Subduction zones are sites of the world’s largest earthquakes. The nature of the interface between the down going oceanic lithosphere and the overriding plate allow for earthquake ruptures to extend for hundreds of kilometers generating large magnitude megathrust events like those offshore Chile and Alaska in the 1960’s, Sumatra in 2004, and Japan in 2011. Earthquakes along subduction zones are the most damaging and costliest in terms of loss of life and economic impact. The Mw=8.8 Maule earthquake offshore Chile in February 2010 ruptured a 500 km segment of the Nazca-South American plate boundary. This event is the 6^th largest megathrust earthquake ever to be recorded and the 2^nd largest to be recorded by modern digital seismic networks. In the immediate wake of the earthquake, an international effort coordinated resources to deploy both broadband and short period seismometers and accelerometers above the rupture zone to capture aftershocks associated with this significant earthquake. The combined data recorded by these stations produced an open international community data volume, IMAD (International Maule Aftershock Deployment). The IMAD dataset provides an exceptional opportunity to investigate processes associated with great earthquakes and to image the anatomy of a subduction zone.

A primary outcome from this project is a uniform catalog of aftershock seismicity of the complete IMAD dataset. Extremely high seismicity following the mainshock (over 100,000 earthquakes during the recording period) requires automated procedures. The spatial and temporal patterns of seismicity combined with the frequency-magnitude distribution of earthquakes after a large magnitude megathrust make implementation of standard automatic earthquake detection and location methodologies difficult. Improvements in routine high quality earthquake detection and location from earthquake aftershock sequences have the potential to improve seismic hazard analysis and earthquake real-time warning systems. Our work combines local tuning of detection and location algorithms for automated processing and quality control calibrated by analyst review to produce a uniform catalog of events. The uniform catalog provides a basis for research into the spatial and temporal patterns of deformation in the subduction zone following the large magnitude mainshock. It also serves as a basis for additional studies aimed at imaging the structure of the subduction zone and a variety of geologic process associated with subduction.

Analysis of the aftershock catalog indicates complex spatial and temporal patterns of seismicity and earthquake focal mechanisms, and earthquake clustering. The majority of larger magnitude aftershocks occur adjacent to areas that ruptured during the mainshock as the surrounding volume of material adjusts to slip associated with the main event. Locations of smaller magnitude events are more diffuse suggesting broader volumetric accommodation of deformation. Larger magnitude aftershocks show evidence of triggering smaller magnitude events (cascading events). While the majority of aftershocks occur along the interface between the subducting and overlying plate, a significant number of events are located within the overlying plate and well into the volcanic arc. Pre-existing structures within the forarc region act to concentrate and in some cases impede aftershock seismicity. 

Last Modified: 07/03/2014
Modified by: Anne S Meltzer