Paleo-Earthquakes along the Zheduotang Fault, Xianshuihe Fault System, Eastern Tibet: Implications for Seismic Hazard Evaluation

Abstract

The Kangding City in eastern Tibet is at high risk due to frequent strong earthquakes along the Xianshuihe sinistral strike-slip fault bounding the Chuandian Block to the northeast. The knowledge of paleo-seismicity recurrence along this fault system is key to the evaluation of earthquake hazards in this region; thus, more accurate paleoseismic information are required. We examined the paleo-seismicity along the Zheduotang fault in the central segment of the Xianshuihe fault system by applying the field investigation, trenching, and Quaternary dating methods (e.g., OSL and ¹⁴C). Field observations found ∼8.5 m offset of stream by sinistral slip along the Zheduotang fault. We trenched the central fault zone of the Zheduotang fault and found that the colluvial wedges and five buried, discontinuous, A-soil horizons progressively have been offset in the shallow graben on the SW-side of the main fault indicative of the paleo-earthquakes. The dating results of OSL and ¹⁴C, in line with existing data, enable us to establish the paleo-seismic history of the Zheduotang fault. It shows at least eight surface ruptures in the last 7500 years identified from displaced buried soils, colluvial wedges and terraces. Our study reveals ∼100 years minimum paleo-earthquake recurrence, suggesting potential large earthquakes in the Kangding area in the future.

Keywords

Tibetan Plateau / Xianshuihe fault system / paleo-seismicity / trench / recurrence / geophysics

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