New Constraints on Recent Large Earthquakes along the Xidatan Dongdatan Segment of the Kunlun Fault, Western China

摘要

Field investigation and paleoseismic study constrain the offset and timing of recent large earthquakes on the Xidatan–Dongdatan segment of the strike-slip Kunlun fault, northern Tibet. Displaced terrace risers and gullies preserved on the lowest and youngest terrace in the central part of the Xidatan–Dongdatan valley indicate that the offset produced by the most recent earthquake is 3–6 m, which is much smaller than what has been previously estimated; however, it is consistent with the slip of historical earthquakes along the Kunlun fault and recent well-recorded large earthquakes on other strike-slip faults. Accumulated offsets on higher terraces indicate repeated seismic activity of the Kunlun fault. We assume a 150 ± 20-km- long surface rupture for the most recent event based on roughly continuous linear features on remote-sensing images and distinct mole tracks in the field. The lack of seismicity records in the region earlier than 100 years ago led us to carry out paleoseismic investigation. Samples collected from the faulted upper layer show that the most recent large event on the Xidatan–Dongdatan segment is not older than 663 yr B.P. At least three prehistoric events are identified on the trench wall. Due to a lower constraint on the offset produced by the most recent earthquake, it would be necessary to reevaluate the seismic behavior of the Xidatan–Dongdatan segment.