Late Pleistocene–Holocene paleoseismology of the Batang fault (central Tibet plateau, China)

Abstract

The Yushu segment of the Ganzi–Yushu fault system (central Tibet plateau) is mainly composed by the Yushu fault and the Batang fault. The 2010 Ms 7.1 Yushu earthquake occurred on the Yushu fault, causing huge loss of lives and widespread damages to the densely populated Yushu area. So far, much effort has been devoted to the surface rupture and paleoseismology of the Yushu fault, while the late Quaternary activity of the Batang fault has not received much attention. The Batang fault has a clear geomorphic expression with fault scarps, sag ponds, push-ups, systematic offset of fluvial terraces, and alluvial fans along its trace. Integrated methods of geomorphological mapping, outcrop analysis, trench excavation and logging, optically stimulated luminescence (OSL), and radiocarbon (14C) dating are employed to study the latest Pleistocene and Holocene paleoseismology of the Batang fault. Several paleoearthquakes are identified from geomorphic and stratigraphic evidence between 22ka and after 2.7ka. The oldest event (E1) occurred after 22kaBP, E2 prior to 14kaBP, E3 within 14 and 9.5kaBP, E4 within 8.0–7.8kaBP, E5 prior to 6.7kaBP, the penultimate event (E6) occurred within 4.3–4.0kaBP, and the most recent event (E7) occurred after 2.7kaBP. The average recurrence interval of paleoearthquakes for the Batang fault is about 2000a in the last ~8kaBP, and the relapse time of the latest paleoearthquake is <2.7ka. Co-seismic displacement of the most recent surface-rupturing event is about 3m, as deduced from the offsets of the youngest terrace risers and of small gullies. Empirical equations between co-seismic displacement and earthquake magnitude reveal that the average magnitude of these events is about 7.3. This study contributes important information for the seismic hazard assessment of the densely populated Yushu area.