Search

Receiver function (RF) analysis is an indispensable method that is widely utilized to image the deep structure of the crust and upper mantle. Although the P -wave receiver function (PRF) has the advantages of a higher signal-to-noise ratio and higher resolution than S -wave receiver function, the information about P -to- S converted (Ps) phases from velocity discontinuities of the crust and upper mantle is usually obstructed by multiples from shallower crustal interfaces. Sometimes it is difficult to identify useful information about lithospheric discontinuities. In this paper, we propose a method for suppressing multiples and isolating the Ps phases of RFs. This task is accomplished by exploiting the differences in arrival times resulting from the slowness between the conversion and the multiples that occur at the same interface in the PRFs and by separating them in the Radon domain, which enables removal of crustal and sedimentary multiples. This method can effectively remove multiples and isolate the useful signals of Ps phases contained in the PRFs. We test the method on synthetic PRFs and demonstrate that crustal multiples can be effectively eliminated or suppressed and that the Ps phase of lithospheric discontinuities can be coherently traced. Next, we apply the method to real PRF data collected from the seismic station of the China Array seismic experiment (Phase II and Phase III) in the Ordos block and its adjacent area, and successfully obtain an improved common conversion point stacking image of lithospheric discontinuity structures in the depth domain, particularly for detecting the lithosphere–asthenosphere boundary. [ABSTRACT FROM AUTHOR]

The Shanxi Rift located in the central part of the North China Craton (NCC) as a boundary between the Ordos block and the Huabei basin. The Shanxi graben system is a Cenozoic rift and originated from back-arc spreading related to westward subduction of the western Pacific and far field effects caused by northward subduction of the Indian plate. It has also had strong earthquake activity in China since the Quaternary. To investigate the tectonic evolution and tectonic setting of strong earthquakes in the Shanxi Rift, we apply the receiver function H - κ stacking method to determine the crustal thickness and average Vp/Vs ratio in the area. The results show that the thickness of the crust increases from approximately 30 km in the Huabei basin to approximately 47 km in the Yinshan Mountains with a close correlation between the Moho depth and topography. The Yuncheng, Linfen and Taiyuan grabens have varying degrees of crustal thinning. The crustal average Vp/Vs ratio in the Shanxi Rift has significant heterogeneity; the high Vp/Vs ratio (~ 1.85) are found in the Datong and Yuncheng grabens, and Vp/Vs ratio of the Taiyuan and Linfen grabens is approximately 1.75 which close to the global average value ~ 1.782. Combining the observations in this study with previous research, we suggest that the grabens in the Shanxi Rift experienced extensional deformation from south to north and that the possibility of strong earthquakes in the central part of the Shanxi seismic belt is greater than that on the northern and southern sides. [ABSTRACT FROM AUTHOR]

We collected continuous ambient noise data recorded between 2014 and 2015 at 288 broadband stations. Phase velocity maps of Rayleigh waves are constructed from 2 to 35 s periods. Combining phase dispersions at long periods (40, 45, 50, 55, and 60 s) obtained from earthquake data, we construct a three‐dimensional crustal S‐wave velocity (Vs) model with a lateral resolution of ∼20 km beneath the Qilian orogenic belt (QLOB) and its surrounding areas. The velocity structure above 20 km is constrained by faults and agrees well with subblocks. The middle‐lower crustal shear wave velocity in the QLOB is relatively low and has an unevenly distributed low‐velocity zone (LVZ, Vs < 3.4 km/s) at depths of 20–40 km, while that in the Alxa block is normal except for a narrow region protruding through the Longshou Shan. Deformation of the upper and lower crust in the QLOB is decoupled, and the growth of northern Tibet occurs through ductile lower crustal thickening and upper crustal overthrusting. The emergence of the mid‐crust LVZ in the QLOB could be due to high heat flow, more felsic composition of the mid‐lower crust, and especially shear heating. The weak lower crust from the QLOB to the Alxa block through the Longshou Shan is conducive to the expansion of the plateau, and the active front of northern Tibet is north of the Longshou Shan. Plain Language Summary: The magnificent Tibetan Plateau (TP) was formed by the collision of the Indian and Eurasian plates during the Cenozoic. Although various models of TP uplift have been proposed, the growth and lateral expansion of the northern TP remain uncertain. The Qilian orogenic belt (QLOB), as the young edge of the TP, has become of major interest to researchers. In this study, we obtain a high‐resolution 3‐D image of the crustal S‐wave velocity (Vs) structure in the QLOB and its surrounding areas using continuous ambient noise data recoded by a dense seismic array via an ambient noise imaging technique. The results show that the middle‐lower crustal shear wave velocity in the QLOB is relatively low and has an unevenly distributed low‐velocity zone (Vs < 3.4 km/s) at depths of 20–40 km, while that in the Alxa block is normal except for the narrow region protruding through the Longshou Shan. The results shed new light on the crustal structure in the study area and improve our understanding of the growth of northern Tibet. Key Points: High‐resolution 3‐D crustal shear wave velocity images beneath the Qilian orogenic belt are obtained via ambient noise imagingThe growth of northern Tibet in the crust occurs through ductile lower crustal thickening and upper crustal overthrustingThe active front of northern Tibet is north of the Longshou Shan [ABSTRACT FROM AUTHOR]

We present high‐resolution 3D images of the crustal S‐wave velocity structure beneath northeastern Tibet, via ambient noise imaging techniques. The data come from continuous recordings taken in one year by a seismic array consisting of 366 broadband stations in the study region. The results show a substantial and pervasive middle crust low‐velocity structure (<3.4 km/s) beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The growth of the northeastern Tibetan Plateau in the study region is manifested in its northeastward expansion and thickening driven by crustal channel flow, accompanied with upper crust shortening. Plain Language Summary: The growth mechanisms of the Tibetan Plateau (TP) have been considered controversial for decades. Expansion of the northeastern TP and the interaction with its peripheral area have become of major interest to researchers. In this study, we present a high‐resolution 3D image of the crustal S‐wave velocity structure beneath this area by analyzing the continuous ambient noise data recoded by a dense seismic array via ambient noise imaging techniques. The results show a substantial and pervasive middle crust low‐velocity structure beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The channel flow slows down gradually with its outward protrusion. The upper and lower crust is decoupled. In addition to the crustal channel flow, upper crust shortening takes part in the growth of the northeastern Tibet. Key Points: High‐resolution 3D crustal shear‐wave velocity images beneath the northeastern Tibetan margin via ambient noise imaging techniquesSubstantial and pervasive middle crustal channel flow is found beneath the northeastern TibetThe northeastward expansion of the northeastern Tibet is driven by crustal channel flow, accompanied with upper crust shortening [ABSTRACT FROM AUTHOR]

We present high‐resolution 3D images of the crustal S‐wave velocity structure beneath northeastern Tibet, via ambient noise imaging techniques. The data come from continuous recordings taken in one year by a seismic array consisting of 366 broadband stations in the study region. The results show a substantial and pervasive middle crust low‐velocity structure (<3.4 km/s) beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The growth of the northeastern Tibetan Plateau in the study region is manifested in its northeastward expansion and thickening driven by crustal channel flow, accompanied with upper crust shortening. Plain Language Summary: The growth mechanisms of the Tibetan Plateau (TP) have been considered controversial for decades. Expansion of the northeastern TP and the interaction with its peripheral area have become of major interest to researchers. In this study, we present a high‐resolution 3D image of the crustal S‐wave velocity structure beneath this area by analyzing the continuous ambient noise data recoded by a dense seismic array via ambient noise imaging techniques. The results show a substantial and pervasive middle crust low‐velocity structure beneath the plateau region, which partially protrudes northeastward across the West Qinling fault, reflecting channel flow from inside the plateau and material extrusion in the periphery. The channel flow slows down gradually with its outward protrusion. The upper and lower crust is decoupled. In addition to the crustal channel flow, upper crust shortening takes part in the growth of the northeastern Tibet. Key Points: High‐resolution 3D crustal shear‐wave velocity images beneath the northeastern Tibetan margin via ambient noise imaging techniquesSubstantial and pervasive middle crustal channel flow is found beneath the northeastern TibetThe northeastward expansion of the northeastern Tibet is driven by crustal channel flow, accompanied with upper crust shortening [ABSTRACT FROM AUTHOR]

We assessed the seismic potential around the northeastern edge of the Longmenshan fault zone (LFZ) by analyzing the aftershocks of the 2008 Mw 7.9 Wenchuan earthquake, focusing on the right-lateral strike-slip Qingchuan fault (QCF). The data used in the present study were collected from a dense network of broadband seismographs, installed after the Mw 7.9 mainshock by the China Earthquake Administration. We analyzed 440 aftershocks that occurred around the northeastern part of the aftershock area between December 2008 and June 2009, the local magnitudes (ML) of which ranged from 2.0 to 5.2. We determined 127 well-constrained focal mechanism solutions for these aftershocks down to ML 2.5 by using P-wave polarity data in conjunction with body-wave amplitudes. An analysis of the stress tensor inversion revealed that, upon approaching the QCF from the LFZ, the stress field changes from a reverse faulting regime to a mixed regime containing strike-slip components and the orientation of the maximum compressional stress changes from a NW–SE to a WNW–ESE direction. This stress field favors a right-lateral strike-slip movement along the fault. The slip tendency analysis revealed that the QCF is regarded as being favorably oriented to the present-day stress field. The coseismic Coulomb stress changes induced by the mainshock increased along the preferred fault plane in the northeastern half of the QCF, which is further loaded by viscoelastic relaxation. This evidence suggests that the potential for a future earthquake in the QCF is high. [ABSTRACT FROM AUTHOR]

From April, 2003 to September, 2004, a passive broadband seismic array consisting of 60 stations was deployed over the Tianshan orogenic belt by State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration. Among them, 51 stations make up an about 500-km-long profile across the Tianshan Mountains from Kuytun to Kuqa. The receiver function profile and S-wave velocity structure of the crust and upper mantle down to 100 km deep are obtained by using the receiver function method (Liu et al. 1996, 2000). The main results can be summarized as follows: (1) A clear mountain root does not exist beneath the Tianshan Mountains, and the crust-mantle boundaries underneath the stations mostly have transitional structures. This implies that the material differentiation between the crust and mantle is not yet accomplished and the orogenic process is still going on. (2) The crust beneath the Tianshan Mountains has laterally blocked structures in direction perpendicular to the mountain strike, and the crust-mantle boundary has a clear dislocation structure. Both of them correspond to each other. (3) The offsets of the Moho discontinuity are highly correlated to the tectonic borders on the surface and that corresponding to the frontal southern Tianshan fault reaches to 14 km. This manifests that large vertical divergent movement took place between different blocks. This supports the discontinuous model of the Tianshan orogeny, and the Tarim block subduction is restricted only to the southern side of the South Tianshan. (4) Inside the upper and middle crust of the Tianshan Mountains exist several low-velocity bodies correlated with high seismicity located on the mountain-basin jointures on both sides of the mountain and between different blocks, and the low-velocity bodies on the mountain-basin jointures are inclined obviously to the mountain. This implies that the low-velocity bodies may be correlated closely to the thrust and subduction of the basins on both sides of the mountain, the splicing of adjacent blocks and the fast uplift of the Tianshan Mountains. [ABSTRACT FROM AUTHOR]