It is commonly proposed that the subduction of the Pacific plate has been responsible for widespread Holocene intraplate volcanism across NE China and the Korean Peninsula. Yet, how this process drives volcanism and even if it plays a critical role remains a topic of vigorous debate. In this study, using seismic data from four networks across NE China and northern Democratic People's Republic of Korea (DPRK), we analyze shear wave splitting in converted P to S-waves at the Moho (Pms), S-waves from the subducted slab interface (local S), and SKS phases. The Pms phases show a relatively weak crustal anisotropy (<0.25 s), with fast polarization directions aligned sub-parallel to major tectonic features. For the local S and SKS phases, fast polarization directions show significant lateral variations. We further perform a quantitative inversion to show that the depth of the anisotropy is similar to 150 km, thus driven by flow within the asthenosphere associated with Pacific subduction. However, the presence of many null SKS splitting phases, together with scattered local S anisotropy across a wide range of incidence angles suggests a localized region of vertical flow directly beneath Changbaishan volcano. Such patterns correspond well to regional upper-mantle seismic velocity structure, and suggest that a localized upwelling with a relatively deep origin drives volcanism in the Changbaishan region. Furthermore, we infer that this mantle upwelling is deflected to the SW beneath Changbaishan and spreads asymmetrically at the base of the lithosphere, possibly because of the long history of volcanism in the region.

Intracontinental earthquakes usually cause severe casualties and property damage, yet their mechanism is still unclear. The TanLu Fault Zone (TLFZ) has been a typical large intracontinental strike-slip fault in eastern China since the Quaternary, which has hosted many large earthquakes (M >= 6). Generation of large earthquakes is generally closely related to the heterogeneities on and adjacent to the fault plane, which may result from different composition and inclusions of fluids. In this study, we use the receiver function method to obtain detailed distributions of Poisson's ratio and crustal thickness in the central-southern segment of the TLFZ, where the M 8.5 TanCheng earthquake occurred in 1668. We found that the distribution of earthquakes is strongly correlated with the crustal structures, both of which exhibit clear segmentation. The strongly damaged zone (with earthquake intensity >= 10) of the 1668 TanCheng earthquake and present small-to-moderate earthquakes are generally located above a segment that has shallower Moho and particularly higher Poisson's ratio. We propose that the high Poisson's ratio may be caused by intrusive mafic rocks in the ductile lower crust, which plays a role as local stress concentrators and subsequently leads to large intracontinental earthquakes.

Constraining variations of lithospheric structure and deformation across southeastern Tibet and the surrounding region are crucial for understanding the lateral growth of the plateau. Using data from two dense seismic arrays in the SE Tibetan Plateau, we obtained fine-scale Rayleigh-wave phase velocity maps by Eikonal tomography, and further inverted for 3-D shear wave velocity and azimuthal anisotropy of the crust and upper mantle. High velocities and weak lithospheric anisotropy are revealed under Dianzhong Block (DZB), where is covered by the relics of the Emeishan Large Igneous Province, while strong anisotropy is imaged around. We propose that the DZB strengthened by the paleo igneous activity plays an essential role in the evolution along the southeastern plateau margin. On the one hand, the DZB obstructs the migration of plateau material to the southeast. On the other hand, strong deformation is localized along the DZB margins, while the stress due to the plate expansion is transferred further to the Xiaojiang fault, which induced significant deformation within the Yangtze Craton. Furthermore, the lithosphere of DZB deflects the mantle flow driven by the eastward Indian subduction under the northern Indochina block.(c) 2022 Elsevier B.V. All rights reserved.

The conglomerate‐sandstone transition (CST) preserved in foreland basins records the stratigraphic equivalent of the gravel to sand transition (GST) which migrates in response to shortening in steady state orogen‐foreland basin systems. Two seismic profiles in the southern Junggar foreland basin provide the first seismic record of migrating CSTs and an opportunity to quantify its migration history in response to the growth of the northern Tian Shan. We identify the horizontal positions of the CSTs based on the distinct seismic signature of conglomerate versus sandstone and estimate their ages according to magnetostratigraphic sections. The linear‐regression analysis reveals that the CSTs migrated northward at 0.4 ± 0.1 mm/yr along 84°E from ∼23 to ∼6 Ma and at 4.0 ± 1.2 mm/yr along 87°E from ∼3.1 to ∼0.7 Ma. The discrepancy relates to variations in crustal shortening along strike of the range. Temporal deviations in the CST positions suggest the second‐order impacts of climatic change.

Uplift of the western Kunlun range results from the Indian indentation into Eurasia and induced underthrusting of the Tarim lithosphere. This underthrusting keeps pace with migration of the western Kunlun foreland basin. The basin‐scale sequences provide a decipherable record of the migration. To quantify the underthrusting, we analyzed a ∼323.2‐km‐long seismic profile crossing the middle segment of the western Kunlun foreland. We traced seismic reflectors to investigate the architecture of the foreland sequences and assigned ages of reflectors by correlating them with the dated outcropping sections. The foreland sequences consist of four layers. The lowermost Layer 1 starts to lap on the preforeland unit at ∼40 Ma, indicating that the Cenozoic western Kunlun initiated slightly prior to ∼40 Ma. Layer 2 shows a large sharp step northward to exceed the forebulge at ∼25 Ma, suggesting that the modern geomorphology of the Tarim Basin took shape. The southwestern boundary of Layer 4 migrates northeastwards by a fold row relative to that of Layer 3. The gradual retreat of reflector terminations from ∼40 to ∼30 Ma suggests that the Tarim lithosphere is viscoelastic. The linear fitting of the forelandward envelop of reflector termination sites since ∼30 Ma indicates that the Tarim lithosphere underthrusted at an average rate of ∼8.18 mm/yr. This rate comprises the shortening rate of ∼3.8–5.7 mm/yr and the western Kunlun latitudinal propagation rate of ∼4.4–2.5 mm/yr. The abrupt increase in sedimentation rate since ∼11 Ma suggests that western Kunlun had reached its current elevation.

The uplift of the Tibetan Plateau in the Cenozoic has changed the tectonics of the whole Asia and affected the climate and environment significantly. However, the mechanism of the plateau uplift and expansion is still in debate. The southeastern margin of the Tibetan Plateau, as the one of the expansion frontiers, provides the key to understand the tectonic evolution of the plateau. In this study, we review the progress of the researches on the crustal structures in the southeastern plateau margin, especially those achieved after the ChinArray project since 2011. The latest results show that the thickness of the crust descends from the plateau to its southeastern margin with an abrupt change under the plateau boundary. Two independent low-velocity zones are revealed in the lower crust: one under the Songpan-Ganzi terrane which is part of the high plateau, and another orientating NE-SW under the Xiaojian fault zone. We propose that the lower crustal materials extruded from the high plateau are blocked around the plateau margin (i.e., Lijiang-Xiaojinhe fault) by a strong crustal block in the western margin of the Yangtze block. However, the stress is further transferred to the Xiaojiang fault zone and induced the crustal deformations there.

East-central China has experienced multi-stage evolution among different tectonic units; thus the present geological structures are superimposed in a long history. But it is still unclear how different tectonic processes interact with each other, especially how the subsequent activity affects the previous structures. In this study, we determined new high-resolution P and S wave tomography of the upper mantle beneath the east-central China. We imaged the stagnant Pacific slab in the mantle transition zone and the hot low-velocity upper mantle in eastern China while cold high-velocity bodies beneath the Archean cratons in central China. More importantly, we newly revealed two important features. Firstly, a high-velocity zone is found in the uppermost mantle (50-150 km) beneath the Southeast China; its location is comparable to the distribution of the Cretaceous igneous rocks. Thus, we propose that the high-velocity anomalies reflect the remnant mafic rocks in the upper mantle after the volcanic eruption. Secondly, a high-velocity body is revealed in the deep upper mantle (300-500 km) beneath the southwestern Yangtze craton, possibly implying the delaminated cratonic lithosphere in the Early Mesozoic.

The uplift of the Tibetan Plateau in the Cenozoic has greatly affected the tectonics in Asia. But the evolution of the plateau is still unclear. The northeastern Tibetan Plateau is under ongoing expansion and is therefore essential for understanding the tectonic evolution of the plateau. Using data from 675 stations deployed by the ChinArray project, we obtained an anisotropic shear-wave velocity model by Rayleigh-wave phase-velocity Eikonal tomography and further investigated layered anisotropy and deformation patterns in the northeastern Tibetan Plateau. In the upper crust (<20 km depth), the fast directions are parallel with major strike-slip faults. In the lower crust, the fast directions are mostly margin-parallel along the plateau margin (at depths of ∼20 km to Moho), but they are perpendicular to the plateau margin while parallel to the topographic gradient under the high plateau (at depths of ∼40 km to Moho). Our result indicates that there is lower crustal flow under the high plateau due to the differential lateral gravity potential. However, the deep crustal flow is blocked by the surrounding blocks, which results in pure shear along the plateau margin in the northeastern Tibetan Plateau.

The tectonic uplift of the Tibetan Plateau is a focus in the geosciences. Middle-lower crustal flow is a popular model to interpret the geodynamic mechanism on the margin of the Tibetan Plateau. The model predicts different surface and Moho topographies across the plateau boundary due to the different strengths of the surrounding blocks, that is, sharp boundaries on the eastern plateau boundary and gentle variations in the southeastern plateau boundary. Here, we employ receiver function and common conversion point stacking analysis with the seismic waveforms recorded by the dense ChinArray and other local seismic stations to accurately define the Moho topography in southeastern (SE) Tibet. We find that the Moho under the Tibetan Plateau is much deeper than that under the surrounding Yangtze Craton and Indochina block; abrupt Moho changes are found across the southeastern plateau margin, similar to that under the eastern plateau margin. We interpret these sharp Moho variations across the plateau margin to have developed when the Tibetan Plateau was extruded southeastward in the late Miocene. Subsequent gravity collapse resulted in crustal extension and gentle topographic variation, while the sharp Moho slope was preserved.

The 28 March 2019 Mw 5.04 Mangya earthquake damaged eight ongoing drilling boreholes in the oil‐production Yingxiong Ling (YXL) area, southwestern Qaidam of northern Tibet. The borehole damages provide an opportunity to measure directly the coseismic slips, the rupture area, and the seismic moment. The damages reveal the underground rupture area of 45.30 ± 10.24 km 2 , the maximum slip of 400 ± 13 mm, and the seismogenic fault dip of ~38.6°. These parameters generate a seismic moment of (1.81 ± 0.47) × 10 17 Nm and a moment magnitude of 5.47 ± 0.16. Seismic exploration reveals that the geometry of the SZG ramp, the uppermost part of the multibend Yingxiong Ling thrust system, agrees primarily with the rupture plane derived from the borehole damages and one plane of the focal mechanism solution. This suggests that this earthquake resulted from slipping on the ramp. The hanging wall of the YXL thrust system forms the complex fault‐bend fold YXL anticlinorium. Active thrusting and folding along both edges of YXL attest to the southwestern vergence of this thrust system. Growth strata demonstrate average slip rates of the thrust system ranging from ~0.2 to ~0.3 mm/yr. The thrusted and folded recent alluviums along the southwestern edge indicate two thrusting events with coseismic slips of 1.7 ± 0.15 and 3.5 ± 0.15 m at 6.16 ± 0.52 and ~35.91 ka, respectively. The entire rupturing of the thrust system can produce Mw 7.65 ± 0.03 earthquakes.

The Indian plate began to subduct under the Eurasian plate in the late Mesozoic. Since the Eocene, continuous continental collision has resulted in the uplift of the Tibetan Plateau with extensive volcanic activities. Geophysical and geochemical studies have suggested that the Indian plate subducted and that volcanism originated in the deep upper mantle. However, the depth range of the subduction and volcanism and the relationship between them are still unclear. Here, to image the mantle transition zone (MTZ) structures, we deployed new seismic stations and collected as much seismic data as possible from the Tibetan Plateau. We then calculated the receiver functions and analyzed them using the common conversion point stacking method. We found that the MTZ is thickened by similar to 20 km under the Lhasa block, where high-velocity anomalies are obvious in the MTZ. Apparent thinning of the MTZ by similar to 20 km was revealed under the Qiangtang and Songpan-Ganze blocks, confirming a component of depleted mid-oceanic ridge basalt in the magmatic rocks. Our results suggest that the Indian Plate has at least subducted to the MTZ, which has further induced mantle upwelling and volcanism in the Tibetan Plateau.

Abstract Structural heterogeneities in subduction zones can affect slip behaviors of the megathrust faults and the generation of intraslab earthquakes. In this work we study the 3‐D seismic structures (Vp, Vs, and Poisson's ratio) in and around the source zones of the 2018 Anchorage intraslab earthquake (Mw 7.1) and the 1964 Alaska megathrust earthquake (Mw 9.2). The Anchorage earthquake occurred in an anomalous zone within the subducting Yakutat/Pacific plate with a higher Poisson's ratio than the normal slab. Above the source zone, the overriding North American plate shows a low Vs and a high Poisson's ratio. These features indicate that strong dehydration occurs in the source zone and released fluids ascend into the overlying crust. Two areas with long‐term slow slip events in the Upper and Lower Cook Inlet predominantly exhibit a high Poisson's ratio in the lowermost portion of the crust and the cold nose of the mantle wedge, whereas a low Poisson's ratio zone is revealed between them, suggesting that their segmentation is possibly related to localized slab‐releasing fluids. In the Prince William Sound, the rupture of the 1964 Great Alaska earthquake initiated beneath a high‐V and high Poisson's ratio zone of the overlying crust and the large slips occurred beneath a low‐Vs and high Poisson's ratio zone, suggesting that lateral heterogeneities of the overriding plate may have played an important role in the nucleation and rupture processes of the Great Alaska earthquake.

The eastern margin of the Tibetan plateau is under ongoing expansion. Rise and growth of the Longmenshan are results of the interaction between the Songpan-Ganzi Terrane and the Sichuan Basin. In order to understand the block interactions in the eastern plateau margin, we studied the crustal structures using P wave receiver functions (including H-k staking, CCP stacking, and velocity inversion) with the waveforms recorded by 115 portable stations. The Moho, indicated by clear Ps phases, is generally deeper in the Songpan-Ganzi Terrane than in the Sichuan Basin, while a step is notable under the Longmenshan fault zone. We found a low velocity anomaly in the mid-lower crust below the Songpan-Ganzi Terrane and Longmenshan fault zone, which may imply the accumulated partial melting materials in the deep crust under the eastern plateau margin. Clear P-to-s converted phases are found within the crust of the Sichuan Basin. They look as apparent huge anticline structures, which may be caused by ancient crustal deformation under the stable craton.

The southeastern (SE) Tibetan plateau is uplifting accompanying strong seismicity, but the relationship between the crustal structure and tectonic process in this region is still unclear. Seismic anisotropy provides important clues for the deformation mechanism. Here we applied the harmonic decomposition approach and further conducted a Markov-Chain-Monte-Carlo (MCMC) inversion to analyze the crustal anisotropy from receiver functions using waveforms recorded by dense stations in the SE Tibetan plateau. More spatial details on the crustal anisotropy and interface are determined consequently. While the anisotropies in the upper crust are relatively weak (~2%), the anisotropies in the mid-lower crust are mostly stronger than 4%. The fast polarization directions (FPDs) in the mid-lower crust show a dominant circular pattern, in good coherence with the topographic contours, indicating that the crustal deformations in the SE Tibetan plateau may be mainly controlled by the gravity potential. Because of the significant Moho steps along the plateau margin, the extruded deep crustal materials are blocked by the strong crust around so that the minerals are aligned to be sub-parallel to the plateau margins.

Evaporitic salt is prevailed in marine sedimentary basins, and the discovered hydrocarbon reservoirs are generally associated with salt structures in the world; accordingly salt structures have attracted much attention from academic and industry during the past decade. Tarim Basin that locates in northwest China, is the largest marine sedimentary basin in China with great hydrocarbon resources potential. Previous studies of salt structures in this basin mainly focus on its strong sealing capacity and structural traps created by salt structures. However, besides its extreme impermeability and low viscosity, rock salt has another unique thermal properties, featured by a large thermal conductivity as high as 5~6 W/(m.K), usually 2~3 times greater than that of other common sedimentary rocks, but a relatively low radiogenic heat production. This strong contrast in thermal properties could change the evolving thermal regime and associated thermal history of the source rocks around salt bodies, but has not been understood well. Herein based on the theoretical models and interpreted salt bearing seismic profiles from the Kuqa Foreland Basin, northern Tarim Basin, we use the 2D finite element numerical experiments to investigate the impacts of salt structures on basin geothermal regime and associated hydrocarbon thermal evolution. Our results show that, owing to its high efficiency in heat conduction, the salt rocks would result in obviously positive temperature anomalies (3~13%) above the salt body and negative temperature anomalies (11~35%) in the subsalt, enhancing and restraining the thermal maturation of source rocks above and below the salt body, respectively. The amplitude and extent of geothermal effects of salt structures depend on the thermal conductivity, geometry, thickness and burial depth of the salt bodies. The thermally affected area around the salt body can be 2 time of salt radius laterally and 2~3 times of salt thickness vertically. Salt structures in the Kuqa Foreland Basin can prominently cool the subsalt formation temperature and accordingly reduce the thermal maturity (Ro) of Jurassic source rocks as much as 18%, enabling the source rocks to be still of gas generation other than over-mature stage as expected previously, which is favor for deep hydrocarbon preservation below salt. In particular, salt structures in the west and east Kuqa Foreland Basin show strong differences in their thickness, geometric pattern, burial depth and composition, the thermal effects of salt structures on thermal maturation of subsalt source rocks should differ accordingly, which is supported by the observed tempo-spatial variation of Ro for Jurassic source rocks in this basin. Finally, we propose that the geothermal effects of salt structures will be of great importance in the deep hydrocarbon resources potential assessment and exploration in marine sedimentary basins in China.

青藏高原东北缘是青藏高原隆升的前缘地带,其构造变形特征一直是研究的热点.前人在该区域进行过面波成像研究,但不同结果存在较明显的差异,可能与不同成像方法的分辨率有关,此次研究分别使用基于射线的方法和基于程函方程的方法进行了瑞利波相速度成像.笔者对比了20 s、30 s和60 s的成像结果,两种方法的结果表现出相似的速度特征.总体的速度特征与研究区域的主要构造单元分布相吻合,青藏高原东北缘表现出低速异常,鄂尔多斯块体表现出高速异常.在银川河套地堑,基于程函方程的成像在20 s和30 s得到更明显的低速异常,低速异常体的分布与地堑的轮廓吻合更好,说明基于程函方程的方法对数据利用更充分.

We investigate 3‐D seismic structures (Vp, Vs, and Poisson's ratio) and Vp azimuthal anisotropy in the source area of the 2018 Eastern Iburi earthquake (M 6.7) in Hokkaido, Japan. Its mainshock occurred at the edge of a high‐Vp (2–4%) seismogenic zone. Significant low‐Vs (−1% to −3%) and high Poisson's ratio (2–7%) anomalies are imaged in and below the source zone and extend to the upper surface of the subducting Pacific slab, most likely reflecting ascending fluids released by the slab dehydration. A high consistency between the fault plane and the low‐Vs and high Poisson's ratio anomalies indicates that the fluids may have entered the fault and affected the rupture nucleation. A high‐V (1–3%) anomaly is revealed in the fore‐arc mantle wedge and connects with the high‐V seismogenic zone, probably reflecting a lithospheric fragment and contributing to cool down the mantle wedge. Complex seismic anisotropy is revealed in the crust in and around the source area, which may reflect complicated stress regime and strong structural heterogeneities there.

We present high‐resolution 3‐D images of P wave velocity (Vp), azimuthal anisotropy (AAN), and radial anisotropy (RAN) down to 900‐km depth beneath Alaska obtained by inverting a large number of high‐quality arrival time data from local earthquakes and teleseismic events simultaneously. Our results show that the high‐Vp Pacific slab has subducted down to 450‐ to 500‐km depths. A prominent slab gap is revealed at depths of 65–120 km near the Wrangell volcanic field, which is likely a slab tear acting as a channel that provides ascending mantle materials to generate magmas feeding the surface volcanoes. In the back‐arc mantle wedge near the eastern slab edge, the AAN exhibits trench‐parallel fast‐velocity directions (FVDs), which may reflect along‐strike mantle flow. The FVDs in the subducting Pacific slab are nearly east‐west, which may indicate fossil anisotropy formed at the mid‐ocean ridge. A negative RAN is revealed within the subducting slab, which may be caused by the fast plate subduction with a steep dip angle. Trench‐normal FVDs of the AAN are revealed in the mantle below the Pacific slab, which may reflect mantle flow entrained by the subducting slab. A positive RAN is revealed in the mantle beneath the Yakutat slab, indicating that its shallow subduction flattens the mantle flow below the slab to be subhorizontal. Along‐strike FVDs of the AAN around the eastern slab edge may indicate the edge‐induced toroidal mantle flow.

The Tarim Basin became a closed continental sedimentary basin in the Cenozoic due to uplift of the western Kunlun, Tian Shan and the Altyn Tagh ranges in the context of the Indian-Asia collision. A north-northeast trending seismic profile across the basin reveals that Cenozoic strata comprise a wedge of sediments in the southern and northern regions generated by flexural subsidence overlain by a more uniform regional sediment drape. We obtain the subsidence profiles across the basin at similar to 26 Ma, similar to 13 Ma, similar to 5 Ma and the present day using backstripping based on the sedimentary architecture shown in the seismic profile. We use a numerical finite elastic plate to model these subsidence profiles. Our modelling indicates that the southern and northern flexural depressions started to interfere to form a single flexural bulge within the basin since late Paleogene times. The flexural bulge migrated similar to 52 km toward the western Kunlun range since similar to 26 Ma, reflecting a decrease in the ratio of loads of the western Kunlun range versus the Tian Shan. We separate the sediment drape from the flexural subsidence according to the preceding modelling results. Our separating demonstrates that the thickness of the drape increased from 230 +/- 30 mat similar to 26 Ma to 1910 +/- 200 mat present, occupying similar to 30% of Cenozoic strata in the profile. The rise in the base level since the Paleogene is estimated as 356 +/- 80 m by correcting for sediment loading of the drape. We adopt a decreasing basin width to model the evolution of the flexural subsidence, suggesting significant uplifting of the western Kunlun range and the Tian Shan from similar to 26 Ma to similar to 13 Ma, relative stable elevations in these ranges from similar to 13 Ma to similar to 5 Ma, and their rapid uplifts since similar to 5 Ma.

Since the Late Cenozoic, the central-southern Longmen Shan (LMS) region is characterized by a two-decollement thrust-fold system with a localized upper evaporite weaker layer just beneath the Sichuan Basin and the lower stronger decollement beneath the LMS. To date, the role of upper decollement and erosion in shaping the structural deformation of the LMS remains unknown. The investigation of this question may shed lights on the assessment of the structural evolution and the further discrimination of mountain building mechanism. In this work, a 2D finite difference method is applied with regards to the variations of viscosity/friction angle, and lengths of upper decollement under different erosion rates. Two types of numerical models are setup, with purely lower-upper frictional (FF) decollements and lower-frictional upper-viscous (FV) decollements. Tectonic evolution with FF models exhibits large similarity with that of FV models. Meanwhile, our results underline the presence of in-sequence fault propagation procedures during most of the stages. The development of the boundary ramp, the Range Frontal Blind fault, is strongly induced by a prerequisite with upper decollement of necessary length. The activation of Beichuan/Pengguan faults or blind ramp piercing to the surface is extremely mechanically sensitive to the viscosity of the salt decollement, erosion rate, and the length of the upper decollement. Out-of-sequence thrusting, shallow and possible basal accretion processes beneath the Sichuan Basin are found when deformation transfers from the thick-skinned LMS to the thin-skinned Sichuan Basin at the very late stage, supporting upper crustal shortening dominates the mountain building mechanism.