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

Abstract

AbstractThe 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 (M8.0) 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.