Geochemistry Of Mercury In Wenchuan Earthquake Fault Zone

The 2008 Ms 8.0 Wenchuan earthquake was occurred in Sichuan Province in China on May 12,2008. It caused huge casualties and property losses. The Wenchuan earthquake fault scientific drilling project (WFSD) was quickly carried out in Wenchuan earthquake fault zone after the main shock, which aims to study a series of scientific problems related to the earthquake.Elemental mercury is an important tool in the earthquake induced underground fluid research, and is used to study active fault and earthquake preparation process. In China, mercury monitoring is one of the most successful approaches to observe the underground fluid activities. We conducted the geochemical research of mercury and mercury isotope within the Longmenshan fault zone by the assistant of WFSD project, and we mainly discussed the geochemistry and response of mercury and its isotopes to Wenchuan earthquake. It will help us to better understand the roles underground fluid activities played during the Wenchuan earthquake preparation stage.This paper analyzed the geochemical characteristics of elemental mercury and its isotopes in the fault zone after the Wenchuan earthquake. The results from WFSD observation showed that higher mercury concentration appeared in the Wenchuan earthquake coseismic damage zone, which were probably caused by earthquake induced permeability increase which leads to deep hydrothermal fluid upwelling. Higher values of mercury indicated that the Wenchuan earthquake damaging zone within the Yingxiu-Beichuan fault zone is geometrically asymmetric. Mercury isotope compositions showed that there were different isotope fractionation characteristics of MDF and MIF between different rocks. The differences of mercury isotope compositions and its fractionation mechanism in the fault gouges were highly possible caused by the high temperature fluid flow in the fault zone, and this feature reflected the deep fluid in response to large earthquake.The mercury concentration anomalies were detected in the Bajiaomiao outcrop, along the Wenchuan earthquake surface rupture zone. Mercury is easier to concentrate in fault gouges than fault breccia and bedrock. Higher mercury enrichment factor in the fault gouge layers indicated that direct underground mercury emissions happened during the earthquake. High mercury contents in the black gouge revealed that the Hongkou outcrop was highly enriched with organic material and clay mineral. Also, mercury migration process model in the fault zone was proposed in this paper, due to mercury migration and enrichment in the surface and underground of Wenchuan earthquake fault zone. Earthquake damaged the country rocks and created abundant conductive passage for underground flow, and that lead to the deep fluid upwelling within the damage zone.The results showed that the structure of Wenchuan earthquake damaging zone within the Yingxiu-Beichuan fault zone, mercury isotope fractionation revealed high temperature fluid flow caused by earthquake, and the migration and enrichment of elemental mercury in fault zone. The results prove that the deep fluid flow happened in the Yingxiu-Beichuan fault zone, within the Longmenshan Belt. The results enrich the content of mercury research in earthquake monitoring and forecast. Mercury and its isotopes can be used as an effective tool to probe the fluid response to earthquake, and provide an important reference value in the method of earthquake monitoring and forecast in the future.