Abstract

Historic, as well as teleseismically, and locally recorded seismicity of the subduction margin of Copiapo, northern Chile is analysed. An on- and off-shore temporary network was deployed during 2 months in the region in order to obtain a detailed definition of the Wadati-Benioff zone. An average dip angle of 20° along the subduction thrust interplate contact was determined; this value is similar to that observed along the Chilean margin, suggesting that there are no variations in the dip angle of the Nazca plate for depths less than 50-60 km. Locally recorded data do not provide seismic evidence to determine whether subhorizontal subduction exists north of latitude 28°S. Teleseismically recorded events exhibit a low rate of occurrence of inland earthquakes, with a tendency for epicentres to be located off-shore; in contrast, locally recorded seismicity reveals a homogeneous epicentral distribution, without a predominance of off-shore events. Along the subduction thrust contact there is a reverse stress regime with the greatest compression axis (?1) horizontal and oriented perpendicular to the strike of the trench. Events located above the main decollement are in a normal stress regime with the minimum compressive stress axis ?3 horizontally oriented parallel to the convergence direction. The events located below the coupled interplate contact also lie in a normal faulting regime but the ?3 axis plunges almost parallel to the subducting plate. The intermediate depth fault plane solutions exhibit a substantial scatter, suggesting a complicated faulting regime similar to that observed in previous studies of northern Chile. They are associated with a normal faulting stress regime in which ?3 is oriented in a N14°E direction parallel to the strike of the trench. High resolution bathymetric data and seismicity located above the thrust contact suggest that seamounts are being subducting. © 2002 Elsevier Science B.V. All rights reserved.