2002 Volume 2002 Issue 22 Pages 99-110
The Ms 8.1 Central Kunlun earthquake of 14 November 2001was triggered by the active Kunlun fault in the Central Kunlun mountain area, northern Tibet. A nearly 400-km-long co-seismic surface rupture zone occurred along the western segment of the Kunlun fault. Field investigations show that the surface ruptures are distributed in a zone with width ranging from few to several hundreds of meters, generally from 5m to 50m. The surface rupture zone is composed of distinct shear faults, extensional cracks, and mole tracks. The leftlateral offsets are measured by using the surface deformation markers such as present-day glacier, moraine, stream channel, gully, and road, which vary from few tens of cm to 16.3m, but generally from 4m to 8m. The maximum displacement up to 16.3m was observed across a rupture zone of 550m wide. Both the rupture length and maximum displacement are the largest among the co-seismic surface rupture zones ever reported worldwide. The co-seismic deformation characteristics of surface markers reveal that the earthquake had a purely strike-slip focal mechanism. Both the geological and geomorphological evidence indicates that the geometry of ruptures is controlled by the pre-existing Kunlun fault. The large amounts of strike-slip and rupture length produced by the earthquake support the hypothesis that the Kunlun fault plays an important role of strike-slip partitioning in the rapid eastward extrusion of Tibet to accommodate the continuing penetration of Indian plate into Euro-Asia plate. The Central Kunlun earthquake provides an exceptional opportunity to study the geometry of co-seismic rupture structures along a large strike-slip fault for further understanding the relationship between the fault geometry and rupturing process.
