[S01-3] Open session III

[S01-3-02] Anatomy of a subduction zone – seismicity structure of the northern Chilean forearc from >100,000 relocated earthquake hypocenters

^○Bernd Schurr, Christian Sippl (Deutsches GeoForschungsZentrum, Potsdam, Germany)

We present a catalog of >100k well-located earthquake hypocenters for the northern Chilean forearc region, between the latitudes of 18.5 deg. S and 24 deg. S. The events span the period between 2007-2014 and were extracted from the Integrated Plate boundary Observatory Chile (IPOC) permanent station network dataset. Using this new, high-resolution set of hypocenters, we can outline the slab structure in unprecedented detail, including slab topography or the resolution of structures inside the zone of intermediate-depth seismicity. For the compilation of the catalog, we relied on an automated multi-step process for event detection, association and phase picking. The earthquake hypocenters were then relocated in a 2.5D velocity model for the Northern Chile forearc with a probabilistic approach allowing uncertainty estimation. In a final step, double-difference relocation incorporating cross-correlation based phase lag times was performed, which further sharpened event clusters. The majority of all >100k earthquakes are located at intermediate depths (80 and 140 km) inside the subducted slab. This area of pervasive activity extends along the entire strike of the investigated area, but shows a clear offset at 21 deg. S, which may hint at a slab tear at this location. Further updip, a triple seismic zone at depths between 40 and around 80 km is visible, which grades into the highly active event cluster at intermediate depths: below the plate interface, which is clearly delineated by seismic activity, a second parallel band of hypocenters only about 5 km below likely corresponds to earthquakes occurring within the oceanic crust or close to the oceanic Moho. A third band of earthquakes, paralleling the other two at about 20-25 km below the interface, clearly indicates the presence of seismicity in the oceanic lithospheric mantle. Seismicity in the upper plate is pervasive through the entire crustal thickness near the coast but gets shallower towards the volcanic arc.