Adrian van Kan, Keith Julien, Benjamin Miquel, Edgar Knobloch
Geophysical and astrophysical fluid flows are typically buoyantly driven and are strongly constrained by planetary rotation at large scales. Rapidly rotating Rayleigh-B'enard convection (RRRBC) provides a paradigm for direct numerical simulations (DNS) and laboratory studies of such flows, but the accessible parameter space remains restricted to moderately fast rotation (Ekman numbers $rm Ek gtrsim 10^{-8}$), while realistic $rm Ek$ for astro-/geophysical applications are significantly smaller. Reduced equations of motion, the non-hydrostatic quasi-geostrophic equations describing the leading-order behavior in the limit of rapid rotation ($rm Ek to 0$) cannot capture finite rotation effects, leaving the physically most relevant part of parameter space with small but finite $rm Ek$ currently inaccessible. Here, we introduce the rescaled incompressible Navier-Stokes equations (RiNSE), a reformulation of the Navier-Stokes-Boussinesq equations informed by the scalings valid for $rm Ekto 0$. We provide the first full DNS of RRRBC at unprecedented rotation strengths down to $rm Ek=10^{-15}$ and below and show that the RiNSE converge to the asymptotically reduced equations.
地球物理和天体物理流体流动通常由浮力驱动，在大尺度上受到行星自转的强烈制约。快速旋转瑞利对流（RRRBC）为此类流体的直接数值模拟（DNS）和实验室研究提供了范例，但可获取的参数空间仍然局限于中速旋转（Ekman 数 $rm Ek gtrsim 10^{-8}$），而用于地球/地球物理应用的现实 $rm Ek$ 则要小得多。描述快速旋转（$rm Ek to 0$）极限中前导阶行为的非流体静力学准地转方程无法捕捉有限旋转效应，使得参数空间中物理上最相关的、具有较小但有限的 $rm Ek$ 的部分目前无法进入。在这里，我们引入了重标定不可压缩纳维-斯托克斯方程（RiNSE），它是纳维-斯托克斯-布西尼斯克方程的一种形式，其标定结果对 $rm Ekto 0$ 有效。我们首次提供了前所未见的旋转强度低至$rm Ek=10^{-15}$及以下的RRRBC的完整DNS，并证明RiNSE收敛于渐近简化方程。
{"title":"Bridging the Rossby number gap in rapidly rotating thermal convection","authors":"Adrian van Kan, Keith Julien, Benjamin Miquel, Edgar Knobloch","doi":"arxiv-2409.08536","DOIUrl":"https://doi.org/arxiv-2409.08536","url":null,"abstract":"Geophysical and astrophysical fluid flows are typically buoyantly driven and\u0000are strongly constrained by planetary rotation at large scales. Rapidly\u0000rotating Rayleigh-B'enard convection (RRRBC) provides a paradigm for direct\u0000numerical simulations (DNS) and laboratory studies of such flows, but the\u0000accessible parameter space remains restricted to moderately fast rotation\u0000(Ekman numbers $rm Ek gtrsim 10^{-8}$), while realistic $rm Ek$ for\u0000astro-/geophysical applications are significantly smaller. Reduced equations of\u0000motion, the non-hydrostatic quasi-geostrophic equations describing the\u0000leading-order behavior in the limit of rapid rotation ($rm Ek to 0$) cannot\u0000capture finite rotation effects, leaving the physically most relevant part of\u0000parameter space with small but finite $rm Ek$ currently inaccessible. Here, we\u0000introduce the rescaled incompressible Navier-Stokes equations (RiNSE), a\u0000reformulation of the Navier-Stokes-Boussinesq equations informed by the\u0000scalings valid for $rm Ekto 0$. We provide the first full DNS of RRRBC at\u0000unprecedented rotation strengths down to $rm Ek=10^{-15}$ and below and show\u0000that the RiNSE converge to the asymptotically reduced equations.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"35 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142252788","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}
Jing Sun, Sigmund Slang, Thomas Elboth, Thomas Larsen Greiner, Steven McDonald, Leiv-J Gelius
For economic and efficiency reasons, blended acquisition of seismic data is becoming more and more commonplace. Seismic deblending methods are always computationally demanding and normally consist of multiple processing steps. Besides, the parameter setting is not always trivial. Machine learning-based processing has the potential to significantly reduce processing time and to change the way seismic deblending is carried out. We present a data-driven deep learning-based method for fast and efficient seismic deblending. The blended data are sorted from the common source to the common channel domain to transform the character of the blending noise from coherent events to incoherent distributions. A convolutional neural network (CNN) is designed according to the special character of seismic data, and performs deblending with comparable results to those obtained with conventional industry deblending algorithms. To ensure authenticity, the blending was done numerically and only field seismic data were employed, including more than 20000 training examples. After training and validation of the network, seismic deblending can be performed in near real time. Experiments also show that the initial signal to noise ratio (SNR) is the major factor controlling the quality of the final deblended result. The network is also demonstrated to be robust and adaptive by using the trained model to firstly deblend a new data set from a different geological area with a slightly different delay time setting, and secondly deblend shots with blending noise in the top part of the data.
{"title":"A convolutional neural network approach to deblending seismic data","authors":"Jing Sun, Sigmund Slang, Thomas Elboth, Thomas Larsen Greiner, Steven McDonald, Leiv-J Gelius","doi":"arxiv-2409.07930","DOIUrl":"https://doi.org/arxiv-2409.07930","url":null,"abstract":"For economic and efficiency reasons, blended acquisition of seismic data is\u0000becoming more and more commonplace. Seismic deblending methods are always\u0000computationally demanding and normally consist of multiple processing steps.\u0000Besides, the parameter setting is not always trivial. Machine learning-based\u0000processing has the potential to significantly reduce processing time and to\u0000change the way seismic deblending is carried out. We present a data-driven deep\u0000learning-based method for fast and efficient seismic deblending. The blended\u0000data are sorted from the common source to the common channel domain to\u0000transform the character of the blending noise from coherent events to\u0000incoherent distributions. A convolutional neural network (CNN) is designed\u0000according to the special character of seismic data, and performs deblending\u0000with comparable results to those obtained with conventional industry deblending\u0000algorithms. To ensure authenticity, the blending was done numerically and only\u0000field seismic data were employed, including more than 20000 training examples.\u0000After training and validation of the network, seismic deblending can be\u0000performed in near real time. Experiments also show that the initial signal to\u0000noise ratio (SNR) is the major factor controlling the quality of the final\u0000deblended result. The network is also demonstrated to be robust and adaptive by\u0000using the trained model to firstly deblend a new data set from a different\u0000geological area with a slightly different delay time setting, and secondly\u0000deblend shots with blending noise in the top part of the data.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211762","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 phase diagram and sound velocities of the Fe-Si binary alloy, crucial for understanding the Earth's core, are determined at inner core boundary pressure with textit{ab-initio} accuracy through deep-learning-aided hybrid Monte Carlo simulations. A complex phase diagram emerges close to the melting temperature, where a re-entrance of the body-centered cubic (bcc) phase is observed. The bcc structure is stabilized by a pronounced short-range ordering of the Si atoms. The miscibility gap between the short-range ordered bcc structure and the long-range ordered cubic B2 structure shrinks with increasing temperature and the transition becomes continuous above 6000 K. We find that a bcc Fe-Si solid solution reproduces crucial geophysical data such as the low shear sound velocity and the seismic anisotropy of the inner core much better than other structures.
通过深度学习辅助的混合蒙特卡洛模拟，确定了内核边界压力下Fe-Si二元合金的相图和声速，这对理解地核至关重要。在接近熔化温度时，出现了复杂的相图，并观察到体心立方（bcc）相的重新进入。短程有序的 bcc 结构与长程有序的立方 B2 结构之间的混溶隙随着温度的升高而缩小，在 6000 K 以上转变变得连续。我们发现，bcc Fe-Si 固溶体比其他结构更好地再现了关键的地球物理数据，例如内核的低剪切声速和地震各向异性。
{"title":"Short-range order stabilizes a cubic Fe alloy in Earth's inner core","authors":"Zhi Li, Sandro Scandolo","doi":"arxiv-2409.08008","DOIUrl":"https://doi.org/arxiv-2409.08008","url":null,"abstract":"The phase diagram and sound velocities of the Fe-Si binary alloy, crucial for\u0000understanding the Earth's core, are determined at inner core boundary pressure\u0000with textit{ab-initio} accuracy through deep-learning-aided hybrid Monte Carlo\u0000simulations. A complex phase diagram emerges close to the melting temperature,\u0000where a re-entrance of the body-centered cubic (bcc) phase is observed. The bcc\u0000structure is stabilized by a pronounced short-range ordering of the Si atoms.\u0000The miscibility gap between the short-range ordered bcc structure and the\u0000long-range ordered cubic B2 structure shrinks with increasing temperature and\u0000the transition becomes continuous above 6000 K. We find that a bcc Fe-Si solid\u0000solution reproduces crucial geophysical data such as the low shear sound\u0000velocity and the seismic anisotropy of the inner core much better than other\u0000structures.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We explore phase equilbria on the MgO-Fe join as a prototype of lithophile-core interaction in terrestrial planets. Our simulations, based on density functional theory, are based on a two-phase method: fluids of initially pure MgO and Fe compositions are allowed to establish a dynamic equilbrium across a near-planar interface. Methods for analyzing the composition and other properties of the two coexisting phases show that MgO behaves as a component, with indistinguishable Mg and O concentrations in Fe-rich and oxide-rich phases. The phase diagram is well described as that of a symmetric regular solution, a picture confirmed by independent one-phase determinations of the enthalpy, entropy, and volume of mixing. The critical temperature, above which there is complete miscibility across the MgO-Fe join is 7000 K at 68 GPa, and 9000 K and 172 GPa. The rate of MgO exsolution from the Fe-rich liquid on cooling is similar to that found in previous experimental studies, and is too small to drive a dynamo.
{"title":"MgO Miscibility in Liquid Iron","authors":"Leslie Insixiengmay, Lars Stixrude","doi":"arxiv-2409.07681","DOIUrl":"https://doi.org/arxiv-2409.07681","url":null,"abstract":"We explore phase equilbria on the MgO-Fe join as a prototype of\u0000lithophile-core interaction in terrestrial planets. Our simulations, based on\u0000density functional theory, are based on a two-phase method: fluids of initially\u0000pure MgO and Fe compositions are allowed to establish a dynamic equilbrium\u0000across a near-planar interface. Methods for analyzing the composition and other\u0000properties of the two coexisting phases show that MgO behaves as a component,\u0000with indistinguishable Mg and O concentrations in Fe-rich and oxide-rich\u0000phases. The phase diagram is well described as that of a symmetric regular\u0000solution, a picture confirmed by independent one-phase determinations of the\u0000enthalpy, entropy, and volume of mixing. The critical temperature, above which\u0000there is complete miscibility across the MgO-Fe join is 7000 K at 68 GPa, and\u00009000 K and 172 GPa. The rate of MgO exsolution from the Fe-rich liquid on\u0000cooling is similar to that found in previous experimental studies, and is too\u0000small to drive a dynamo.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211764","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}
To separate seismic interference (SI) noise while ensuring high signal fidelity, we propose a deep neural network (DNN)-based workflow applied to common shot gathers (CSGs). In our design, a small subset of the entire to-be-processed data set is first processed by a conventional algorithm to obtain an estimate of the SI noise (from now on called the SI noise model). By manually blending the SI noise model with SI-free CSGs and a set of simulated random noise, we obtain training inputs for the DNN. The SI-free CSGs can be either real SI-free CSGs from the survey or SI-attenuated CSGs produced in parallel with the SI noise model from the conventional algorithm depending on the specific project. To enhance the DNN's output signal fidelity, adjacent shots on both sides of the to-be-processed shot are used as additional channels of the input. We train the DNN to output the SI noise into one channel and the SI-free shot along with the intact random noise into another. Once trained, the DNN can be applied to the entire data set contaminated by the same types of SI in the training process, producing results efficiently. For demonstration, we applied the proposed DNN-based workflow to 3D seismic field data acquired from the Northern Viking Graben (NVG) of the North Sea, and compared it with a conventional algorithm. The studied area has a challenging SI contamination problem with no sail lines free from SI noise during the acquisition. The comparison shows that the proposed DNN-based workflow outperformed the conventional algorithm in processing quality with less noise residual and better signal preservation. This validates its feasibility and value for real processing projects.
为了在分离地震干扰（SI）噪声的同时确保高信号保真度，我们提出了一种基于深度神经网络（DNN）的工作流程，应用于普通震源采集（CSG）。在我们的设计中，首先用传统算法处理整个待处理数据集的一小部分，以获得 SI 噪声的估计值（以下称为 SI 噪声模型）。通过将 SI 噪声模型与无 SI CSG 和一组模拟随机噪声进行手动混合，我们获得了 DNN 的训练输入。无 SI CSG 可以是来自调查的真实无 SI CSG，也可以是与传统算法的 SI 噪声模型并行生成的 SI 减弱 CSG，具体取决于具体项目。为了提高 DNN 输出信号的保真度，待处理镜头两侧的邻近镜头被用作额外的输入通道。我们训练 DNN 将 SI 噪声输出到一个通道，将无 SI 的镜头和完整的随机噪声输出到另一个通道。训练完成后，DNN 即可应用于受训练过程中相同类型 SI 污染的整个数据集，从而高效地生成结果。为了进行演示，我们将所提出的基于 DNN 的工作流程应用于从北海北维京海湾（NVG）获取的三维地震现场数据，并与传统算法进行了比较。研究区域的 SI 污染问题极具挑战性，在采集过程中没有一条帆线不受 SI 噪声的影响。比较结果表明，所提出的基于 DNN 的工作流程在处理质量上优于传统算法，噪声残留更少，信号保存更好。这验证了它在实际处理项目中的可行性和价值。
{"title":"DNN-based workflow for attenuating seismic interference noise and its application to marine towed streamer data from the Northern Viking Graben","authors":"Jing Sun, Song Hou, Alaa Triki","doi":"arxiv-2409.07890","DOIUrl":"https://doi.org/arxiv-2409.07890","url":null,"abstract":"To separate seismic interference (SI) noise while ensuring high signal\u0000fidelity, we propose a deep neural network (DNN)-based workflow applied to\u0000common shot gathers (CSGs). In our design, a small subset of the entire\u0000to-be-processed data set is first processed by a conventional algorithm to\u0000obtain an estimate of the SI noise (from now on called the SI noise model). By\u0000manually blending the SI noise model with SI-free CSGs and a set of simulated\u0000random noise, we obtain training inputs for the DNN. The SI-free CSGs can be\u0000either real SI-free CSGs from the survey or SI-attenuated CSGs produced in\u0000parallel with the SI noise model from the conventional algorithm depending on\u0000the specific project. To enhance the DNN's output signal fidelity, adjacent\u0000shots on both sides of the to-be-processed shot are used as additional channels\u0000of the input. We train the DNN to output the SI noise into one channel and the\u0000SI-free shot along with the intact random noise into another. Once trained, the\u0000DNN can be applied to the entire data set contaminated by the same types of SI\u0000in the training process, producing results efficiently. For demonstration, we\u0000applied the proposed DNN-based workflow to 3D seismic field data acquired from\u0000the Northern Viking Graben (NVG) of the North Sea, and compared it with a\u0000conventional algorithm. The studied area has a challenging SI contamination\u0000problem with no sail lines free from SI noise during the acquisition. The\u0000comparison shows that the proposed DNN-based workflow outperformed the\u0000conventional algorithm in processing quality with less noise residual and\u0000better signal preservation. This validates its feasibility and value for real\u0000processing projects.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"63 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211763","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}
Emmanuel Jacquet, Cornelis Dullemond, Joanna Drążkowska, Steven Desch
Meteorites, and in particular primitive meteorites (chondrites), are irreplaceable probes of the solar protoplanetary disk. We review their essential properties and endeavour to place them in astrophysical context. The earliest solar system solids, refractory inclusions, may have formed over the innermost au of the disk and have been transported outward by its expansion or turbulent diffusion. The age spread of chondrite components may be reconciled with the tendency of drag-induced radial drift if they were captured in pressure maxima, which may account for the non-carbonaceous/carbonaceous meteorite isotopic dichotomy. The solid/gas ratio around unity witnessed by chondrules, if interpreted as nebular (non-impact) products, suggests efficient radial concentration and settling at such locations, conducive to planetesimal formation by the streaming instability. The cause of the pressure bumps, e.g. Jupiter or condensation lines, remains to be ascertained.
{"title":"The early Solar System and its meteoritical witnesses","authors":"Emmanuel Jacquet, Cornelis Dullemond, Joanna Drążkowska, Steven Desch","doi":"arxiv-2409.07212","DOIUrl":"https://doi.org/arxiv-2409.07212","url":null,"abstract":"Meteorites, and in particular primitive meteorites (chondrites), are\u0000irreplaceable probes of the solar protoplanetary disk. We review their\u0000essential properties and endeavour to place them in astrophysical context. The\u0000earliest solar system solids, refractory inclusions, may have formed over the\u0000innermost au of the disk and have been transported outward by its expansion or\u0000turbulent diffusion. The age spread of chondrite components may be reconciled\u0000with the tendency of drag-induced radial drift if they were captured in\u0000pressure maxima, which may account for the non-carbonaceous/carbonaceous\u0000meteorite isotopic dichotomy. The solid/gas ratio around unity witnessed by\u0000chondrules, if interpreted as nebular (non-impact) products, suggests efficient\u0000radial concentration and settling at such locations, conducive to planetesimal\u0000formation by the streaming instability. The cause of the pressure bumps, e.g.\u0000Jupiter or condensation lines, remains to be ascertained.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211765","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}
Tim Hageman, Jessica Mejía, Ravindra Duddu, Emilio Martínez-Pañeda
Full thickness crevasses can transport water from the glacier surface to the bedrock where high water pressures can open kilometre-long cracks along the basal interface, which can accelerate glacier flow. We present a first computational modelling study that describes time-dependent fracture propagation in an idealised glacier causing rapid supraglacial lake drainage. A novel two-scale numerical method is developed to capture the elastic and viscoelastic deformations of ice along with crevasse propagation. The fluid-conserving thermo-hydro-mechanical model incorporates turbulent fluid flow and accounts for melting/refreezing in fractures. Applying this model to observational data from a 2008 rapid lake drainage event indicates that viscous deformation exerts a much stronger control on hydrofracture propagation compared to thermal effects. This finding contradicts the conventional assumption that elastic deformation is adequate to describe fracture propagation in glaciers over short timescales (minutes to several hours) and instead demonstrates that viscous deformation must be considered to reproduce observations of lake drainage rate and local ice surface elevation change. As supraglacial lakes continue expanding inland and as Greenland Ice Sheet temperatures become warmer than -8 degree C, our results suggest rapid lake drainages are likely to occur without refreezing, which has implications for the rate of sea level rise.
{"title":"Ice viscosity governs hydraulic fracture that causes rapid drainage of supraglacial lakes","authors":"Tim Hageman, Jessica Mejía, Ravindra Duddu, Emilio Martínez-Pañeda","doi":"arxiv-2409.05478","DOIUrl":"https://doi.org/arxiv-2409.05478","url":null,"abstract":"Full thickness crevasses can transport water from the glacier surface to the\u0000bedrock where high water pressures can open kilometre-long cracks along the\u0000basal interface, which can accelerate glacier flow. We present a first\u0000computational modelling study that describes time-dependent fracture\u0000propagation in an idealised glacier causing rapid supraglacial lake drainage. A\u0000novel two-scale numerical method is developed to capture the elastic and\u0000viscoelastic deformations of ice along with crevasse propagation. The\u0000fluid-conserving thermo-hydro-mechanical model incorporates turbulent fluid\u0000flow and accounts for melting/refreezing in fractures. Applying this model to\u0000observational data from a 2008 rapid lake drainage event indicates that viscous\u0000deformation exerts a much stronger control on hydrofracture propagation\u0000compared to thermal effects. This finding contradicts the conventional\u0000assumption that elastic deformation is adequate to describe fracture\u0000propagation in glaciers over short timescales (minutes to several hours) and\u0000instead demonstrates that viscous deformation must be considered to reproduce\u0000observations of lake drainage rate and local ice surface elevation change. As\u0000supraglacial lakes continue expanding inland and as Greenland Ice Sheet\u0000temperatures become warmer than -8 degree C, our results suggest rapid lake\u0000drainages are likely to occur without refreezing, which has implications for\u0000the rate of sea level rise.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211796","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}
Understanding the orientation of geological structures is crucial for analyzing the complexity of the Earths' subsurface. For instance, information about geological structure orientation can be incorporated into local anisotropic regularization methods as a valuable tool to stabilize the solution of inverse problems and produce geologically plausible solutions. We introduce a new variational method that employs the alternating direction method of multipliers within an alternating minimization scheme to jointly estimate orientation and model parameters in both 2D and 3D inverse problems. Specifically, the proposed approach adaptively integrates recovered information about structural orientation, enhancing the effectiveness of anisotropic Tikhonov regularization in recovering geophysical parameters. The paper also discusses the automatic tuning of algorithmic parameters to maximize the new method's performance. The proposed algorithm is tested across diverse 2D and 3D examples, including structure-oriented denoising and trace interpolation. The results show that the algorithm is robust in solving the considered large and challenging problems, alongside efficiently estimating the associated tilt field in 2D cases and the dip, strike, and tilt fields in 3D cases. Synthetic and field examples show that the proposed anisotropic regularization method produces a model with enhanced resolution and provides a more accurate representation of the true structures.
{"title":"Robust Estimation of Structural Orientation Parameters and 2D/3D Local Anisotropic Tikhonov Regularization","authors":"Ali Gholami, Silvia Gazzola","doi":"arxiv-2409.05754","DOIUrl":"https://doi.org/arxiv-2409.05754","url":null,"abstract":"Understanding the orientation of geological structures is crucial for\u0000analyzing the complexity of the Earths' subsurface. For instance, information\u0000about geological structure orientation can be incorporated into local\u0000anisotropic regularization methods as a valuable tool to stabilize the solution\u0000of inverse problems and produce geologically plausible solutions. We introduce\u0000a new variational method that employs the alternating direction method of\u0000multipliers within an alternating minimization scheme to jointly estimate\u0000orientation and model parameters in both 2D and 3D inverse problems.\u0000Specifically, the proposed approach adaptively integrates recovered information\u0000about structural orientation, enhancing the effectiveness of anisotropic\u0000Tikhonov regularization in recovering geophysical parameters. The paper also\u0000discusses the automatic tuning of algorithmic parameters to maximize the new\u0000method's performance. The proposed algorithm is tested across diverse 2D and 3D\u0000examples, including structure-oriented denoising and trace interpolation. The\u0000results show that the algorithm is robust in solving the considered large and\u0000challenging problems, alongside efficiently estimating the associated tilt\u0000field in 2D cases and the dip, strike, and tilt fields in 3D cases. Synthetic\u0000and field examples show that the proposed anisotropic regularization method\u0000produces a model with enhanced resolution and provides a more accurate\u0000representation of the true structures.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211786","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}
Elastodynamic Green's functions are an essential ingredient in seismology as they form the connection between direct observations of seismic waves and the earthquake source. They are also fundamental to various seismological techniques including physics-based ground motion prediction and kinematic or dynamic source inversions. In regions with established 3D models of the Earth's elastic structure, 3D Green's functions can be computed using numerical simulations of seismic wave propagation. However, such simulations are computationally expensive which poses challenges for real-time ground motion prediction. Here, we use a reduced-order model (ROM) approach that enables the rapid evaluation of approximate Green's functions. The ROM technique developed approximates three-component surface velocity wavefields obtained from numerical simulations of seismic wave propagation. We apply our ROM approach to a 50 km x 40 km area in the greater Los Angeles area accounting for topography, site effects, 3D subsurface velocity structure, and viscoelastic attenuation. The ROM constructed for this region enables rapid computation (0.001 CPU hours) of complete, high-resolution, 0.5 Hz surface velocity wavefields that are accurate for a shortest wavelength of 1.0 km. Using leave-one-out cross validation, we measure the accuracy of our Green's functions in both the time-domain and frequency-domain. Averaged across all sources and receivers, the error in the rapid seismograms is less than 0.01 cm/s. We demonstrate that the ROM can accurately and rapidly reproduce simulated seismograms for generalized moment tensor sources in our region, as well as kinematic sources by using a finite fault model of the 1987 Mw 5.9 Whittier Narrows earthquake as an example. We envision that our rapid, approximate Green's functions will be useful for constructing rapid ground motion synthetics with high spatial resolution.
弹性动力格林函数是地震学的基本要素，因为它们构成了地震波直接观测结果与震源之间的联系。它们也是各种地震学技术的基础，包括基于物理的地动预测和运动学顺序动力源反演。在建立了地球弹性结构三维模型的地区，可以使用地震波传播的数值模拟计算三维格林函数。然而，这种模拟计算成本高昂，给实时地动预测带来了挑战。在此，我们采用了一种降低阶数模型（ROM）方法，可以快速评估近似格林函数。所开发的 ROM 技术可近似计算地震波传播数值模拟中获得的三分量表面速度波场。我们将 ROM 方法应用于大洛杉矶地区 50 km x 40 km 的区域，考虑了地形、场地效应、三维地下速度结构和粘弹性衰减。为该区域构建的 ROM 能够快速计算（0.001 CPU 小时）完整的高分辨率 0.5 Hz 表面速度波场，该波场在最短波长为 1.0 km 时是精确的。我们采用 "留一 "交叉验证的方法，测量了格林函数在时域和频域的精度。对所有震源和接收器进行平均，快速地震图的误差小于 0.01 厘米/秒。我们以 1987 年 Mw 5.9 Whittier Narrows 地震的有限断层模型为例，证明 ROM 可以准确、快速地再现本地区广义矩张量震源的模拟地震图以及运动震源的模拟地震图。我们预计，我们的快速近似格林函数将有助于构建具有高空间分辨率的快速地动合成模型。
{"title":"Reduced-order modeling for complex 3D seismic wave propagation","authors":"John M. Rekoske, Dave A. May, Alice-Agnes Gabriel","doi":"arxiv-2409.06102","DOIUrl":"https://doi.org/arxiv-2409.06102","url":null,"abstract":"Elastodynamic Green's functions are an essential ingredient in seismology as\u0000they form the connection between direct observations of seismic waves and the\u0000earthquake source. They are also fundamental to various seismological\u0000techniques including physics-based ground motion prediction and kinematic or\u0000dynamic source inversions. In regions with established 3D models of the Earth's\u0000elastic structure, 3D Green's functions can be computed using numerical\u0000simulations of seismic wave propagation. However, such simulations are\u0000computationally expensive which poses challenges for real-time ground motion\u0000prediction. Here, we use a reduced-order model (ROM) approach that enables the\u0000rapid evaluation of approximate Green's functions. The ROM technique developed\u0000approximates three-component surface velocity wavefields obtained from\u0000numerical simulations of seismic wave propagation. We apply our ROM approach to\u0000a 50 km x 40 km area in the greater Los Angeles area accounting for topography,\u0000site effects, 3D subsurface velocity structure, and viscoelastic attenuation.\u0000The ROM constructed for this region enables rapid computation (0.001 CPU hours)\u0000of complete, high-resolution, 0.5 Hz surface velocity wavefields that are\u0000accurate for a shortest wavelength of 1.0 km. Using leave-one-out cross\u0000validation, we measure the accuracy of our Green's functions in both the\u0000time-domain and frequency-domain. Averaged across all sources and receivers,\u0000the error in the rapid seismograms is less than 0.01 cm/s. We demonstrate that\u0000the ROM can accurately and rapidly reproduce simulated seismograms for\u0000generalized moment tensor sources in our region, as well as kinematic sources\u0000by using a finite fault model of the 1987 Mw 5.9 Whittier Narrows earthquake as\u0000an example. We envision that our rapid, approximate Green's functions will be\u0000useful for constructing rapid ground motion synthetics with high spatial\u0000resolution.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"410 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211766","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}
Earth's geodynamo has operated for over 3.5 billion years. The magnetic field is currently powered by thermocompositional convection in the outer core, which involves the release of light elements and latent heat as the inner core solidifies. However, since the inner core nucleated no more than 1.5 billion years ago, the early dynamo could not rely on these buoyancy sources. Given recent estimates of the thermal conductivity of the outer core, an alternative mechanism may be required to sustain the geodynamo prior to nucleation of the inner core. One possibility is a silicate dynamo operating in a long-lived basal magma ocean. Here, we investigate the structural, thermal, buoyancy, and magnetic evolution of an Earth-like terrestrial planet. Using modern equations of state and melting curves, we include a time-dependent parameterization of the compositional evolution of an iron-rich basal magma ocean. We combine an internal structure integration of the planet with energy budgets in a coupled core, basal magma ocean, and mantle system. We determine the thermocompositional convective stability of the core and the basal magma ocean, and assess their respective dynamo activity using entropy budgets and magnetic Reynolds numbers. Our conservative nominal model predicts a transient basal magma ocean dynamo followed by a core dynamo after 1 billion years. The model is sensitive to several parameters, including the initial temperature of the core-mantle boundary, the parameterization of mantle convection, the composition of the basal magma ocean, the radiogenic content of the planet, as well as convective velocity and magnetic scaling laws. We use the nominal model to constrain the range of basal magma ocean electrical conductivity and core thermal conductivity that sustain a dynamo.
{"title":"Thermal and magnetic evolution of an Earth-like planet with a basal magma ocean","authors":"Victor Lherm, Miki Nakajima, Eric G. Blackman","doi":"arxiv-2409.06031","DOIUrl":"https://doi.org/arxiv-2409.06031","url":null,"abstract":"Earth's geodynamo has operated for over 3.5 billion years. The magnetic field\u0000is currently powered by thermocompositional convection in the outer core, which\u0000involves the release of light elements and latent heat as the inner core\u0000solidifies. However, since the inner core nucleated no more than 1.5 billion\u0000years ago, the early dynamo could not rely on these buoyancy sources. Given\u0000recent estimates of the thermal conductivity of the outer core, an alternative\u0000mechanism may be required to sustain the geodynamo prior to nucleation of the\u0000inner core. One possibility is a silicate dynamo operating in a long-lived\u0000basal magma ocean. Here, we investigate the structural, thermal, buoyancy, and\u0000magnetic evolution of an Earth-like terrestrial planet. Using modern equations\u0000of state and melting curves, we include a time-dependent parameterization of\u0000the compositional evolution of an iron-rich basal magma ocean. We combine an\u0000internal structure integration of the planet with energy budgets in a coupled\u0000core, basal magma ocean, and mantle system. We determine the\u0000thermocompositional convective stability of the core and the basal magma ocean,\u0000and assess their respective dynamo activity using entropy budgets and magnetic\u0000Reynolds numbers. Our conservative nominal model predicts a transient basal\u0000magma ocean dynamo followed by a core dynamo after 1 billion years. The model\u0000is sensitive to several parameters, including the initial temperature of the\u0000core-mantle boundary, the parameterization of mantle convection, the\u0000composition of the basal magma ocean, the radiogenic content of the planet, as\u0000well as convective velocity and magnetic scaling laws. We use the nominal model\u0000to constrain the range of basal magma ocean electrical conductivity and core\u0000thermal conductivity that sustain a dynamo.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"80 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142211785","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}
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