A double-layered seismic zone in Arica, northern Chile

A double-layered seismic zone is determined in Arica, northern Chile using locally recorded events. At depths greater than 100 km two planes of seismicity can be observed : one dipping at approximtely 30°E with approximately 10 km of thickness and a second parallel plane 20-25 km deeper, with the same average thickness. Fault plane solutions for both layers show a wide variability, even between nearby events. The genesis of the Arica double seismic zone seems to be independent of the age, the relative convergence rate and direction of the Nazca plate, because all of these parameters are almost the same along the whole northern Chile and a clear separation of the seismicity into two layers is only observed around the Arice elbow. Moreover, it cannot be responsible for the double layered seismic zone because no similar significant changes are observed in the other well studied double seismic zones. (Résumé d'auteur