Weakness of the Intracontinental Strike-Slip Kunlun Fault and Implications for Tibetan Tectonics

ABSTRACT

An analysis of fault-related fold structures and the focal mechanisms of large earthquakes reveals that the maximum horizontal stress is oriented sub-perpendicular to the intracontinental strike-slip Kunlun Fault, which triggered the 1997 Mw 7.6 Manyi and 2001 Mw 7.8 Kunlun earthquakes upon the northern Tibetan Plateau. Based on seismic inversion results and in situ measurements of stress performed immediately before and after the 2001 Mw 7.8 Kunlun earthquake, a low shear stress of <1 MPa is estimated for the Kunlun Fault, which is an order of magnitude less than the shear strength obtained from laboratory measurements but compatible with that measured along the San Andreas Fault. Geological and geophysical evidence confirms that the Kunlun Fault is rheologically weak and that it plays an important role in accommodating eastward extrusion of the Tibetan Plateau in response to ongoing continental collision between the Indian and Eurasian plates.