Slip rate on the Kunlun fault at Hongshui Gou, and recurrence time of great events comparable to the 14/11/2001, Mw∼7.9 Kokoxili earthquake

A field study of the surface rupture of the 14 November 2001, Mw similar to 7.9 Kokoxili (or Kunlun Shan) earthquake near Hongshui Gou (35.9 degrees N, 92.2 degrees E), a site with exceptional geomorphic offsets long identified on SPOT images, yields bounds on this earthquake return time and on the slip-rate along the Kusai Hu segment of the Kunlun Fault. Measurements of the sinistral coseismic and cumulative offsets of four distinct strath-terrace risers and of rill channels incised in the adjacent fan bajada, complemented by post-earthquake, metric-resolution satellite image restoration, are 3 +/- 0.5 m, 6 +/- 1 m, 31 +/- 2 m, 63 +/- 5 m, and 110 +/- 10 m. The smallest offset is unambiguously that of the 14/11/2001 earthquake. The 31 and 63 m riser offsets, which have thermoluminescence ages of 2885 +/- 285 and 5960 +/- 450 yr, respectively, imply an average slip rate of 10.0 +/- 1.5 mm/yr, almost identical to that found 200 km eastwards, in Xidatan, using Be-10 cosmogenic dating of surface pebbles. The repetitive seismic slip (similar to 3 m) implies an average recurrence time of 300 +/- 50 yrs for earthquakes comparable to the 14/11/2001 event. This new data increases the body of evidence suggestive of local characteristic slip during large earthquakes and firmly corroborates the millennial eastward extrusion rate (1 cm/yr) of north-central Tibet relative to the Qaidam. (c) 2005 Elsevier B.V. All rights reserved.