Associated With Wfsd Drilling "repeat Earthquake" Wenchuan Aftershock Sequence Of Part Of The Research

The slip rate of a fault is an important parameter for estimating the activity of the fault, and reflects the long term and average activity of tectonic deformation.’Repeating earthquakes’are usually regarded as a sequence of earthquakes having approximately the same waveforms, magnitudes, focal mechanisms and recurrence intervals, and occurred on the same patch of fault. The study of’repeating earthquakes’provides a new method for inferring the slip rate at depth along active faults and understanding the deformation process.This paper focused on the aftershocks of the Wenchuan earthquake in period2008.10.01-2011.09.15and20km around the1st and the3rd drilling of the Wencuan Fault Scientific Drill Program. Based on the digital waveforms recorded by the regional and mobile stations in Longmen Shan fault zone and the observation of the China National Seismograph Network, using cross correlation results of the three components of the waveforms, we identified the’repeating earthquakes’in the study area, and analyzed their characteristics. The results show that near-source stations are important in detecting’repeating events’. We observed a kind of’negative correlating events’which have nearly opposite waveforms at three components. After having analyzed the M-t distribution and the occurring sequence of the doublets, the possibility that the polarity of the instrument inversed is excluded, and based on the characteristics of P and S phases, we consider that it might be caused by the difference in focal mechanism.We relocated the events using double-difference method, and analyzed the relocation results utilizing the high degree similarity between’repeating earthquakes’. Nonnegligible error may exists when using double-difference method to get the position of a single event, and’repeating earthquake’may provide a possible method for evaluating the location level.Based on the identified’repeating earthquakes’, slip rates around the two drills are estimated. The results showed that there is no essential difference between the two drills. Similar to the Omri’s Law, the slip rates decreased with time and gradually stabilized in the range of about10mm/yr. The results need to be compared with deep exploration from drilling and surface observation from GPS and InSAR, and further study is needed on whether this revealed the healing process of the fault zone.