Physics of the Earth and Planetary Interiors最新文献

{"title":"Recognition of the causative fault of the 2017 MW 4.9 Malard (Tehran, Iran) earthquake from directivity analysis of the recorded ground motions","authors":"Saeid Naserieh ,&nbsp;Mehrdad Pakzad ,&nbsp;Hadi Ghofrani ,&nbsp;Mohsen Dezvareh ,&nbsp;Ehsan Karkooti ,&nbsp;Ali Moradi ,&nbsp;Mohammad Shahvar","doi":"10.1016/j.pepi.2023.107116","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107116","url":null,"abstract":"<div><p>On December 20, 2017, a light shallow earthquake (M_w 4.9) with a purely strike-slip mechanism occurred on a hidden unknown fault, 30 km west of the city of Tehran. The purpose of this study is to determine the causative fault plane based on the directivity effect that was observed during this shallow crustal depth earthquake, referred to as the Malard earthquake. This was achieved by using data from 96 seismic and accelerometer stations, and employing a variety of methods.</p><p>For the analysis of the directivity effect, we employed methods including empirical Green's function deconvolution in the frequency domain, inversion of corrected ground motions based on empirical models, and comparison of relative peak ground acceleration and velocity between the mainshock and the largest aftershock. All approaches indicate that the Malard earthquake occurred on a previously unknown fault with a strike of 71°, a steep southward dip, and a confirmed left-lateral strike-slip mechanism, as evidenced by the analysis of aftershock distribution. The earthquake exhibited a strong directivity effect, with rupture propagating unilaterally from the hypocenter to the southwest at a velocity of 2.5 km/s.</p><p>In addition to enhancing our understanding of active earthquake sources in the densely populated areas of Iran, the findings of this study will also contribute to future earthquake risk assessments in the Tehran region. However, it's important to note that Tehran was situated in the backward zone of the Malard earthquake rupture, where the least ground motion was recorded. Future earthquakes on this fault may exhibit different propagation patterns, toward the city. The determination of a preferred propagation direction can only be achieved probabilistically through the study of a substantial number of earthquakes in the region. The absence of recorded ground motion data will lead to significant uncertainty in predicting the propagation direction of future earthquakes, which must be taken into consideration during hazard analysis.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107116"},"PeriodicalIF":2.3,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92061973","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":"Source rupture process of the March 18th, 2021, Mw6.0 Béjaia (Algeria) earthquake associated with the Western segment – A link with the August 1856 Djidjelli earthquakes (Io = VIII-IX, M ≥ 6)","authors":"Amar Benfedda ,&nbsp;Khadidja Abbes ,&nbsp;Abdelhakim Ayadi ,&nbsp;Said Maouche ,&nbsp;Youcef Bouhadad ,&nbsp;Mohamed Salah Boughacha ,&nbsp;Mourad Bezzeghoud","doi":"10.1016/j.pepi.2023.107115","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107115","url":null,"abstract":"<div><p>A strong offshore earthquake (M_w6.0) struck Béjaia city (eastern Algeria) on March 18th, 2021. This earthquake was followed by several aftershocks among the M_w5.2 that occurred 13 min after the main shock. Moreover, another earthquake (M_w5.0) occurred in the same zone one year later on March 19th, 2022. Near-field digital accelerograph records were used to study the earthquake and its related aftershocks. First, the March 2021 (M_w6.0) main shock, six of its main aftershocks, and the March 19th, 2022 (M_w5.0) earthquake were located. These epicentres are distributed in a 10 km-long and 2 to 3 km-wide NE–SW-trending area, with depths ranging between 8 km and 14 km. Second, using waveform inversion, the seismic moment and the focal mechanism of the three events (the March 18th, 2021, main shock and its strongest aftershock (M_w5.2) that occurred 13 min after the main shock and the March 19th, 2022 (M_w5.0) earthquake) were determined. These focal mechanisms exhibit reverse faulting with a short lateral component. Third, the source rupture process of the March 18th, 2021 (M_w6.0), earthquake was calculated from waveform inversion to obtain the moment–release distribution on a finite fault. The nodal plane oriented N74E seems to be associated with the activated fault plane. Considering the seismotectonic framework of the region, the fault that activated during the 2021 earthquake sequence is offshore. This fault, called the Western Segment, which is situated in the western part of the reverse fault system, is also at the origin of the Djidjelli historical earthquakes of August 21st, and 22nd, 1856 (Io = VIII-IX, M ≥ 6.6).</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107115"},"PeriodicalIF":2.3,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0031920123001413/pdfft?md5=8e7576a8ae2f781c3be50b50b7ec6705&pid=1-s2.0-S0031920123001413-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92061972","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":"Multiple segmentation and seismogenic evolution of the 6th February 2023 (Mw 7.8 and 7.7) consecutive earthquake ruptures and aftershock deformation in the Maras triple junction region of SE-Anatolia, Turkey","authors":"Mustafa Toker ,&nbsp;Evrim Yavuz ,&nbsp;Murat Utkucu ,&nbsp;Fatih Uzunca","doi":"10.1016/j.pepi.2023.107114","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107114","url":null,"abstract":"<div><p><span><span><span>On 6th February 2023 (UTC), two consecutive and catastrophic earthquakes with moment magnitudes (Mw) 7.8 and 7.7 struck the Maras Triple Junction (MTJ) region in SE Anatolia along with dozens of </span>aftershocks<span>, causing numerous casualties and significant building damage, and generating the most complex and longest surface ruptures ever observed in Turkey. The main driving mechanisms of this complex double event are still unresolved and remain controversial, even though they are likely linked with conventional fault activations, recurrence intervals and seismic gaps. Here, the aim was to gain insight into the source regimes and rupture processes of both events and their relationship with resolved fault focal solutions for the observed aftershocks, and to present an interpretation that accounts for the most puzzling aspects of the fault rupture models. In line with this, the co-seismic slip distributions of these two events were examined by joint analyses of </span></span>centroid<span> moment tensor (CMT) and finite-fault source inversions using regional and teleseismic broadband observations. Inversion results indicate that both earthquakes were left-lateral strike-slip events, and the main ruptures extended mainly from close to NNE to SSW and E to W, with maximum slips of ∼6.5–10 m, mostly confined to a shallow depth range of ≤ ∼10–15 km and extending to the surface, indicating bilateral source processes with an average rupture velocity of ∼3.5–5.5 km/s. The estimated total seismic moment range was 4.94–8.22 × 10</span></span>²⁰<span> N m, associated with ∼352–152 km long (along strike) and ∼ 25 km wide (along dip) fault planes at focal depth of ∼10 km. Regional CMT results indicate nearly pure normal-slip and left-lateral normal oblique-slip focal mechanisms<span> and shallow centroid depths (≤ ∼15 km) for the early aftershock distribution that are obviously complementary with the co-seismic bilateral rupture propagations. This result highlights that double pull-apart branching of focal mechanisms for aftershock occurrence implies interacting fault ruptures embedded in the MTJ area, where two sub−/supershear-rupturing faults meet, thus explaining multiple segmentation<span> and seismogenic evolutions of two interrelated mainshocks, i.e. “triple junction earthquakes”. The results reveal that the MTJ tends to migrate to the SSW and likely drives the SSW-stepping of the left-lateral strike-slip shear (∼136 km). This accounts for the peak slips, long co-seismic fault ruptures and the associated faulting styles. Hence, the co-seismic faulting apparently distributed across the MTJ may reflect triple junction migration, and thus large extension at the core of the Anatolian-Arabian plates, leading to very high seismic hazard in similar junction regions of the country.</span></span></span></p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107114"},"PeriodicalIF":2.3,"publicationDate":"2023-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92043576","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":"Reappraisal of the 1926, Jersey earthquake source parameters","authors":"D. Baumont ,&nbsp;D. Amorèse ,&nbsp;J. Benjumea ,&nbsp;F. Ego ,&nbsp;J.-P. Tardivel ,&nbsp;P. Arroucau","doi":"10.1016/j.pepi.2023.107113","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107113","url":null,"abstract":"<div><p><span><span>The Cotentin peninsula is a region located on the northeastern edge of the Armorican Massif (France) that hosts several nuclear and radioactive waste facilities. A recent publication raised some issues regarding the source parameters of the 1926, Jersey earthquake, one of the key reference earthquakes for assessing the </span>seismic hazard at the nuclear sites. In this study, we performed in-depth analyses on both the instrumental and macroseismic data to reappraise the source parameters. While the instrumental epicentral location was fairly well constrained at about mid-distance between the Jersey Island and the Cotentin peninsula, the focal depth could not be retrieved due to the resolution limits associated with a sparse seismological network and to the uncertainties on the phase picking. Different </span><em>M</em>_S formulations applicable for moderate magnitude events recorded at regional distances were implemented to better account for the epistemic uncertainties, resulting in an estimation of M_S equal to 5.1 ± 0.3. Regarding the moment magnitude M_W<span>, we performed a broad series of waveform modeling accounting for a broad set of source parameterizations and signal processing techniques. The magnitude M</span>_W of the Jersey earthquake is estimated to 5.4 ± 0.3 although these evaluations are strongly influenced by the period range adopted to fit the observations. We also carried out the evaluation of both M_S and M_W magnitudes by modeling the macroseismic field with results (M_S = 5.1 ± 0.3; Mw = 5.3 ± 0.3) that are consistent with the instrumental estimates. Regarding the focal depth, the macroseismic analyses shed light on this parameter, even though the results depend on the assumption made on the presumed epicentral intensity (∼18 km for I₀ = VI-VII and ∼ 12 km for I₀ = VII).</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107113"},"PeriodicalIF":2.3,"publicationDate":"2023-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92043575","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":"Mapping of stress and structure controlled upper crustal anisotropy in Kumaon-Gharwal Himalaya","authors":"V. Pavan Kumar ,&nbsp;D. Srinagesh ,&nbsp;Prantik Mandal ,&nbsp;Jyotima Kanaujia ,&nbsp;B. Naresh ,&nbsp;P. Solomon Raju","doi":"10.1016/j.pepi.2023.107112","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107112","url":null,"abstract":"<div><p><span><span>Shear wave splitting analysis of local earthquakes provides valuable insights into the structure and stress controlled upper crustal anisotropy signatures. We examine these signatures at the Kumaon-Garhwal </span>Himalaya<span> and provides an excellent example of anisotropic crustal structure<span> in the ongoing continent-continent collision settings between Indian and the Eurasian plates. A total of 256 local earthquakes were selected for the analysis (1.0 ≤ M ≤ 5.4) between January 2017 and February 2021, recorded at a dense network of 51 broadband stations. The result indicates the observed crustal anisotropy is parallel to stress-aligned micro-cracks far from the major Himalayan fault zones and structure parallel near the fault zones. The dominant fast polarization directions (FPD) in the Inner Lesser Himalaya (ILH) and Higher Himalaya, are consistent with the maximum compressive horizontal stress directions (SH</span></span></span>_max<span>), essentially influenced by the local stress field. Whereas in the Outer Lesser Himalaya (OLH) and Sub Himalaya, fast directions are sub-parallel to the structural trends, suggesting that the anisotropy is associated with the shear fabric from recent deformation episodes related to structural induced anisotropy. The computed normalized delay times show a mean value of 1 ms/km, within the OLH and Sub-Himalaya, while in ILH and Higher Himalaya, this value increases up to 5.3 ms/km. The associated crack densities are 0.0038 and 0.0207, with shear wave velocity anisotropy of 0.38% and 2.07% respectively. Significant scatter within the depth range of 10–15 km is observed in normalized delay times, suggesting the source of anisotropy within the upper crust.</span></p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107112"},"PeriodicalIF":2.3,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92043577","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":"Thermal convection and dynamo action with stable stratification at the top of the Earth's outer core","authors":"Priyabrata Mukherjee,&nbsp;Swarandeep Sahoo","doi":"10.1016/j.pepi.2023.107111","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107111","url":null,"abstract":"<div><p>The outer core of the Earth, filled with electrically conducting fluid, undergoes thermochemical convection due to super-adiabatic temperature gradients. Near the core-mantle boundary, fluid flow may be restricted due to sub-adiabatic temperature gradients or accumulated light elements forming a layer of stable stratification. The present study investigates the behavior of thermal convection with various buoyancy profiles, using non-uniform radial distribution of heat sources, mimicking the combined presence of convective and stable zones. Role of such modified convection in the evolution and resulting morphology of saturated magnetic fields is the main focus of this study. Apart from the reduction in the threshold for onset, the length scale of the convective instabilities is enhanced with stable stratification, while the frequency is reduced. Despite the confinement of convection to unstable regions, rapid rotation favors penetrative radial convective flows. In presence of a stably stratified layer, the dynamo action is suppressed due to the radial confinement of buoyancy, Coriolis, and Lorentz forces. The suppression of vortex stretching, indicated by the relative asymmetry in axial helicity provides further understanding of the mechanism behind the magnetic field structure. As the stratification becomes stronger, the dynamo action leads to magnetic fields with enhanced axial dipole field strength, although the strength of the dynamo is reduced. The confinement of the toroidal component of the magnetic field to localized concentrated patches in regions of stable stratification near the equatorial plane also inhibits the growth of magnetic fields. Nevertheless, enhanced buoyancy forcing may overcome the suppression of dynamo action and lead to strongly convecting dipolar dominated Earth-like dynamos even with moderate stratification.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107111"},"PeriodicalIF":2.3,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49726329","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":"Earthquake location based on Distributed Acoustic Sensing (DAS) as a seismic array","authors":"K. Lentas ,&nbsp;D. Bowden ,&nbsp;N.S. Melis ,&nbsp;A. Fichtner ,&nbsp;M. Koroni ,&nbsp;K. Smolinski ,&nbsp;A. Bogris ,&nbsp;T. Nikas ,&nbsp;C. Simos ,&nbsp;I. Simos","doi":"10.1016/j.pepi.2023.107109","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107109","url":null,"abstract":"<div><p>We present a simple and fast method to estimate preliminary earthquake location coordinates using Distributed Acoustic Sensing (DAS). Strain rate data is recorded on a 25-km long fibre-optic cable located in the northern suburbs of Athens (Greece). We apply frequency - wavenumber analysis on two segments of the cable forming an L-shaped seismic array, which offers good azimuthal sensitivity, whereas, the spatial resolution (spacing) and signal coherency control the ability to reliably resolve the apparent slowness of an incoming wavefield, and hence, to estimate the hypocentral distance to the array. We attempt to locate a local earthquake (2021/9/23, <span><math><msub><mi>M</mi><mi>L</mi></msub></math></span>=3.4, Thiva) NW to the DAS array (approximately 50 km NW of Athens), and a regional earthquake (2021/10/12, <span><math><msub><mi>M</mi><mi>W</mi></msub></math></span>=6.3, off the East coast of Crete) using <span><math><mi>S</mi></math></span>-wave onsets filtered within two frequency bands (0.5 Hz - 2.5 Hz and 1.0 Hz - 5.0 Hz). The obtained backazimuths agree with the observed backazimuths based on the locations reported by the Institute of Geodynamics, National Observatory of Athens (NOA) for both earthquakes, with our location for the local earthquake being roughly 10 km South of the NOA location, whereas, the location that we obtained for the regional earthquake suggested larger errors in distance, projected in our slowness estimation, possibly due to the array spatial resolution and the complex structure of the Hellenic subduction zone.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"344 ","pages":"Article 107109"},"PeriodicalIF":2.3,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49726095","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":"Shear wave velocity structure of the upper crust in north Xiaojiang fault zone in SE Tibet via short-period ambient noise dense seismic array","authors":"Si Chen ,&nbsp;Rui Gao ,&nbsp;Zhanwu Lu ,&nbsp;Yao Liang ,&nbsp;Wei Cai ,&nbsp;Lifu Cao ,&nbsp;Zilong Chen ,&nbsp;Guangwen Wang","doi":"10.1016/j.pepi.2023.107110","DOIUrl":"https://doi.org/10.1016/j.pepi.2023.107110","url":null,"abstract":"<div><p>The Xiaojiang Fault Zone (XJF) is an important boundary fault on the southeast border of the Tibetan Plateau, with a complex subterranean structure and strong tectonic activity. In the present study, 252 seismograph stations were deployed in the northern section of the XJF to collect ambient noise data in a span of 35 days. The minimum resolution attained was 2 km × 2 km to develop a high-precision underground velocity structure model. The velocity model helped in revealing that the low-velocity distribution originated below the XJF. It was also found that the fault, which is the primary channel for magma to rise, might be the cause of the upper crustal deformation of the XJF. The Dongchuan mining area is located to the west of the XJF, which has a low-velocity structure. However, the high-velocity structure appeared on both sides of the ore body. It is speculated that the ore was formed by magma intrusion. The intrusion serves as a heat source for the mining area and promotes deposit formation.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"344 ","pages":"Article 107110"},"PeriodicalIF":2.3,"publicationDate":"2023-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49726132","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":"Investigation of the porosity of L/LL4 ordinary chondrite Bjurböle using synchrotron radiation microtomography and scanning electron microscopy: Implications for parent body evolution","authors":"A.-J. Soini ,&nbsp;I.T. Kukkonen ,&nbsp;H. Suhonen ,&nbsp;B. Lukić ,&nbsp;T. Kohout ,&nbsp;A.V. Luttinen","doi":"10.1016/j.pepi.2023.107087","DOIUrl":"10.1016/j.pepi.2023.107087","url":null,"abstract":"<div><p>Porosity is an essential property of chondritic meteorites and is closely related to the genesis, thermal evolution, metamorphism, and thermal properties of the meteorite parent bodies. We study porosity, its texture, and shapes at sub-micron resolution in 3D and 2D within a 0.35 cm³ sample of the L/LL4 ordinary chondrite (OC) Bjurböle using two techniques, synchrotron radiation microtomography (SRμCT) and scanning electron microscopy (SEM). We employ automated segmentation tools that can be applied to both SRμCT and SEM data. Successful segmentation results can be achieved by combining visual qualitative examination and machine learning algorithms.</p><p>We report novel measurement results of three-dimensional porosity properties of Bjurböle, such as aspect ratio and connectivity of void spaces, and compare the results of 2D and 3D porosity analysis. The Bjurböle sample in this study is a complex, highly porous, and friable medium and the dominant type of porosity is intergranular, continuous porosity, which contains almost all porosity volume. The shapes of the void volumes have an important effect on the connectivity of the porosity and thermal transport properties. Positive correlations between void diameter and aspect ratio as well as void volume and connectivity are present in Bjurböle, which indicate that smaller voids have lower aspect ratios and lower connectivity. In Bjurböle, small, near-spherical voids with few connections have the highest relative frequency, whereas larger void spaces with higher aspect ratios and connectivity are significantly fewer. Completely isolated pores, i.e., voids surrounded by solid material, also have a high relative frequency, and they exist within the chondrules and the matrix. However, the volume percentage of these pores is negligible compared to that of the continuous porosity.</p><p>Our results support the previously measured high porosities of Bjurböle. The volume percentage of intergranular void spaces, in particular in the matrix, and the measured high porosities are not in line with the results of thermal evolution and sintering models of chondritic parent bodies regarding petrologic type 4, which implies that Bjurböle originates from a parent body with an initial onion shell structure that fragmented during or after its metamorphic peak and quickly reaccreted into a rubble pile.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"343 ","pages":"Article 107087"},"PeriodicalIF":2.3,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43140972","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":"Equation of state for Mg3Al2Si3O12 pyrope: Implications for post-garnet transitions and mantle dynamics","authors":"Anna M. Dymshits ,&nbsp;Peter I. Dorogokupets ,&nbsp;Igor S. Sharygin ,&nbsp;Anton F. Shatskiy","doi":"10.1016/j.pepi.2023.107086","DOIUrl":"10.1016/j.pepi.2023.107086","url":null,"abstract":"&lt;div&gt;&lt;p&gt;Mantle convection is the dominant process driving the upwelling of hot materials and subduction of cold slabs. These processes are density-dependent and influenced by post-spinel and post-garnet transitions in the mantle transition zone (MTZ)/ lower mantle (LM). Knowledge of the Clapeyron slope of these transformations is used to express the dynamics of mantle blocks and is necessary for understanding the deep Earth. Here, we provide the Kunc-Einstein equation of state (EoS) for the pyrope Mg&lt;sub&gt;3&lt;/sub&gt;Al&lt;sub&gt;2&lt;/sub&gt;Si&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt; (Prp) calculated from a joint analysis of the experimentally measured isobaric heat capacity, bulk moduli, thermal expansion, pressure (P), unit cell volume (V), temperature (T) data. Based on our model, the bulk modulus and its pressure derivatives were K&lt;sub&gt;0,T0&lt;/sub&gt; = 168.5 GPa, K′&lt;sub&gt;0,&lt;em&gt;T&lt;/em&gt;&lt;/sub&gt; = 4.77, and V&lt;sub&gt;0&lt;/sub&gt; = 1501.7 Å. The optimised parameters include two Einstein temperatures, i.e., θ&lt;sub&gt;1&lt;/sub&gt; = 331 and θ&lt;sub&gt;2&lt;/sub&gt; = 1093 K, Grüneisen parameter at ambient condition γ&lt;sub&gt;0&lt;/sub&gt; = 1.77, infinite compression γ&lt;sub&gt;∞&lt;/sub&gt; = 0 with β = 1.12 and an intrinsic anharmonicity parameter a&lt;sub&gt;0&lt;/sub&gt; = –20. The value for the thermal expansion coefficient was calculated to be α = 2.33·10&lt;sup&gt;−5&lt;/sup&gt; K&lt;sup&gt;−1&lt;/sup&gt;, and the thermodynamic Grüneisen parameter was estimated as γ&lt;sub&gt;th&lt;/sub&gt; = 1.42. The obtained EoS for Prp and the preliminarily fitted EoS for Al-bearing akimotoite (Al-Aki), in combination with literature data on bridgmanite (Bdm) and corundum (Crn), allowed the calculation of the phase diagram of the system with 75 mol% MgSiO&lt;sub&gt;3&lt;/sub&gt; + 25 mol% Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; under LM conditions. The transformation from Prp to Bdm + Crn was computed at 24 GPa and 1570 K and exhibited a slightly positive Clapeyron slope (d&lt;em&gt;P&lt;/em&gt;/d&lt;em&gt;T&lt;/em&gt; = 2.1 MPa/K). The stability field of Al-Aki was detected at &lt;em&gt;T&lt;/em&gt; = 1250–1570 K and &lt;em&gt;P&lt;/em&gt; = 23–27 GPa. At &lt;em&gt;P&lt;/em&gt; values higher than 24–27 GPa, the Al-Aki transforms into a Bdm + Crn assemblage with a highly negative Clapeyron slope. Calculations of sound velocities for the studied phases showed that the transformation from Prp to Bdm + Crn increased &lt;em&gt;V&lt;/em&gt;&lt;sub&gt;&lt;em&gt;p&lt;/em&gt;&lt;/sub&gt; and V&lt;sub&gt;s&lt;/sub&gt; by up to 9 and 20%, respectively. Such a big jump in the sound velocities indicates that the post-garnet transition is a better candidate than the post-Aki transition for producing a double discontinuity at the base of the MTZ, in combination with the transformation of ringwoodite into the Bdm + ferropericlase assemblage. The increase in sound velocities associated with the formation and dissolution of Al-Aki is unlikely to be sensitive to the MTZ. The combination of post-garnet, post-spinel, and post-Aki transitions near 660–720 km depths may have sluggished both the upwelling hot mantle and the subducted cold plates. The stagnant, hot LM material at the base of MTZ warmed the harzburgite and eclogite layers st","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"343 ","pages":"Article 107086"},"PeriodicalIF":2.3,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44763495","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}