A New Surface Rupture of the 1556 Huaxian M ∼ 8.5 Earthquake Revealed by Rock Surface Luminescence Dating of a Bedrock Fault Scarp and Colluvial Wedges

Abstract Bedrock fault scarps and their associated colluvial wedges provide key evidence for reconstructing paleoearthquakes. We apply rock surface luminescence dating to a bedrock scarp on the Huashan fault in central China, using OSL‐depth profiles (DPs) from multiple heights. Results reveal two coseismic displacements of 6.8 and >1.0 m. The two phases of exposure ages inferred from OSL‐DPs of the bedrock fault surface above ground (0.4 ± 0.3 and 1.1 ± 0.4 ka) are consistent with burial ages of slices from the fault surface covered by the colluvial wedge. These ages also correlate with historical earthquakes, including the 1556 Huaxian M ∼ 8.5 event with slip of 6.8 m, confirming rupture of the western Huashan fault. A magnitude of M8.3 inferred from multiple fault rupture lengths agrees with seismic intensity estimates. The fitted OSL‐DPs of bedrock samples buried or being buried by the colluvial wedge, together with the burial ages of slices, reveal the exposure and burial history of the wedge.