Branch fault discovered in Tangshan fault zone on the Kaiping-Guye boundary, North China

Abstract

Abstract One outcrop of the NE–SW-trending fault with a steep occurrence and grown gouge was discovered in the north segment of the Tangshan fault zone during a field survey near Jujialing village on the Kaiping-Guye boundary of Hebei province, North China. This zone has received less attention in seismic geologic surveys. In addition, three neighboring and parallel NE trending scarps with heights in the range of 1–1.5 m were discovered on the generally flat terrain close to the fault outcrop. The geochemical and multi-electrode resistivity surveys revealed sudden huge fluctuations in the Hg concentration within short distances from the fault outcrop and the three surface scarps. The multi-electrode resistivity survey also revealed a resistivity structure with extreme horizontal discontinuity, indicating the presence of a subsurface fault zone with a width of 40–50 m and a SE dip. This finding confirmed that the three surface NE trending scarps were late Quaternary fault scarps. Following an examination of the focal mechanism solutions and survey findings, it is suggested that the newly detected fault trending toward the northeast could be an unexplored branch fault in the flower structure of the northern section of the Tangshan fault zone. It is marked by recent activity that is mainly controlled by the right-lateral strike-slip. The discovery of this active fault is critical for an accurate assessment of the seismic hazard of north segment of the Tangshan fault zone.