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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]

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]

• 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]