Fault segmentation and earthquake history of the Kunlun fault, China

Abstract:

Among the several large strike-slip faults that participate into the eastward motion of the Tibetan plateau, the Kunlun fault has hosted two major instrumental earthquakes, in 1997 and 2001. These two events, respectively of magnitude Mw=7.6 and Mw=7.8, have ruptured together a section of about 600km along the west end of the fault. This is about half of the total length of the Kunlun fault. Magnitude 7 to 7.5 earthquakes have also been reported in 1937 and 1963 along the eastern section of the Kunlun fault, indicating almost total failure of the fault in less than a century. The central segment of Xidatan-Dongdatan, about 150km long, is the only one segment where no instrumental and historical rupture is clearly documented.

The 2001 earthquake has provided us with a unique opportunity to document in details co-seismic deformation, based on correlation of optical satellite images, high resolution imagery and extensive field measurements. Comparison with cumulative slip documented in several sites brings new evidences for characteristic slip behavior along specific section of this rupture. Ruptures along the eastern segments of the Kunlun fault had not been documented in details at the time of earthquake. Using high-resolution imagery in conjunction with field survey, we bring new constrains on the extent of 1937 earthquake rupture and its related co-seismic offsets. Two paleoseismic trenches have been opened along the segments where no instrumental or historical events are known. One trench is open across the Xidatan segment, along the central part of the Kunlun fault. The second trench has been opened across the Maqen segment, along the most eastern segment of the fault. Both trenches show recent activity with 3 to 4 events visible in each trench. Preliminary dating indicates that 4 events have occurred along the Xidatan segment since 2400BP. The last event is probably younger than 663BP. These data allow us to propose a tentative earthquake history of the Kunlun fault, to be compared to the few other strike-slip faults that are well documented and to test if one can improve our understanding of the way large strike-slip faults rupture.