The Wenchuan Earthquake Fault Scientific Drilling (WFSD) Project

Abstract

After the devastating Wenchuan earthquake on May 12, 2008, the Wenchuan earthquake Fault Scientific Drilling (WFSD) project was carried out in the Longmenshan fault zone, eastern margin of the Tibetan Plateau, which is the world’s most rapid scientific drilling response to large earthquakes. The WFSD project provides an excellent opportunity for geoscientists to explore the formation mechanism of earthquakes. For now, six boreholes have been drilled along the coseismic ruptures of the Yingxiu–Beichuan and Guanxian–Anxian faults. The WFSD project aims to reveal the composition, structure, morphology, and tectonic properties of the Wenchuan earthquake fault zone at deep depths based on multidisciplinary observations, measurements, and analyses, to explore the physical and chemical behavior of the seismogenic faults and their energy states, as well as their rupture processes during the Wenchuan earthquake. All these studies provide evidence to further understand the stress conditions, the causes of rupture nucleation and propagation, the role of fluids in earthquake nucleation, propagation and cessation, and the seismogenic mechanism of seismic faults. At present, some important research results have been achieved: (1) The structure of the Wenchuan earthquake fault zone has been verified; (2) thermal pressurization was an important fault-weakening mechanism during the Wenchuan earthquake, and graphite can be considered as an indicator for the large earthquakes; (3) the lowest faulting frictional coefficient in the world has been obtained, and for the first time, prompt fault healing has been recorded; (4) a tectonic framework of the Longmenshan fault belt and a new formation model for the Wenchuan earthquake have been proposed; (5) the spatial relationship between seismic activities and the different sections of the Longmenshan thrust belt has been established based on accurate aftershocks relocation and seismic array observations near the boreholes; (6) the relationship between the characteristics of fluid and seismic activities in the fault zone at deep depth has been discovered, which provides the scientific basis for determining the formation process of large earthquakes.