THE M(W)=8.1 ANTOFAGASTA (NORTH CHILE) EARTHQUAKE OF JULY 30, 1995 - FIRST RESULTS FROM TELESEISMIC AND GEODETIC DATA

A strong (M(W) = 8.1) subduction earthquake oc occurred on July 30, 19 95 in Antofagasta (northern Chile). This is one of the largest events during this century in the region. It ruptured the southernmost portio n of a seismic gap between 18 degrees S and 25 degrees S. In 1992 we h ad used GPS to survey a network with about 50 benchmarks covering a re gion nearly 500 km long (N-S) and 200 km wide (E-W). Part of these mar ks were re-surveyed with GPS after the 1995 earthquake. Comparison wit h 1992 positions indicate relative horizontal displacement towards the trench reaching 0.7 m. The inland subsided several decimeters. The Me jillones Peninsula was uplifted by more than 15 cm. Teleseismic body-w ave modelling of VBB records gives a subduction focal mechanism and so urce time function with three distinct episodes of moment release and southward directivity. Modelling the displacement field using a disloc ation with uniform slip in elastic half-space suggests a rupture zone with 19 degrees-24 degrees eastward dip extending to a depth no greate r than 50 km with N-S length of 180 km and an average slip of about 5 m. The component of right-lateral slip inferred both from the teleseis mic and geodetic data does not require slip partitioning at the plate boundary. That the well-constrained northern end of the 1995 rupture z one lies under the southern part of the Mejillones Peninsula increases the probability for a next rupture in the gap north of it.