Physics of the Earth and Planetary Interiors最新文献

Lithospheric structure beneath the Upper Indus Basin and its adjacent regions from inversion of surface wave dispersion

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-27 DOI: 10.1016/j.pepi.2025.107345

Deepak Kumar , G. Suresh , M.L. Sharma , Siddharth Dey , S.C. Gupta

We propose an enhanced model of the crust and upper mantle structure beneath the Upper Indus Basin, derived from the combined inversion of Rayleigh and Love wave group velocity dispersion data from 164 seismic events recorded by 58 stations, covering periods from 4 to 100 s. By using the Genetic Algorithm approach within this joint inversion process, we developed a detailed shear wave velocity model for the region. The earthquakes were categorized into three clusters based on their epicentral locations, allowing for a detailed analysis beneath the western, central, and eastern segments of the Upper Indus Basin. The analysis shows a gradual increase in crustal thickness from the west to the east, with an average thickness of ∼61.8 km and a shear wave velocity ∼ 4.6 km/s. The Lithosphere-Asthenosphere Boundary (LAB) is identified at a depth of 160 km, indicated by a velocity decrease of about 1.6 %. Our results also reveal a sedimentary cover of ∼4 km and we postulate a felsic crust similar to southern Pamir, which could have resulted from the loss of mafic lower crust by lithospheric delamination or foundering due to gravitational instability. We state the absence of mid-crustal low velocity layer within the Basin and also discard the possibility of any requirement for radial anisotropy, based on the adequate fit of Rayleigh and Love the dispersion data with minimal uncertainty. The study provides a significant refinement of the crustal and upper mantle structure of the Upper Indus Basin, contributing valuable insights into regional tectonics.

{"title":"Lithospheric structure beneath the Upper Indus Basin and its adjacent regions from inversion of surface wave dispersion","authors":"Deepak Kumar , G. Suresh , M.L. Sharma , Siddharth Dey , S.C. Gupta","doi":"10.1016/j.pepi.2025.107345","DOIUrl":"10.1016/j.pepi.2025.107345","url":null,"abstract":"<div><div>We propose an enhanced model of the crust and upper mantle structure beneath the Upper Indus Basin, derived from the combined inversion of Rayleigh and Love wave group velocity dispersion data from 164 seismic events recorded by 58 stations, covering periods from 4 to 100 s. By using the Genetic Algorithm approach within this joint inversion process, we developed a detailed shear wave velocity model for the region. The earthquakes were categorized into three clusters based on their epicentral locations, allowing for a detailed analysis beneath the western, central, and eastern segments of the Upper Indus Basin. The analysis shows a gradual increase in crustal thickness from the west to the east, with an average thickness of ∼61.8 km and a shear wave velocity ∼ 4.6 km/s. The Lithosphere-Asthenosphere Boundary (LAB) is identified at a depth of 160 km, indicated by a velocity decrease of about 1.6 %. Our results also reveal a sedimentary cover of ∼4 km and we postulate a felsic crust similar to southern Pamir, which could have resulted from the loss of mafic lower crust by lithospheric delamination or foundering due to gravitational instability. We state the absence of mid-crustal low velocity layer within the Basin and also discard the possibility of any requirement for radial anisotropy, based on the adequate fit of Rayleigh and Love the dispersion data with minimal uncertainty. The study provides a significant refinement of the crustal and upper mantle structure of the Upper Indus Basin, contributing valuable insights into regional tectonics.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"362 ","pages":"Article 107345"},"PeriodicalIF":2.4,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143725250","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}

引用次数: 0

Shared periodicities between the length of day and the geomagnetic field at millennial timescales

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-27 DOI: 10.1016/j.pepi.2025.107350

M. Puente-Borque , F.J. Pavón-Carrasco , S.A. Campuzano , A. González-López , M. Folgueira , M.L. Osete

The dynamics of Earth's outer core control the geomagnetic field and produce variations in the length of day (LOD). This phenomenon has been extensively studied at decadal and interannual scales but is still little known on the millennial timescale. Reconstructed variations in the length of day from ancient records of eclipses exhibit an oscillating component with a millennial period that cannot be explained by tidal effects, glacial isostatic adjustment or the ocean and atmospheric dynamics. In this work, frequency analysis and correlation techniques have been applied to LOD variations and to the dipole and quadrupole geomagnetic field provided by paleomagnetic reconstructions. We found that the non-tidal fluctuations of the LOD are correlated with the paleosecular variation of the Earth's magnetic field over the last three millennia. In particular, LOD maxima occur when the eccentric dipole shifts towards the Pacific region and the geocentric dipole becomes more axial, and LOD minima correspond to a more centred eccentric dipole and a more tilted geocentric dipole towards Atlantic region. These results provide new information about the coupling between the Earth's rotation and the paleosecular variation of the geomagnetic field on millennial time scales.

{"title":"Shared periodicities between the length of day and the geomagnetic field at millennial timescales","authors":"M. Puente-Borque , F.J. Pavón-Carrasco , S.A. Campuzano , A. González-López , M. Folgueira , M.L. Osete","doi":"10.1016/j.pepi.2025.107350","DOIUrl":"10.1016/j.pepi.2025.107350","url":null,"abstract":"<div><div>The dynamics of Earth's outer core control the geomagnetic field and produce variations in the length of day (LOD). This phenomenon has been extensively studied at decadal and interannual scales but is still little known on the millennial timescale. Reconstructed variations in the length of day from ancient records of eclipses exhibit an oscillating component with a millennial period that cannot be explained by tidal effects, glacial isostatic adjustment or the ocean and atmospheric dynamics. In this work, frequency analysis and correlation techniques have been applied to LOD variations and to the dipole and quadrupole geomagnetic field provided by paleomagnetic reconstructions. We found that the non-tidal fluctuations of the LOD are correlated with the paleosecular variation of the Earth's magnetic field over the last three millennia. In particular, LOD maxima occur when the eccentric dipole shifts towards the Pacific region and the geocentric dipole becomes more axial, and LOD minima correspond to a more centred eccentric dipole and a more tilted geocentric dipole towards Atlantic region. These results provide new information about the coupling between the Earth's rotation and the paleosecular variation of the geomagnetic field on millennial time scales.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"362 ","pages":"Article 107350"},"PeriodicalIF":2.4,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143768158","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}

引用次数: 0

Joint interpretation of potential field data using independent Lpq norm inversion and geological modeling: Application to Iron targeting in Central Iran

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-24 DOI: 10.1016/j.pepi.2025.107347

Bardiya Sadraeifar , Reza Ghanati , Mohammad Hakim Rezayee , Maysam Abedi , Seyed Hossein Hosseini , Vahid E. Ardestani

Solving applied geophysical inverse problems using the

L_{pq}

norm (mixed

L_{p}

norm) is a well-established deterministic method, particularly in potential-field inversions. This approach minimizes the objective function by integrating

L_{p}

norms (

0 \leq p \leq 2

) for the smallness and smoothness terms in the regularization function, offering high flexibility in controlling the sparsity and smoothness of the recovered models. This study focuses on the computational aspects and parameters of the model structure term that significantly influence the generation of density and susceptibility models. We investigate how different combinations of

L_{p}

norms and scaling constants for the smallness and smoothness terms affect the recovery of various geometrical structures and the delineation of iron ore resources. The initial phase of our study involves testing these parameters using a synthetic model designed for gravity and magnetic susceptibility inversion, incorporating a complex dataset. Subsequently, we apply mixed

L_{p}

norm inversion with different norm combinations to ground-based potential field data from an iron ore deposit in the Bafq metallogenic belt, central Iran. This region is characterized by a reverse fault that has induced a north-south trend in hematite-magnetite mineralization. A key focus of this study is the impact of employing identical versus non-identical norms in the smoothness term of the model structure. By adjusting the level of compactness to match the target trend, we generate a geologically more interpretable model. Following the inversion, we assess the effectiveness of various combinations of

L_{p}

norm in delineating mineralized zones by comparing the inverted models to a lithological model obtained via co-kriging interpolation of borehole data. The results reveal significant hematite mineralization, with high-grade deposits predominantly located in the hanging wall of the fault and lower-grade deposits in the footwall. The magnetite mineralization, while less extensive, exhibits a spatial distribution similar to that of hematite, though it is typically shallower in comparison.

{"title":"Joint interpretation of potential field data using independent Lpq norm inversion and geological modeling: Application to Iron targeting in Central Iran","authors":"Bardiya Sadraeifar , Reza Ghanati , Mohammad Hakim Rezayee , Maysam Abedi , Seyed Hossein Hosseini , Vahid E. Ardestani","doi":"10.1016/j.pepi.2025.107347","DOIUrl":"10.1016/j.pepi.2025.107347","url":null,"abstract":"<div><div>Solving applied geophysical inverse problems using the <span><math><msub><mi>L</mi><mi>pq</mi></msub></math></span> norm (mixed <span><math><msub><mi>L</mi><mi>p</mi></msub></math></span>norm) is a well-established deterministic method, particularly in potential-field inversions. This approach minimizes the objective function by integrating <span><math><msub><mi>L</mi><mi>p</mi></msub></math></span> norms (<span><math><mn>0</mn><mo>≤</mo><mi>p</mi><mo>≤</mo><mn>2</mn></math></span>) for the smallness and smoothness terms in the regularization function, offering high flexibility in controlling the sparsity and smoothness of the recovered models. This study focuses on the computational aspects and parameters of the model structure term that significantly influence the generation of density and susceptibility models. We investigate how different combinations of <span><math><msub><mi>L</mi><mi>p</mi></msub></math></span> norms and scaling constants for the smallness and smoothness terms affect the recovery of various geometrical structures and the delineation of iron ore resources. The initial phase of our study involves testing these parameters using a synthetic model designed for gravity and magnetic susceptibility inversion, incorporating a complex dataset. Subsequently, we apply mixed <span><math><msub><mi>L</mi><mi>p</mi></msub></math></span> norm inversion with different norm combinations to ground-based potential field data from an iron ore deposit in the Bafq metallogenic belt, central Iran. This region is characterized by a reverse fault that has induced a north-south trend in hematite-magnetite mineralization. A key focus of this study is the impact of employing identical versus non-identical norms in the smoothness term of the model structure. By adjusting the level of compactness to match the target trend, we generate a geologically more interpretable model. Following the inversion, we assess the effectiveness of various combinations of <span><math><msub><mi>L</mi><mi>p</mi></msub></math></span> norm in delineating mineralized zones by comparing the inverted models to a lithological model obtained via co-kriging interpolation of borehole data. The results reveal significant hematite mineralization, with high-grade deposits predominantly located in the hanging wall of the fault and lower-grade deposits in the footwall. The magnetite mineralization, while less extensive, exhibits a spatial distribution similar to that of hematite, though it is typically shallower in comparison.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"362 ","pages":"Article 107347"},"PeriodicalIF":2.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143715064","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}

引用次数: 0

Strong compositional gradient in the Earth's inner core?

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-23 DOI: 10.1016/j.pepi.2025.107349

Hitoshi Gomi , Kei Hirose

Dynamic motions in the Earth's solid inner core driven by thermo-chemical buoyancy, such as plume convection and translation, have been proposed to explain seismic observations. The inner core should be chemically homogeneous if it is actively agitated. However, its high thermal conductivity may suppress such motions. Here we computed the equations of state for six hundred and ninety-three different Fe-Ni-Si-S-H alloys and compared their density (ρ) and bulk sound velocity (V_Φ) profiles with inner core seismic reference models. While such calculations were made at static conditions, we additionally calculated the Helmholtz energy by using the quasi-harmonic approximation to obtain the ρ and V_Φ of hexagonal close-packed (hcp) alloys under high temperatures relevant to the inner core. The results demonstrate that the changes in ρ of these hcp alloys along the inner core P-T profile are comparable to the radial ρ gradients shown by the PREM and AK135 models, but none of the Fe-Ni-Si-S-H alloys explain the gentle gradients in V_Φ of these reference models. Given that the PREM and AK135 models provide the correct V_Φ gradient, it suggests compositional stratification in the solid inner core, much stronger than can be developed upon crystallization from a homogeneous liquid outer core. The inner core might have crystallized from a chemically stratified liquid core (S-poor and H-rich toward the centre), which possibly formed as a result of liquid immiscibility between S-rich and H-rich liquids.

{"title":"Strong compositional gradient in the Earth's inner core?","authors":"Hitoshi Gomi , Kei Hirose","doi":"10.1016/j.pepi.2025.107349","DOIUrl":"10.1016/j.pepi.2025.107349","url":null,"abstract":"<div><div>Dynamic motions in the Earth's solid inner core driven by thermo-chemical buoyancy, such as plume convection and translation, have been proposed to explain seismic observations. The inner core should be chemically homogeneous if it is actively agitated. However, its high thermal conductivity may suppress such motions. Here we computed the equations of state for six hundred and ninety-three different Fe-Ni-Si-S-H alloys and compared their density (<em>ρ</em>) and bulk sound velocity (<em>V</em><sub>Φ</sub>) profiles with inner core seismic reference models. While such calculations were made at static conditions, we additionally calculated the Helmholtz energy by using the quasi-harmonic approximation to obtain the <em>ρ</em> and <em>V</em><sub>Φ</sub> of hexagonal close-packed (hcp) alloys under high temperatures relevant to the inner core. The results demonstrate that the changes in <em>ρ</em> of these hcp alloys along the inner core <em>P-T</em> profile are comparable to the radial <em>ρ</em> gradients shown by the PREM and AK135 models, but none of the Fe-Ni-Si-S-H alloys explain the gentle gradients in <em>V</em><sub>Φ</sub> of these reference models. Given that the PREM and AK135 models provide the correct <em>V</em><sub>Φ</sub> gradient, it suggests compositional stratification in the solid inner core, much stronger than can be developed upon crystallization from a homogeneous liquid outer core. The inner core might have crystallized from a chemically stratified liquid core (S-poor and H-rich toward the centre), which possibly formed as a result of liquid immiscibility between S-rich and H-rich liquids.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"362 ","pages":"Article 107349"},"PeriodicalIF":2.4,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143715058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Unraveling composite magnetic fabrics through tensor decomposition

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-22 DOI: 10.1016/j.pepi.2025.107346

David Finn , Josef Jezek , Stuart A. Gilder , Michael R. Wack , Felix Ostermeier , Michael Jackson , Robert S. Coe , Michael J. Branney

Magnetic anisotropy plays a central role in many petrofabric and paleomagnetic studies. Anisotropy is typically represented by a second-order symmetric tensor that reflects the combined contributions from mineral populations with differing grain sizes, orientation distributions and particle scale anisotropies. Thus, the quality of geologically significant information obtained from magnetic anisotropy data depends on our ability to disentangle the complexity of these coexisting fabrics. In this study, we present a least-squares technique that can be employed in combination with additional geological or other supporting evidence to separate measured anisotropy tensors into independent contributions with distinct physical meaning. The analysis is readily adaptable and widely applicable to interpreting composite hybrid magnetic anisotropies, like those which arise from tectonic forces.

Here, we revisit published deposition experiments and anisotropy of anhysteretic remanence (AARM) measurements to demonstrate the usefulness of the tensor decomposition approach. Remanence anisotropy measurements are decomposed into idealized tensorial sub-components originating from the preferred alignment of particles parallel to the magnetic field (field-aligned fabric) and within the bedding plane (sedimentary fabric). The least-squares decomposition isolates the field-aligned fabric by subtracting the sedimentary-compaction fabric. After subtraction of the sedimentary fabric, quantitative paleofield strength and direction can be directly inferred from the field-aligned subfabric.

{"title":"Unraveling composite magnetic fabrics through tensor decomposition","authors":"David Finn , Josef Jezek , Stuart A. Gilder , Michael R. Wack , Felix Ostermeier , Michael Jackson , Robert S. Coe , Michael J. Branney","doi":"10.1016/j.pepi.2025.107346","DOIUrl":"10.1016/j.pepi.2025.107346","url":null,"abstract":"<div><div>Magnetic anisotropy plays a central role in many petrofabric and paleomagnetic studies. Anisotropy is typically represented by a second-order symmetric tensor that reflects the combined contributions from mineral populations with differing grain sizes, orientation distributions and particle scale anisotropies. Thus, the quality of geologically significant information obtained from magnetic anisotropy data depends on our ability to disentangle the complexity of these coexisting fabrics. In this study, we present a least-squares technique that can be employed in combination with additional geological or other supporting evidence to separate measured anisotropy tensors into independent contributions with distinct physical meaning. The analysis is readily adaptable and widely applicable to interpreting composite hybrid magnetic anisotropies, like those which arise from tectonic forces.</div><div>Here, we revisit published deposition experiments and anisotropy of anhysteretic remanence (AARM) measurements to demonstrate the usefulness of the tensor decomposition approach. Remanence anisotropy measurements are decomposed into idealized tensorial sub-components originating from the preferred alignment of particles parallel to the magnetic field (field-aligned fabric) and within the bedding plane (sedimentary fabric). The least-squares decomposition isolates the field-aligned fabric by subtracting the sedimentary-compaction fabric. After subtraction of the sedimentary fabric, quantitative paleofield strength and direction can be directly inferred from the field-aligned subfabric.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"362 ","pages":"Article 107346"},"PeriodicalIF":2.4,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143715065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Revising the seismic source of the 1979 Tumaco-Colombia earthquake (Mw = 8.1) for future tsunami hazard assessment

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-20 DOI: 10.1016/j.pepi.2025.107344

Bruno Adriano , Cesar Jimenez , Erick Mas , Shunichi Koshimura

The 1979 Great Tumaco earthquake occurred on 12 December and had a moment magnitude of Mw = 8.1. Its epicenter was located about 10 km offshore the Colombia-Ecuador Pacific border. This earthquake generated a catastrophic tsunami that destroyed several small communities on South America's Pacific coast. Several locations in Central America and in Hawaii also recorded tsunami waves with heights up to 50 cm. Thus, understanding this event's source characteristics and effects is vital for future tsunami hazard assessments in countries in the Pacific Ocean. This study revised the earthquake source using a joint inversion of tsunami waves and geodetic records. Further, this study also analyzed the tsunami propagation characteristics on the Pacific coast of North and South America using the revised earthquake source model.

The inversion results indicate that the earthquake source presented main slip asperities north of the epicenter, with a maximum slip of 3.40 m. It also presented a second large slip of 2.87 m, located south of the epicenter. The earthquake also generated a ground subsidence of up to 50 cm along the Ecuador-Colombia coastline. The uplifted zone was estimated beneath the sea, with the most significant displacement area north of the epicenter, with a maximum uplift of 1.16 m. The comparison between the observed and simulated tsunami waveforms of the 1979 Tumaco earthquake shows that, in general, there is a good correlation for the first period of the tsunami waveforms. The tsunami simulation results suggest a maximum coastal tsunami height of 3.5 m along the coast of Panama and Costa Rica, about 600 km from the earthquake source area.

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引用次数: 0

Rapid geomagnetic variations and stable stratification at the top of Earth's core

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-11 DOI: 10.1016/j.pepi.2025.107335

Julien Aubert

Probing the possible presence and physical properties of a stably stratified layer atop Earth's core is crucial to better determine the past history and heat budget of the planet. This has previously been done by ascribing a variety of interannual to decadal geomagnetic variations to hydromagnetic waves internal to the layer. This study presents the first self-consistent simulation of the stratified layer dynamics in interplay with the underlying core convection, in physical conditions matching those of Earth's core. Magneto-Archimedes-Coriolis waves of decadal periods appear in stratified layers deeper than a few tens of kilometers and with Brunt-Väisälä frequency matching the rotation rate of the planet. However, the level at which core convection excites these waves is generally insufficient to account for observed geomagnetic variations in this period range. Strong stratification is furthermore deleterious to a number of observed features that unstratified models are successful at reproducing. Fluid flow at the core surface decouples from the interior and becomes strongly dissimilar to geomagnetic inferences. Magnetic jerks and their corresponding near-equatorial, rapidly alternating magnetic acceleration patterns also disappear, because the supporting interannual magneto-Coriolis waves are impeded by the stratified layer. This negative impact on the reproduction of the observed rapid geomagnetic variations limits the possible extent of a stable top layer to the first few tens of kilometers beneath Earth's core surface.

{"title":"Rapid geomagnetic variations and stable stratification at the top of Earth's core","authors":"Julien Aubert","doi":"10.1016/j.pepi.2025.107335","DOIUrl":"10.1016/j.pepi.2025.107335","url":null,"abstract":"<div><div>Probing the possible presence and physical properties of a stably stratified layer atop Earth's core is crucial to better determine the past history and heat budget of the planet. This has previously been done by ascribing a variety of interannual to decadal geomagnetic variations to hydromagnetic waves internal to the layer. This study presents the first self-consistent simulation of the stratified layer dynamics in interplay with the underlying core convection, in physical conditions matching those of Earth's core. Magneto-Archimedes-Coriolis waves of decadal periods appear in stratified layers deeper than a few tens of kilometers and with Brunt-Väisälä frequency matching the rotation rate of the planet. However, the level at which core convection excites these waves is generally insufficient to account for observed geomagnetic variations in this period range. Strong stratification is furthermore deleterious to a number of observed features that unstratified models are successful at reproducing. Fluid flow at the core surface decouples from the interior and becomes strongly dissimilar to geomagnetic inferences. Magnetic jerks and their corresponding near-equatorial, rapidly alternating magnetic acceleration patterns also disappear, because the supporting interannual magneto-Coriolis waves are impeded by the stratified layer. This negative impact on the reproduction of the observed rapid geomagnetic variations limits the possible extent of a stable top layer to the first few tens of kilometers beneath Earth's core surface.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"362 ","pages":"Article 107335"},"PeriodicalIF":2.4,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143642229","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Archaeointensity study of pottery from the Maya settlements of La Blanca and Chilonché (Petén, Guatemala): New data to constrain the geomagnetic field evolution in Central America

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-03-11 DOI: 10.1016/j.pepi.2025.107343

M. Gómez-Paccard , A. Chauvin , R. Bonilla-Alba , C. Vidal-Lorenzo , M. Salas

Accurate determination of the spatio-temporal variation of the geomagnetic field before direct measurements relies on reliable archaeomagnetic data. This study presents new archaeointensity data from Central America, a region with paucity of archaeomagnetic data. We specifically investigate 71 Maya pottery fragments collected at the “La Blanca” and “Chilonché” archaeological sites in Guatemala, with ages ranging between 600 and 1100 CE. We employed the classical Thellier-Thellier palaeointensity method, including partial thermoremanent magnetization (pTRM) checks, TRM anisotropy, and cooling rate corrections at the specimen level. Out of 252 specimens analyzed, only 50 from 14 fragments yielded successful results. The fragment-mean intensities obtained meet modern standards and are considered technically robust. Our findings indicate significant variability even among samples from the same period, likely due to age disparities among fragments, undetected issues in magnetic properties of the analyzed potteries and fluctuations in geomagnetic intensity. To better understand this variability, acquiring new data with higher precision dating, ideally at multi-decadal intervals, is essential. A comparison with selected previous palaeointensities, regional palaeosecular variation curves from Mexico, and global geomagnetic field models' predictions confirms that the current understanding of geomagnetic field strength evolution in Central America is unsatisfactory due to the low number of archaeomagnetic data and their significant dispersion. In this context, new high-quality palaeointensity data are required to serve as a constrain for establishing the geomagnetic field behavior in Central American during the first millennium CE and to contribute improving regional and global geomagnetic field reconstructions.

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引用次数: 0

Spectral characteristics and implications of located low-frequency marsquakes and impact events from InSight SEIS observations

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-02-27 DOI: 10.1016/j.pepi.2025.107334

Weijia Sun , Hrvoje Tkalčić , Jieying Chen , Sheng Wang

The frequency characteristics of recorded ground motion are crucial to understanding seismic wavefield originating in marsquakes and interior structures of Mars, such as seismic velocity and discontinuities. Based on the frequency content, the Marsquake Service (MQS) categorized marsquakes into low-frequency (LF) and high-frequency (HF) families and further classified them into subcategories. For example, the LF family consists of two types: low frequency (LF; < 1 Hz) and broadband (BB; predominantly <2.4 Hz). Previous studies have presented the frequency characteristics of a few significant marsquakes. With the recent application of new techniques, more marsquakes with a quality high enough to be characterized as “QB” have been located. These newly located marsquakes have the potential to constrain the internal structure of Mars, but seven of them occurring during sols 0–1011 and their spectral characteristics have not been discussed yet. Here, we first summarize these seven LF-type, B-quality marsquakes: S0185a, S0325a, S0407a, S0409d, S0484b, S0916d, and S0918a following the standard procedures of Marsquake Service. Additionally, we examine the characteristics of the two largest impact events, S1000a and S1094b, classified as BB events. We determined the frequency bounds in the Butterworth bandpass filter of all A- and B-quality LF-family marsquakes and the two impact events. We found that most LF-family marsquakes have an upper bound frequency no larger than 1 Hz, except for S0235b, reaching 1.1 Hz. Moreover, the P- and S-wave arrivals of marsquakes present highly varied spectral behaviors based on the analysis of the spectral ratio between P and S waves. We finally discuss the implications of the highly varied spectrum and S-to-P spectral ratio for these marsquakes.

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引用次数: 0

Three-dimensional magnetotelluric inversion with structurally guided regularization constraint

IF 2.4 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Physics of the Earth and Planetary Interiors

Pub Date : 2025-02-22 DOI: 10.1016/j.pepi.2025.107333

Dieno Diba , Han Song , Makoto Uyeshima , Yoshiya Usui

We propose a novel technique for the structurally regularized three-dimensional magnetotelluric inversion scheme. In the proposed method, the structural resemblance between the inverted electrical resistivity model and the independently derived guiding model is enforced by controlling the weights of the roughness operator for regularization. Using a simple mathematical function, we forced the weights to be small across presumed discontinuities in the guiding model, allowing for sharp changes in resistivity values across the discontinuity. We forced the weights to be large along blocks with similar values in guiding physical parameters, enforcing smooth changes of resistivity along the blocks. Numerical inversion tests indicate that the new guided inversion produces a resistivity model that closely approximates the true model, surpassing the results of both conventional smooth inversion and cross-gradient inversion, particularly when a perfectly correlated guiding model is used. We applied our guided inversion method to magnetotelluric data in Southern Tohoku, Northeast Japan, with structural constraints from a seismic velocity structure. Given the non-uniqueness problem of MT inversion, guided inversion enables the exploration of alternative resistivity structures that are more consistent with geological or geophysical models than those produced by conventional smooth inversion, therefore expanding the possibility of interpretation. We suggest that the proposed inversion method can serve as an alternative to the commonly used cross-gradient method, especially in the absence of objective schemes for the simultaneous selection of multiple trade-off parameters in the objective function.

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引用次数: 0