‘Repeating earthquakes’ associated with the WFSD-1 drilling site

• Investigating ‘repeating earthquakes’ surrounding the WFSD-1 drilling site
• Estimating deep slip rate using ‘repeating earthquake’ clusters
• Slip rate averaged at about 5 mm/year, with a weak attenuating trend.
• The result is independent of logging data and ground surface measurement.

We cross-correlated three-component seismic waveforms to find ‘repeating events’ among the aftershocks of the 2008 Wenchuan earthquake centered at the WFSD-1 drilling site during and after the drilling. The aftershocks selected occurred from 2008/10/01 to 2011/09/15, with a magnitude range of ML 1.4–5.5. Using the 1–10 Hz bandpass filtered waveforms recorded by the regional and mobile seismic stations, 518 ‘repeating events’ are identified with the criterion that for at least one station the three components of seismograms all have cross-correlation coefficients larger than 0.8. Using 12 ‘repeating multiplets’, defined by the criterion that each pair of events in the ‘multiplet’ must be ‘repeating pairs’, fault slip rates are estimated. Slip rate was averaged at about 5 mm/year, being within the range of the deformation rate before the Wenchuan earthquake obtained by ‘repeating earthquakes’, with a weak attenuating trend, and a suspected disturbance by a strong aftershock.