Pub Date : 2025-10-08DOI: 10.1016/j.pepi.2025.107458
Jinfeng Li , Yufeng Lin , Keke Zhang
The dynamics of Earth’s liquid outer core are essential for understanding geomagnetic field variations. Conventional kinematic inversion methods are typically limited to recovering flow structures near the core–mantle boundary. In contrast, dynamic inversion approaches such as geomagnetic data assimilation have the potential to retrieve flow structures at greater depths. However, the practical application of dynamic inversion remains challenging due to observational limitations and computational constraints. In this study, we propose an inversion method that lies between the kinematic and dynamic approaches. It is based on the full vector form of the magnetic induction equation under the frozen flux assumption combined with an inertial mode representation of the flow. This method leverages the expected rotation-dominated core flows together with observational constraints, enabling the recovery of both core-surface flows and some deeper flow structures. The inversion process is realized through physics-informed neural networks. Synthetic dynamo simulations demonstrate that our inversion framework is able to capture large-scale 3-D core flow patterns. Moreover, by utilizing high-precision magnetic data from the Swarm constellation and the Macau Science Satellite-1, we reconstruct a 3-D core flow model within Earth’s outer core over the past decade. Our 3-D core flow model reveals a dominant planetary gyre in the Atlantic hemisphere and pronounced shear-induced helical flow structures in the Pacific hemisphere, characterized by significant downwelling beneath Latin America and upwelling beneath the Indian Ocean.
{"title":"Reconstruction of 3-D core flows using magnetic data from Swarm and MSS-1","authors":"Jinfeng Li , Yufeng Lin , Keke Zhang","doi":"10.1016/j.pepi.2025.107458","DOIUrl":"10.1016/j.pepi.2025.107458","url":null,"abstract":"<div><div>The dynamics of Earth’s liquid outer core are essential for understanding geomagnetic field variations. Conventional kinematic inversion methods are typically limited to recovering flow structures near the core–mantle boundary. In contrast, dynamic inversion approaches such as geomagnetic data assimilation have the potential to retrieve flow structures at greater depths. However, the practical application of dynamic inversion remains challenging due to observational limitations and computational constraints. In this study, we propose an inversion method that lies between the kinematic and dynamic approaches. It is based on the full vector form of the magnetic induction equation under the frozen flux assumption combined with an inertial mode representation of the flow. This method leverages the expected rotation-dominated core flows together with observational constraints, enabling the recovery of both core-surface flows and some deeper flow structures. The inversion process is realized through physics-informed neural networks. Synthetic dynamo simulations demonstrate that our inversion framework is able to capture large-scale 3-D core flow patterns. Moreover, by utilizing high-precision magnetic data from the Swarm constellation and the Macau Science Satellite-1, we reconstruct a 3-D core flow model within Earth’s outer core over the past decade. Our 3-D core flow model reveals a dominant planetary gyre in the Atlantic hemisphere and pronounced shear-induced helical flow structures in the Pacific hemisphere, characterized by significant downwelling beneath Latin America and upwelling beneath the Indian Ocean.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107458"},"PeriodicalIF":1.9,"publicationDate":"2025-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145320409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-03DOI: 10.1016/j.pepi.2025.107457
Mohammad Filbandi Kashkouli , Matthew J. Comeau , Abolghasem Kamkar-Rouhani , Alireza Arab-Amiri
Salt diapirs are prominent geological features, formed by the piercing of buoyant salt within overlying strata, with implications for basin evolution, tectonic deformation, and resource accumulation. In this study, we investigate the Shurab salt diapirs in northwestern Central Iran—an area with five known near-surface diapirs—whose subsurface geometries and interconnections at depth remain unclear due to the complex structural settings. To address these challenges, we generated a 3D electrical resistivity model from an array of 183 magnetotelluric (MT) measurements. Phase tensor and resistivity phase tensor analyses confirmed the presence of multidimensional conductivity structures. A range of modeling tests were performed to ensure a robust result, and final models were validated against seismic data and borehole logs, as well as previous 2D electric modeling. The resulting 3D resistivity model provides new insight into the geometry, depth, and interconnectedness of the salt diapirs and superior resolution of diapir flanks compared to seismic data. High resistivity zones at shallow depths correspond to dry salt, while lower resistivity at greater depths indicates brine-saturated regions. Notably, Diapirs No. 4 and 5 were found to be interconnected at depth, sharing a root zone and likely originating from a common evaporite layer. Tectonic analysis suggests that active fault systems—including the Sen-Sen, Ab-Shirin, and Dehnar faults—have played key roles in guiding salt migration and shaping diapir structures. This study highlights the effectiveness of using MT data to image complex salt structures and underscores the importance of integrated geophysical approaches in tectonically active regions.
{"title":"Improved characterization of the 3D structure of salt diapirs with electrical resistivity models","authors":"Mohammad Filbandi Kashkouli , Matthew J. Comeau , Abolghasem Kamkar-Rouhani , Alireza Arab-Amiri","doi":"10.1016/j.pepi.2025.107457","DOIUrl":"10.1016/j.pepi.2025.107457","url":null,"abstract":"<div><div>Salt diapirs are prominent geological features, formed by the piercing of buoyant salt within overlying strata, with implications for basin evolution, tectonic deformation, and resource accumulation. In this study, we investigate the Shurab salt diapirs in northwestern Central Iran—an area with five known near-surface diapirs—whose subsurface geometries and interconnections at depth remain unclear due to the complex structural settings. To address these challenges, we generated a 3D electrical resistivity model from an array of 183 magnetotelluric (MT) measurements. Phase tensor and resistivity phase tensor analyses confirmed the presence of multidimensional conductivity structures. A range of modeling tests were performed to ensure a robust result, and final models were validated against seismic data and borehole logs, as well as previous 2D electric modeling. The resulting 3D resistivity model provides new insight into the geometry, depth, and interconnectedness of the salt diapirs and superior resolution of diapir flanks compared to seismic data. High resistivity zones at shallow depths correspond to dry salt, while lower resistivity at greater depths indicates brine-saturated regions. Notably, Diapirs No. 4 and 5 were found to be interconnected at depth, sharing a root zone and likely originating from a common evaporite layer. Tectonic analysis suggests that active fault systems—including the Sen-Sen, Ab-Shirin, and Dehnar faults—have played key roles in guiding salt migration and shaping diapir structures. This study highlights the effectiveness of using MT data to image complex salt structures and underscores the importance of integrated geophysical approaches in tectonically active regions.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107457"},"PeriodicalIF":1.9,"publicationDate":"2025-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145320564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-24DOI: 10.1016/j.pepi.2025.107456
Ming Gong , Michael I. Bergman
Seismic attenuation can be intrinsic or due to scattering. The relative role of each for Earth's inner core is uncertain. Whereas intrinsic attenuation depends primarily on the material, temperature, and pressure, scattering is primarily a function of microstructure, that is, grain size, shape, texture, as well as single-crystal elastic anisotropy. Here we studied experimentally scattering of ultrasonic compressional waves in a hexagonal close-packed (hcp) Zn-rich Sn alloy, for two microstructures that are likely relevant to the inner core: textured, large columnar dendritic crystals typical of directional solidification, and untextured, equiaxed, ‘fine-grained’ crystals that can result from diffusion creep. We also studied the wavelength/grain size dependence of scattering for these two microstructures. We used a Zn-rich Sn alloy not because we expect it to have intrinsic attenuation similar to Fe under inner core conditions, but because its hcp crystal structure is the likely phase of the Fe alloy in the inner core, making it suitable for understanding the role of microstructure on scattering in the inner core. For the purpose of scaling the experiments to the inner core, pressure and temperature affect scattering primarily through their effects on the elastic constants of Fe and inner core growth dynamics, both of which we account for.
We developed an algorithm using the pulse-echo technique to experimentally determine a scattering quality factor QZ. We set criteria to determine, and measured, the energy per cycle in the first echo T1, which is a measure of the transmitted energy, and the energy per cycle that is reflected before the first echo R1, which represents the scattered energy. In order to facilitate comparison with seismic quality factors we defined a scattering quality factor QZ= (R1+ T1)/R1. Scaling QZ from the laboratory experiments to the inner core depends on the magnitude of the single-crystal wave speed anisotropy, which is known for Zn, but uncertain for Fe under inner core conditions, so we scaled the experimental results for single-crystal Fe elastic anisotropy between 5 and 20 %.
As expected, we found a directionally solidified microstructure has a highly anisotropic QZ, showing almost no scattering in the growth direction, whereas in the transverse directions scattering attenuation in the inner core may be comparable to intrinsic attenuation. Taking into account the anisotropy factor for scattering in polycrystalline, anisotropic material, our results predict randomly oriented, equiaxed 10 km-sized grains in the inner core would exhibit more scattering attenuation that the total inferred seismic attenuation, ruling out such a microstr
{"title":"An experimental ultrasonic method to determine a scattering quality factor, with application to earth's inner core","authors":"Ming Gong , Michael I. Bergman","doi":"10.1016/j.pepi.2025.107456","DOIUrl":"10.1016/j.pepi.2025.107456","url":null,"abstract":"<div><div>Seismic attenuation can be intrinsic or due to scattering. The relative role of each for Earth's inner core is uncertain. Whereas intrinsic attenuation depends primarily on the material, temperature, and pressure, scattering is primarily a function of microstructure, that is, grain size, shape, texture, as well as single-crystal elastic anisotropy. Here we studied experimentally scattering of ultrasonic compressional waves in a hexagonal close-packed (hcp) Zn-rich Sn alloy, for two microstructures that are likely relevant to the inner core: textured, large columnar dendritic crystals typical of directional solidification, and untextured, equiaxed, ‘fine-grained’ crystals that can result from diffusion creep. We also studied the wavelength/grain size dependence of scattering for these two microstructures. We used a Zn-rich Sn alloy not because we expect it to have intrinsic attenuation similar to Fe under inner core conditions, but because its hcp crystal structure is the likely phase of the Fe alloy in the inner core, making it suitable for understanding the role of microstructure on scattering in the inner core. For the purpose of scaling the experiments to the inner core, pressure and temperature affect scattering primarily through their effects on the elastic constants of Fe and inner core growth dynamics, both of which we account for.</div><div>We developed an algorithm using the pulse-echo technique to experimentally determine a scattering quality factor <em>Q</em><sub><em>Z</em></sub>. We set criteria to determine, and measured, the energy per cycle in the first echo <em>T</em><sub><em>1</em></sub>, which is a measure of the transmitted energy, and the energy per cycle that is reflected before the first echo <em>R</em><sub><em>1</em></sub>, which represents the scattered energy. In order to facilitate comparison with seismic quality factors we defined a scattering quality factor <em>Q</em><sub><em>Z</em></sub> <em>= (R</em><sub><em>1</em></sub> <em>+ T</em><sub><em>1</em></sub><em>)/R</em><sub><em>1</em></sub>. Scaling <em>Q</em><sub><em>Z</em></sub> from the laboratory experiments to the inner core depends on the magnitude of the single-crystal wave speed anisotropy, which is known for Zn, but uncertain for Fe under inner core conditions, so we scaled the experimental results for single-crystal Fe elastic anisotropy between 5 and 20 %.</div><div>As expected, we found a directionally solidified microstructure has a highly anisotropic <em>Q</em><sub><em>Z</em></sub>, showing almost no scattering in the growth direction, whereas in the transverse directions scattering attenuation in the inner core may be comparable to intrinsic attenuation. Taking into account the anisotropy factor for scattering in polycrystalline, anisotropic material, our results predict randomly oriented, equiaxed 10 km-sized grains in the inner core would exhibit more scattering attenuation that the total inferred seismic attenuation, ruling out such a microstr","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107456"},"PeriodicalIF":1.9,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145221139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-22DOI: 10.1016/j.pepi.2025.107453
C. Beghein , J. Li
The largest seismic event ever detected on Mars occurred on May 4, 2022, likely situated just north of the hemispherical dichotomy, east of the landing site, and south of Cerberus Fossae. This event was unique in that it generated both Love and Rayleigh waves, including fundamental and higher modes, providing us with a rare opportunity to determine whether seismic radial anisotropy is present on Mars. We performed non-linear waveform modeling and used a Niching Genetic Algorithm to find acceptable velocity models. Our analysis revealed that seismic anisotropy is necessary in the top 40 km, with the fast direction for seismic wave propagation being horizontal, similar to previous results solely based on fundamental mode surface wave group velocity dispersion. Our new models display layering with varying degrees of anisotropy. We found anisotropic parameter ξ = 1.0-1.2 between 5 and 20 km depth and ξ = 1.2-1.3 at 25–30 km depth. No significant anisotropy was detected below 35 km. While the origin of the anisotropy is still being debated, it is characteristic of a medium with a vertical symmetry axis and could result from both magmatic events and impacts. We propose that the anisotropy layering reflects different stages in the formation history of the Martian crust.
{"title":"Seismic anisotropy layering in the Martian lowlands crust","authors":"C. Beghein , J. Li","doi":"10.1016/j.pepi.2025.107453","DOIUrl":"10.1016/j.pepi.2025.107453","url":null,"abstract":"<div><div>The largest seismic event ever detected on Mars occurred on May 4, 2022, likely situated just north of the hemispherical dichotomy, east of the landing site, and south of Cerberus Fossae. This event was unique in that it generated both Love and Rayleigh waves, including fundamental and higher modes, providing us with a rare opportunity to determine whether seismic radial anisotropy is present on Mars. We performed non-linear waveform modeling and used a Niching Genetic Algorithm to find acceptable velocity models. Our analysis revealed that seismic anisotropy is necessary in the top 40 km, with the fast direction for seismic wave propagation being horizontal, similar to previous results solely based on fundamental mode surface wave group velocity dispersion. Our new models display layering with varying degrees of anisotropy. We found anisotropic parameter <em>ξ</em> = 1.0-1.2 between 5 and 20 km depth and <em>ξ</em> = 1.2-1.3 at 25–30 km depth. No significant anisotropy was detected below 35 km. While the origin of the anisotropy is still being debated, it is characteristic of a medium with a vertical symmetry axis and could result from both magmatic events and impacts. We propose that the anisotropy layering reflects different stages in the formation history of the Martian crust.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107453"},"PeriodicalIF":1.9,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145158427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The solid cores of moderate-sized terrestrial planets are hypothesized to comprise face-centered cubic (fcc) FeSi alloys, making it essential to understand the elastic properties of these materials under extreme conditions (high temperatures and pressures) for constraining planetary core compositions. However, there are few studies on the elastic properties of fcc-Fe–Si alloys. We report comprehensive measurements of longitudinal elastic wave velocities (VP) and densities (ρ) for fcc-Fe and fcc-Fe–5Si (5 wt% Si) alloys at pressures up to 15 GPa and temperatures to 1700 K, utilizing simultaneous in situ ultrasonic measurements, X-ray radiography, and X-ray diffraction techniques. Our findings reveal that the VP difference between pure Fe and Fe5Si was minimal at 6–8 GPa but diverged significantly at 12–14 GPa, demonstrating that Si incorporation increases the pressure dependence of VP. Linear regression of VP–ρ relationships yielded distinct equations for fcc-Fe (VP [m/s] = 1.35(16) × ρ [kg/m3] − 5.3(14) × 103) and fcc-Fe–5Si (VP [m/s] = 2.09(17) × ρ [kg/m3] − 10.6(13) × 103). Critically, although the VP of the fcc-Fe–5Si alloy closely matched Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport mission predictions for the Martian inner core, its density exceeded observational constraints by 800–1000 kg/m3. This discrepancy suggests the presence of additional light elements—potentially H—that could reduce density without substantially modifying elastic wave velocities, providing a novel constraint on Martian core composition.
{"title":"Elastic wave velocity and density of fcc-Fe and fcc-Fe–Si alloys at high pressures and temperatures","authors":"Masaya Kumagai , Tatsuya Sakamaki , Osamu Ikeda , Sho Kakizawa , Noriyoshi Tsujino , Yuji Higo , Akio Suzuki","doi":"10.1016/j.pepi.2025.107455","DOIUrl":"10.1016/j.pepi.2025.107455","url":null,"abstract":"<div><div>The solid cores of moderate-sized terrestrial planets are hypothesized to comprise face-centered cubic (<em>fcc</em>) Fe<img>Si alloys, making it essential to understand the elastic properties of these materials under extreme conditions (high temperatures and pressures) for constraining planetary core compositions. However, there are few studies on the elastic properties of <em>fcc</em>-Fe–Si alloys. We report comprehensive measurements of longitudinal elastic wave velocities (<em>V</em><sub>P</sub>) and densities (<em>ρ</em>) for <em>fcc</em>-Fe and <em>fcc</em>-Fe–5Si (5 wt% Si) alloys at pressures up to 15 GPa and temperatures to 1700 K, utilizing simultaneous in situ ultrasonic measurements, X-ray radiography, and X-ray diffraction techniques. Our findings reveal that the <em>V</em><sub>P</sub> difference between pure Fe and Fe<img>5Si was minimal at 6–8 GPa but diverged significantly at 12–14 GPa, demonstrating that Si incorporation increases the pressure dependence of <em>V</em><sub>P</sub>. Linear regression of <em>V</em><sub>P</sub>–<em>ρ</em> relationships yielded distinct equations for <em>fcc</em>-Fe (<em>V</em><sub>P</sub> [m/s] = 1.35(16) × <em>ρ</em> [kg/m<sup>3</sup>] − 5.3(14) × 10<sup>3</sup>) and <em>fcc</em>-Fe–5Si (<em>V</em><sub>P</sub> [m/s] = 2.09(17) × <em>ρ</em> [kg/m<sup>3</sup>] − 10.6(13) × 10<sup>3</sup>). Critically, although the <em>V</em><sub>P</sub> of the <em>fcc</em>-Fe–5Si alloy closely matched Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport mission predictions for the Martian inner core, its density exceeded observational constraints by 800–1000 kg/m<sup>3</sup>. This discrepancy suggests the presence of additional light elements—potentially H—that could reduce density without substantially modifying elastic wave velocities, providing a novel constraint on Martian core composition.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107455"},"PeriodicalIF":1.9,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145158428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hugoniot data for nickel (Ni) were extended to 305 GPa through plate-impact experiments using a two-stage light gas gun. Combining our results with previously published data, we determined the shock velocity (Us)–particle velocity (Up) Hugoniot relation for Ni to be: . The thermodynamic parameters of Ni were derived through a joint analysis of the Hugoniot and static compression data, allowing us to extend the equation of state (EOS) to conditions relevant to Earth's inner core. Additionally, we reanalyzed the EOS of iron based on a recently published static compression data. Our study suggests that the density of pure iron is 0.59 (20) g/cm3 higher than that of the inner core. Moreover, adding 10 wt% Ni to iron increases this density deficit by approximately 0.10 g/cm3.
{"title":"Hugoniot equation of state of nickel up to 300 GPa: Implication on the density deficit of earth's solid inner core","authors":"Qing Zhang, Xun Liu, Yishi Wang, Yu Hu, Zehui Li, Haijun Huang","doi":"10.1016/j.pepi.2025.107454","DOIUrl":"10.1016/j.pepi.2025.107454","url":null,"abstract":"<div><div>Hugoniot data for nickel (Ni) were extended to 305 GPa through plate-impact experiments using a two-stage light gas gun. Combining our results with previously published data, we determined the shock velocity (<em>Us</em>)–particle velocity (<em>Up</em>) Hugoniot relation for Ni to be: <span><math><msub><mi>U</mi><mi>s</mi></msub><mo>=</mo><mn>4.653</mn><mfenced><mn>62</mn></mfenced><mo>+</mo><mn>1.420</mn><mfenced><mn>23</mn></mfenced><msub><mi>U</mi><mi>p</mi></msub></math></span>. The thermodynamic parameters of Ni were derived through a joint analysis of the Hugoniot and static compression data, allowing us to extend the equation of state (EOS) to conditions relevant to Earth's inner core. Additionally, we reanalyzed the EOS of iron based on a recently published static compression data. Our study suggests that the density of pure iron is 0.59 (20) g/cm<sup>3</sup> higher than that of the inner core. Moreover, adding 10 wt% Ni to iron increases this density deficit by approximately 0.10 g/cm<sup>3</sup>.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107454"},"PeriodicalIF":1.9,"publicationDate":"2025-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-20DOI: 10.1016/j.pepi.2025.107439
Sunil K. Roy, M. Ravi Kumar
This study comprehensively examines the shear wave splitting measurements of XKS (SKS and PKS) - SKKS pairs on the same seismograms recorded at 357 broadband stations spanning India, to characterize anisotropy in the lowermost mantle. This resulted in the identification of 104 XKS-SKKS pairs at 62 stations, of which 27 pairs were found to be discrepant, based on the difference in splitting intensity of XKS and the corresponding SKKS phases. These discrepant pairs dominantly sample a portion of the lowermost mantle beneath Southeast Asia and the Indian Ocean. The majority of these pairs represent null-split and split-split cases, with the delay time of SKKS being larger than that of XKS for the latter. This suggests that the XKS phases primarily sample the isotropic (weakly anisotropic) or anisotropic regions with a cancelling effect in the lowermost mantle, while the corresponding SKKS phases sample the anisotropic region of the D layer. In addition, there are three discrepant pairs in the split-null category, suggesting anisotropy in the vicinity of southern Tibet, where discrepant pairs from other cases are not observed. This implies an apparent change in the anisotropy of the D layer for the regions sampled by XKS and SKKS, although they are associated with high-velocity anomalies. In these regions, the fast polarization azimuths of the discrepant pairs are in the NE-SW and ENE-WSW, and NNE-SSW directions, respectively. These do not coincide with the trend of mantle flow in the lowermost mantle, suggesting an association with paleo-subducted slabs. The observed deformation is probably due to phase transformation of bridgmanite to a more stable post-perovskite, causing Crystallographic Preferred Orientation of the lowermost mantle, which is the candidate mechanism for lowermost mantle anisotropy beneath Southeast Asia and the Indian Ocean.
{"title":"Evidence for lowermost mantle anisotropy from discrepant splitting intensity of XKS and SKKS phases recorded in India","authors":"Sunil K. Roy, M. Ravi Kumar","doi":"10.1016/j.pepi.2025.107439","DOIUrl":"10.1016/j.pepi.2025.107439","url":null,"abstract":"<div><div>This study comprehensively examines the shear wave splitting measurements of XKS (SKS and PKS) - SKKS pairs on the same seismograms recorded at 357 broadband stations spanning India, to characterize anisotropy in the lowermost mantle. This resulted in the identification of 104 XKS-SKKS pairs at 62 stations, of which 27 pairs were found to be discrepant, based on the difference in splitting intensity of XKS and the corresponding SKKS phases. These discrepant pairs dominantly sample a portion of the lowermost mantle beneath Southeast Asia and the Indian Ocean. The majority of these pairs represent null-split and split-split cases, with the delay time of SKKS being larger than that of XKS for the latter. This suggests that the XKS phases primarily sample the isotropic (weakly anisotropic) or anisotropic regions with a cancelling effect in the lowermost mantle, while the corresponding SKKS phases sample the anisotropic region of the D<span><math><msup><mrow></mrow><mrow><mo>″</mo></mrow></msup></math></span> layer. In addition, there are three discrepant pairs in the split-null category, suggesting anisotropy in the vicinity of southern Tibet, where discrepant pairs from other cases are not observed. This implies an apparent change in the anisotropy of the D<span><math><msup><mrow></mrow><mrow><mo>″</mo></mrow></msup></math></span> layer for the regions sampled by XKS and SKKS, although they are associated with high-velocity anomalies. In these regions, the fast polarization azimuths of the discrepant pairs are in the NE-SW and ENE-WSW, and NNE-SSW directions, respectively. These do not coincide with the trend of mantle flow in the lowermost mantle, suggesting an association with paleo-subducted slabs. The observed deformation is probably due to phase transformation of bridgmanite to a more stable post-perovskite, causing Crystallographic Preferred Orientation of the lowermost mantle, which is the candidate mechanism for lowermost mantle anisotropy beneath Southeast Asia and the Indian Ocean.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107439"},"PeriodicalIF":1.9,"publicationDate":"2025-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120915","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-19DOI: 10.1016/j.pepi.2025.107452
Prachi Kar, Mingming Li
Large low-velocity provinces (LLVPs) in Earth's lowermost mantle, characterized by a significant reduction of seismic wave velocities, are among the largest structures in Earth's deep mantle, and their long-term stability plays a crucial role in Earth's thermal and chemical evolution. The stability of LLVPs is greatly controlled by their density anomaly with respect to the background mantle. Although the density anomaly of the LLVPs remains a matter of debate, previous studies suggested that they may have a denser basal layer. In this study, we perform geodynamic simulations to investigate how this basal dense layer affects the long-term stability of LLVPs. We find that in models where LLVP-like thermochemical piles are relatively light and rapidly mix into the background mantle, the presence of a thin, intrinsically denser basal layer can help these piles to survive at the core-mantle boundary (CMB) over timescales comparable to Earth's history. Our results suggest that LLVPs do not need to be denser than the surrounding mantle at all depths to maintain long-term stability. Instead, their density can be stratified, increasing toward the CMB, with a basal dense layer.
{"title":"Long-term survival of large low velocity provinces (LLVPs) due to internal layering","authors":"Prachi Kar, Mingming Li","doi":"10.1016/j.pepi.2025.107452","DOIUrl":"10.1016/j.pepi.2025.107452","url":null,"abstract":"<div><div>Large low-velocity provinces (LLVPs) in Earth's lowermost mantle, characterized by a significant reduction of seismic wave velocities, are among the largest structures in Earth's deep mantle, and their long-term stability plays a crucial role in Earth's thermal and chemical evolution. The stability of LLVPs is greatly controlled by their density anomaly with respect to the background mantle. Although the density anomaly of the LLVPs remains a matter of debate, previous studies suggested that they may have a denser basal layer. In this study, we perform geodynamic simulations to investigate how this basal dense layer affects the long-term stability of LLVPs. We find that in models where LLVP-like thermochemical piles are relatively light and rapidly mix into the background mantle, the presence of a thin, intrinsically denser basal layer can help these piles to survive at the core-mantle boundary (CMB) over timescales comparable to Earth's history. Our results suggest that LLVPs do not need to be denser than the surrounding mantle at all depths to maintain long-term stability. Instead, their density can be stratified, increasing toward the CMB, with a basal dense layer.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107452"},"PeriodicalIF":1.9,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-18DOI: 10.1016/j.pepi.2025.107447
C.C. Finlay , C. Kloss , N. Gillet
The Swarm satellite trio has provided global vector magnetic field measurements, with high precision and absolute accuracy, for the past eleven years. Based on this consistent, high quality, dataset we describe here how Earth’s main (core-generated) magnetic field has evolved between 2014.0 and 2025.0.
At the Earth’s surface, we find that the region in the South Atlantic where the field strength is weakest (below 26,000 nT), has expanded by 0.9% of Earth’s surface area and that the minimum intensity has decreased by 336 nT from 22,430 nT to 22,094 nT. In the northern polar region, we find that in Canada the area of strong field (above 57,000 nT) has diminished, decreasing in size by 0.65% of Earth’s surface area and with the maximum field strength decreasing by 801 nT from 58,832 nT to 58,031 nT. In contrast the corresponding strong field region in Siberia has grown in size, increasing in area by 0.42% of Earth’s surface area, with the maximum field intensity increasing by 260 nT from 61,359 nT to 61,619 nT.
At the core-mantle boundary, reversed flux features under southern Africa have moved westward, converging towards reversed flux features that have moved eastwards under the mid-Atlantic. In the northern polar region a strong flux feature under the Bering strait has moved westwards along the inner-core tangent cylinder. At low latitudes, under Indonesia and the western Pacific, field features have surprisingly moved eastwards. Field accelerations, including oscillations, are found to be most intense at low latitudes.
The Swarm mission has for the past decade been an essential source of global information on the changes taking place in Earth’s main magnetic field. Due to the long timescales of the underlying core processes, extending the mission lifetime for as long as possible, in particular for the higher satellite Swarm Bravo, is expected to yield further scientific insights. A long mission for Swarm Bravo would be an efficient means of ensuring that the present era of high quality geomagnetic observations from space continues as new missions come online.
{"title":"Core field changes from eleven years of Swarm satellite observations","authors":"C.C. Finlay , C. Kloss , N. Gillet","doi":"10.1016/j.pepi.2025.107447","DOIUrl":"10.1016/j.pepi.2025.107447","url":null,"abstract":"<div><div>The <em>Swarm</em> satellite trio has provided global vector magnetic field measurements, with high precision and absolute accuracy, for the past eleven years. Based on this consistent, high quality, dataset we describe here how Earth’s main (core-generated) magnetic field has evolved between 2014.0 and 2025.0.</div><div>At the Earth’s surface, we find that the region in the South Atlantic where the field strength is weakest (below 26,000 nT), has expanded by 0.9% of Earth’s surface area and that the minimum intensity has decreased by 336 nT from 22,430 nT to 22,094 nT. In the northern polar region, we find that in Canada the area of strong field (above 57,000 nT) has diminished, decreasing in size by 0.65% of Earth’s surface area and with the maximum field strength decreasing by 801 nT from 58,832 nT to 58,031 nT. In contrast the corresponding strong field region in Siberia has grown in size, increasing in area by 0.42% of Earth’s surface area, with the maximum field intensity increasing by 260 nT from 61,359 nT to 61,619 nT.</div><div>At the core-mantle boundary, reversed flux features under southern Africa have moved westward, converging towards reversed flux features that have moved eastwards under the mid-Atlantic. In the northern polar region a strong flux feature under the Bering strait has moved westwards along the inner-core tangent cylinder. At low latitudes, under Indonesia and the western Pacific, field features have surprisingly moved eastwards. Field accelerations, including oscillations, are found to be most intense at low latitudes.</div><div>The <em>Swarm</em> mission has for the past decade been an essential source of global information on the changes taking place in Earth’s main magnetic field. Due to the long timescales of the underlying core processes, extending the mission lifetime for as long as possible, in particular for the higher satellite <em>Swarm</em> Bravo, is expected to yield further scientific insights. A long mission for <em>Swarm</em> Bravo would be an efficient means of ensuring that the present era of high quality geomagnetic observations from space continues as new missions come online.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107447"},"PeriodicalIF":1.9,"publicationDate":"2025-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145221140","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Subsurface oceans and brines beneath the thick icy crust of large icy satellites such as Europa, Ganymede, Callisto, and Titan are among the most promising targets for exploring potential habitability. The physical properties of these liquids, particularly viscosity, play a fundamental role in governing fluid dynamics, as well as material and heat transport occurring within high-pressure environments. Although magnesium sulfate (MgSO4) is likely one of the primary dissolved salts in these extra-terrestrial oceans, its viscosity under high-pressure conditions remains poorly understood. In this study, a falling-sphere viscometer was developed with a diamond anvil cell (DAC) to measure the viscosity of 10 wt% MgSO4 solutions at pressures up to 1100 MPa and temperatures ranging from 263 to 313 K. Our results showed that MgSO4 solutions exhibited viscosities more than 1.5 times as high as that of pure water at the same pressure and temperature conditions. At low temperature, the viscosity of MgSO4 solutions increased monotonically with pressure, whereas pure water exhibited a minimum viscosity at ∼200 MPa. This difference reflects the strong ionic effects on the disruption of water structure and construction of hydration shell by Mg2+ and SO42− ions. By extrapolating our findings to subsurface ocean conditions, we estimated that 10 wt% aqueous MgSO4 oceans/brines in icy satellites would have viscosities between 1 and 13 mPa·s at pressures below 700 MPa. This finding suggests that aqueous MgSO4 fluids potentially present in icy satellites can exhibit higher viscosities compared with pure water, whose viscosities are typically limited to the narrow range of 1–2 mPa·s.
{"title":"Viscosity measurements of aqueous magnesium sulfate solutions under high pressure: Implications for subsurface fluids in large icy satellites","authors":"Shunsuke Nozaki , Seiji Kamada , Shin Ozawa , Akio Suzuki","doi":"10.1016/j.pepi.2025.107450","DOIUrl":"10.1016/j.pepi.2025.107450","url":null,"abstract":"<div><div>Subsurface oceans and brines beneath the thick icy crust of large icy satellites such as Europa, Ganymede, Callisto, and Titan are among the most promising targets for exploring potential habitability. The physical properties of these liquids, particularly viscosity, play a fundamental role in governing fluid dynamics, as well as material and heat transport occurring within high-pressure environments. Although magnesium sulfate (MgSO<sub>4</sub>) is likely one of the primary dissolved salts in these extra-terrestrial oceans, its viscosity under high-pressure conditions remains poorly understood. In this study, a falling-sphere viscometer was developed with a diamond anvil cell (DAC) to measure the viscosity of 10 wt% MgSO<sub>4</sub> solutions at pressures up to 1100 MPa and temperatures ranging from 263 to 313 K. Our results showed that MgSO<sub>4</sub> solutions exhibited viscosities more than 1.5 times as high as that of pure water at the same pressure and temperature conditions. At low temperature, the viscosity of MgSO<sub>4</sub> solutions increased monotonically with pressure, whereas pure water exhibited a minimum viscosity at ∼200 MPa. This difference reflects the strong ionic effects on the disruption of water structure and construction of hydration shell by Mg<sup>2+</sup> and SO<sub>4</sub><sup>2−</sup> ions. By extrapolating our findings to subsurface ocean conditions, we estimated that 10 wt% aqueous MgSO<sub>4</sub> oceans/brines in icy satellites would have viscosities between 1 and 13 mPa·s at pressures below 700 MPa. This finding suggests that aqueous MgSO<sub>4</sub> fluids potentially present in icy satellites can exhibit higher viscosities compared with pure water, whose viscosities are typically limited to the narrow range of 1–2 mPa·s.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"368 ","pages":"Article 107450"},"PeriodicalIF":1.9,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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