Journal of Geophysical Research: Solid Earth最新文献

{"title":"Topographic Drag at the Core-Mantle Interface","authors":"R. Monville, D. Cébron, D. Jault","doi":"10.1029/2024jb029770","DOIUrl":"https://doi.org/10.1029/2024jb029770","url":null,"abstract":"The length of day variations with periods from five to one hundred years are mainly due to core-mantle interactions. Assuming a differential velocity between the core and the mantle, we investigate the pressure coupling on a core-mantle boundary (CMB) interface with topography. Including rotation, buoyancy, and magnetic effects in local models of the CMB, we provide a taxonomy of the waves radiated by the core flow along the topography. We obtain the local stress with a perturbation approach and a semi-analytical spectral model built upon these waves. We incorporate planetary curvature effects by considering a “non-traditional” <span data-altimg=\"/cms/asset/4a466dbe-6ce5-4d84-9293-7eae56d217d6/jgrb57203-math-0001.png\"></span><mjx-container ctxtmenu_counter=\"755\" ctxtmenu_oldtabindex=\"1\" jax=\"CHTML\" role=\"application\" sre-explorer- style=\"font-size: 103%; position: relative;\" tabindex=\"0\"><mjx-math aria-hidden=\"true\" location=\"graphic/jgrb57203-math-0001.png\"><mjx-semantics><mjx-mrow><mjx-mi data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"italic\" data-semantic- data-semantic-role=\"greekletter\" data-semantic-speech=\"beta\" data-semantic-type=\"identifier\"><mjx-c></mjx-c></mjx-mi></mjx-mrow></mjx-semantics></mjx-math><mjx-assistive-mml display=\"inline\" unselectable=\"on\"><math altimg=\"urn:x-wiley:21699313:media:jgrb57203:jgrb57203-math-0001\" display=\"inline\" location=\"graphic/jgrb57203-math-0001.png\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><semantics><mrow><mi data-semantic-=\"\" data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"italic\" data-semantic-role=\"greekletter\" data-semantic-speech=\"beta\" data-semantic-type=\"identifier\">β</mi></mrow>$beta $</annotation></semantics></math></mjx-assistive-mml></mjx-container>-plane approximation suited for deep fluid layers and long topography wavelengths. We calculate weakly non-linear flows and characterize the wave drag mechanism. Unlike previous works, our analysis is not restricted to strong stratification or short wavelengths. It reveals the significant impact of the Rossby waves on stress. We also show that these waves are drastically modified when considering two-dimensional topographies instead of simple ridges. For a buoyancy frequency <span data-altimg=\"/cms/asset/5fb1799d-77b3-4947-bb81-4344ee5a8f89/jgrb57203-math-0002.png\"></span><mjx-container ctxtmenu_counter=\"756\" ctxtmenu_oldtabindex=\"1\" jax=\"CHTML\" role=\"application\" sre-explorer- style=\"font-size: 103%; position: relative;\" tabindex=\"0\"><mjx-math aria-hidden=\"true\" location=\"graphic/jgrb57203-math-0002.png\"><mjx-semantics><mjx-mrow><mjx-mi data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"italic\" data-semantic- data-semantic-role=\"latinletter\" data-semantic-speech=\"upper N\" data-semantic-type=\"identifier\"><mjx-c></mjx-c></mjx-mi></mjx-mrow></mjx-semantics></mjx-math><mjx-assistive-mml display=\"inline\" unselectable=\"on\"><math altimg=\"urn:x-wiley:21699313:media:jgrb57203:jgrb57203-math-0002\" display","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"108 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143806297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"GNSS Observations of the Land Uplift in South Africa: Implications for Water Mass Loss","authors":"Christian A. Mielke,&nbsp;Makan A. Karegar,&nbsp;Helena Gerdener,&nbsp;Jürgen Kusche","doi":"10.1029/2024JB030350","DOIUrl":"https://doi.org/10.1029/2024JB030350","url":null,"abstract":"<p>Continuously operating Global Navigation Satellite System (GNSS) base stations in South Africa show a spatially coherent vertical displacement. While one hypothesis attributes this vertical motion to crustal deformation from mantle flow and dynamic topography (Hammond et al., 2021, https://doi.org/10.1029/2021jb022355), we propose an alternative explanation. Our evidence suggests that land water loss from multiple droughts is a major driver of the observed uplift. In this study, we analyze daily Global Positioning System (GPS) height time series from 2000 to 2021. We use singular spectral analysis (SSA) to separate long-term trends and annual and semi-annual signals from noise. The processed time series were inverted into water mass loading on a uniform grid, with the Earth's crust's rheological properties defined by the Preliminary Reference Earth Model (PREM). Our experimental approach show that a 2<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>°</mo>\u0000 <mo>×</mo>\u0000 </mrow>\u0000 <annotation> ${}^{circ}times $</annotation>\u0000 </semantics></math> 2<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>°</mo>\u0000 </mrow>\u0000 <annotation> ${}^{circ}$</annotation>\u0000 </semantics></math> grid resolution provides suitable results for most of South Africa. The GPS-derived total water storage change reconcile well with a GRACE-assimilated solution and a hydrological model at the monthly scale across different provinces, showing correlations of up to 90% and 94%, respectively. The long-term trend averaged over the country shows a considerable correlation of 46% and 53%, respectively. These long-term total water storage trends provide strong evidence that the observed land uplift in South Africa is primarily of hydrological origin.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB030350","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143801811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mantle Transition Zone-Penetrating Upwellings Beneath the Eastern North American Margin and Beyond","authors":"Yantao Luo,&nbsp;Maureen D. Long,&nbsp;Stéphane Rondenay,&nbsp;Scott D. King,&nbsp;Sarah E. Mazza,&nbsp;Jonathan Wolf","doi":"10.1029/2024JB030005","DOIUrl":"10.1029/2024JB030005","url":null,"abstract":"<p>Low-velocity anomalies in the upper mantle beneath eastern North America, including the Northern Appalachian Anomaly (NAA), the Central Appalachian Anomaly (CAA), and the weaker Southern Coastal Anomaly (SCA), have been characterized by many continent-scale and regional seismic studies. Different models have been proposed to explain their existence beneath the passive margin of eastern North America, variously invoking the past passage of hot spot tracks, modern upwelling due to edge-driven convection, or other processes. Depending on the nature and origin of these anomalies, they may influence, and/or be influenced by, the mantle transition zone (MTZ) structure beneath them. Previous receiver function studies have identified an overall thinner MTZ beneath the eastern margin of the US than beneath the continental interior. In this study, we resolve the MTZ geometry beneath these low-velocity anomalies in unprecedented detail using the scattered wavefield migration technique. We find substantially thinned MTZ beneath the NAA and the CAA, and a moderately thinned MTZ beneath the SCA. In all cases, the thinning is achieved via a minor depression of the 410-km discontinuity and a major uplift of the 660-km discontinuity, which suggests the presence of a series of MTZ-penetrating deep upwellings beneath eastern North America. The upwellings beneath eastern North America and a similar style upwelling beneath Bermuda may initiate from ponded thermally buoyant materials below the MTZ fed by hot return flows from the descending Farallon slab in the deep mantle.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143798044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of Crust-Mantle Detachment and Slab Delamination in the Plateau Uplift and Crustal Thickening Process in Southern Tibet","authors":"Zhiqiang Li,&nbsp;You Tian,&nbsp;Dapeng Zhao,&nbsp;Xuan Feng","doi":"10.1029/2024JB029815","DOIUrl":"https://doi.org/10.1029/2024JB029815","url":null,"abstract":"<p>The driving mechanism behind the anomalously thick crust and surface uplift of the Tibetan Plateau remains controversial. Here we present seismic images of the lithosphere in southern Tibet, derived from P and S receiver functions along a newly deployed 200 km-long broadband seismic array that strikes north at 91.15°E longitude. An offset of the Moho discontinuity is revealed at ∼70 km depth beneath the Yarlung-Zangbo suture zone (YZS). The subducted Indian lithospheric mantle is thrusting beneath southern Tibet with a flat-ramp-flat geometry and is undergoing crust-mantle detachment beneath the YZS. As an intermediate stage in the underplating and delamination of the Indian plate, the crust-mantle detachment plays an important role in the process of surface uplift and crustal thickening in southern Tibet. It is the main cause of the Moho offset, facilitating upwelling of asthenospheric materials from the upper mantle to the crust. These materials underplate in the lower crust, promote the formation of juvenile lower crust in southern Tibet, and lead to widespread low-velocity zones within the crust.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143793764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleomagnetic Secular Variation of Early Middle Miocene Volcanics From Vogelsberg (Germany)","authors":"Y. Chi,&nbsp;F. Lhuillier","doi":"10.1029/2024JB031007","DOIUrl":"https://doi.org/10.1029/2024JB031007","url":null,"abstract":"&lt;p&gt;The Earth's magnetic field significantly changed its rate of polarity reversals over the past 200 Myr; yet it remains controversial whether these drastic changes—from a stable state of polarity during the Cretaceous Normal Superchron to more than 10 events per Myr during the Jurassic—are accompanied with similar changes in the directional variability of the field, termed paleosecular variation (PSV). In an effort to better constrain the geomagnetic behavior during the Miocene, we investigated the paleomagnetism of 162 volcanic units (1920 cores) from the Vogelsberg, the largest volcanic mountain range in Central Europe emplaced between 17.6 and 15.2 Ma. We successfully interpreted the paleodirections of 148 volcanic units, which led to a final collection of 127 independent geomagnetic records after correction for serial correlation. After removing the transitional directions, this collection passes the reversal test and yields a paleomagnetic pole located at 161.9°E and 84.5°N (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;A&lt;/mi&gt;\u0000 &lt;mn&gt;95&lt;/mn&gt;\u0000 &lt;/msub&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${A}_{95}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; = 3.2°, &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; $N$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; = 116), which is statistically indistinguishable from the predictions of the latest apparent polar wander paths for stable Europe. Used as a proxy for PSV, the dispersion of the virtual geomagnetic poles &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;S&lt;/mi&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mn&gt;19.1&lt;/mn&gt;\u0000 &lt;mo&gt;°&lt;/mo&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mo&gt;|&lt;/mo&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;17.5&lt;/mn&gt;\u0000 &lt;mo&gt;°&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;20.8&lt;/mn&gt;\u0000 &lt;mo&gt;°&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;(&lt;/mo&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;N&lt;/mi&gt;\u0000 &lt;mo&gt;=&lt;/mo&gt;\u0000 &lt;mn&gt;116&lt;/mn&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mo&gt;)&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${S}_{mathrm{B}}=19.1mathit{{}^{circ}}{mathit{vert }}_{17.5mathit{{}^{circ}}}^{20.8mathit{{}^{circ}}},(N=116)$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; is consistent with a m","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB031007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143793765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seismic Evidence for Large-Scale Intraslab Heterogeneity Beneath Northeast Japan","authors":"Jian Wang,&nbsp;Dengda Zhu,&nbsp;Zhigang Zhang,&nbsp;Jianming He,&nbsp;Ling Chen,&nbsp;Dapeng Zhao,&nbsp;Zhenxing Yao","doi":"10.1029/2024JB030046","DOIUrl":"https://doi.org/10.1029/2024JB030046","url":null,"abstract":"<p>Understanding the heterogeneity within a subducting slab is essential for elucidating its rheological properties, which can significantly affect subduction dynamics. Despite the importance, the fine structure of the slab has remained largely enigmatic due to the limited resolution of seismic tomography. Here, we utilize a deep learning approach, PickNet, to collect a comprehensive data set of arrival-times of the first P and S waves from local earthquakes in Northeast Japan. This enables the determination of a high-resolution (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>0.2</mn>\u0000 <mo>°</mo>\u0000 <mo>×</mo>\u0000 <mn>0.2</mn>\u0000 <mo>°</mo>\u0000 <mo>×</mo>\u0000 <mn>30</mn>\u0000 <mspace></mspace>\u0000 <mtext>km</mtext>\u0000 </mrow>\u0000 <annotation> $0.2mathit{{}^{circ}}times 0.2mathit{{}^{circ}}times 30,text{km}$</annotation>\u0000 </semantics></math>) model of P-wave velocity (Vp), S-wave velocity (Vs), and Vp/Vs ratio within the subducting Pacific slab. Our model reveals a distinct intraslab structure characterized by relatively high Vp (&gt;+3%), slightly high Vs (&lt;+1%), and a high Vp/Vs ratio (&gt;+1%), extending deep into the lithospheric mantle of the slab, approximately <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>0.4</mn>\u0000 <mo>°</mo>\u0000 <mo>×</mo>\u0000 <mn>0.4</mn>\u0000 <mo>°</mo>\u0000 <mo>×</mo>\u0000 <mn>80</mn>\u0000 <mspace></mspace>\u0000 <mtext>km</mtext>\u0000 </mrow>\u0000 <annotation> $0.4mathit{{}^{circ}}times 0.4mathit{{}^{circ}}times 80,text{km}$</annotation>\u0000 </semantics></math> in size between longitudes 140.6°E and 142.0°E, and latitudes 39.8°N and 40.2°N beneath Northeast Japan. This anomalous structure is associated with a decrease or absence in lower-plane intermediate-depth seismicity of the double seismic zone within the slab. This result suggests that the presence of intrusive minerals, potentially affected by increased iron (Fe) content due to hot mantle upwelling, may reduce the viscosity of the slab at lithospheric depths and subsequently diminish the lower-plane seismicity. Our results highlight the presence of rheological heterogeneity within the subducting slab, providing new insights into its role in impacting the deep structure and geodynamics of the Earth, potentially facilitating slab detachment or tearing.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143778183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Why Are Plume Excess Temperatures Much Less Than the Temperature Drop Across the Lowermost-Mantle Thermal Boundary Layer?","authors":"Bernhard Steinberger,&nbsp;Poulami Roy,&nbsp;Michael Pons,&nbsp;Matteo Paul Jopke","doi":"10.1029/2024JB030111","DOIUrl":"https://doi.org/10.1029/2024JB030111","url":null,"abstract":"<p>While temperature drop across the mantle's basal thermal boundary layer (TBL) is likely <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>&gt;</mo>\u0000 </mrow>\u0000 <annotation> ${ &gt;} $</annotation>\u0000 </semantics></math>1,000 K, the temperature anomaly of plumes believed to rise from that TBL is only up to a few hundred Kelvins. Reasons for that discrepancy are still poorly understood and a number of causes have been proposed. Here, we use the ASPECT software to model plumes from the lowermost mantle and study their excess temperatures. We use a mantle viscosity that depends on temperature and depth with a strong viscosity increase from below the lithosphere toward the lower mantle, reaching about <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>1</mn>\u0000 <msup>\u0000 <mn>0</mn>\u0000 <mn>23</mn>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> $1{0}^{23}$</annotation>\u0000 </semantics></math> Pas above the basal TBL, consistent with geoid modeling and slow motion of mantle plumes. With a mineral physics-derived pyrolite material model, the difference between a plume adiabat and an ambient mantle adiabat just below the lithosphere is about two thirds of that at the base of the mantle, for example, 1,280 versus 835 K. 3D models of isolated plumes become nearly steady-state <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mo>&gt;</mo>\u0000 </mrow>\u0000 <annotation> ${ &gt;} $</annotation>\u0000 </semantics></math>10–20 Myr after the plume head has reached the surface, with excess temperature drop compared to an adiabat for material directly from the core-mantle boundary (CMB) usually less than 100 K. In the Earth, plumes are likely triggered by slabs and probably rise preferably above the margins of chemically distinct piles. This could lead to reduced excess temperatures, if plumes are more sheet-like, similar to 2D models, or temperature at their source depth is less than at the CMB. Excess temperatures are further reduced when averaged over the plume conduit or melting region.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB030111","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143784280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Revisiting the Relationship Between Induced Polarization and Surface Conductivity: Ratios From Laboratory to Field","authors":"Youzheng Qi,&nbsp;Yuxin Wu","doi":"10.1029/2024JB030406","DOIUrl":"https://doi.org/10.1029/2024JB030406","url":null,"abstract":"<p>Among the subsurface geophysical methods used in the critical zone investigations, induced polarization (IP) shows great vitality thanks to its unique ability to assess porosity via bulk conduction and estimate permeability through surface conduction and/or polarization. However, such an advantageous separation between bulk and surface is mostly implemented by multi-salinity experiments in the laboratory, which is incredibly difficult to realize in the field. One promising approach to address such an obstinate issue is to gauge the surface conductivity (<i>σ</i>_s) from the quadrature conductivity (<i>σ</i>″) or normalized chargeability (<i>M</i>_n) with the ratios between (<i>l</i> = <i>σ</i>″/<i>σ</i>_s, <i>l</i>_mn = <i>M</i>_n/<i>σ</i>_s). While these ratios are known not to be universal, the underlying principles are not fully understood and relevant theoretical studies are rare, which makes quantitative IP applications difficult. Here we scrutinize the conduction and polarization mechanisms of geomaterials and pinpoint that the two ratios are inherently functions of salinities and frequencies rather than only determined by the properties of the electrical double layer (EDL), hence representative samples from the investigated field must be calibrated in the laboratory and a characteristic frequency should be chosen for their usage. Besides the macro-scale ratios <i>l</i> and <i>l</i>_mn, we define two micro-scale ratios <i>χ</i> and <i>χ</i>_mn directly from the EDL, such that the new ratios exclude the effect of salinity and frequency and offer the opportunity to characterize and monitor changes of the EDL. Our study demonstrates that the existing macro-scale ratios converge toward the values of novel micro-scale ratios at high water salinity.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB030406","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143778239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatiotemporal Patterns of Subsidence and Sea Level Rise in the Samoan Islands 15 Years After the 2009 Samoa-Tonga Earthquake","authors":"Stacey A. Huang,&nbsp;Jeanne M. Sauber,&nbsp;Shin-Chan Han,&nbsp;Richard Ray,&nbsp;Eric Fielding","doi":"10.1029/2024JB029765","DOIUrl":"https://doi.org/10.1029/2024JB029765","url":null,"abstract":"<p>Fifteen years after the 2009 Samoa-Tonga earthquake, rates of subsidence on the Samoan Islands remain elevated compared with pre-earthquake levels. Coastal flooding has become a regular occurrence, increasing coastal erosion, risk of saltwater intrusion in freshwater aquifers, and threats to critical infrastructure. There is an urgent need to characterize ongoing trends in local and regional subsidence and constrain future behavior to inform the development of effective coastal resilience measures. Here, we have leveraged a multi-sensor, multi-frequency remote sensing suite to track changes in subsidence rates on the islands of Upolu (Samoa) and Tutuila (American Samoa). Our updated GPS/GNSS and tide gauge/altimetry records elucidate subsidence relaxation trends since the earthquake, and our analysis of high-resolution InSAR data from the Sentinel-1 mission—overcoming difficulties presented by vegetated terrain and small landmass sizes—reveal an unprecedented view of local subsidence in the Samoan Islands. These local signals need to be accounted for in coastal planning, including for the development of updated flooding thresholds that are relevant to the Samoan Islands and that account for spatial heterogeneities in subsidence. Overall, we find that subsidence on Upolu has nearly returned to pre-earthquake levels; meanwhile, subsidence on Tutuila will likely continue for a few more decades but ease more quickly than previously predicted. Both of these trends should alleviate previously anticipated pressures associated with high subsidence coupled with sea level rise.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB029765","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143778152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Predicting Elastic Moduli of Heterogeneous Porous Media by Percolation Theory and Effective-Medium Approximation","authors":"Nelsy Osorio,&nbsp;Muhammad Sahimi,&nbsp;Reza Barati,&nbsp;Behzad Ghanbarian","doi":"10.1029/2024JB030836","DOIUrl":"https://doi.org/10.1029/2024JB030836","url":null,"abstract":"<p>Predicting geomechanical properties of rock and other types of porous media is essential to accurate modeling of many important processes, such as wave propagations, seismic events, and underground gas storage, and CO₂ sequestration, all of which involve deformation of the pore space. We propose a model to predict the porosity dependence of the Young's and bulk moduli in heterogeneous porous media by combining the universal power law, predicted by percolation theory that describes the behavior of elastic moduli near the percolation threshold of the solid skeletons, and the effective-medium approximation (EMA) for elastic materials that is accurate away from the threshold. The parameters of the model have unambiguous physical meanings, and can, in principle, be measured. We estimate the parameters - the percolation threshold <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>p</mi>\u0000 <mi>c</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${p}_{c}$</annotation>\u0000 </semantics></math>, crossover point <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>p</mi>\u0000 <mi>x</mi>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${p}_{x}$</annotation>\u0000 </semantics></math> between the EMA and percolation power law, the average particle coordination number <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>Z</mi>\u0000 </mrow>\u0000 <annotation> $Z$</annotation>\u0000 </semantics></math>, and the elastic moduli of the solid skeleton by using experimental data or numerical simulations for a wide variety of porous media in both two and three dimensions. Whenever data are available, the predictions are consistent with them. We then predict the elastic moduli for another 10 porous media using the proposed model and the estimated parameters without adjusting any new parameter. The predictions are in most cases in agreement with the data, hence indicating the accuracy of the approach.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":"130 4","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143770236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}