Timing of the Luanshibao Giant Landslide in eastern Tibet: the evidence from paleoseismology

Abstract

Giant paleo-landslides, generally regarded as evidence for strong events of seismic ground motion, can provide clues of paleoearthquakes on active faults. Paleo-landslide timing is commonly used to retrace the rupture history of an active fault. The Luanshibao(LSB) landslide is located in the eastern Tibetan Plateau on the Maoyaba fault, an important segment of the western Litang fault zone with a dominantly left-lateral strike-slip motion of about 4 mm/yr. The LSB giant landslide has been proposed to result from a large earthquake on the Maoyaba fault. However, the paleoearthquakes on the Maoyaba fault remain unknown. We excavated three large trenches across the Maoyaba fault and reconstruct the Maoyaba fault’s rupture history using the OxCal model of sequential radiocarbon dates. The ages of the faulting events in the three trenches are very similar. Our paleoseismological results demonstrate that at least five surface-rupturing events occurred at 620–485, 2540–1880, 3385–2905 cal BP, 5260–4415, and 12240–8895 cal BP. These data suggest that the major LSB landslide is probably related to a large earthquake (Mw∼7.2) of 3385–2905 cal BP. Also, the 10Be exposure ages of bounders on the LSB landslide surface are somewhat older than our trenching result, probably because of non-ignorable inherited components of nuclides on the landslide boulders.