Aysen seismic swarm (January 2007) in southern Chile: analysis using Joint Hypocenter Determination

Abstract

A seismic swarm at the Aysén fjord started in January, 2007, reaching its highest activity between January and April, 2007. It was punctuated by the Mw5.3 23rd January event and the Mw6.2 21st April event which triggered a waterwave due to massive landslides; both with dextral strike slip focal mechanisms. More than 100 events were relocated with the Joint Hypocenter Determination method to study the depth distribution of the events of the swarm recorded by the Chile Ridge Subduction Project local network. The events are associated to a small area of approximately 7 × 7 km located in the Aysén fjord, on one of the main branches of the Liquiñe–Ofqui fault. Distribution in depth is located between 0 and 8 km and presents a west high dip with almost NS strike, consistent with the main trending of the Liquiñe–Ofqui fault and the published focal mechanisms. These characteristics, among others, suggest that the Liquiñe–Ofqui fault is active in this region and thus seismic risk has to be redetermined.