Optical dating of the 12 May 2008, Ms 8.0 Wenchuan earthquake-related sediments: Tests of zeroing assumptions

The 12 May 2008, Ms 8.0 Wenchuan earthquake provided an excellent opportunity to test zeroing assumptions for optical dating of different types of earthquake-related sediments. Using OSL, we investigate the residual dose of the Wenchuan earthquake-related samples in four different depositional settings (flood, earthquake-dammed lake, sand volcanoes, pre-earthquake surface soils). The residual equivalent dose (De) varies with grain size, mineralogy, and the methods used in the De determination. All the samples, except the pre-earthquake surface samples, were poorly bleached with a maximum individual residual dose up to 356 Gy. Despite the poor sensitivity of the coarse-grain quartz samples, the small aliquot results using probability plot method (Jain et al., 2004) overestimate the De when compared to the single grain De from the same sample. Ages from optical dating of paleoearthquakes with short recurrence intervals should be interpreted with caution, and we recommend using the single grain approach in dim, poorly-bleached samples related to paleoearthquakes.