Characterizing the spatial distribution, frequency, geomorphological and geological controls on landslides triggered by the 1933 Mw 7.3 Diexi Earthquake, Sichuan, China

Abstract

Clarifying geomorphological and geological controls on earthquake-induced landslides is difficult. Because an earthquake can transiently release powerful energy and commonly exert a first-order control on the landslide distribution and abundance, the effects of geomorphology and geology on coseismic landslides are easy to be weakened by the seismic factors, particularly for those areas where the valley and the seismogenic fault are aligned. On 25 August 1933, a 7.3-magnitude earthquake struck the Diexi region adjacent to Min River upstream, China. The Diexi region, a tectonically active area with the valley normal or highly oblique to the strike of the seismogenic fault, provides a suitable field site to understand how seismic, geomorphological, and geological factors control earthquake-induced landslides. We present a detailed landslide inventory map caused by the 1933 Mw 7.3 Diexi Earthquake through a multi-temporal inventory, field investigations, and the previous landslide inventory in the Diexi region (885 km2). In our examples, the landslides are close to the seismogenic fault, while the landslides are away from the seismogenic fault as the fault and the valley are not aligned, indicating the influence of seismic motion on earthquake-induced landslides depends on the hillslope characteristics of the landscape. The thick lithological units (Zagunao Unit and C + P Unit) flavor large, wedge, planar slides, and most of which developed in the cataclinal and synclinal slopes, controlled by topographic-bedrock intersection angles. Whereas the thin lithological units are susceptible to small-fragmented slides or falls, not flavoring specific slope types. The inherited litho-tectonic conditions rather than the direction of the strike-slip fault motion control the primary failure aspect. Taken together, we conclude that inherited litho-tectonic conditions exert controls on landslide frequencies, types and size, steep slope gradient, and great topographic relief resulting from the rapid tectonic uplift and shape fluvial incision provide susceptible geomorphological conditions for landslide distribution and clustering. Our study provides new insights into a geomorphological and geological model for predicting earthquake-induced landslides in tectonically active mountainous areas.