Slip-weakening distance estimated at near-fault stations

Abstract

We estimated the slip-weakening distance from the seismograms recorded at near-fault stations, considering the effect of spatio-temporal filtering for a continuous propagation of rupture. This effect is usually observed at some distance away from the fault. We used a Green's function for 2-D anti-plane rupture propagating with constant rupture velocity and instantaneous slip at the crack tip. As a source time function, we used a regularized Yoffe function which is a kinematically good approximation of dynamic slip-weakening behavior. By convolving these functions, near-fault waveforms are computed. As a proxy of slip-weakening distance (Dc), we used Dc', which is defined as a slip at the time of peak slip velocity. Then, Dc' values can be computed as a function of the distance from the fault. This procedure is applied to the observation of the 2000 western Tottori, Japan, earthquake (MW6.6) as well as the 2002 Denali, Alaska, earthquake (MW7.9). We estimated Dc' at about 0.3 m at GSH station (∼100 m away from the fault) for the Tottori earthquake and that at about 2.5 m at PS10 station (∼3 km away from the fault) for the Denali earthquake. We confirmed that both estimates are not affected by the spatio-temporal smoothing.