Characteristics of Raman Spectra of Minerals in the Veins of Wenchuan Earthquake Fault Zone
XIE Chao1, 2, ZHOU Ben-gang1, LIU Lei2, ZHOU Xiao-cheng2, YI Li2, CHEN Zhi2, CUI Yue-ju2, LI Jing3, CHEN Zheng-wei2, DU Jian-guo2*
1. Key Laboratory of Active Tectonics and Volcano, Institution of Geology, China Earthquake Administrition, Beijing 100029, China 2. CEA Key Laboratory of Earthquake Prediction (Institute of Earthquake Science, China Earthquake Administration), Beijing 100036, China 3. Institute of Disaster Prevention, Yanjiao 065201, China
Abstract：Quartz in the veins at the Shenxigou section of Wenchuan earthquake fault zone was investigated by micro-Raman spectroscopic measurement, and the distribution of compressive stress in the fault zone was estimated by the frequency shifts of the 464 cm-1 vibrational mode of quartz grains in the veins. It was showed that the 464 cm-1 peak arising from the quartz grains in the veins near the fault plane shifts by 3.29 cm-1, and the corresponding compressive stress is 368.63 MPa, which is significantly lower than the stress accumulation on both sides due to multi-stage events. Stress accumulation increased with moving away from the fault plane in the footwall with the offset of the 464 cm-1 peak arising from the quartz grains in the veins increasing, which can reach 494.77 MPa at a distance of 21 m with a high offset of 4.40 cm-1 of the 464 cm-1 peak. The compressive stress gets the maximum value of 519.87 MPa at a distance of 10 m from the fault plane in the hanging wall with the offset of the 464 cm-1 peak arising from the quartz grains in the veins being 4.62 cm-1, followed by a sudden drop in stress accumulation, and it drops to 359.59 MPa at a distance of 17 m. Because of moving away from the foult plane at the edge of the foult zone, the stress drops to 359.59 MPa with a small value of 464 cm-1 peak offset 3.21 cm-1 at a distance of 27 m from the fault plane in the hanging wall due to the little effect by the fault activity. Therefore, the stress of Wenchuan earthquake fault zone is partially released, but the rest of the stress distribution is uneven, and there is also a high stress accumulation in somewhere in the fault zone, which reflects that the mechanical properties of the rocks in the fault zone have a characteristic of unevenness in space.
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