Detecting shallow sedimentary structures in Sanhe and Tangshan seismic regions using H/V spectral ratio method

In the Sanhe and Tangshan seismic regions and their adjacent areas, the shallow crustal sedimentary structures detecting using H/V spectral ratio method has important scientific significance for regional seismic hazard risk assessment and engineering seismic fortification. In this paper, according to the data of a dense seismic sounding profile passing through the Sanhe and Tangshan seismic regions, the characteristics of the shallow crustal sedimentary structure, the site resonance frequency and the degree of vulnerability to damage in the Sanhe and Tangshan seismic regions and adjacent areas are obtained by using the H/V spectral ratio method. The results show that the thickness of loose sediment layer in the studied area is about 100–800 m, showing the characteristics of shallow in the northwest and deep in the southeast. The sedimentary thickness of the Tongxian uplift in the northwest of the exploration profile is about 350–450 m, the sedimentary interface fluctuates gently, and the sedimentary thickness of Dachang depression is about 300–600 m, with significant lateral variation characteristics. There are two sets of obvious sedimentary interfaces in the shallow part of the Tangshan earthquake region in the southeastern part of the survey line. The depth of the upper layer interface is about 100 m and is horizontally distributed. The depth of the lower layer interface is about 300–800 m, and gradually deepens toward the southeast. The site magnification factor of the Sanhe and Tangshan earthquake regions is about 3–4, and the site’s vulnerability to damage is greater than 20, showing that the surface buildings are more vulnerable to damage.