10Be dating and seismic origin of Luanshibao rock avalanche in SE Tibetan Plateau and implications on Litang active fault

Abstract

Moderate-large earthquakes usually trigger a large number of landslides. The prehistoric large landslides can be analyzed to determine the probability of its seismic origin, and further recognized as an indicator of fault activity and earthquake intensity. Based on field investigation, high-resolution satellite image interpretation and cosmogenic exposure dating of landslide deposit, the paper presents a large, long-runout Luanshibao rock avalanche (the LSB rock avalanche), southeast Tibet. The study reveals that (1) the LSB rock avalanche straddles the Litang active strike-slip fault and deposits on the open-flat Quaternary Maoya basin, with a deposit volume of 67 Mm3 and an apparent coefficient of friction of 0.22. (2) Totally, 8 granite blocks from the proximal to the medial part of deposit dated by the Terrestrial Cosmogenic Nuclide method suggests an average 10Be exposure age of 3510 ± 346 a B.P. for the LSB rock avalanche; (3) the spatial-temporal intercutting relationships among the LSB rock avalanche, Quaternary sediments, and the Litang active fault suggest five strong paleoseismic events in the Maoya basin, which is temporally in accordance to the result defined by paleoearthquake-trench research; (4) the corresponding maximum magnitude could reach MW 7.1 ± 0.1 by the empirical equations between landslide volume and earthquake magnitude. It suggests that the Maoya section of Litang fault is probably more dangerous than other sections due to the high density of large co-seismic landslides, which could present useful reference for the alignment selection of future Sichuan-Tibet railway.