution theories. The agreement between experimental measurements and theoretical predictions is reasonably good for the sandstone tested, providing that the three porosity model can be applied for pressure- and frequency-dependent elastic moduli estimations for a viscoelastic pore-infill-saturated sandstone. Evaluating the combined squirt flow mechanism responsible for the observed moduli dispersion and attenuation is of great importance to reduce potential errors in seismic AVO inversion and 4D seismic monitoring of gas-hydrate or bitumen-saturated reservoir, especially for reservoir rocks with complex microstructures and heterogeneous pore types.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141384485","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：