Copiapó_Experiment_Catalogue

The subduction of different features such as oceanic ridges, fractures zones or seamounts are important for the accurate characterization of subduction zones. These structures may affect the along-dip variability of seismic behavior and eventually trigger slow earthquakes. Here we studied the along- dip influence of the Copiapó ridge subduction in the Atacama region, North-Central Chile, an area where seismic swarms, low coupling values and slow earthquakes have been reported. We built a seismic catalog including repeating earthquakes and non-volcanic tremors (NVT), and performed a 3-D tomography for P-wave velocity and Vp/Vs ratio. We identify along-dip segmentation involving 4 distinct segments: (1) a locked seismogenic zone (20 to 35 km depth), hosting ordinary clustered micro-seismicity and repeating earthquakes; (2) a transition zone (35 to 42 km) with non-volcanic tremor and low seismicity; (3) a zone (42 to 60 km) without seismicity and with slow-slip events and (4) a deep zone with more abundant seismicity. The velocity models show differences among these zones: while low velocity anomalies of Vp and Vs, and Vp/Vs ratio between 1.76 and 1.82 are observed in the deep zone, higher velocities are present in the other areas. These features indicate that SSE are located in a zone with higher pore fluid pressure. We propose that these geodynamic differences are generated by the subduction of heterogenic seamounts associated to the Copiapó ridge.