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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 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]

The Yinchuan-Hetao (YC-HT) graben is the boundary zone between the Ordos and the Alax blocks in NW China, which shows tectonic patterns distinct from the Haiyuan arcuate and Liupanshan thrust belts to the south. As a Cenozoic rift, the YC-HT graben originated from back-arc spreading related to westward subduction of the western Pacific, but its deformation and development may have been more influenced by the extension of the northeastern Tibetan Plateau (NETP) since the Quaternary. To investigate the dynamics of deep deformation of the YC-HT graben and adjacent regions, we apply the receiver function method to obtain the seismic structure in this area. Our results show that the depth of the Moho beneath the YC-HT graben is ∼50 km and significantly greater than that beneath the Alxa and Ordos blocks. The crust of the Ordos block is characterized by a layered structure, and the intracrustal structure below the YC-HT graben has undergone significant deformation. The Vp/Vs ratio in a local area of the western Hetao graben is as high as ∼1.9. By combining our observations with previous geophysical and geological studies, we speculate that the influence of NETP expansion has reached the YC-HT graben at depth. Meanwhile, the upper and lower crust experienced different deformation modes in this area, which manifested as elastic deformation in the upper crust and plastic deformation in the lower crust. [Display omitted] • Crustal velocity discontinuity structure and Vp/Vs ratios are obtained in the northwestern border of the Ordos, NW China. • Thickened crust and high Vp/Vs anomalies in the crust dominate the Yinchuan-Hetao graben. • Upper and lower crust beneath the Yinchuan-Hetao graben have undergone extensional and thickening deformation respectively. [ABSTRACT FROM AUTHOR]

• 1. Ambient noise tomography with topography correction is used to study the 3D crustal velocity structure. • 2. The S-wave velocity structure controls the downward stretch of the Longmen Shan faults. • 3. The expansion of the middle-lower crustal low-velocity layer is responsible for the growth of eastern Tibet. The Longmen Shan (LMS) fault zone is located on the eastern margin of the Tibetan Plateau and is a representative area for studying the eastward growth of the plateau. In this study, we present a 3-D crustal S-wave velocity structure beneath the LMS fault zone and its adjacent regions with a lateral resolution of ∼ 10 km down to a depth of 25 km from data recorded at 57 stations over one year using seismic ambient noise imaging techniques. The high and steep topography of the LMS is considered when building the high-resolution image of the upper and middle crust. The imaging provides further evidence for the high-angle listric characteristics of the LMS faults south of Beichuan, and the feature disappears toward the north, indicating differences in deformation from south to north. The structural characteristics are well correlated with the aftershock distribution and the rupture of the Wenchuan earthquake, which indicate a change in the mechanism from mostly thrust in the south to mostly strike slip in the north. The velocity structure controls the downward stretch of the faults. The results support that crustal channel flow is responsible for the growth of eastern Tibet. The eastward movement of the weak crustal material was blocked by the hard crust surrounding the Minshan uplift, resulting in great differences in the velocity structures and fault properties south and north of Beichuan. [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]

• Propose an input time-delay model to approximate the major effect of valve dynamics. • Propose an ESO-based output feedback controller with valve dynamics compensation. • The closed-loop system stability analysis is completed by using an LK functional. • The effectiveness of the proposed controller is verified via comparative experiments. Valve dynamics play an important role in the high-dynamic tracking performance of hydraulic systems. However, how to effectively compensate them remains an issue. From the frequency-domain analysis, it is recognized that the core effect of valve dynamics is the phase lag within the frequency range of interest. In this paper, a time-delay model which does not increase the entire system order is innovatively proposed to approximate the valve dynamics. As a result, the "explosion of complexity" in the backstepping control could be greatly alleviated. By introducing an auxiliary signal and incorporating a concept of desired-trajectory-based feedforward compensation, a practical output feedback backstepping controller is proposed for the motion control of a hydraulic actuator with integration of a robust delay compensating feedback and an extended state observer (ESO). The constructed ESO provides the estimates of both unmeasurable states and matched uncertainty, which ensures that the proposed controller only uses the output information and improves the system robustness. In addition, the valve dynamics are effectively compensated by the robust delay compensating feedback which contains a finite integral of past control values. The Lyapunov-based closed-loop system stability analysis using a Lyapunov-Krasovskii functional revealed that a uniformly ultimately bounded tracking performance is guaranteed by the proposed controller. Comparative experiments were conducted to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]