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In this study, we used the Pn tomography method to obtain detailed velocity and anisotropy structures of the uppermost mantle beneath Sakhalin–Kuril–Kamchatka region for improving the understanding of plate subduction, arc–arc collision, and volcanism. We found low Pn velocities beneath volcanoes and areas characterized by pronounced tectonic activity and high Pn velocities with strong anisotropy in the subducting plate. Low Pn velocity anomalies beneath southern Sakhalin connected the low‐velocity anomalies in the mantle and crust, indicating the ascent of fluid or melt, and may provide a magmatic source for the rear‐arc Rishiri volcano. In the absence of plate subduction, low‐velocity anomalies and north–south Pn anisotropy manifested beneath northern Kamchatka, revealing the lateral propagation of mantle flow beneath this northern region. We suggest that the eastern boundary of the slab window at the Kamchatka–Aleutian junction is likely to be located near the Komandorsky Islands. Plain Language Summary: The Northwest Pacific region is prone to recurrent earthquakes and volcanic activities, attributable to plate subduction and multiple plate interactions. This study, focuses on elucidating the uppermost mantle structure beneath the Sakhalin–Kuril–Kamchatka region using seismic tomography. Beneath the island chain featuring volcanoes and areas with a lot of tectonic activity, seismic waves travel slower. This phenomenon implies the possible presence of magma or hot materials beneath these regions. In southern Sakhalin, a linkage is established through low Pn velocities connecting areas of low seismic wave velocity in the deeper mantle and crust. This linkage suggests a conduit for fluids or molten materials, potentially feeding for the Rishiri volcano situated beyond the volcanic arc. Strong low velocities, coupled with north–south Pn fast directions are identified beneath northern Kamchatka, indicating the northward propagation of mantle flow. Our imaging analysis suggests that the eastern edge of the slab window (the region where the plate is absent) at the Kamchatka–Aleutian junction is likely proximate to the Komandorsky Islands. This study provides new seismological insights into the plate collision and subduction processes as well as the deep structures in the Sakhalin–Kuril–Kamchatka region. Key Points: Low Pn velocities clarify the upward path of the mantle‐derived thermal material beneath Sakhalin and its influence on surface volcanismStrong low Pn velocities and N–S anisotropy beneath northern Kamchatka signify the lateral propagation of mantle flow directed northwardThe eastern boundary of the slab window at the Kamchatka–Aleutian junction may be located near the Komandorsky Islands [ABSTRACT FROM AUTHOR]

The eastern Tibetan Plateau (TP) is crucial to the exploration of plateau outgrowth mechanisms. Teleseismic attenuation may provide constraints on anelasticity in the lithosphere‐asthenosphere system and may therefore improve the understanding of plateau outgrowth and material extrusion. This study use dense array data across the eastern TP to measure relative attenuation from teleseismic P‐wave phases. These observations are then used to invert a 2D relative attenuation map and a 3D Qp−1 model. Weak attenuation is observed beneath the Sichuan Basin and most of the Dianzhong Block at depths of both 0–100 km and 100–200 km (Qp−1 < 0.003). Strong attenuation is observed beneath the eastern TP and southwestern Dianzhong Block at depths of 0–100 km (Qp−1 ∼ 0.01–0.13), but underneath the eastern TP only at depths of 100–200 km (Qp−1 ∼ 0.013–0.015). These results suggest a cratonic lithosphere underneath the Dianzhong Block similar to that beneath the Sichuan Basin. We assume that this is the cooled lithosphere remnant of the Permian Emeishan plume. In contrast, strong attenuation beneath the eastern TP would indicate a thick lower crust and asthenosphere with intense heating. The boundary between strong and weak attenuation lies close to the Longmenshan‐Xiaojinhe faults. We infer that the materials extruded eastward from the eastern TP cross this boundary into the southwestern Dianzhong Block in the lower crust, but stop at this boundary in the asthenosphere. Plain Language Summary: Seismic attenuation describes the energy consumption of seismic waves which reflects subsurface anelasticity and so can provide constraints on the ductile materials in the lower crust and the asthenosphere. Here we present a 2D relative attenuation map and a 3D upper mantle Qp−1 model for the eastern Tibetan Plateau. We find weak attenuation at depths above 200 km beneath the Sichuan Basin and most of the Dianzhong Block. Strong attenuation is observed beneath the southwestern Dianzhong Block at crustal depths, and underneath the eastern Tibetan Plateau at both crustal and asthenospheric depths. Our results suggest that the lithosphere beneath the Dianzhong Block has similar cratonic features to that beneath the Sichuan Basin. A thick and hot lower crust and asthenosphere with strong heat activity beneath the eastern Tibetan Plateau are also indicated by our attenuation images. Strong and weak attenuation are bordered by the Longmengshan‐Xiaojinhe faults. We would infer that the ductile materials extruded from the Tibetan Plateau cross this boundary into the southwestern Dianzhong Block in the lower crust, but not in the asthenosphere. Key Points: Weak attenuation observations beneath the Dianzhong Block suggest the lithosphere there has similar cratonic features to that beneath the Sichuan BasinA thick lower crust and asthenosphere with strong heat activity beneath the eastern Tibetan Plateau are inferred from strong‐attenuation observationsThe eastward extrusion of the Tibetan Plateau crosses the Xiaojinhe Fault into the southwestern Dianzhong Block in the lower crust, but not in the asthenosphere [ABSTRACT FROM AUTHOR]

How the crust in the core of the Eastern Himalayan Syntaxis (EHS) deforms responding to the India‐Asia collision remains ambiguous. Here we present the first high‐resolution receiver functions image of crustal structure along a new NW‐SE trending dense nodal array crossing the core of the EHS. Two sets of low velocity zones (LVZs) are clearly observed: one with a flat style beneath the western Lhasa terrane and Higher Himalaya at 18–20 km depth and the other with two west‐dipping shapes below the western Yarlung‐Zangbo suture within 10–30 km depth. These LVZs caused by partial melting and aqueous fluids are disconnected, impeding the formation of crustal flow. A discontinuous east‐dipping intra‐crustal discontinuity and a sharp Moho offset of 7 km under the Aniqiao‐Motuo shear zone are identified, suggesting that the underthrusting of the Indian lower crust and pure shear mechanisms jointly dominate crustal deformation in the core of the EHS. Plain Language Summary: The tectonic evolution of the Eastern Himalayan Syntaxis (EHS) involves complex tectonic activities such as collision, subduction, and rapid exhumation, making the EHS an ideal site for studying the dynamics of continental collision processes. Strong crustal shortening occurs during the formation of the EHS, but the specific mechanism that accommodates this crustal deformation remains unclear. In this study, we construct a novel seismic image of crustal structure with unprecedented details along a recently deployed dense nodal array that traverses the core of the EHS. We observe two unconnected groups of low velocity zones, which call into question the validity of the crustal flow model in the core of the EHS. Our observations indicate that the underthrusting of the Indian lower crust and pure shear mechanisms, rather than a model of vertically coherent deformation, account for the present crustal deformation in the core of the EHS. Key Points: First high‐resolution image of crustal structure in the core of the Eastern Himalayan Syntaxis is constructed from P receiver functionsTwo disconnected groups of low velocity zones are observed in upper to middle crust, which prevents the development of crust flowAn intra‐crustal interface and a Moho offset we find suggest that underthrusting and pure shear mechanisms dominate crustal deformation [ABSTRACT FROM AUTHOR]

Eastern Asia is a prime location for the study of intracontinental tectono‐magmatic activity. For instance, the origin of widespread intraplate volcanism has been one of the most debated aspects of East Asian geological activity. Measurements of attenuation of teleseismic phases may provide additional constraints on the source regions of volcanism by sampling the upper mantle. This study uses data from three seismic arrays to constrain lateral variations in teleseismic P wave attenuation beneath the Central Asian Orogenic Belt and the North China Craton. We invert relative observations of attenuation for a 2‐D map of variations in attenuation along with data and model uncertainties by applying a Hierarchical Bayesian method. As expected, low attenuation is observed beneath the Ordos block. High attenuation is observed beneath most of the volcanoes (e.g., the Middle Gobi volcano, the Bus Obo volcano, and the Datong volcano) in the study area, and estimated asthenospheric Qp values span from 95 to 200. These values are within the range of globally average asthenosphere. We infer that these volcanoes may tap melt from ambient asthenosphere and occur where the lithosphere is thin, which is consistent with previous petrologic studies. More complex mantle drivers of volcanism are not rejected but are not needed to explain eruptions in this area. In contrast, at the Xilinhot‐Abaga volcanic site, the observed low attenuation (as low as beneath the Ordos block) excludes a typical shallow melting column. Fluids from the subducted Pacific plate may initiate the deep melting and would be consistent with petrological constraints. Plain Language Summary: Seismic attenuation, the loss of energy in a seismic wave as it passes through a medium, provides complementary constraints on the Earth's interior to those provided by the more common studies of seismic velocity. We present the first map of the attenuation experienced by the first arriving P phase from distant earthquakes in the Central Asian Orogenic Belt and North China Craton. The P phase from distant earthquakes travels nearly vertically beneath the stations that record them, and so variations in their attenuation reflect variations in the attenuation below the stations. We find low attenuation beneath the Ordos Block and high attenuation beneath most of the volcanic sites in the study region (e.g., the Middle Gobi volcano, the Bus Obo volcano, and the Datong volcano), where our results suggest that the asthenosphere is as about as attenuating as normal asthenosphere across the globe. We infer most of the volcanism in this portion of Eastern Asia taps melt from the ambient asthenosphere where the lithosphere is thin. This hypothesis is consistent with previous petrologic studies and does not require invoking unusual conditions such as a mantle plume. Counterintuitively, low attenuation is observed beneath the Xilinhot‐Abaga volcanic site, which excludes a shallow melting column beneath most volcanoes and requires a deep source. Taken together, our results support the hypothesis that lithospheric thickness is a primary driver of variations in the composition of erupted lavas. Key Points: The teleseismic P wave attenuation is obtained in the Central Asian Orogenic Belt and North China CratonMost volcanism in study area may tap melt from ambient asthenosphere and occur where the lithosphere is thinA thick lithosphere and a deep magma source are inferred beneath the Xilinhot‐Abaga volcanic site [ABSTRACT FROM AUTHOR]

To explore the west‐east variations in the underthrusting Indian lithosphere, we investigate the lithospheric structure using P and S receiver functions obtained from a west‐east linear array of 19 broadband stations spanning the Tethyan Himalaya at 85.5–88.5°E. Our observations of the Main Himalayan Thrust (MHT) and Moho serving as the top and bottom boundaries at depths of 42–54 km and 60–72 km, respectively, suggest that a thinning Indian lower crust with an eastward inclined geometry is underthrusting beneath the Tethyan Himalaya. An intra‐crustal low velocity zone (LVZ) immediately above the MTH at depths of 32–42 km is imaged, likely resulting from the presence of crustal dehydration partial melting. We propose that this LVZ induces the southward extrusion of melt‐weakened crustal material with itself as a channel and facilitates the development of duplexing structures, by which Indian lower crustal materials could be accreted into the Himalayan wedge along the north‐south mid‐crustal ramp in the MHT. The eastward dipping lithosphere‐asthenosphere boundary is clearly observed ranging from 90 to 126 km, which generally coincides with the changing trends of the MHT and Moho. These observations can be attributed to the eastward steepening subduction angle of the Indian lithosphere. Key Points: We investigate the west‐east lithospheric structure beneath the Tethyan Himalaya using P and S receiver functionsThe Main Himalayan Thrust, Moho and a low velocity zone characterized by the pronounced eastward inclined trends are clearly imagedThe eastward dipping shape of the underthrusting Indian lithosphere is likely caused by the eastward steepening subduction angle [ABSTRACT FROM AUTHOR]

We present detailed lithospheric images of the NE Tibetan Plateau by applying the depth migration technique to S receiver functions derived from 113 broadband stations. Our migrated images indicate that the lithosphere‐asthenosphere boundary (LAB) lies at depths of 105–120 km beneath the Qilian terrane and reaches depths of 126–140 km below the Alxa and Ordos blocks. The most prominent variation in the LAB depth is the presence of LAB steps of no less than 20 km in the transition zone between the active NE Tibetan Plateau and the surrounding cratonic Alxa and Ordos blocks, which conflicts with the model of southward subduction of the Alxa and Ordos blocks. Furthermore, the marked LAB steps occur at 130 ± 10 km away from the southern surficial boundary faults between the NE Tibetan Plateau and the surrounding tectonic provinces, corresponding to the North Qilian fault and the Liupanshan fault, respectively. Therefore, we propose that these scenarios of LAB can be attributed to the delamination of fragmented mantle lithosphere in the transition zone between the NE Tibetan Plateau and the surrounding Alxa and Ordos blocks, triggered by lateral asthenospheric flow. In addition, our observations of a thin lithosphere with thickness of 107–115 km beneath the Songpan‐Ganzi terrane and the west Qinlin orogen greatly facilitate the process of underlying lateral asthenospheric flow. The isostatic uplift of the plateau caused by the delamination of fragmented mantle lithosphere, together with increased horizontal compressive stress, may have led to the outward growth of the NE Tibetan Plateau. Key Points: We present the detailed images of the LAB beneath the NE Tibetan Plateau using S receiver functionsThe marked LAB steps occur at 130 +/‐ 10 km away from the boundary faults between the NE Tibetan Plateau to the surrounding blocksThe asthenospheric flow leads to the delamination of fragmented mantle lithosphere beneath southern edges of the Alxa and Ordos blocks [ABSTRACT FROM AUTHOR]

Abstract: In recent years, many small‐ to moderate‐size earthquakes occurred in central northern Oklahoma, likely associated with wastewater injection. The most recent one is the M5.8 Pawnee earthquake occurred on 3 September 2016. It is still not clear what controls the locations of these injection‐induced earthquakes. Here we conduct 2‐D Pg wave tomography with anisotropy to image seismogenic structures in this region, using more than 10 years of Pg arrivals recorded by 81 seismic stations. Our high‐resolution Pg wave tomography shows two high‐velocity zones with northwest fast direction alternated by low‐velocity zones with northeast fast direction. The two dominant anisotropy directions are consistent with conjugated microfractures from surface faults and two nodal planes from focal mechanisms of moderate‐size earthquakes. Most moderate‐size (M > 4) earthquakes occurred either close to the boundaries between high‐ and low‐seismic velocity zones or within the high‐velocity zones, suggesting that they are associated with geological boundaries of different basement rock properties or with strong material properties in the upper crust. We suggest that although these moderate‐size earthquakes were induced by fluid injection, their spatial locations were likely controlled by local geologic structures. [ABSTRACT FROM AUTHOR]

We analyze the teleseismic waveform data recorded by 42 temporary stations from the Y2 and ANTILOPE-1 arrays using the P and S receiver function techniques to investigate the lithospheric structure beneath western Tibet. The Moho is reliably identified as a prominent feature at depths of 55-82 km in the stacked traces and in depth migrated images. It has a concave shape and reaches the deepest location at about 80 km north of the Indus-Yarlung suture (IYS). An intracrustal discontinuity is observed at ~55 km depth below the southern Lhasa terrane, which could represent the upper border of the eclogitized underthrusting Indian lower crust. Underthrusting of the Indian crust has been widely observed beneath the Lhasa terrane and correlates well with the Bouguer gravity low, suggesting that the gravity anomalies in the Lhasa terrane are induced by topography of the Moho. At ~20 km depth, a midcrustal low-velocity zone (LVZ) is observed beneath the Tethyan Himalaya and southern Lhasa terrane, suggesting a layer of partial melts that decouples the thrust/fold deformation of the upper crust from the shortening and underthrusting in the lower crust. The Sp conversions at the lithosphere-asthenosphere boundary (LAB) can be recognized at depths of 130-200 km, showing that the Indian lithospheric mantle is underthrusting with a ramp-flat shape beneath southern Tibet and probably is detached from the lower crust immediately under the IYS. Our observations reconstruct the configuration of the underthrusting Indian lithosphere and indicate significant along strike variations. [ABSTRACT FROM AUTHOR]

We use teleseismic body waveforms to explore S-wave layered velocity structures beneath 30 portable digital seismic stations deployed around western Yunnan Province. Results show that the Moho depth in this region is ∼40 km and decreases in general from north to south, consistent with previous geophysical studies. Associated with this lateral variation of the Moho depth, the lower crust above the Moho discontinuity has a 15–25 km thick zone with an S-wave velocity lower than that of the upper crust. This lower velocity zone might be interpreted as a lower crust weak channel, which may mechanically partially decouple the upper-crust deformation from the underlying mantle. Thus, the inverted S-wave velocity structure could provide new evidence for the lateral flow of lower crust in the build-up of the south-eastern Tibetan plateau. [ABSTRACT FROM AUTHOR]