Estimates of fault dimensions for small earthquakes using stopping phases

Abstract

We propose a new method to estimate the fault dimensions of small earthquakes based on stopping phases without assuming a rupture velocity. We detected two high-frequency stopping phases being the Hilbert transforms of each other for several earthquakes at two local stations, during an earthquake swarm at the eastern offshore of Ito in the Izu peninsula, Japan, which started on March 2, 1997. If we assume the geometry of fault to be circular, we can determine relative locations of nearest and farthest edges of the circular fault employing the difference of arrival times between these two stopping phases. Applying this method to several small earthquakes in the swarm, we succeeded in estimating the fault dimensions of these earthquakes. We also could determine the fault plane from two nodal planes by comparing the fault radii obtained at individual station.