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Machine Learning Emulation of High Resolution Inundation Maps 机器学习模拟高分辨率淹没图
Geophysical Journal International Pub Date : 2024-04-24 DOI: 10.1093/gji/ggae151
E. B. Storrøsten, Naveen Ragu Ramalingam, S. Lorito, M. Volpe, C. Sánchez-Linares, F. Løvholt, Steven J. Gibbons
{"title":"Machine Learning Emulation of High Resolution Inundation Maps","authors":"E. B. Storrøsten, Naveen Ragu Ramalingam, S. Lorito, M. Volpe, C. Sánchez-Linares, F. Løvholt, Steven J. Gibbons","doi":"10.1093/gji/ggae151","DOIUrl":"https://doi.org/10.1093/gji/ggae151","url":null,"abstract":"\u0000 Estimating coastal tsunami impact for early-warning or long-term hazard analysis requires the calculation of inundation metrics such as flow-depth or momentum flux. Both applications require the simulation of large numbers of scenarios to capture both the aleatory variability and the epistemic tsunami uncertainty. A computationally demanding step in simulating inundation is solving the nonlinear shallow water (NLSW) equations on meshes with sufficiently high resolution to represent the local elevation accurately enough to capture the physics governing the flow. This computational expense is particularly challenging in the context of Tsunami Early Warning where strict time constraints apply. A Machine Learning (ML) model that predicts inundation maps from offshore simulation results with acceptable accuracy, trained on an acceptably small training set of full simulations, could replace the computationally expensive NLSW part of the simulations for vast numbers of scenarios and predict inundation rapidly and with reduced computational demands. We consider the application of an encoder-decoder based neural network to predict high-resolution inundation maps based only on more cheaply calculated simulated time-series at a limited number of offshore locations. The network needs to be trained using input offshore time-series and the corresponding inundation maps from previously calculated full simulations. We develop and evaluate the ML model on a comprehensive set of inundation simulations for the coast of eastern Sicily for tens of thousands of subduction earthquake sources in the Mediterranean Sea. We find good performance for this case study even using relatively small training sets (order of hundreds) provided that appropriate choices are made in the specification of model parameters, the specification of the loss function, and the selection of training events. The uncertainty in the prediction for any given location decreases with the number of training events that inundate that location, with a good range of flow depths needed for accurate predictions. This means that care is needed to ensure that rarer high-inundation scenarios are well-represented in the training sets. The importance of applying regularization techniques increases as the size of the training sets decreases. The computational gain of the proposed methodology depends on the number of complete simulations needed to train the neural network, ranging between 164 and 4196 scenarios in this study. The cost of training the network is small in comparison with the cost of the numerical simulations and, for an ensemble of around 28000 scenarios, this represents a 6 to 170-fold reduction in computing costs.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140665522","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}
引用次数: 0
Terraced slope metasurface in granular media 颗粒介质中的梯田斜坡元表面
Geophysical Journal International Pub Date : 2024-04-22 DOI: 10.1093/gji/ggae150
N. Aravantinos-Zafiris, K. A. Chondrogiannis, H. R. Thomsen, V. Dertimanis, A. Colombi, M. M. Sigalas, E. Chatzi
{"title":"Terraced slope metasurface in granular media","authors":"N. Aravantinos-Zafiris, K. A. Chondrogiannis, H. R. Thomsen, V. Dertimanis, A. Colombi, M. M. Sigalas, E. Chatzi","doi":"10.1093/gji/ggae150","DOIUrl":"https://doi.org/10.1093/gji/ggae150","url":null,"abstract":"\u0000 In this work, the propagation and attenuation of vertically polarized surface waves when interacting with terraced slopes is studied experimentally and numerically. To validate the devised simulation, a laboratory-scale physical model is tested in order to examine the attenuation properties of this well-known artificial landform. The experiment involves formation of a terraced slope, in a laboratory setup, via use of an unconsolidated granular medium made of silica microbeads. This granular medium exhibits a gravity-induced power-law stiffness profile, resulting in a depth-dependent velocity profile. A piezoelectric actuator was used to excite vertically polarized surface acoustic modes localized near the surface of the medium. The three components of the particle velocity field of these modes were measured by means of a three-dimensional laser Doppler vibrometer. In accordance with the terraced slope, a simple inclined plane was further tested to investigate and highlight the differences in terms of wave propagation along these two different ground formations. The results of this research provide significant experimental evidence that the terraced slopes form mechanisms which attenuate low frequency surface waves, thus acting as metasurfaces. This work suggests the use of laboratory-scale physical models to investigate the wave propagation in different landforms, which extend beyond typical horizontal ground morphologies, and which could be linked to atypical wave propagation properties, possibly even influencing propagation of seismic waves.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140675734","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}
引用次数: 0
Surface Loading on a self-gravitating, linear viscoelastic Earth: moving beyond Maxwell 自重力线性粘弹性地球的表面载荷:超越麦克斯韦
Geophysical Journal International Pub Date : 2024-04-22 DOI: 10.1093/gji/ggae149
H. C. P. Lau
{"title":"Surface Loading on a self-gravitating, linear viscoelastic Earth: moving beyond Maxwell","authors":"H. C. P. Lau","doi":"10.1093/gji/ggae149","DOIUrl":"https://doi.org/10.1093/gji/ggae149","url":null,"abstract":"\u0000 Constitutive laws are a necessary ingredient in calculations of glacial isostatic adjustment (GIA) or other surface loading problems (e.g., loading by ocean tides). An idealized constitutive law governed by the Maxwell viscoelastic model is widely used but increasing attention is being directed towards more intricate constitutive laws that, in particular, include transient rheology. In this context, transient rheology collectively refers to dissipative mechanisms activated in addition to creep modeled by the Maxwell viscoelastic model. Consideration of such viscoelastic models in GIA is in its infancy and to encourage their wider use, we present constitutive laws for several experimentally derived transient rheologies and outline a flexible method in which to incorporate them into geophysical problems, such as the viscoelastic deformation of the Earth induced by surface loading. To further motivate this need, we demonstrate, via the Love number collocation method, how predictions of crustal displacement depart significantly between Earth models that adopt only Maxwell viscoelasticity and those with transient rheology. Throughout this paper, we highlight the differences in terminology and emphases between the rock mechanics, seismology, and GIA communities, which have perhaps contributed towards the relative scarcity in integrating this broader and more realistic class of constitutive laws within GIA. We focus on transient rheology since the associated deformation has been demonstrated to operate on timescales that range from hours to decades. With ice mass loss enhanced at similar timescales as a consequence of anthropogenically caused climate change, the ability to model GIA with more accurate constitutive laws is an important tool to investigate such problems.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140675862","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}
引用次数: 0
Converted Wave Tomography Based on Inverse Level Set and Adjoint Formulation 基于反电平集和相加公式的转换波断层成像技术
Geophysical Journal International Pub Date : 2024-04-22 DOI: 10.1093/gji/ggae147
C. A. Niño, C. Duarte, W. Agudelo, D. A. Sierra, M. D. Sacchi
{"title":"Converted Wave Tomography Based on Inverse Level Set and Adjoint Formulation","authors":"C. A. Niño, C. Duarte, W. Agudelo, D. A. Sierra, M. D. Sacchi","doi":"10.1093/gji/ggae147","DOIUrl":"https://doi.org/10.1093/gji/ggae147","url":null,"abstract":"\u0000 Shear wave velocity (Vs) is a fundamental property of elastic media whose estimation from PS converted waves is challenging and requires modeling the boundary where P to S conversion occurs. This paper presents a PS tomography where seismic wave conversion/reflection points correspond to reflectors modelled with the level-set function set to zero (φ(x, z) = 0). The proposed method aims for stable Vs inversion in a seismic acquisition setting using multicomponent receivers. Synthetic models simulating true Vs, Vp and the location of the geological reflector are used in the study. The inversion starts by locating a flat reflector, φ(x, z) = 0, which defines the zone Ω1 between the surface and the reflector, where the initial Vs and Vp fields are also set. To calculate the traveltimes of incident PT (P wave that propagates in Ω1 from source to the reflector) , converted PS, and reflected PP waves, for both observed and modelled data (forward problem), the methodology proposed by Rawlinson and Sambridge is adopted. This method uses the arrival times of the P-waves, Tpt, from the seismic source at each reflector point as secondary sources generating the times Tps and Tpp. These times are calculated as a solution to the Eikonal equation by using the Fast Marching method. The PS and PP residual times are minimized by updating Vs, Vp, and φ(x, z) = 0 through adjoint variables designed from a formulation using Lagrange Multipliers in a variational context. The performance of the algorithm is evaluated for models with synclinal, sinusoidal and monoclinal reflector geometries using numerical tests considering the inversion of: 1) φ, given the true values of Vs and Vp; 2) φ and Vs, given the true value of Vp; 3) φ and Vp, given the true value of Vs; and 4) the three parameters φ, Vs, and Vp, simultaneously. Good results are obtained by inverting Vs and φ, given the true value of Vp. The simultaneous inversion of the three parameters exhibits promising results, despite the illumination problems caused by the different distribution of the PS, PP, and PT time gradients due to the geometry of the reflectors and the acquisition setting (sources-receivers in the same plane). The proposed tomography estimates Vs and reflector positions which could help in statics corrections and improve the lithological characterization of near surface.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140677410","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}
引用次数: 0
Constraints from GPS measurements on plate-coupling within the Makran Subduction Zone and tsunami scenarios in the Western Indian Ocean 全球定位系统测量对马克兰俯冲带内板块耦合的制约和西印度洋的海啸情况
Geophysical Journal International Pub Date : 2024-02-05 DOI: 10.1093/gji/ggae046
Guo Cheng, William D Barnhart, David Small
{"title":"Constraints from GPS measurements on plate-coupling within the Makran Subduction Zone and tsunami scenarios in the Western Indian Ocean","authors":"Guo Cheng, William D Barnhart, David Small","doi":"10.1093/gji/ggae046","DOIUrl":"https://doi.org/10.1093/gji/ggae046","url":null,"abstract":"\u0000 Plate-coupling estimates and previous seismicity indicate that portions of the Makran megathrust of southern Pakistan and Iran are partially coupled and have the potential to produce future magnitude 7 + earthquakes. However, the GPS observations needed to constrain coupling models are sparse and lead to an incomplete understanding of regional earthquake and tsunami hazard. In this study, we assess GPS velocities for plate-coupling of the Makran subduction zone with specific attention to model resolution and the accretionary prism rheology. We use finite element model-derived Green's functions to invert for the interseismic slip deficit under both elastic and viscoelastic Earth assumptions. We use the model resolution matrix to characterize plate-coupling scenarios that are consistent with the limited spatial resolution afforded by GPS observations. We then forward model the corresponding tsunami responses at major coastal cities within the western Indian Ocean basin. Our plate-coupling results show potential segmentation of the megathrust with varying coupling from west to east, but do not rule out a scenario where the entire length of the megathrust could rupture in a single earthquake. The full subduction zone rupture scenarios suggest the Makran may be able to produce earthquakes up to Mw 9.2. The corresponding tsunami model from the largest earthquake event (Mw 9.2) estimates maximum wave heights reaching 2 to 5 meters at major port cities in the Northern Arabian Sea region. Cities on the west coast of India are less affected (1-2 m). Coastlines bounding eastern Africa, and the Strait of Hormuz, are the least affected (< 1 m).","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139803850","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}
引用次数: 0
Constraints from GPS measurements on plate-coupling within the Makran Subduction Zone and tsunami scenarios in the Western Indian Ocean 全球定位系统测量对马克兰俯冲带内板块耦合的制约和西印度洋的海啸情况
Geophysical Journal International Pub Date : 2024-02-05 DOI: 10.1093/gji/ggae046
Guo Cheng, William D Barnhart, David Small
{"title":"Constraints from GPS measurements on plate-coupling within the Makran Subduction Zone and tsunami scenarios in the Western Indian Ocean","authors":"Guo Cheng, William D Barnhart, David Small","doi":"10.1093/gji/ggae046","DOIUrl":"https://doi.org/10.1093/gji/ggae046","url":null,"abstract":"\u0000 Plate-coupling estimates and previous seismicity indicate that portions of the Makran megathrust of southern Pakistan and Iran are partially coupled and have the potential to produce future magnitude 7 + earthquakes. However, the GPS observations needed to constrain coupling models are sparse and lead to an incomplete understanding of regional earthquake and tsunami hazard. In this study, we assess GPS velocities for plate-coupling of the Makran subduction zone with specific attention to model resolution and the accretionary prism rheology. We use finite element model-derived Green's functions to invert for the interseismic slip deficit under both elastic and viscoelastic Earth assumptions. We use the model resolution matrix to characterize plate-coupling scenarios that are consistent with the limited spatial resolution afforded by GPS observations. We then forward model the corresponding tsunami responses at major coastal cities within the western Indian Ocean basin. Our plate-coupling results show potential segmentation of the megathrust with varying coupling from west to east, but do not rule out a scenario where the entire length of the megathrust could rupture in a single earthquake. The full subduction zone rupture scenarios suggest the Makran may be able to produce earthquakes up to Mw 9.2. The corresponding tsunami model from the largest earthquake event (Mw 9.2) estimates maximum wave heights reaching 2 to 5 meters at major port cities in the Northern Arabian Sea region. Cities on the west coast of India are less affected (1-2 m). Coastlines bounding eastern Africa, and the Strait of Hormuz, are the least affected (< 1 m).","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139863731","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}
引用次数: 0
Characterisation of heterogeneities in the sandy facies of the Opalinus Clay (Mont Terri underground rock laboratory, Switzerland) 奥帕里努斯粘土砂质面的异质性特征(瑞士蒙特泰里地下岩石实验室)
Geophysical Journal International Pub Date : 2024-01-05 DOI: 10.1093/gji/ggad494
Stefan Lüth, Florian Steegborn, F. Heberling, T. Beilecke, Dirk Bosbach, G. Deissmann, Horst Geckeis, Claudia Joseph, Axel Liebscher, Volker Metz, Dorothee Rebscher, Karsten Rink, Trond Ryberg, Stephan Schennen
{"title":"Characterisation of heterogeneities in the sandy facies of the Opalinus Clay (Mont Terri underground rock laboratory, Switzerland)","authors":"Stefan Lüth, Florian Steegborn, F. Heberling, T. Beilecke, Dirk Bosbach, G. Deissmann, Horst Geckeis, Claudia Joseph, Axel Liebscher, Volker Metz, Dorothee Rebscher, Karsten Rink, Trond Ryberg, Stephan Schennen","doi":"10.1093/gji/ggad494","DOIUrl":"https://doi.org/10.1093/gji/ggad494","url":null,"abstract":"\u0000 This contribution is presenting a multidisciplinary investigation of heterogeneities in a clay rock formation, based on seismic tomography, logging, and core analysis, as a reconnaissance study for a diffusion experiment. Diffusion experiments in clay rock formations provide crucial experimental data on diffusive transport of radionuclides (RN) in extremely low hydraulic conductivity media. Previous diffusion experiments, conducted, e.g. in the Mont Terri underground rock laboratory within the relatively homogeneous shaly facies of Opalinus Clay, and modelling studies of these experiments have demonstrated that the clay rock could sufficiently well be described as a homogeneous anisotropic medium. For other lithofacies, characterised by larger heterogeneity, such simplification may be unsuitable, and the description of heterogeneity over a range of scales will be important. The sandy facies of the Opalinus Clay exhibits a significantly more pronounced heterogeneity compared to the shaly facies, and a combined characterisation and RN diffusion study has been initiated to investigate various approaches of heterogeneity characterisation and subsequent diffusion in a heterogeneous environment. As an initial step, two inclined exploratory boreholes have been drilled to access the margins of the experiment location. These boreholes have been used to acquire a cross-hole tomographic seismic data set. Optical, natural gamma and backscattering logging were applied and rock cores were analysed. The integrated results of these investigations allowed the identification of an anomalous brighter layer within the investigated area of the sandy facies of approximately 1 m thickness and with its upper bound at roughly 10 m depth within the inclined exploratory wells. Mineralogical analyses revealed only slight variations throughout the rock cores and indicated that the anomalous layer exhibited a slightly higher quartz content, and locally significantly higher calcite contents, accompanied by a lower content of clay minerals. The anomalous layer was characterised by reduced natural gamma emissions, due to the lower clay content, and increased neutron backscattering likely indicating an increased porosity. Seismic P-wave velocities, derived from anisotropic tomography, exhibited a maximal gradient near the top of this layer. The transition from the overlaying darker rock matrix into this layer has been identified as an appropriate location for the setup of a tracer diffusion experiment in a heterogeneous environment.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139382974","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}
引用次数: 0
Aftershock forecasts based on incomplete earthquake catalogs: ETASI model application to the 2023 SE Türkiye earthquake sequence 基于不完整地震目录的余震预测:ETASI 模型在 2023 年土尔其东南部地震序列中的应用
Geophysical Journal International Pub Date : 2024-01-05 DOI: 10.1093/gji/ggae006
S. Hainzl, T. Kumazawa, Y. Ogata
{"title":"Aftershock forecasts based on incomplete earthquake catalogs: ETASI model application to the 2023 SE Türkiye earthquake sequence","authors":"S. Hainzl, T. Kumazawa, Y. Ogata","doi":"10.1093/gji/ggae006","DOIUrl":"https://doi.org/10.1093/gji/ggae006","url":null,"abstract":"\u0000 The Epidemic-Type Aftershock Sequence (ETAS) model is the state-of-the-art approach for modeling short-term earthquake clustering and is preferable for short-term aftershock forecasting. However, due to the large variability of different earthquake sequences, the model parameters must be adjusted to the local seismicity for accurate forecasting. Such an adjustment based on the first aftershocks is hampered by the incompleteness of earthquake catalogs after a mainshock, which can be explained by a blind period of the seismic networks after each earthquake, during which smaller events with lower magnitudes cannot be detected. Assuming a constant blind time, direct relationships based only on this additional parameter can be established between the actual seismicity rate and magnitude distributions and those that can be detected. The ETAS-Incomplete (ETASI) model uses these relationships to estimate the true ETAS parameters and the catalog incompleteness jointly. In this study, we apply the ETASI model to the SE Türkiye earthquake sequence, consisting of a doublet of M7.7 and M7.6 earthquakes that occurred within less than half a day of each other on February 6, 2023. We show that the ETASI model can explain the catalog incompleteness and fits the observed earthquake numbers and magnitudes well. A pseudo-prospective forecasting experiment shows that the daily number of detectable m ≥ 2 can be well predicted based on minimal and incomplete information from early aftershocks. However, the maximum magnitude (Mmax ) of the next day’s aftershocks would have been overestimated due to the highly variable b value within the sequence. Instead, using the regional b value estimated for 2000-2022 would have well predicted the observed Mmax  values.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139381214","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}
引用次数: 0
Co-estimation of core and lithospheric magnetic fields by a maximum entropy method 用最大熵法共同估算地核和岩石圈磁场
Geophysical Journal International Pub Date : 2024-01-05 DOI: 10.1093/gji/ggae008
Mikkel Otzen, Christopher C Finlay, C. Kloss
{"title":"Co-estimation of core and lithospheric magnetic fields by a maximum entropy method","authors":"Mikkel Otzen, Christopher C Finlay, C. Kloss","doi":"10.1093/gji/ggae008","DOIUrl":"https://doi.org/10.1093/gji/ggae008","url":null,"abstract":"\u0000 Satellite observations of the geomagnetic field contain signals generated in Earth’s interior by electrical currents in the core and by magnetized rocks in the lithosphere. At short wavelengths the lithospheric signal dominates, obscuring the signal from the core. Here we present details of a method to co-estimate separate models for the core and lithospheric fields, which are allowed to overlap in spherical harmonic degree, that makes use of prior information to aid the separation. Using a maximum entropy method we estimate probabilistic models for the time-dependent core field and the static lithospheric field that satisfy constraints provided by satellite observations while being consistent with prior knowledge of the spatial covariance and expected magnitude of each field at its source surface. For the core field, we find that between spherical harmonic degree 13 and 22 power adds coherently to the established structures, and present a synthetic test that illustrates the aspects of the small scale core field that can reliably be retrieved. For the large scale lithospheric field we also find encouraging results, with the strongest signatures below spherical harmonic degree 13 occurring at locations of known prominent lithospheric field anomalies in north-Eastern Europe, Australia and eastern North America. Although the amplitudes of the small scale core field and large scale lithospheric field are underestimated we find no evidence that obvious artefacts are introduced. Compared with conventional maps of the core-mantle boundary field our results suggest more localized normal flux concentrations close to the tangent cylinder, and that low latitude flux concentrations occur in pairs of opposite polarity. Future improvements in the recovery of the small scale core field and large scale lithospheric field will depend on whether more detailed prior information can be reliably extracted from core dynamo and lithospheric magnetisation simulations.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139381587","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}
引用次数: 0
A comprehensive theory for 1D (an)elastic medium deformation due to plane-wave fluid pressure perturbation 平面波流体压力扰动导致一维(非)弹性介质变形的综合理论
Geophysical Journal International Pub Date : 2024-01-05 DOI: 10.1093/gji/ggae005
Zongbo Xu, Philippe Lognonné
{"title":"A comprehensive theory for 1D (an)elastic medium deformation due to plane-wave fluid pressure perturbation","authors":"Zongbo Xu, Philippe Lognonné","doi":"10.1093/gji/ggae005","DOIUrl":"https://doi.org/10.1093/gji/ggae005","url":null,"abstract":"\u0000 Atmospheric and oceanic pressure perturbations deform the ground surface and the seafloor, respectively. This mechanical deformation, where the fluid perturbations propagate as plane waves, occurs not only on Earth but also on other planets/bodies with atmospheres, such as Mars, Titan, and Venus. Studying this type of deformation improves our understanding of the mechanical interaction between the fluid layer (atmosphere/ocean) and the underlying solid planet/body, and aids investigation of subsurface structures. In this study, we utilize eigenfunction theory to unify existing theories for modelling this deformation and to comprehensively demonstrate possible scenarios of this deformation in homogeneous and 1D elastic media, including static loading, air-coupled Rayleigh waves, and leaky-mode surface waves. Our computations quantitatively reveal that the deformation amplitude generally decays with depth and that reducing seismic noise due to Martian atmosphere requires deploying seismometers at least 1 m beneath Martian surface. We also apply our theory to illustrate how this deformation and the corresponding air-to-solid energy conversion vary on different planetary bodies. Finally, we discuss how medium anelasticity and other factors affect this deformation.","PeriodicalId":502458,"journal":{"name":"Geophysical Journal International","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139384226","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}
引用次数: 0
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