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Analysis of the available Moho models for the Sikhote Alin region revealed significant discrepancies between them both in depth for individual sites and isolines over the entire area of the orogenic belt. In this study, results of the two-dimensional power spectrum analysis of the gravity field based on a digital model of the Bouguer gravity field were used to calculate the crustal thickness (Moho depth). The data from seven seismic profiles were employed to adjust the new model. The new model and its correlation with structural and geological data allowed the following conclusions to be made. (1) The span of Moho depth variations for the southern part of the continental Far East of Russia is just over 18 km, with extreme values of 42.4 and 24.0 km. The Moho is deepest (41–42 km) beneath mountain ranges and massifs: Sikhote Alin in the east and Yam Alin and Aesop in the north-west. The Moho is most shallow (27–30 km) beneath the sedimentary basins Khanka, Partizan-Sukhodol, Suifun in the south, Middle Amur and Lower Amur in the central part of the study area, and Upper Zeya and Uda in the north-west. (2) Correlation of the Moho estimates derived from the Airy model and the power spectrum of the Bouguer gravity field shows significant positive correlation. The Moho depths practically coincide over 11% of the area, with a difference of ± 5%. The Moho depth discrepancies are in the range of 5–15% over 48% of the study area, and over the rest of the study area (41%), discrepancies are in the range of 15–30%. (3) A comparison between the new gravity Moho model and the geological and structural data shows that the model is highly correlated with the development of Cretaceous–Early Eocene orogenic and post-orogenic granitoid massifs and Cretaceous–Pliocene extrusive igneous rocks. The former geographically coincide with two linear zones in the Moho relief with depths of more than 35 km, and the latter with the Mesozoic–Cenozoic sedimentary basins and the East Sikhote Alin volcano–plutonic belt.

The location and origin of Neoproterozoic‐Cambrian sutures provide keys to understand the formation and evolution of the supercontinent Gondwana. The Larsemann Hills is located near a major Neoproterozoic‐Cambrian suture zone in the Prydz Belt, but has not been examined locally by comprehensive geophysical studies. In this study, we analyzed data collected from a one‐dimensional (1D) joint seismic‐MT array deployed during the 36th Chinese National Antarctic Research Expedition. We found that a sharp Moho discontinuity offset of 6–8 km shows up in the stacked image of teleseismic P‐wave receiver function analysis; coinciding with the abrupt Moho offset, a near‐vertical channel with (a) low resistivity extending to the uppermost mantle depths, and (b) high crustal Poisson's ratio in the crust is identified. These findings provide evidence for the determination of the location and collisional nature of the Prydz belt or a portion of it. Plain Language Summary Our study seeks to unravel the history of a supercontinent called Gondwana. We do this by exploring ancient geological features known as sutures. These sutures are like stitches that hold the Earth's crust together, and they're crucial in understanding how continents were once connected. We specifically focused on a place in Antarctica called the Larsemann Hills, which is located near an important suture zone. This region hasn't received much attention from scientists until now. During the 36th Chinese National Antarctic Research Expedition, we made some exciting discoveries. We found a clear boundary in the Earth's crust, a bit like a seam in a piece of clothing. At the same time, we noticed a unique underground pathway. This pathway had special properties, suggesting that it reaches deep into the Earth's mantle. It's a bit like finding a hidden treasure beneath the Earth's surface. Our findings strongly suggest a connection between these underground discoveries and the ancient sutures in the Earth's crust. In other words, we're piecing together a puzzle that can help us learn more about the Earth's past and how continents have moved over millions of years. Key Points A distinct Moho discontinuity offset of 6–8 km is found in the stacked image obtained from P‐wave receiver function In conjunction with the abrupt Moho offset, a nearly vertical conduit with low resistivity and high Poisson's ratio is identified These geophysical results provide crucial evidence for determining the collisional nature and location of the Prydz orogenic belt

Oceanic lithosphere descends into Earth’s mantle at subduction zones and drives material exchange between Earth’s surface and its deep interior. The subduction process creates chemical and thermal heterogeneities in the mantle, with the strongest gradients located at the interfaces between subducted slabs and the surrounding mantle. Seismic imaging of slab interfaces is key to understanding slab compositional layering, deep-water cycling and melting, yet the existence of slab interfaces below 200 km remains unconfirmed. Here, we observe two sharp and slightly dipping seismic discontinuities within the mantle transition zone beneath the western Pacific subduction zone that coincide spatially with the upper and lower bounds of the high-velocity slab. Based on a multi-frequency receiver function waveform modelling, we found the upper discontinuity to be consistent with the Mohorovičić discontinuity of the subducted oceanic lithosphere in the mantle transition zone. The lower discontinuity could be caused by partial melting of sub-slab asthenosphere under hydrous conditions in the seaward portion of the slab. Our observations show distinct slab–mantle boundaries at depths between 410 and 660 km, deeper than previously observed, suggesting a compositionally layered slab and high water contents beneath the slab.Two seismic discontinuities in the mantle transition zone beneath the western Pacific represent subducted slab interfaces that could be the slab Moho and partially molten sub-slab asthenosphere, according to an analysis of seismic data.

A M6.8 earthquake struck the High Atlas Mountains in Morocco on 8 September 2023, ending a 63‐year seismic silence. We herein attempt to clarify the seismogenic fault and explore the underlying mechanism for this seismic event based on multiple data sets. Utilizing probabilistic Bayesian inversion on interferometric radar data, we determine a seismogenic fault plane centered at a depth of 26 km, striking 251° and dipping 72°, closely aligned with the Tizi n’Test fault system. Given a hypocenter at the Moho depth, the joint inversion of radar and teleseismic data reveals that the rupture concentrates between depths of 12 and 36 km, offsetting the Mohorovičić discontinuity (Moho) at ∼32 km. Considering a strong link between magma activity and failure in lower crust, we propose that the triggering of the earthquake possibly was mantle upwelling that also supports the high topography. Plain Language Summary On 8 September 2023, a devastating earthquake with a magnitude of 6.8, struck the High Atlas Mountains in Morocco, breaking a 63‐year seismic silence. In this work we utilized geodetic, seismic, and seismicity data to investigate the earthquake, pinpointing its origin within the Tizi n’Test fault system at 12–36 km depths and causing displacement of the Mohorovičić discontinuity (Moho), where Earth's crust meets the mantle. Highlighting the impact of the mantle upwelling, this event underscores its significance in shaping regional topography and driving crustal deformation along established faults, leading to unusual, significant seismic activity in areas of minimal plate convergence. This earthquake highlights the importance of incorporating deep crustal dynamics into seismic hazard evaluations, challenging traditional risk models with its implications on earthquake genesis far from tectonic boundaries. Key Points Interferometric radar data, Bayesian inversion techniques and teleseismic data reveal the seismogenic fault and underlying mechanisms The seismogenic fault centered at a depth of 26 km, striking 251° and dipping 72°, closely aligned with the Tizi n’Test fault system We propose that the 2023 M6.8 earthquake in Morocco was possibly triggered by mantle upwelling on a steep fault that offsets the Moho

We present a new digital Moho depth map of the Carpathian-Pannonian region. The map was produced by compiling Moho discontinuity depth data, which were obtained by interpretation of seismic measurements taking into account the results of 2-D and 3-D integrated geophysical modelling. The resultant map is characterized by significant Moho-depth variations. The trends and features of the Moho in this region were correlated with tectonic units.

Forecast of eruptive activity is a core challenge in volcanology. Here, we present an actual forecast for the end of the 2021 La Palma eruption. Using continuous GNSS data, we identified a co‐eruptive quasi‐exponential deflation trend. Assuming mass conservation, magma upflow from an overpressurized reservoir drives the eruptive process. The forecast was carried out during the eruption, however there was uncertainty in the key percentage of drop in driving pressure necessary to stop this eruption. In hindcast, we explore how forecast uncertainty reduces with increase in ingested near‐real time data. We conclude that precise forecasts could have been possible, but only after twice a characteristic exponential decay time‐scale, providing error estimates of 45% of the actual duration. We verify the mass conservation assumption using eruptive material volumes and propose that the eruption dynamics was controlled by a main reservoir at a depth close to Moho discontinuity beneath Cumbre Vieja volcano. Plain Language Summary The forecast, an actual prediction of the temporal or spatial characteristics of a future event, of when a volcanic eruption will end is challenging. This is reflected in the scarcity of literature about it. During the 2021 eruption of La Palma, we used GNSS geodetic data that tracks the change in shape of a volcano to make such a forecast. We exploited a temporal decaying pattern of this data and some basic assumptions that could be interpreted as when the eruption would stop. The forecast was made before the eruption ended, although it was too uncertain to have practical implications. With the eruption already over, we looked back at the data and found that the more information we could have analyzed, the more accurate the forecast could have been. We conclude that accurate forecasts could be possible after twice the characteristic time of the decay process has passed. Key Points Using deformation data, the end of La Palma eruption, although uncertain, was possible to forecast Extensive end of eruption hindcasts to understand bounds on method applicability for La Palma eruptions Real‐time ground deformation interpretation could represent a simple and powerful tool for La Palma volcano monitoring

The Afro‐Arabian region is one of the few places on land, where rifting processes at divergent plate boundaries can be thoroughly investigated. One of the crucial factors in understanding rifting processes involves assessing the crustal thickness. In this study, gravity data from the Earth Gravitational Model 2008 is used to create a seamless map of the depth to the Moho interface. Unlike many previous investigations that focused on specific localized areas, within the region, results from the current study provide a comprehensive view. The depth obtained from the current investigation aligns well with findings from earlier studies, exhibiting a bias of 0.69 km and a standard deviation of 3.89 km. Within the region, maximum and minimum depths to the Moho interface are observed beneath the northwest Ethiopian Plateau and the Gulf of Aden Rift (GAR), respectively. Analyzing profiles across the Red Sea, Main Ethiopian, and GARs, the study concluded that the Southern Main Ethiopian Rift is in an earlier stage of the rifting process, while the GAR is at an advanced stage. Furthermore, the interpretation of the current findings led to the inference that there might exist two potential plume tails driving the rifting process in the East Africa Rift—one originating from the Afar region and the other from South Kenya. This inference primarily relies on the isostatic compensation stages observed in the various rift systems throughout the region. Key Points Moho depth from the Earth Gravitational Model 2008 model is derived with a bias of 0.69 km and a standard deviation of ±3.89 km when compared to prior studies The maximum depth to the Moho interface is 42.9 km beneath the NW Ethiopian Plateau and the shallowest depth is 5.3 km beneath the Gulf of Aden Rift The Southern Main Ethiopian Rift is at an early stage of rifting and two mantle plume tails are potentially driving the rifting process

The Azores Triple Junction offers a unique opportunity to investigate the interplay between volcanism and tectonic activity. After 60 years of quiescence in São Jorge Island, in March 2022, the island experienced a volcano-tectonic unrest, accompanied by widely felt earthquakes and surface deformation. We conducted an extensive study of this anomalous activity throughout 2022, through a purely automated analysis based on a deep-learning approach for seismic activity, combined with the processing and analysis of data from GNSS stations in the archipelago. The joint interpretation of ground deformation and seismicity suggests a failed magmatic eruption, which we have summarized in a four-stage conceptual model. The unrest began on 16 March 2022 with a period of vertical uplift that lasted for 2 days. On 19 March, the deformation reversed with a burst of seismicity that marked a rapid dike intrusion in the crust which abruptly stopped a few kilometers under the surface. Over the following weeks, the relocated seismicity suggests an intense overpressure near the Moho discontinuity and reveals, in great detail, a lateral magmatic expansion in a sill-like pattern. Finally, from the second week of April until the end of the year a decrease in seismic activity and a lack of deformation registered, indicates a decline and stabilization of the volcano-tectonic process.

Continental arcs are the sites of production of continental crust, but the origin of these magmatic systems is not well understood. Although a number of processes have been suggested to be important, the role of water migrating from slab to surface during subduction has been underappreciated. Directly below the Moho, hot (approximately 1,100 °C), hydrous basaltic magmas fractionate as they cool to the regional geotherm at 750 to 800 °C, ultimately solidifying as mafic underplates. Cooling and fractionation cause water to exsolve and ascend, triggering fluid-fluxed melting of overlying mafic underplates and other crust. Melting of prior mafic underplates buffers temperatures and generates the voluminous, juvenile low-K magmas of Cordilleran batholiths. These granitoid magmas comprise a low-temperature slurry of melt and residue, and recrystallize into silicic mush during adiabatic ascent. Such hydrous mushes are intermittently infused by hotter, more mafic magmas, which hybridize and facilitate ascent and, potentially, eruption. Fluid-fluxed melting overcomes many of the general petrological and geochemical problems associated with models dominated by fractional crystallization. The role of water during repeated episodes of mafic underplating is critical to generate the juvenile granitoid infrastructure of the continents.Migration of water from the slab to the surface during subduction is highlighted as a key process in the formation of continental crust.

The crustal structure beneath the Japanese islands, including depth distributions of the Conrad and Moho discontinuities, was estimated using a tomographic inversion of regional body wave arrival times. Depth distributions of the bottom of the surface layer, the Conrad, and the Moho were modeled with two‐dimensional B spline functions, while velocity distributions in layers were expressed by three‐dimensional B spline functions. The depth of the discontinuities and the velocity in the layers were estimated simultaneously by the least squares method. The velocity structure was sequentially estimated from shallower parts to deeper parts to avoid correlation between them. This sequential analysis provided improved depth resolution. The deepest region of the Moho discontinuity was located in central Honshu, reaching about 40 km. The Moho discontinuity was generally deep in the central part of the islands, whereas it was relatively shallow in the Kanto, southwestern Chubu, and Chugoku districts in Honshu and in northern Kyushu. Some of the shallow Moho regions would be related to graben formation due to tensile tectonic stress since the Miocene. The results were compared with those of seismic refraction surveys and receiver function analyses, and it was found that the obtained model was consistent with many of these studies.