Features of Deep Crustal Structure Beneath the Wutai Mountain Area of Shanxi Province

Abstract

In this paper, the deep crustal structures in Wutai mountain area are studied by using deep seismic sounding (DSS) data obtained from wide-angle reflection/refraction profiles which pass through Shanxi downfaulted zone and Wutai mountain area. The results show that the crust in this area presents obviously layered structures. The boundary interface between upper and lower crust is determined by means of reliable intra-crust reflected waves P3 that can be traced continuously. The thickness of upper crust is 23∼28km, and the depth of Moho discontinuity is 39∼43 km. The Moho discontinuity in Wutai mountain area is the deepest in this region. In Wutai mountain and its adjacent areas, the crust structures have strong inhomogeneous characteristics. The large-scale low velocity bodies in upper crust and strong intra-crust reflected wave groups can be regarded as a sign of magma activity in deep crust. The breaking of intra-crust interfaces and the local discontinuation of seismic wave group Pm as well as existence of deep crustal faults and so on indicate that the crust in this region suffered violent squeeze, deformation, and tectonic activities. Therefore the complex topography and anomalous structural characteristics in deep and shallow crust have been formed in this region.

Shear-wave velocity structure of the crust and uppermost mantle in the Shanxi rift zone

“…The A-A 0 profile traverses the Datong basin, Xinding basin, and Wutaishan uplift to the east, which belongs to the Yingxian-Fuping segment of Zibo-Yingxian DSS profile (Zhao et al 2006). The phase-and shear-wave velocity variations are similar to the velocity structure revealed by the DSS profile.…”

“…These low-velocity areas include: Datong, Xinding, Taiyuan, Linfen basins, and Yuxian basin in the Taihang mountain uplift. Shanxi geological data (Xing and Ye 1991) and the results of DSS (Zhu et al 1994Liu et al 2000;Zhao et al 1999Zhao et al , 2006 indicated that the thickness of sedimentary layers in these areas is between 1.4 and 5.1 km. The thicknesses of the Taiyuan basin and Datong basin are between 3.5 and 3.9 km, and the thickest sediment is located in the Yuncheng basin.…”

“…In order to minimize the search space, improve the inversion efficiency, and diminish the non-uniqueness of the inversion, we constructed the reference model using a two-step (2015) 28(2):135-149 139 procedure. In the first step, at all points we collected DSS results (Zhu et al 1994Liu et al 2000;Zhao et al 1999Zhao et al , 2006, referred to the previous work on the Moho and lithosphere (Xing et al 2002), the AK135 model (http://rses.anu.edu.au/seismology/ak135/ ak135f.html) and the Moho thickness (Xing et al 2002) and P/S velocity ratio determined by H-K stacking on teleseismic receiver functions ). Considering that the longest period in the phase velocity dispersion curve is 75 s, the depth in the inversion was set from the Earth's surface to a depth of 200 km.…”

“…This was consistent with the previous results about Moho discontinuity at the same locations. (Zhao et al 2006).…”

“…In the past two decades, a large number of geophysical studies have been done to image the velocity structure in Shanxi rift, including deep seismic sounding (DSS) (Zhu et al 1994Liu et al 2000;Zhao et al 1999Zhao et al , 2006, waveform modeling (Zhang et al 2003b), teleseismic receiver function (Ge et al 2011;Wu et al 2011;Tang et al 2010), body-wave tomography (Wang 2005;Xu et al 1997;Zhang et al 2011), ambient seismic noise and two-station analysis Fang 2010;Tang et al 2011), surface-wave tomography , and magnetotelluric sounding (Wei et al 2006;Zhao et al 1997). These results have provided us the overall information of the crust and upper mantle in this region.…”