Evidence for earthquake interaction in Central Chile: The July 1997-September 1998 sequence

Abstract

Seven Mw > 6 events occurred between July 1997 and January 1998 along the shallow dipping subduction zone of Central Chile. We used body waveform modeling and master event relocation to study them. During July 1997, typical shallow interplate thrust events located close from each other followed a southward migration path and were located close from each other. On 15 October, the largest shock of the series (Mw=7.1) occurred at 68 km depth. From the directivity, we found that its rupture plane was almost vertical with a downward rupture. It was a down-dip compressional mechanism which is rare in Chile. Then, several thrust events occurred above it, along the plate interface. The rupture zones of the July 1997 events followed a cascade pattern with strong stress interaction. The slab push event of 15 October does not seem to have been triggered by static stress transfer from the July swarm.