THE OCTOBER 9, 1995 COLIMA-JALISCO, MEXICO EARTHQUAKE (M-W-8) - AN AFTERSHOCK STUDY AND A COMPARISON OF THIS EARTHQUAKE WITH THOSE OF 1932

Data from portable seismographs and a permanent local network (called RESCO) are used to locate the aftershocks of the October 9, 1995 Colim a-Jalisco earthquake (M-w 8.0). The maximum dimension of the aftershoc k area, which is rectangular in shape, is 170 km x 70 km. Our study sh ows that the mainshock nucleated similar to 24 km south of Manzanillo, near the foreshock of October 6, 1995 (M-w 5.8), and propagated simil ar to 130 km to the NW and similar to 40 km to SE. The aftershock area lies offshore and is oriented parallel to the coast. The observed sub sidence of the coast is a consequence of this offshore rupture area. T he aftershocks reach unusually close to the trench (within 20 km). Thi s may be due to lack of sediments with high pole pressure at shallow d epth. There are some similarities between this earthquake and the two great earthquakes of 1932 (3 June, M-s 8.1; 18 June, M-s 7.8) which oc curred in this region. In both cases the aftershocks were located offs hore and the coastline subsided. The sum of seismic moments and the ru pture lengths of the 1932 events (1.8x10(21) N-m and 280 km, respectiv ely), however, were greater than the 1995 earthquake. Also comparison df seismograms of 1932 and 1995 earthquakes show great differences. It seems that the 1995 event is not a repeat of either June 3 or June 18 , 1932 earthquakes.