Paleo-earthquakes of the Dachaidan fault in western Qaidam basin, northeast of the Tibetan Plateau, China

Abstract The Dachaidan fault, an important active fault within the northern marginal fault system of the Qaidam basin along the northeastern margin of the Tibetan Plateau, has received limited scientific attention in the past. In recent years, several M>6 earthquakes near the fault have drawn significant research interest to its seismic potential. This study investigates the seismically active Dachaidan fault, a critical geological hazard threatening Dachaidan in western China's Qinghai Province. Absence of paleoseismic studies on this fault has resulted in structurally critical data gaps, constraining our understanding of large-magnitude earthquake recurrence, spatial segmentation, and rupture intensity distribution along the fault. To address this problem, we conducted trench excavation, analysis, and stratigraphic radiocarbon ages dating based on high-resolution satellite imagery and geomorphic field surveys. Five paleo-earthquakes were identified: EI without specific age, EII within 7800–7200 yr B.P., EIII within 6300–4800 yr B.P., EIV within 3900 yr B.P. to ~2900 yr B.P., and EV after 1900 yr B.P., which indicates four events since the Holocene with an average recurrence interval of 2000 ± 300 yr in the past ~8000 yr B.P. Fault landforms and trenches suggest the most recent event occurred with a coseismic dextral offset of ~1.3 m. Empirical equations between coseismic offset and earthquake magnitude reveal that the magnitude of one event is 7.1 ± 0.2.