OSL and AMS14C Dating of the Penultimate Earthquake at the Leigu Trench along the Beichuan Fault, Longmen Shan, in the Northeast Margin of the Tibetan Plateau

Paleoseismic studies conducted along the surface rupture of the Wenchuan earthquake of 12 May 2008 (the 5.12 event) provide important information regarding the earthquake reccurrence intervals and slip rates of the Longmen Shan fault zone. The Leigu trench was excavated along the middle segment of the surface rupture of the Yingxiu-Beichuan fault zone. Based on the syntectonic sedimentary structure, two earthquake events, including the 5.12 event, were identified at this site. This study utilizes optically stimulated luminescence (OSL) dating of samples collected from the Leigu trench section, using SMAR (sensitivity-corrected multiple aliquot regenerative-dose) protocols. AMS(14)C dating was also carried out on charcoal from the same sediments. OSL ages are generally consistent with the calibrated AMS(14)C ages (calibrated year B. P.) for the same units. The last major earthquake event in this region, on the scale of the 5.12 event, occurred between 2.1 +/- 0.2 ka and 1.1 +/- 0.2 ka.