ESTIMATES OF FAULT DIMENSIONS FOR SMALL EARTHQUAKES USING STOPPING PHASES

We propose a new method to estimate the fault dimensions of small eart hquakes based on stopping phases without assuming a rupture velocity. We detected two high frequency stopping phases being the Hilbert trans forms of each other for several earthquakes at two local stations, dur ing an earthquake swarm at the eastern offshore of Ito in the Izu peni nsula, Japan, which started on March 2, 1997. If we assume the geometr y of fault to be circular, we can determine relative locations of near est and farthest edges of the circular fault employing the difference of arrival times between these two stopping phases. Applying this meth od to several small earthquakes in the swarm, we succeeded in estimati ng the fault dimensions of these earthquakes. We also could determine the fault plane from two nodal planes by comparing the fault radii obt ained at individual station.