Physics of the Earth and Planetary Interiors最新文献

{"title":"Spectral characteristics and implications of located low-frequency marsquakes and impact events from InSight SEIS observations","authors":"Weijia Sun ,&nbsp;Hrvoje Tkalčić ,&nbsp;Jieying Chen ,&nbsp;Sheng Wang","doi":"10.1016/j.pepi.2025.107334","DOIUrl":"10.1016/j.pepi.2025.107334","url":null,"abstract":"<div><div>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; &lt; 1 Hz) and broadband (BB; predominantly &lt;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.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107334"},"PeriodicalIF":2.4,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143551096","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}

{"title":"Three-dimensional magnetotelluric inversion with structurally guided regularization constraint","authors":"Dieno Diba ,&nbsp;Han Song ,&nbsp;Makoto Uyeshima ,&nbsp;Yoshiya Usui","doi":"10.1016/j.pepi.2025.107333","DOIUrl":"10.1016/j.pepi.2025.107333","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107333"},"PeriodicalIF":2.4,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143550985","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}

{"title":"On the possibility of convection in the Venusian crust","authors":"Viatcheslav S. Solomatov,&nbsp;Chhavi Jain","doi":"10.1016/j.pepi.2025.107332","DOIUrl":"10.1016/j.pepi.2025.107332","url":null,"abstract":"<div><div>We evaluate the possibility of convection in the Venusian crust by utilizing recently developed scaling laws for the onset of convection in temperature- and stress-dependent viscosity fluids, heated from below or from within. We find that crustal convection can occur within plausible ranges of surface heat flux, crustal thickness, and rheologies. Crustal convection can occur at subsolidus temperatures if the grain size is less than 0.1 mm and the crust is relatively thick, close to the gabbro-eclogite transition. For larger grain sizes, particularly where deformation occurs through dislocation creep, crustal convection is likely to occur only at supersolidus temperatures. If crustal convection does occur in the Venusian crust, it would increase heat transport efficiency in the crust and affect the interior dynamics and evolution of the planet. It would also generate thermal variations within the crust that would affect the constraints on the elastic thickness and the heat flux from gravity and topography data analysis. Further investigation of the two-phase dynamics of a partially molten crust is essential for a better understanding of crustal convection and accurate interpretation of surface observations.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107332"},"PeriodicalIF":2.4,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510628","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}

{"title":"Effect of chemistry on the compressibility and high-pressure structural evolution of the CaFe2O4-type aluminous silicate phase","authors":"Giacomo Criniti ,&nbsp;Tiziana Boffa Ballaran ,&nbsp;Alexander Kurnosov ,&nbsp;Takayuki Ishii ,&nbsp;Elena-Marie Rogmann ,&nbsp;Konstantin Glazyrin ,&nbsp;Timofey Fedotenko ,&nbsp;Daniel J. Frost","doi":"10.1016/j.pepi.2025.107331","DOIUrl":"10.1016/j.pepi.2025.107331","url":null,"abstract":"<div><div>Approximately 22–26 vol% of a basaltic phase assemblage at lower mantle conditions is comprised of a (Na,Mg,Fe²⁺)(Al,Si,Fe³⁺)₂O₄ phase with CaFe₂O₄-type (CF-type) structure. Previous experimental studies attempted to determine the equation of state of the CF-type phase but reported contrasting compressibility values, even for samples with the same composition. Therefore, the elastic properties of the CF-type phase remain, to date, largely unconstrained. Here, we conducted single-crystal X-ray diffraction (SCXRD) measurements in the diamond anvil cell (DAC) at high pressure and room temperature on three samples of CF-type phase with compositions Na_0.90(1)Al_1.03(2)Si_1.00(2)O₄ (NaCF), Na_0.66(4)Mg_0.28(4)Al_1.22(3)Si_0.78(3)O₄ (MgCF) and Na_0.62(2)Mg_0.19(1)Fe²⁺_0.17(1)Fe³⁺_0.080(4)Al_1.20(3)Si_0.70(1)O₄ (FeCF). A multi-sample loading approach was employed for most DAC runs, where two samples were loaded in the same sample chamber to reduce possible systematic deviations between datasets, thus enhancing internal consistency and corroborating data reproducibility. Experiments on the NaCF and MgCF samples were conducted up to ∼50 GPa, while the FeCF sample was compressed to ∼72 GPa to better characterize the effect of the spin crossover of octahedrally coordinated Fe³⁺. We found the isothermal bulk modulus (<em>K</em>_T0) to increase with decreasing NaAlSiO₄ content, accompanied by only a slight decrease in its pressure derivative (<em>K'</em>_T0). Analysis of the crystal structures of the three samples at high pressure allowed compositional trends to be determined also for the interatomic bonds and polyhedral compressibility, as well as the distortion indices. These suggest an overall stiffening of the A site with increasing Mg²⁺ and Fe²⁺ content, as well of the two B sites with increasing Al³⁺ and Fe³⁺ content. Enhanced compressibility of the unit cell and octahedral B sites was observed between ∼26–42 GPa in the FeCF sample, suggesting a pressure-induced spin crossover of Fe³⁺, in agreement with some previous observations. Finally, trends in the elastic properties from experimental studies conducted along the NaAlSiO₄-MgAl₂O₄ join are discussed and used as a proxy to evaluate the reliability of end-member properties for the CF-type phase employed in most recent mineral physical and thermodynamic databases. Our analysis suggests current mineral physical models might underestimate densities and overestimate bulk sound velocities of NaAlSiO₄-rich CF-type phases with basaltic composition.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107331"},"PeriodicalIF":2.4,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143512264","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}

{"title":"A 6-year quasi-periodicity in the geomagnetic secular acceleration pulses over 1932–2022","authors":"R. Sidorov ,&nbsp;A. Soloviev ,&nbsp;Sh. Bogoutdinov","doi":"10.1016/j.pepi.2025.107330","DOIUrl":"10.1016/j.pepi.2025.107330","url":null,"abstract":"<div><div>Recent studies suggest that the secular variation dynamics of the geomagnetic field exhibits periodic patterns that indicate underlying wave processes in the Earth's core. However, analytical models of the core geomagnetic field based on geographically sparse and noisy observatory data have apparent limitations for studying fine structure of its spatiotemporal variations. The advent of satellite measurements of the full geomagnetic field vector in 1999 removed this limitation and made it possible to produce reliable and highly accurate models of the secular variation that allow downward continuation to the core-mantle boundary. These models have revealed rapid core field variations on a time scale of the order of 10 years. In particular, the 6-year quasi-periodicity in the second time derivative of the geomagnetic field has been discovered. In this research, we build on our previous works to extract the secular variation and secular acceleration signal from the magnetic observatory datasets over a longer period. As a result, our approach to data analysis has made it possible to confirm the existence of a 3-year quasi-periodicity of secular acceleration pulses of alternating polarity over 90-year period (1932–2022), i.e. far before the advent of the space era. The proposed methodology does not imply an intermediate production of a core field model, as done according to classical approaches.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107330"},"PeriodicalIF":2.4,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143465133","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}

{"title":"SeisTeC: A neural network tool to constrain mantle thermal and chemical properties from seismic observables","authors":"Ashim Rijal,&nbsp;Laura Cobden,&nbsp;Jeannot Trampert","doi":"10.1016/j.pepi.2025.107317","DOIUrl":"10.1016/j.pepi.2025.107317","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Three-dimensional variations of wave speeds and density have identified the presence of seismically distinct structures in the Earth's mantle. To determine the thermochemical properties and dynamic relevance of these structures, it is crucial to understand the relationship between seismic properties and temperature and composition. However, multiple thermochemical parameters influence seismic wave speeds simultaneously. A given wave speed pair (compressional and shear) and density can be generated by many possible combinations of thermochemical parameters, which makes the inversion of wave speeds and density for thermochemical parameters a non-unique problem. We have developed a tool which efficiently captures the mapping between seismic wave speeds (and density) and thermochemical properties, with the capacity to represent both the inherent trade-offs between parameters as well as data uncertainties. These trade-offs and uncertainties are represented by the posterior probability density function provided by a neural network. We demonstrate the concept for seismic wave speeds and density, but the same tool can also be adapted for other parameters such as attenuation or properties of seismic discontinuities. SeisTeC is available to the wider community and is intended to facilitate interpretations of seismic structures inside the Earth, or in general, any planetary bodies.&lt;/div&gt;&lt;div&gt;Our tool is based on a neural network, which implicitly learns the non-linear mapping between temperature and bulk composition. We chose the example of the lower mantle and expressed composition in terms of six end-member oxides (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;SiO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mi&gt;MgO&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;msub&gt;&lt;mi&gt;Al&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msub&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mi&gt;FeO&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;msub&gt;&lt;mi&gt;Na&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;mi&gt;CaO&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) and modelled seismic wave speeds and density at appropriate temperature and pressure conditions. Wave speeds and density are calculated for 750,000 thermochemical models, whose temperature and composition are selected at random from pre-defined ranges, using thermodynamic modelling. We train neural networks with wave speeds plus or minus density as the input, and temperature and bulk composition as target outputs. The networks then approximate a probability density function for each output, which allows us to interpret seismic observables in terms of physical parameters, crucially, with uncertainties. When working with wave speeds (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;V&lt;/mi&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;V&lt;/mi&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;) only, we find trade-offs between pairs of parameters such as temperature - &lt;span&gt;&lt;math&gt;&lt;mi&gt;FeO&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;SiO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; - &lt;span&gt;&lt;math&gt;&lt;mi&gt;MgO&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;SiO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; - &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;Na&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;m","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107317"},"PeriodicalIF":2.4,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143465132","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}

{"title":"Radial structure of the Earth: (I) Model concepts and data","authors":"Pritwiraj Moulik ,&nbsp;Göran Ekström","doi":"10.1016/j.pepi.2025.107319","DOIUrl":"10.1016/j.pepi.2025.107319","url":null,"abstract":"&lt;div&gt;&lt;div&gt;A framework is introduced for developing a radial reference model that incorporates diverse observations and techniques for improving the constraints on bulk Earth structure. This study describes new modeling concepts and reference datasets while features of the reference Earth model REM1D and geological interpretations are discussed in a companion manuscript. Recent measurements from various techniques have improved in precision and are broadly consistent, and are summarized as best estimates with uncertainties. We construct a reference dataset comprising normal-mode eigenfrequencies and quality factors, surface-wave dispersion curves, impedance constraints and travel-time curves from body waves, and astronomic-geodetic observations. Classical radial reference models do not account for the theoretical effects and observational biases resulting from heterogeneity in the crust and mantle. We address three issues that account for lateral variations in the modeling of average elastic, anelastic and density structure. First, current ray coverage of traveling waves is biased towards structure in the northern hemisphere, leading to faster velocities especially in the lower mantle. Second, horizontal wavelength of the heterogeneity that a traveling wave encounters is assumed to be much greater than that of the corresponding normal mode in most ray-theoretical and finite-frequency formulations of wave propagation. Effects of the full volumetric sensitivity on local eigenfrequencies and phase velocities that are ignored with this approximation exceed the data uncertainty for both fundamental spheroidal (Rayleigh waves, T &lt;span&gt;&lt;math&gt;&lt;mo&gt;≥&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 220 s) and toroidal modes (Love waves, T &lt;span&gt;&lt;math&gt;&lt;mo&gt;≥&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 120 s); waves at these longer periods cannot be modeled solely in terms of radial variations along the ray path. Third, non-linear effects from the strongly heterogeneous crustal structure are substantial for shorter-period waves (T &lt;span&gt;&lt;math&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 100 s) and need to be accounted for while deriving radial models. After accounting for these issues on heterogeneity, rapid convergence for average structure is facilitated by utilizing &lt;em&gt;a priori&lt;/em&gt; constraints from recent literature, analytical sensitivity kernels that account for physical dispersion, and a flexible parameterization comprising polynomial functions and cubic B-splines. By adopting a higher order polynomial for density than the elastic structure, artifacts that imply strong inhomogeneity and non-adiabaticity are avoided in potentially well-mixed regions like the outer core. Derivative properties like the gradient of bulk modulus with pressure (&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mi&gt;κ&lt;/mi&gt;&lt;mo&gt;′&lt;/mo&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; = &lt;span&gt;&lt;math&gt;&lt;mi&gt;dκ&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;dp&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) and the Bullen's stratification parameter &lt;span&gt;&lt;math&gt;&lt;mfenced&gt;&lt;msub&gt;&lt;mi&gt;η&lt;/mi&gt;&lt;mi&gt;B&lt;/mi&gt;&lt;/msub&gt;&lt;/mfenced&gt;&lt;/math&gt;&lt;/span&gt; are adjusted in the core to match expectations fr","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107319"},"PeriodicalIF":2.4,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143551095","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}

{"title":"Radial structure of the Earth: (II) Model features and interpretations","authors":"Pritwiraj Moulik ,&nbsp;Göran Ekström","doi":"10.1016/j.pepi.2025.107320","DOIUrl":"10.1016/j.pepi.2025.107320","url":null,"abstract":"&lt;div&gt;&lt;div&gt;A new reference model is presented for the spherically-averaged profiles of elasticity, density and attenuation, which reflect the bulk composition, temperature profile and dominant processes of the Earth's heterogeneous interior. This study discusses the features of REM1D and geological interpretations while the underlying modeling concepts and reference datasets are described in a companion manuscript. All physical parameters in REM1D vary smoothly between the Mohorovičić and 410-km discontinuity, thereby excluding the 220-km discontinuity in earlier models. REM1D predicts arrival times of major body-wave phases in agreement (±0.8 s, normalized misfit &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;ψ&lt;/mi&gt;&lt;mi&gt;pb&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 0.25 s) with widely used but theoretically incomplete isotropic models optimized for earthquake location. Substantial radial anisotropy is present only in the shallowest mantle (∼250 km) with peak values of shear-wave (&lt;em&gt;a&lt;/em&gt;&lt;sub&gt;&lt;em&gt;S&lt;/em&gt;&lt;/sub&gt; = 3.90 %, &lt;span&gt;&lt;math&gt;&lt;mi&gt;ξ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; = 1.08) and compressional-wave anisotropy (&lt;em&gt;a&lt;/em&gt;&lt;sub&gt;&lt;em&gt;P&lt;/em&gt;&lt;/sub&gt; = 3.78 %, &lt;span&gt;&lt;math&gt;&lt;mi&gt;ϕ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; = 0.93) between ∼125–150 km, consistent with textures that can form by the alignment of intrinsically anisotropic minerals in this deforming region. The upper mantle (24.4–410 km) is the most dissipative region with a finite bulk attenuation (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;mi&gt;κ&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;∼&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 386) and strong shear attenuation (&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;Q&lt;/mi&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;∼&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 60–80) that peaks at a depth of ∼150–175 km in the mechanically weak asthenosphere. An olivine-rich pyrolitic composition is broadly consistent with REM1D structure in the upper mantle and extended transition zone (&lt;span&gt;&lt;math&gt;&lt;mo&gt;≲&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt; 800 km) with step changes across the 410-km and 650-km discontinuities. Features of the lower mantle can be reconciled with: (i) effects of thermally driven convection throughout the central lower mantle (771–2741 km) leading to an apparent subadiabaticity in the stratification parameter &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;η&lt;/mi&gt;&lt;mi&gt;B&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, (ii) effects of spin transitions in iron-bearing minerals that manifest as distinct linear segments in modulus and Poisson's ratios (&lt;span&gt;&lt;math&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;κ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;, &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;) on either side of a complex transition region (∼1300–1700 km, 52–73 GPa), (iii) a thermal boundary layer with steeper superadiabatic gradients than near the surface, which ultimately exceed the critical gradients for both &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;v&lt;/mi&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;v&lt;/mi&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; (but not for density &lt;span&gt;&lt;math&gt;&lt;mi&gt;ρ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) at a depth of 2741 km, and (iv) chemical stratification in the bottom ∼500–750 km of the mantle that acts to suppress the thermal effects. Signatures of this th","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107320"},"PeriodicalIF":2.4,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143479207","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}

{"title":"Flat 410 and 660 discontinuities beneath northeastern Japan: Implication for a sub-slab wet plume hypothesis","authors":"K. Miyazaki,&nbsp;J. Nakajima","doi":"10.1016/j.pepi.2025.107316","DOIUrl":"10.1016/j.pepi.2025.107316","url":null,"abstract":"<div><div>Recent seismic tomography studies have shown that distinct low-velocity anomalies exist below subducting slabs in many subduction zones and these anomalies are interpreted as a hot plume from the lower mantle. However, it is still unclear how high are the temperatures in the sub-slab low-velocity anomaly regions. Here, we conduct receiver function analysis and estimate the horizontal temperature variation in the mantle transition zone by determining the depth variation of 410 and 660 discontinuities beneath northeastern Japan. The obtained results show that the depth of the two discontinuities changes little, which suggests no distinct thermal heterogeneities over the study area. Therefore, we infer that the major cause of the sub-slab low-velocity anomaly is attributable not to high-temperature anomaly but to the presence of a small amount (∼0.2 wt%) of hydrous minerals, which can explain the sub-slab low-velocity anomalies and the flat 410 and 660 discontinuities.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"361 ","pages":"Article 107316"},"PeriodicalIF":2.4,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143394579","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}

{"title":"Reassessment of focal depth estimates of small-to-moderate magnitude continental earthquakes in Western to Central Africa with the optimal period of Rayleigh wave amplitude spectra using sparse regional seismic data","authors":"John Somiah ,&nbsp;Sidao Ni ,&nbsp;Xiaohui He","doi":"10.1016/j.pepi.2025.107322","DOIUrl":"10.1016/j.pepi.2025.107322","url":null,"abstract":"<div><div>We investigate the focal depths of earthquakes in West and Central Africa using regional seismic data collected over the past two decades. Due to limited seismic network coverage, reliable source depth estimates are sparse in global earthquake catalogs for this region. To address this gap, we exploit the sensitivity of short-period (0.5–20 s) Rayleigh waves to source depths. Using the optimal period of Rayleigh wave amplitude spectra, we used an automated method to estimate earthquake focal depths. This method enabled us to resolve the depths of fifteen small-to-moderate earthquakes (mb 4.0–5.0) occurring in the region between 2000 and 2023. The focal depths ranged from approximately 3.3 km to 16 km, indicating that seismicity in the region is primarily confined to the upper crust. This finding is consistent with previous studies suggesting shallow crustal seismicity in the area. We conclude that the shallow stress regime in West and Central Africa reflects a localized weakness zone in the upper crust. Our study demonstrates the effectiveness of using the optimal Rayleigh wave period method to accurately determine focal depths of small-to-moderate earthquakes, particularly in regions with sparse seismic station coverage.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"360 ","pages":"Article 107322"},"PeriodicalIF":2.4,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143372154","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}