Reevaluation of the Seismogenic Fault of the 1654 M8.0 Tianshui Earthquake: Evidence from Geology, Geomorphology, and Chronology along the Lixian-Luojiapu Fault

AbstractA historically documented M8.0 earthquake occurred in Tianshui, Gansu, China, in 1654. Its epicenter was located near the Lixian-Luojiapu fault in the triangular area at the conjunction of the Tibetan Plateau, North China block and South China block. Due to the lack of geologic and geomorphologic evidence and precise chronologic constraints, the seismogenic fault of this large event remains controversial. This work attempted to further address this issue. Based on data from unmanned aerial vehicle measurements, field investigations, analysis of typical fault profiles, and 14C dating, we determined the age of the latest slip on the Lixian-Luojiapu fault and the corresponding surface rupture range. In combination with historical earthquake data for this region, our work suggests that two sections of the Lixian-Luojiapu fault, the Tanchang-Lixian subsegment and the eastern portion of the Lixian-Luojiapu subsegment, were indeed involved in the surface rupturing of the 1654 Tianshui M8.0 earthquake. The scratches on the fault plane indicate that this seismic rupturing exhibited a left-lateral slip with a normal component and the maximum vertical displacement by this shock on the Tanchang-Lixian subsegment was 1.7±0.2 m. We suggest that the Tanchang-Lixian subsegment and the eastern portion of the Lixian-Luojiapu subsegment of the Lixian-Luojiapu fault and the West Qinling fault in the north jointly constituted the seismogenic structure of the Tianshui M8.0 earthquake based on a previous trench study. Located in the triangular zone between the Tibetan Plateau and the North China and South China blocks, tectonic stress accumulates rapidly on the Lixian-Luojiapu fault, resulting in a high potential of moderate to strong earthquakes, and this issue should be given more attention in the future.