Hot Spring Gas Geochemistry in Western Sichuan Province, China After the Wenchuan Ms 8.0 Earthquake

Chao Xie,Wanchun Wang,Jianwu Cheng,Jianguo Du,Zhi Chen,Li Yi,Lei Liu,Xiaocheng Zhou,Yuejü Cui,Liming Yang

doi:10.3319/tao.2015.01.05.01(tt)

Abstract

The chemical components, He, Ne, and C isotropic ratios of gas samples collected thrice from 32 hot springs in western Sichuan Province, southwestern China in June and October 2008 and June 2009 were investigated in order to discuss the relationship between hot spring gas geochemistry and the Wenchuan Ms 8.0 earthquake. The data showed that the 3^He/4^He and δ^(13)C_(CO2) values in spring gases in the Longmenshan fault (LMSF), Xianshuihe fault (XSHF), and Minjiang fault (MJF) zones increased obviously after the great earthquake. It was estimated that up to 62% of mantle helium contributed to the spring gas in the Kangding region based on the maximum 3He/4He (7.42×10^(-6)) in June 2008. Over time the mantle derived fluid contribution to the hot springs gradually decreased, but the crustal gas components: CO_2 and CH_4 derived from organic matter and radiogenic He increased. The gas geochemical data suggested that more mantle fluids migrated into the crust in western Sichuan Province after the Wenchuan Ms 8.0 earthquake.

Highlights

The Wenchuan Ms 8.0 earthquake occurred on 12 May 2008 in the Longmenshan fault (LMSF) zone at the eastern margin of Tibet plateau
The boundary faults (LMSF, Xianshuihe fault (XSHF), Minjiang fault (MJF), Anninghe fault (ANHF), Zemuhe fault (ZMHF)) among these three blocks in western Sichuan Province play an important role in generating devastating earthquakes with more than 80% of historical earthquakes having magnitude over 7.0 occurring along the boundary faults (Wen et al 2008; Zhang 2013)
The variations in the isotopic ratios of helium, carbon and gas compositions of gases in the hot springs of western Sichuan Province lead to the following conclusions

Summary

Introduction

The Wenchuan Ms 8.0 earthquake occurred on 12 May 2008 in the Longmenshan fault (LMSF) zone at the eastern margin of Tibet plateau. Earthquakes are usually accompanied with geochemical variations of gases from hot springs. The obvious variations of gas geochemistry related to the great earthquakes have been found around the world, especially in active fault zones in which permeability was enhanced (Du et al 2008a; Bräuer et al 2009). Gas components, such as CO2, He, H2, Rn, N2, gaseous hydrocarbons, etc.

Methods

Results

Discussion

Conclusion