Offshore-aftershock sequence of the Mw8.1 2014 Iquique earthquake

On 1 April 2014, a Mw 8.1 earthquake ruptured a portion of the subduction zone in northern Chile offshore Iquique between 19.5°S to 21°S. A large earthquake had been expected in the subduction zone off northern Chile, because it had not ruptured in a megathrust earthquake since a M 8.8 event in 1877. The 2014 earthquake did only affect the northern region of the 1877 rupture and left an unbroken segment to the South. In December 2014 we deployed an offshore network of 15 ocean-bottom-seismometers between 19°S and 22°S using the Chilean Navy ship OPV Toro, covering the aftershock zone of the 2014 Iquique event and the un-ruptured offshore domain in the South. The network was recovered in November 2015 with RV SONNE. The observed seismicity allows to constrain the structure of the marine forearc. Most of the seismicity occurs in the region of the coseismic slip of the 2014 event between 19.5 and 21°S. The spatial distribution of seismicity is irregular: Seismicity in seismogenic depths is highly concentrated forming well-defined clusters. Some of these clusters show repeating events. Almost no faulting is observed in the outer rise and the majority of events is located 30 km eastwards of the trench. The downgoing Wadati-Benioff zone is readily identifiable as an east dipping structure. We focus on the distribution of hypocentral depths in order to resolve activity in the overriding crust. The microseismicity will be located based on a minimum 1-D velocity model with station corrections and we relate the seismicity distribution to the background seismicity, bathymetry and regional tectonics.