Investigation and magnitude re‐evaluation of the 1955 Zheduotang earthquake, eastern Tibetan Plateau, China

Abstract

Rupture lengths and displacements of historical earthquakes are significant components of the accurate magnitude estimates required for understanding fault behaviour and earthquake recurrence patterns. Along the Xianshuihe–Xiaojiang fault system on the eastern Tibetan Plateau, 36 large historical earthquakes have been recorded during the past ~700 years, many of which still require detailed investigation. In this study, we reinvestigated the coseismic surface rupture produced by the 1955 M 7.5 Zheduotang earthquake. The Zheduotang Fault, which is the source fault of the 1955 event, is one of the main faults of the central Xianshuihe fault zone, with a left‐lateral strike‐slip rate of 3.4 mm/year according to our measurements and the ages of offset terraces. High‐resolution Google Earth images and field observations reveal that the surface ruptures of this earthquake were characterized by left‐lateral offsets of gullies, animal paths, alluvial terraces, and fans. The coseismic surface rupture length caused by the 1955 earthquake could be up to ~43 km, with mainly horizontal displacements of 0.6–1.7 m. Based on empirical relationships between magnitude and coseismic surface rupture length for large earthquakes, the magnitude of the 1955 Zheduotang earthquake is re‐evaluated to be MW 7.0. Our study demonstrates the necessity of re‐evaluating previous magnitude estimates of historical earthquakes in western China.