Late Holocene earthquake history of the central Altyn Tagh fault, China

Abstract

The Altyn Tagh fault accommodates sinistral motion between the Tibetan Plateau and the Tarim block within the India-Eurasia collision zone. We used well-preserved evidence for surface-rupturing earthquakes to reconstruct the earthquake history for the central Altyn Tagh fault. We identified three geometric fault segments bounded by left steps and a bend. Geomorphic offsets indicate that the most recent event had maximum surface displacement of ;5.5 m in the west (38.58N, 90.08E), ;7 m in the central part of our study area, and ;4 m in the east (38.88N, 91.58E). The 14 C dates and trench logs of disrupted sediments indicate that these offsets occurred either in a single earthquake with a surface- rupture length .240 km dated as 680 6 108 yr B.P. or as two events. If there were two events, the westernmost recent event occurred 518 6 268 yr ago, whereas the eastern event occurred 650 6 80 yr ago and had a surface rupture length .155 km. We find two events in the past 0.8-2.2 k.y. in the west and two or three events in the east, yielding recurrence intervals of 0.7 6 0.4 k.y. and 1.1 6 0.3 k.y., respectively. These recurrence rates for major earthquakes are lower than expected if the long-term fault slip rate is .20 mm/yr. Explanations for the discrepancy include an overdue major earthquake, or accelerated deformation elsewhere in the India-Eurasia orogen.