Abstract

The magnitude (Mw) 6.9 (Ms 7.1) Yushu earthquake of 14 April 2010 ruptured the Yushu fault of the preexisting strike-slip Ganzi–Yushu fault zone, which is an extension of the Xianshuihe fault. The earthquake resulted in widespread damage in high mountain regions of the central Tibetan Plateau. Field surveys and analyses of an excavated trench and outcrop reveal that three morphogenic earthquakes have occurred on the Yushu fault in the past millennium. Paleoseismic evidence, historical records, and radiocarbon age data show that (1) the penultimate large-magnitude earthquake (i.e., prior to the 2010 Yushu earthquake) occurred within the past 570 yr, corresponding to the 1738 M 7.1 earthquake; and (2) the third most recent event occurred between A.D. 650 and A.D. 1100, suggesting a recurrence interval of 450–680 yr for large earthquakes associated with surface rupture of the Yushu fault in the past millennium. An average slip rate of ∼2–5 mm/yr is estimated for the Yushu fault. These results are consistent with those obtained from long-term geological evidence and GPS observations. Most of the strain energy on the Ganzi–Yushu fault zone, resulting from northeastward motion of the Tibetan Plateau in response to north–south shortening of the plateau due to ongoing northward penetration of the Indian Plate into the Eurasian Plate, is released as seismic slip.

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