Frictional Strength of Faults: Evidence for Post Seismic Deformation

Frictional coefficient of faults is investigated using the approach described in Iio (1997) where the orientation of a fault plane relative to the maximum compression direction is related through the equation β = 1/2 arctan (1/μ), where β is the angle between the direction of the maximum compression and the fault plane orientation, and μ is coefficient of friction. The data used are the frequency distribution of azimuth and plunges of P- and T-axes of focal mechanisms. The relation between β and μ is illustrated for different types of faults. Aftershocks of 2011 Lake Van earthquake (Mw=7.2) are utilized to demonstrate the technique. Focal mechanisms for about 400 aftershocks (Mw>3.5) are retrieved showing mostly reverse and strike-slip faulting mechanisms. The frequency distribution of P-axis azimuths of the mechanisms are utilized as an approach to investigate the frictional strength of faults on and around the ruptured fault. The azimuth of predominant frequency of P-axis distribution determined separately for reverse and strike-slip focal mechanism are close to the orientation of the maximum compressive stress axis pointing out low frictional coefficients that is likely due to post-seismic deformation.