Late Holocene earthquake history of the central Altyn Tagh fault, China (original) (raw)
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 ϳ5.5 m in the west (38.5؇N, 90.0؇E), ϳ7 m in the central part of our study area, and ϳ4 m in the east (38.8؇N, 91.5؇E). The 14 C dates and trench logs of disrupted sediments indicate that these offsets occurred either in a single earthquake with a surfacerupture length Ͼ240 km dated as 680 ؎ 108 yr B.P. or as two events. If there were two events, the westernmost recent event occurred 518 ؎ 268 yr ago, whereas the eastern event occurred 650 ؎ 80 yr ago and had a surface rupture length Ͼ155 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 ؎ 0.4 k.y. and 1.1 ؎ 0.3 k.y., respectively. These recurrence rates for major earthquakes are lower than expected if the long-term fault slip rate is Ͼ20 mm/yr. Explanations for the discrepancy include an overdue major earthquake, or accelerated deformation elsewhere in the India-Eurasia orogen.
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