Physics of the Earth and Planetary Interiors最新文献

{"title":"Evolution and disappearance of the paleo-West Pacific Anomaly: Implications to the future of South Atlantic Anomaly","authors":"Yaochen Yue ,&nbsp;Jiawei Gao ,&nbsp;Fei He ,&nbsp;Yong Wei ,&nbsp;Shuhui Cai ,&nbsp;Huapei Wang ,&nbsp;Yuqi Wang ,&nbsp;Zhaojin Rong ,&nbsp;Zhonghua Yao ,&nbsp;Wei Lin ,&nbsp;Yongxin Pan","doi":"10.1016/j.pepi.2024.107214","DOIUrl":"10.1016/j.pepi.2024.107214","url":null,"abstract":"<div><p>Palaeomagnetic and modern geomagnetic measurements indicate that the South Atlantic Anomaly (SAA) has undergone rapid changes over the past few hundred years. Its minimum intensity decreased at an average rate of 26 not yr⁻¹, accompanied by a continuous westward drift and spatial expansion. Recently, a secondary minimum of SAA emerged near southern Africa, leading to speculation that expansion of the SAA could indicate an impending geomagnetic reversal. Here, we focus on the evolution and disappearance of the paleo-West Pacific Anomaly (WPA), as another SAA-like structure, which may have implications for the future of SAA evolution. We regard the WPA as SAA-like due to its feature and its association with a reversal flux patch on the core-mantle boundary. Consequently, we suggest that the observed evolutionary pattern in the WPA can serve as a reference for other negative anomalies, such as the SAA. By analysing models that combine datasets of archaeomagnetic and historical records, such as gufm1 and HistKalmag, it is found that the WPA occurred between 1600 and 1820 CE. Over its duration, the WPA experienced phases of rapid expansion, drift, and division. Eventually, its primary component faded away, giving rise to a new segment that continued to expand. The initial two evolutionary phases of the WPA are similar to the evolution of the SAA over the past century. According to the WPA's evolution, it suggests that the current state of the SAA may correspond to an early stage of splitting. Forecasts based on the evolution of the WPA indicate a rapid expansion of the anomalous region in the short term, followed by a gradual reduction in its primary component and continued expansion of a new local minimum. This study provides valuable insight into the evolution of the SAA and highlights the potential utility of the WPA as an evolutionary reference for such geomagnetic phenomena.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"353 ","pages":"Article 107214"},"PeriodicalIF":2.3,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141276684","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":"A 3D computational model for ground motion simulation in Peninsular India","authors":"K.P. Sreejaya,&nbsp;S.T.G. Raghukanth","doi":"10.1016/j.pepi.2024.107208","DOIUrl":"https://doi.org/10.1016/j.pepi.2024.107208","url":null,"abstract":"<div><p>Due to the gradual and constant accumulation of seismic energy, Peninsular India (PI) is typically considered seismically stable with low to moderate seismicity. The seismic studies in Peninsular India always resorted to synthetic ground motion simulations, because of the limited instrumentation and hence lack of recorded data. In the absence of a well-defined medium model for PI, the usual practice is to use simple site proxies or one-dimensional velocity structures for ground motion simulations. However, the region consists of multi-scale geometric complexities, significant topography, and sedimentary basins and is surrounded by deep oceans. Thus, the radiated seismic wave field in the region is influenced by the medium properties and in the absence of a well-defined tomography model the reliable estimation of seismic hazard is a challenging problem in PI. Therefore, the seismic wave propagation in PI can be investigated using numerical simulation with reliable 3D computational model for PI, incorporating the knowledge of the underlying Earth structure. Hence, the present study attempts to develop a sophisticated three-dimensional (3D) medium model of Peninsular India for physics-based ground motion simulations for regional earthquakes. This is aided by the availability of one-dimensional (1D) velocity models and the crustal structure from the receiver function analysis which provides valuable insight into the variation of material properties in the region. In the present study, &gt;100 s of 1D velocity profiles are collected from various literature, which is then grouped under 23 different geological regions identified in PI (as per GSI (2000)). The averaged material properties are assigned per each geological region and the information on sediment depths, basin geometry, topography, and bathymetry are incorporated. We use the spectral element method (SEM) to calibrate our 3D computational model by simulating synthetic seismograms and comparing them to recorded ground motions for two past earthquakes: the 2001 Mw 7.6 Bhuj earthquake and the 1997 Mw 5.8 Jabalpur earthquake. Further, the seismic waveforms at the near field of 2001 Mw 7.6 Bhuj event are simulated using a refined regional model. The spatial variability of associated seismic intensities and peak ground velocity (PGV) amplification are investigated. In addition, a study of the impact of model depth truncation and sphericity on ground motion is also conducted. The implemented medium model is the first of its kind for Peninsular India and can reliably be used in seismic wave propagation studies in the region. The simulated outcomes from the model are of engineering importance as these results can be used for seismic hazard assessment of the region.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"353 ","pages":"Article 107208"},"PeriodicalIF":2.3,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141312777","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":"Lateral electrical conductivity variations along the Main Himalayan thrust in the northwestern Himalayas: Insights from 3D Magnetotelluric forward modeling","authors":"S. Dhamodharan ,&nbsp;Khasi Raju ,&nbsp;Prasanta K. Patro","doi":"10.1016/j.pepi.2024.107213","DOIUrl":"10.1016/j.pepi.2024.107213","url":null,"abstract":"<div><p>Understanding the arc parallel variation on the geometry of the Main Himalayan Thrust (MHT) is as important as understanding the arc perpendicular variation in the Himalayas. The geometric variability of the MHT holds significant implications for the occurrence of major and great earthquakes. Three-dimensional magnetotelluric (MT) forward modeling enables the investigation of potential crustal models along the MHT in northwest Himalayas. MT impedance tensors were computed utilizing the 3D forward modeling code MTD3FWD. Previously established MT resistivity and seismic velocity models from various sectors of the northwestern Himalayas were employed as inputs for generating the resistivity mesh necessary for 3D forward modeling. The computed impedance tensors by 3D forward computation were cross-referenced with the original published MT data to validate their accuracy. A lateral resistivity cross section is also derived from the 3D forward model along the sub-Himalaya and lesser-Himalaya region to study the lateral heterogeneity. The lateral resistivity cross-section reveals significant heterogeneity within the crust, marked by both high and low-resistive structures and a possible lateral ramp along the MHT. The geometry of the lateral MHT showcases a gradual incline within the Himachal sector and a steep ramp within the Garhwal and Kumaun sectors in the northwestern Himalayas. The crustal architecture exhibits distinct nearly-vertical resistive and conductive features beneath the study area. Consequently, the crust within this region is characterized by considerable heterogeneity, influenced by a network of subsurface faults and ridges. The Delhi Haridwar Ridge, which exhibits high resistivity, plays a significant role in dictating the lateral dip of the MHT and exerting control over seismic activity patterns in the region.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"353 ","pages":"Article 107213"},"PeriodicalIF":2.3,"publicationDate":"2024-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141139033","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":"Seismic evidence for possible entrainment of rising plumes by subducting slab induced flow in three subduction zones surrounding the Caribbean Plate","authors":"Morvarid Saki ,&nbsp;Sara Aniko Wirp ,&nbsp;Magali Billen ,&nbsp;Christine Thomas","doi":"10.1016/j.pepi.2024.107212","DOIUrl":"10.1016/j.pepi.2024.107212","url":null,"abstract":"<div><p>The dynamic processes associated with subducting tectonic plates and rising plumes of hot material are typically treated separately in dynamical models and seismological studies. However, various types of observations and related models indicate these processes overlap spatially. Here we use precursors to PP and SS reflecting off mantle transition zone discontinuities to map deflections of these discontinuities near three subduction zones surrounding the Caribbean Plate: 1) Lesser Antilles, 2) Middle America and 3) northern South American subduction zones. In all three regions slow seismic anomalies are present behind the sinking slab within the transition zone in tomographic images. Using array methods, we identify precursors and verify their in-plane propagation for M_W ≥ 5.8 events occurring between the years 2000 and 2020 by generating a large number of source receiver combinations with reflection points in the area, including crossing ray paths. The measured time lag between PP/SS arrivals and their corresponding precursors on robust stacks are used to measure the depth of the mantle transition zone discontinuities. In all three areas we find evidence for upward deflection of the 660 discontinuity behind the sinking slab, consistent with the presence of hot plume material (average temperature anomalies of 180 to 620 K), while there is not a corresponding downward deflection of the 410 km discontinuity. One interpretation of these disparate observations is suggested based on comparison to existing models of mantle convection and subduction: plume material rising across 660 km discontinuity could be entrained by lateral flow in the transition zone induced by the nearby sinking slab, and thus delaying the rise of hot material across the 410 km discontinuity.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107212"},"PeriodicalIF":2.3,"publicationDate":"2024-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0031920124000700/pdfft?md5=f75837acafbb78dc85c551a3a064f091&pid=1-s2.0-S0031920124000700-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141055267","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":"Spatial variation of body wave attenuation in Garhwal-Kumaun Himalaya region, India","authors":"Rahul Biswas,&nbsp;Prantik Mandal,&nbsp;Satish Saha,&nbsp;Raju Prathigadapa,&nbsp;M. Shekar,&nbsp;R. Vijaya Raghavan","doi":"10.1016/j.pepi.2024.107211","DOIUrl":"10.1016/j.pepi.2024.107211","url":null,"abstract":"<div><p>We have investigated the spatial variation of body wave attenuation in Garhwal-Kumaun Himalaya region from the datasets of 465 well located earthquakes, recorded at 52 broadband stations between 2017 and 2020. The body wave attenuation parameters <span><math><msub><mi>Q</mi><mi>P</mi></msub></math></span> and <span><math><msub><mi>Q</mi><mi>S</mi></msub></math></span> were estimated at each station by applying the extended coda normalization method for five different central frequencies ranging from 1.5 to 18 Hz. Strong frequency-dependent body wave attenuation was observed at each station over the whole region. Also, we found a significant variation of <span><math><msub><mi>Q</mi><mi>P</mi></msub></math></span> and <span><math><msub><mi>Q</mi><mi>S</mi></msub></math></span> from north to south which is consistent with geotectonic diversity beneath the study region. We have also made separate estimations of frequency-dependent relations for Garhwal and Kumaun Himalaya region in order to investigate the lateral variation in attenuation characteristics, and obtained the frequency-dependent relations as follows: <span><math><msub><mi>Q</mi><mi>P</mi></msub><mo>=</mo><mfenced><mrow><mn>30</mn><mo>±</mo><mn>3</mn></mrow></mfenced><msup><mi>f</mi><mfenced><mrow><mn>1.05</mn><mo>±</mo><mn>0.05</mn></mrow></mfenced></msup></math></span>, <span><math><msub><mi>Q</mi><mi>S</mi></msub><mo>=</mo><mfenced><mrow><mn>143</mn><mo>±</mo><mn>20</mn></mrow></mfenced><msup><mi>f</mi><mfenced><mrow><mn>0.88</mn><mo>±</mo><mn>0.07</mn></mrow></mfenced></msup></math></span> for the Garhwal Himalaya region and <span><math><msub><mi>Q</mi><mi>P</mi></msub><mo>=</mo><mfenced><mrow><mn>31</mn><mo>±</mo><mn>1</mn></mrow></mfenced><msup><mi>f</mi><mfenced><mrow><mn>1.09</mn><mo>±</mo><mn>0.02</mn></mrow></mfenced></msup></math></span>, <span><math><msub><mi>Q</mi><mi>S</mi></msub><mo>=</mo><mfenced><mrow><mn>121</mn><mo>±</mo><mn>11</mn></mrow></mfenced><msup><mi>f</mi><mfenced><mrow><mn>1.00</mn><mo>±</mo><mn>0.04</mn></mrow></mfenced></msup></math></span> for the Kuamun Himalaya region. Obtained <span><math><mi>Q</mi></math></span> values indicate strong body wave attenuation for both the region with no significant lateral variation. It may suggest the presence of crustal level folding, faulting, aqueous fluids, and metamorphic fluids below both the regions. Also, the ratios of <span><math><msub><mi>Q</mi><mi>S</mi></msub></math></span>/<span><math><msub><mi>Q</mi><mi>P</mi></msub></math></span> are high (<span><math><mo>&gt;</mo><mn>1</mn></math></span>) for the entire analyzed frequency range, suggesting a significant level of heterogeneity and tectonic complexities in the crust of the study region.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107211"},"PeriodicalIF":2.3,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141051381","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":"Midcrustal moderate-size earthquake occurrence in paleovolcanic structures off Jeju Island, South Korea","authors":"Junhyung Lee,&nbsp;Tae-Kyung Hong,&nbsp;Seongjun Park,&nbsp;Byeongwoo Kim","doi":"10.1016/j.pepi.2024.107210","DOIUrl":"10.1016/j.pepi.2024.107210","url":null,"abstract":"<div><p>A series of midcrustal moderate-size earthquakes occurred in the Korean Peninsula recently. A midcrustal <span><math><msub><mi>M</mi><mi>L</mi></msub><mn>4.9</mn></math></span> strike-slip earthquake with a fault-plane strike in N-S occurred on December 14, 2021 at the southwestern offshore region of Jeju Island, South Korea. The fault plane orientation and slip sense (faulting mechanism) hardly conform with the regional stress field. The deep focal depth and N-S directional strike-slip motion require transient changes in the medium properties and stress field. Strong ground motions of the midcrustal earthquake induce preferential dynamic stress changes in NE-SW direction, triggering subsequent aftershocks in NE-SW-directional adjacent faults. Both the static and dynamic stress changes caused by the mainshock contribute to the aftershock sequence. The number and focal depths of aftershocks decrease with distance from the mainshock. The different fault-plane orientations between the mainshock and aftershocks suggest earthquake nucleations in independent fault structures. The mainshock occurred in aseismic midcrustal paleovolcanic structure on the outskirt of a high seismicity region. The <span><math><msub><mi>M</mi><mi>L</mi></msub><mn>4.9</mn></math></span> earthquake suggests possible nucleation of earthquake in seismically-inactive paleotectonic structures, successively incurring aftershocks conforming to the ambient stress. The mainshock and aftershocks suggest that paleotectonic structures may behave as source structures to spawn earthquakes.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107210"},"PeriodicalIF":2.3,"publicationDate":"2024-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141055566","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":"A supervised machine learning approach for estimating plate interface locking: Application to Central Chile","authors":"Sebastián Barra ,&nbsp;Marcos Moreno ,&nbsp;Francisco Ortega-Culaciati ,&nbsp;Roberto Benavente ,&nbsp;Rodolfo Araya ,&nbsp;Jonathan Bedford ,&nbsp;Ignacia Calisto","doi":"10.1016/j.pepi.2024.107207","DOIUrl":"10.1016/j.pepi.2024.107207","url":null,"abstract":"<div><p>Estimating locking degree at faults is important for determining the spatial distribution of slip deficit at seismic gaps. Inverse methods of varying complexity are commonly used to estimate fault locking. Here we present an innovative approach to infer the degree of locking from surface GNSS velocities by means of supervised learning (SL) algorithms. We implemented six different SL regression methods and apply them in the Central Chile subduction. These methods were first trained on synthetic distributions of locking and then used to infer the locking from GNSS observations. We tested the performance of each algorithm and compared our results with a least squares inversion method. Our best results were obtained using the Ridge regression, which gives a root mean square error (RMSE) of 1.94 mm/yr compared to GNSS observations. The ML-based locking degree distribution is consistent with results from the EPIC Tikhonov regularized least squares inversion and previously published locking maps. Our study demonstrates the effectiveness of machine learning methods in estimating fault locking and slip, and provides flexible options for incorporating prior information to avoid slip instabilities based on the characteristics of the training set. Exploring uncertainties in the physical model during training could improve the robustness of locking estimates in future research efforts.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107207"},"PeriodicalIF":2.3,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141046448","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":"A new moment tensor catalogue of light to moderate earthquakes in Palu-Koro and Matano faults, Sulawesi, based on the regional network in Indonesia: Fault analysis and insight","authors":"Dian Kusumawati ,&nbsp;David P. Sahara ,&nbsp;Nanang T. Puspito ,&nbsp;Mudrik R. Daryono ,&nbsp;Andri D. Nugraha ,&nbsp;Muhamad Sadly ,&nbsp;Bambang S. Prayitno ,&nbsp;Daryono Daryono ,&nbsp;Nova Heryandoko ,&nbsp;Supriyanto Rohadi","doi":"10.1016/j.pepi.2024.107209","DOIUrl":"10.1016/j.pepi.2024.107209","url":null,"abstract":"<div><p>Starting from 2009, substantial improvements in the regional seismic network operating in Sulawesi, as part of the Meteorological, Climatological, and Geophysical Agency (BMKG) station deployment, allowed us to determine earthquake mechanism for 140 shallow (5–60 km) light to moderate size (3.8 ≤ M_w ≤ 6.1) earthquakes between 2009 and 2018 along the Palu-Koro and Matano faults, through moment tensor inversion. Ten (10) out of the 140 solutions obtained in this study were found in the International Seismological Centre Bulletin and used as validation. The double-couple mechanism of the best solutions (variance reduction ≥0.4 and condition number ≤ 7.5) is further used to analyze the Palu-Koro and Matano segments. We observed that the Donggala segment of the Palu-Koro fault shows variable earthquake mechanism types. Whereas the two subsequent segments, the Palu and Saluki segments, show predominate oblique strike-slip with normal and reverse mechanisms. The Matano fault is characterized by strike-slip mechanisms, with normal mechanisms also observed. The normal mechanisms depict the pull-apart system in the Matano segment, manifested as Matano Lake. The results of this work improve our understanding of regional tectonics.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107209"},"PeriodicalIF":2.3,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141055410","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":"Condition for metal fragmentation during Earth-forming collisions","authors":"Augustin Maller ,&nbsp;Maylis Landeau ,&nbsp;Laetitia Allibert ,&nbsp;Sébastien Charnoz","doi":"10.1016/j.pepi.2024.107199","DOIUrl":"10.1016/j.pepi.2024.107199","url":null,"abstract":"<div><p>The long-term evolution of the deep Earth depends on its initial temperature and composition. These were set by the large planetary collisions that formed the Earth. After each collision, the metallic core of the impactor fell into a molten silicate magma ocean. Previous investigations showed that, as it sank, the impactor core fragmented into drops. The overall fragmentation of the core controlled the efficiency of chemical transfers between the impactor metal and the magma ocean, and, as a consequence, the composition of the Earth's core and mantle. However, because previous studies lack an impact stage, it is unclear whether the projectile core fragmented during the impact at Earth's surface, or deeper in the magma ocean.</p><p>To answer this question, we conduct laboratory experiments modeling the collision of single-phase and two-phase impactors. In a first series of experiments, we investigate the impact of a single-phase centimetric liquid volume, representing the impactor core, onto a lighter immiscible liquid, representing the magma ocean. Our experiments approach the dynamical regime of planetary collisions for which inertia is large compared to surface tension. Varying the velocity and size of the impactor, we determine the conditions under which the impactor fragments into drops. We find that fragmentation occurs when the Froude number, which measures the relative importance of inertia to gravity, is larger than 40, regardless of surface tension. This fragmentation results from the growth of a turbulent Rayleigh-Taylor instability at the interface between the impacting liquid and the target pool. In contrast, when <span><math><mi>Fr</mi><mo>&lt;</mo><mn>10</mn></math></span>, the impactor remains coherent. In a second series of experiments, we use two-phase impactors to show that these results hold for impactors that are differentiated into a core and a mantle.</p><p>Applied to planet formation, our results suggest that the core of impactors less than 330 km in radius impacting at the escape velocity onto an Earth-sized planet fully fragments into droplets during the impact process, whereas the core of a giant Mars-sized impactor remains coherent. We derive a model for the depth at which the impactor core fragments in the magma ocean as a function of the impactor size and velocity. This model predicts that impactors with a radius less than 800 km fully fragment before reaching the bottom of the magma ocean. For velocities higher than twice the escape speed, some degree of fragmentation is unavoidable for any impactor size.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107199"},"PeriodicalIF":2.3,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141045357","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":"Significant variations in the structure and composition of the crust beneath northwestern India: Imprints of magmatism","authors":"B. Gowthami,&nbsp;D.S. Saju,&nbsp;G. Mohan","doi":"10.1016/j.pepi.2024.107198","DOIUrl":"10.1016/j.pepi.2024.107198","url":null,"abstract":"<div><p>Northwestern India was affected by the Neoproterozoic Malani and Erinpura magmatism, Cretaceous rifting, and magmatism associated with the Deccan precursors. Receiver function analysis was done using 1704 RFs from 18 stations to image and decipher the imprints of the magmatic events and comprehend the crustal modifications in terms of variations in structure and composition. The H-κ grid search and neighbourhood inversion techniques are used to retrieve the crustal structure and Vp/Vs ratios (<span><math><mi>κ</mi></math></span>). The study reveals significant variations in the crustal thickness (H = 34 km to 43 km), composition (<span><math><mi>κ</mi><mspace></mspace></math></span>=1.74 to 1.92) and shear wave velocity structure across northwestern India. The terrains encompassing the Erinpura granite and the Malani igneous suite in the vicinity of the Barmer rift are characterized by a thick (H ≥ 41 km) crust with felsic to intermediate composition (<span><math><mi>κ</mi></math></span> ≤ 1.81). The crust beneath the southern part of the Marwar basin is ≈ 38–40 km thick with mafic composition (<span><math><mi>κ</mi><mspace></mspace></math></span>&gt; 1.81). The region around the Barmer rift has a thin crust (H = 34–36 km) with intermediate to mafic composition. The region hosting the Early Cretaceous to Paleogene alkaline complexes exhibits a high Vp/Vs ratio (<span><math><mi>κ</mi><mspace></mspace></math></span>= 1.91) that may be associated with mafic cumulates emplaced by magmatic events that overprint the signatures of the Malani event. The crust is heterogeneous with low/high velocity intracrustal layers that reflect the fractionation of magma at different depths. The mafic residue, together with magmatic intrusions, results in a mafic lowermost crust with high shear velocities of 3.9–4.0 km/s beneath most stations. Overall, northwestern India is characterized by a thick crust with intermediate crustal composition and intracrustal layering resulting from large scale magmatic events linked to the Neoproterozoic reorganization of plates and younger magmatic events.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"352 ","pages":"Article 107198"},"PeriodicalIF":2.3,"publicationDate":"2024-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140761767","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}