Probing Fine Crustal Structure in the Beijing Region Using a Deep Seismic Reflection Profile

Abstract

The fine crustal structure and tectonics of the Beijing region are explored by using a 100 km long, NW-trending deep seismic reflection profile. This profile passed through the Sanhe-Pinggu earthquake (M 8.0) area and main faults in the Beijing region. The results show that the crust beneath the investigated area is divided into upper and lower crust by a strong reflective zone at about 6∼7 s TWT. The thickness of the upper and lower crust is about 18∼21 km and 13∼15 km, respectively. There are rich reflective layers and clear structural patterns above 3∼4 s TWT as well as obviously different structural features along the profile. In the west of the Sanhe-Pinggu earthquake area, the stacked deep seismic reflection section shows 2∼3 groups of strong reflective layers and a series of basement faults. In the east of the Sanhe-Pinggu earthquake area, there is a set of dense, west-dipping, reflective strata with relatively strong energy, which have the typical characteristics of a sedimentary basin. The largest depth of the sedimentary basin is about 8∼9 km. The deep fault in crust revealed by the deep seismic reflection profile has a steep plane, and it cuts and disturbs the lower crust and crust-mantle transitional zone. This deep fault extends upwards into the upper crust, and joins the crustal deep structure to the shallow fault. The profile reveals that the deep-shallow fault system represents the major deep-shallow tectonic feature in the study region.

High‐Resolution 3D Shallow S Wave Velocity Structure of Tongzhou, Subcenter of Beijing, Inferred From Multimode Rayleigh Waves by Beamforming Seismic Noise at a Dense Array

“…The locations of the known faults such as Nanyuan-Tongxian fault (F3) and Xiadian fault (F1) are indicated with black solid lines. The results from deep seismic sounding show (Liu et al, 2009(Liu et al, , 2011 that there are two faults with SE-dipping at the location of Xiadian fault, namely F1 and F12 shown in Figure 17. F1 is a relative new fault that possibly cut the Moho, and F1-2 is a listric fault that was cut by F1 at 450-m depth, as shown in Figure 17.…”

Shallow Crustal Structures and Buried Active Faults Revealed by Seismic Reflection Profiles in the Northwest of Beijing Plain

“…Nearby Gaoliying and Tianzhu, it is 700∼800 m thick, and less than 300 m in the Jingxi swell and Tongxian swell. The reflector T G has good lateral continuity and high signal-noise ratio, considering other data of geology and DSS in this region [19,20,28] , it is reasonable to interpret T G as the reflection from the upper boundary of the crystalline basement. This basement undulates strongly and has profound segmentation along the profile.…”

“…Previous survey results show that in the study area, the bottom of the crystalline basement is usually 3∼5 km deep with maximum 8∼10 km, and crust is 32∼38 km thick [13∼15, 19,20] . To image the fine structure from the near surface to the bottom of the crystalline basement, we have completed a mid-deep seismic profile with targeted depths 6∼8 km in the study area (MDSP in Fig.…”

Late Quaternary activity of the Xiadian west concealed fault east to Beijing and its tectonic significance

“…Xiadian fault is the seismogenic structure of the Sanhe Pinggu Ms8 earthquake in 1679. The deep seismic detection results show the direct exposure of the deep fault cutting through the whole crust on the surface (Fig 2) [11]. There is about 10 km seismic deformation zone on the surface.…”

“…A horst is sandwiched between the two faults. By analyzing the results of deep seismic exploration (Fig 2) [11,28,44], it can be concluded that the Xiadian fault, Xiadian west fault and Daxing fault belong to the same deep fault, which is the branch of the deep activity of the deep fault in the shallowed part of the crust. They may have formed an echelon assemblage on the plane, forming a large fault zone.…”