Progress in the study of the Wenchuan earthquake faulting

Abstract

After the 2008 Wenchuan earthquake, questions as to how earthquakes occur and when the next large earthquake happens have been asked. These questions are involved in the scientific questions which have been unsolved by geologists and geophysicists, for examples, how do faults rupture? How do faults heal in preparation for the next earthquake? The authors are trying to answer these questions by investigating the internal structures of the Wenchuan earthquake fault zone, fault friction behavior and healing process. The principal slip zone of the Wenchuan earthquake was determined by detailed research based on the WFSD-1 core and outcrop investigation. The dynamic weakening and friction behavior of the Wenchuan earthquake fault was analyzed by long-term temperature monitoring. Long-term hydrological monitoring reveals permeability variations in the Wenchuan fault zone which indicate fault healing process. Based on the information obtained, this paper discusses the Wenchuan earthquake faulting process and the above questions. It is confirmed that the Wenchuan earthquake fault zone(the Yingxiu-Beichuan fault zone) was 105~240 m wide and consisted of 5 different units with different fault rocks, where seismic events occurred repeatedly with multiple coseismic fault weakening mechanisms. Coseismic graphitization occurred during the Wenchuan earthquake; the lowest dynamic friction coefficient(0.02) was measured, and for the first time, the signals showing quick fault healing were recorded. These results not only directly answer the key questions that have puzzled geologists and seismophysiccal researchers for decades but also have important significance for improving the seismic faulting theory and understanding the Wenchuan earthquake fault mechanisms, thus providing a theoretical basis for seismic prevention and disaster mitigation.