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The Banda Arc in eastern Indonesia has a complex tectonic history involving oceanic and continental subduction, arc‐continent collision and slab rollback. Among these the subduction rollback that began at 16 Ma shaped the regional tectonic configuration, causing notable upper plate extension evidenced by the Banda Sea and Weber Deep. However, the effects of subduction rollback on the lower plate remain less understood. The Aru Trough, part of subducting Australian continental margin, shows strong deformation and high seismicity, making it ideal for studying these effects. Utilizing multibeam bathymetry, seismic reflection profiles, GPS observations, seismicity and focal mechanisms, we investigate the crustal deformation, driving mechanisms and seismic risks in the Aru Trough under the background of Banda slab rollback. The Aru Trough shaped like an inverted triangle narrows from 160 to 40 km southward. It has a fast 53.8 mm/yr extensional rate at present, when combined with its maximum width suggesting a 3 Ma age. High‐angle faults (>60°) are present at its margins and interior. The trough has a high density of seismicity up to 5.9 events per 25 km2, with dominant normal and strike‐slip events, consistent with observed deformational patterns. The low seismic b‐value of 0.82 ± 0.01 suggests a high‐stress state with potential for strong earthquakes (Mw ≥ 6.5). Our findings indicate that lower plate deformation is profoundly influenced by subduction rollback, oblique arc‐continent collision and regional strike‐slip faulting. Understanding deformation in the Aru Trough is crucial for grasping the broader tectonic evolution of the Banda Arc and assessing seismic risks. Key Points: The Aru Trough is deformed by extension as evidenced by high‐angle normal faults and fast present‐day extensional rate of 53.8 mm/yrThe Aru Trough was initiated by slab rollback at 3 Ma with subsequent evolution affected by arc‐continent collision and strike‐slip faultingSeismicity in the Aru Trough shows a high density and low seismic b‐value, indicating high stress and a potential for strong earthquakes [ABSTRACT FROM AUTHOR]

The seismicity of the Philippines and Taiwan provides insight into the tectonics and seismic hazards of a region characterized by subduction and collision. We summarize the seismotectonics of the Philippines and Taiwan by documenting the distribution of hypocenters for earthquakes of magnitude M ≥ 4.6 and focal mechanisms for earthquakes of magnitude M ≥ 5.0 over ∼21 years. We quantify seismicity rates (earthquake frequency) and compare seismicity distributions with proposed tectonic and faulting models. 6,187 earthquakes of magnitude M ≥ 4.6 occurred between 1 January 2000 and 31 March 2021, 79% at depths <70 km and 70% having magnitudes M < 5.0. Approximately 88 earthquakes of magnitude M ≥ 5.0 occur per year, with 12 events of magnitude M ≥ 7.0 occurring since January 2000. Seismic activity decreases exponentially between 50 and 210 km depth at a rate ∼10% faster than the global average. Intermediate and deep earthquakes at depths >70 km trace the Wadati‐Benioff zones of subducting slabs, most of which are only seismically active to depths of ∼250 km. The distribution of earthquakes at depths >70 km is likely influenced by the subduction of young lithosphere, slab tearing, and phase boundary interactions between depths of 410 and 660 km. Shallow earthquakes at depths ≤70 km are generated by megathrust, crustal, and intraslab faulting. Crustal thrust and strike‐slip faulting are the most abundant and prevalent sources of damaging earthquakes. The Philippines and Taiwan are subject to high seismic risk, similar to nearby Indonesia. Plain Language Summary: The Philippines‐Taiwan region is tectonically active with frequent earthquakes. We summarize the geographical distribution, sources, and frequency of earthquakes in the region over 21 years, compare distributions to proposed tectonic models, and investigate earthquake hazards. This region experiences on average 88 earthquakes per year of magnitudes ≥5.0. Twelve events of magnitudes ≥7.0 occurred between January 2000 and March 2021. Most earthquake activity is shallow and occurs at depths ≤70 km. In some regions, such as Southern Mindanao in the Philippines, seismicity extends to depths >600 km. Shallow earthquakes are generated by various faulting sources, and seismic hazards are abundant and seismic risk is high, as several population centers are located near active faults. Key Points: We summarize seismotectonics of the Philippines‐Taiwan region using hypocenters, focal mechanisms, seafloor age, and tectonic modelsShallow seismicity is abundant, consisting of thrust, strike‐slip, and normal faulting, which all pose serious seismic hazardsSubduction zone seismicity occurs at depths ∼100–250 km for young (20–40 Ma) oceanic lithosphere, and up to 680 km for older (60–80 Ma) [ABSTRACT FROM AUTHOR]

This study provides a global assessment of the abundance of the major oxides in the deep continental crust. The combination of geochemistry and seismology better constrains the composition of the middle and lower continental crust better than either discipline can achieve alone. The inaccessible nature of the deep crust (typically >15 km) forces reliance on analog samples and modeling results to interpret its bulk composition, evolution, and physical properties. A common practice relates major oxide compositions of small‐ to medium‐scale samples (e.g., medium to high metamorphic grade terrains and xenoliths) to large scale measurements of seismic velocities (Vp, Vs, Vp/Vs) to determine the composition of the deep crust. We provide a framework for building crustal models with multidisciplinary constraints on composition. We present a global deep crustal model that documents compositional changes with depth and accounts for uncertainties in Moho depth, temperature, and physical and chemical properties. Our 3D compositional model of the deep crust uses the USGS Global Seismic Structure Catalog (Mooney, 2015) and a compilation of geochemical analyses on amphibolite and granulite facies lithologies (Sammon & McDonough, 2021, https://doi.org/10.1029/2021JB022791). We find a SiO2 gradient from 61.2 ± 7.3 to 53.3 ± 4.8 wt.% from the middle to the base of the crust, with the equivalent lithological gradient ranging from quartz monzonite to gabbronorite. In addition, we calculate trace element abundances as a function of depth from their correlations with major oxides. From here, other lithospheric properties, such as Moho heat flux (21.6−5.6+16.0 ${21.6}_{-5.6}^{+16.0}$ mW/m2), are derived. Plain Language Summary: Using many different geophysical and geochemical techniques together helps us understand the composition of the bottom two‐thirds of the continental crust. We cannot sample much of the continental crust directly because of how deep it is. Instead, we rely on rocks that have been brought to the surface and measurements of the speed of seismic waves traveling through the crust in order to determine what the deepest parts of the crust are made of. Accounting for various factors, such as crust temperature and tectonic setting, allows us to create a large‐scale model for the composition of the deep crust. Key Points: We present a global model for the composition of the deep continental crust constrained by geochemical and geophysical dataCrustal SiO2 content decreases with increasing depth, and compositions correlate to relative depth rather than absolute depthMoho heat flux is predicted at 21.6−5.6+16.0 ${21.6}_{-5.6}^{+16.0}$ mW/m2 [ABSTRACT FROM AUTHOR]

A high‐resolution 3D crustal and upper‐mantle shear‐wave velocity model of Northeast China is established by joint inversion of receiver functions and fundamental‐mode Rayleigh wave phase velocities. The teleseismic data used to calculate receiver functions are collected from 107 CEA permanent sites and 118 NECESSArray portable stations. Rayleigh wave dispersion measurements are extracted from an independent tomographic study. Our model exhibits significant detail in S wave velocity structure. Particularly, we observe a nearly constant S wave velocity of 3.4–3.6 km/s from shallow to deep crystalline crust under the study area, which we attribute to a high thermal gradient. Some modestly positive S wave velocity anomalies in the crust beneath the Songliao basin are interpreted as solidified late‐Mesozoic mafic intrusions. In the upper mantle, we confirm the local presence of low‐velocity zones below the Changbai mountains and Lesser Xing'an mountain range, consistent with asthenospheric mantle upwelling models. Furthermore, moderately low shear velocities imaged beneath the Halaha and Abaga volcanoes indicate possible pathways of magma ascent through the lithospheric mantle from the asthenosphere. At a regional scale, the average lithosphere‐asthenosphere boundary depth increases from ∼70 km under the greater Changbai mountains to ∼100 km below the Songliao basin, and reaches ∼110–120 km beneath the Greater Xing'an mountain range in the west. The conjectured dense mantle lid under the Songliao basin, characterized by fast S velocities, may have prevented sublithospheric melts from migrating to the surface. Plain Language Summary: Northeast China is a unique region with a combination of ancient Precambrian geology, active seismicity, and volcanism. The presence of widely distributed volcanoes in this region is enigmatic and their origin has been widely debated. We use available seismic data to create a high‐resolution 3D shear‐wave velocity model for the crust and upper mantle of Northeast China. Our model reveals significant multiscale seismic velocity anomalies in the crust, mantle lithosphere and asthenosphere that we associate with the volcanic/magmatic processes. The lithospheric thickness gradually increases from ∼70 km beneath the Changbai mountains to ∼120 km some 1,000 km to the west. Our results provide novel constraints on the crustal and upper‐mantle structure of Northeast China and help to interpret the mechanism behind active volcanism and the geodynamic setting. Key Points: A nearly constant velocity in the crust may be due to a high thermal gradient and local high crustal velocities may denote mafic intrusionsLow S velocities are imaged in the upper mantle below the largest active volcanoes and locally the lithospheric mantle is thinned or absentThe lithosphere is ∼70 km thick below the greater Changbai mountains and thickens to ∼120 km under the Great Xing'an mountains in the west [ABSTRACT FROM AUTHOR]

The Caribbean plate is an enclosed oceanic basin whose formation and evolution are controversial. In the most commonly accepted model, the Caribbean plate is mainly composed of the Caribbean Large Igneous Province (CLIP) and the buoyant characteristic of this oceanic plateau resisted subduction and allowed an eastward migration to its present position north of South America. In this study, we integrate a broad range of geophysical and geomorphological data to define structural elements and present‐day tectonics of the Caribbean plate and the surrounding region. We present a Bouguer gravity anomaly map and a new crustal thickness map that documents large areas of normal‐thickness oceanic crust within the Venezuela and Colombia basins of the Caribbean plate. Selected cross sections of seismicity and P‐wave anomalies from a seismic tomographic model depict the present‐day geometry of subducting oceanic plates within the Caribbean region. We observe that rather than resisting subduction, as expected for the thick crust of a buoyant large igneous province, the subduction of the Caribbean plate can be traced to a depth of 600 km beneath NW South America. This, together with the crustal thickness map, implies that a significant area of the Caribbean plate, including the subducted portion, is composed of normal‐thickness oceanic crust. As proposed by the Pacific origin model, the Caribbean plate likely migrated eastward from the Pacific Ocean as an oceanic plate mostly with normal‐thickness crust and limited portions of the crust thickened by hot spot volcanism (CLIP). Plain Language Summary: The Caribbean plate and northern South America are studied using topography and multiple geophysical data sets, including gravity, magnetics, crustal thickness, seismicity, and seismic images of the upper mantle. These data sets were used to analyze crustal properties as well as the past and present interaction of tectonic plates in this region. Our results show large areas of ocean crust with normal thickness within the Caribbean plate. Seismicity in the circum‐Caribbean subduction zones rarely exceeds 200 km in depth, whereas seismic imaging shows subducting slabs reach a depth of 600 km or more. This implies that subduction has been long‐lived at these active margins. These results also show that the Caribbean plate is subducting beneath NW South America, something that would not be expected for the thick crust of a buoyant large igneous province. As proposed by the Pacific origin model, the Caribbean plate migrated eastward from the Pacific Ocean as an oceanic plate mostly with normal‐thickness crust and limited portions of the crust thickened by hot spot volcanism. Key Points: A new crustal thickness map and gravity maps reveal large areas of normal‐thickness oceanic crust within the Caribbean plateP‐wave seismic tomography images show that the subducted Caribbean plate reaches 660 km depth, but slab seismicity terminates at 200 kmCombined seismicity, gravity, and magnetic maps reveal the active tectonics of the circum‐Caribbean accretionary and magmatic boundary [ABSTRACT FROM AUTHOR]

Indonesian seismicity provides important insights into the tectonics and hazards of a region that is, characterized by a remarkable diversity in faulting, including subduction, extension, thrusting, and strike‐slip faulting. We present a synthesis of Indonesian seismotectonics by documenting the distributions of hypocenters (≥M 4.6) and focal mechanisms (≥M 5.0) over ∼20 years, quantifying seismicity rates, and comparing observed seismicity trends with recent tectonic and tomography models. Of the 20,622 events ≥M 4.6 observed in the study region, ∼77% are shallow (≤70 km depth) and of magnitudes 70 km depth traces subducting slabs with geometry consistent with tomography models. Seismicity rates increase in the Mantle Transition ZoneShallow seismicity generated by diverse faulting is consistent with regional tectonic and faulting models, posing seismic hazards [ABSTRACT FROM AUTHOR]

Active source seismology provides a critical constraint on the global crustal structure. However, the heterogeneous data coverage means that interpolation is necessary to fill the gap between seismic profiles. This has the potential to cause large uncertainties especially if the data are interpolated over a large distance. In previous models, geological intuition was often employed to ensure reasonable results. To investigate crustal model uncertainty, we apply geostatistical analysis to a database of active seismic investigations. Unlike previous models, our workflow in the construction of the crustal model is completely transparent. Apart from the points from the database, we only use an a priori separation in oceanic and continental domains. We calculate global maps of Moho depth and average P wave velocity in the crystalline crust. Additionally, we obtain the interpolation error and error covariance. Overall, our results agree with previous global crustal models such as Crust1.0. Our uncertainty estimates show that the Moho depth uncertainty in the most well studied areas such as North America and Europe is less than 4 km but can reach 10 km or more in frontier regions such as most of Africa. P wave velocity shows the same pattern, but is less accurate overall, due to more small‐scale variation. We demonstrate the benefit of having a numerical estimate of uncertainty by propagating the uncertainty to the residual topography. We see two main uses for our crustal model in the geophysical research community: (1) as a starting model for inversions focusing on the crust and upper mantle and (2) as a starting point for including other pointwise information about crustal structure, for example, from passive seismology. Key Points: A data‐driven approach is presented to determine crustal structure and its uncertainty on a global scaleUncertainty of crustal thickness is less than 4 km in well‐studied areas and reaches 12 km in poorly studied regions [ABSTRACT FROM AUTHOR]

Extension and rifting of the lithosphere is fundamental to the evolution of the continents, but the mechanism by which the lithosphere thins under extension remains enigmatic. Using a new dense array of magnetotelluric data from the rifted margin of southeast China, we resolve the three‐dimensional electrical resistivity structure of the lithosphere to constrain the process of rifting and thinning. Our results reveal a brittle‐ductile transition zone in the Cathaysia Block, featuring low electrical resistivity and low seismic velocity at 15‐ to 20‐km depth. A southeast directed dip is resolved for the Jiangshan‐Shaoxing Fault—a suture zone originally formed by the Neoproterozoic collision of Yangtze and Cathaysia Blocks. This boundary fault had been reactivated to different extents by the Early Paleozoic and Early Mesozoic intracontinental orogenies of south China. Its present structural style, however, was interpreted as a lithospheric‐scale detachment fault that acted during the Late Mesozoic extension and rifting. Given the asymmetries of topography, electrical resistivity, Bouguer gravity anomaly, and Late Mesozoic volcanism across the Gan‐Hang Rift, we propose an asymmetric simple shear extension model for the south China rift system. Water content of up to 0.1 wt% and melt fraction of up to 1% are estimated at 70‐km depth beneath the central Wuyi Mountains, suggesting hydration and partial melting of the mantle lithosphere. The hydration weakening of the mantle lithosphere promoted both the gravitational instability and convective removal of the lowermost lithosphere in south China. Key Points: MT data reveal a brittle‐ductile transition zone featuring low electrical resistivity at 15‐ to 20‐km depth in the Cathaysia BlockThe Jiangshan‐Shaoxing Fault is a SE dipping fault acting as a low‐angle detachment in the Mesozoic simple shear extensionHydration weakening of the upper mantle is essential to the gravitational instability and convective removal of the lowermost lithosphere [ABSTRACT FROM AUTHOR]

We measured phase velocities at 13 periods from 20 s to 143 s using Rayleigh wave data recorded at recently installed, dense (135) broadband seismic stations in the Arabian shield and determined the shear-wave velocity structure. Our results clearly reveal a 300 km wide upper mantle seismic low-velocity zone (LVZ) beneath the western Arabian shield at a depth of 60 km and with a thickness of 130 km. The LVZ has a north-south trend and follows the late-Cenozoic volcanic areas. The lithosphere beneath the western Arabian shield is remarkably thin (60-90 km). The 130 km thick mantle LVZ does not appear beneath the western Red Sea and the spreading axis. Thus, the Red Sea at 20°-26°N is an asymmetric rift, with thin lithosphere located east of the Red Sea axis, as predicted by the low-angle detachment model for rift development. Passive rifting at the Red Sea and extensional stresses in the shield are probably driven by slab pull from the Zagros subduction zone. The low shear-wave velocity (4.0-4.2 km/s) and the geometry of LVZ beneath the western shield indicate northward flow of hot asthenosphere from the Afar hot spot. The upwelling of basaltic melt in fractures or zones of localized lithospheric thinning has produced extensive late Cenozoic volcanism on the western edge of the shield, and the buoyant LVZ has caused pronounced topography uplift there. Thus, the evolution of the Red Sea and the Arabian shield is driven by subduction of the Arabian plate along its northeastern boundary. [ABSTRACT FROM AUTHOR]