Normal- and oblique-slip of the 2008 Yutian earthquake: Evidence for eastward block motion, northern Tibetan Plateau

Abstract

The 2008 Yutian Mw 7.1 earthquake occurred in a junction area of the Altyn Tagh, Karakax and Kunlun fault systems and becomes a most northerly normal faulting event in the northern Tibetan Plateau. High resolution satellite image interpretation and field investigation indicate that the surface rupture zone produced by the Yutian earthquake is ~31km long along the Yulong Kashgar fault, a NS-trending fault at the western piedmont of a snow-covered mountain at the headwater of the Yulong Kashgar River, about 20km south of the Ashikule volcanoes. The surface rupture zone along the Yulong Kashgar fault consists of four different types of surface ruptures with both normal- and oblique-slip components. The maximum left-lateral slip and vertical offset, we measured in the field, are ~3.6m and ~3.3m, respectively. This NS-trending seismogenic fault belongs to one of the boundary faults between the Qaidam–Qilian and the western Kunlun blocks. Thus, the Yutian earthquake is as a result of abrupt normal- and oblique-slip faulting, which fits the eastward escape of the Qaidam–Qilian block, relative to the western Kunlun block. This surface rupture pattern supports the eastward block-like motion model whose deformation takes place mainly along the block boundaries delineated by mega-strike-slip faults in the northern Tibetan Plateau. More important may be that the Yutian earthquake has implication on future earthquake risk along the boundary faults of the Qaidam–Qilian block.