Adaptability of ESR dating of fault gouge in aseismic region: A case study on Hangzhou region, China

Abstract

ESR dating has been widely used in seismic assessment. In this paper, we collected fault gouge samples system-atically for ESR (Electron Spin Resonance) dating, and sediment samples of overlying strata, and offset strata for OSL (Optically Stimulated Luminescence) dating along Xiaoshan-Qiuchuan fault (XQF) trending NE-SW, Xiaofeng-Sanmen fault (XSF) trending NW-SE, and Changhua-Putuo fault (CPF) trending E-W. In the same fault outcrop, the ESR data of fault gouge is greater than the OSL data of the strata offset by fault. Therefore, the ESR data of fault gouge colleted in Hangzhou region do not represent the time of weak fault movement in Late Quaternary region, but represent the strong fault movements in Late Cenozoic. The episode of fault movement in Late Cenozoic could be speculated according to the ESR data: 1.00–0.58 Ma, there were strong fault movements along the XSF, XQF and CPF in Hangzhou region; 0.58–0.45 Ma, the fault movements of all faults became weaker and did not zero ESR signals significantly for ESR dating of fault movements; 0.45–0.20 Ma, there were strong fault movements along part of XQF; 0.1–0.01 Ma, there were fault movements along the XSF only, but the fault movements were not strong enough to reset the ESR signal; Since 0.01 Ma, the Hangzhou region tends to be stable. In addition, the XSF might be the division line of fault segmentation of XQF; there were strong fault movements along the southwest segment of XQF during 0.45 Ma to 0.20 Ma; while the fault movements along the northeast segment of XQF mainly occurred during 1.00–0.58 Ma.