HR: 09:00h
AN: S41A-05    [PDF]
TI: SEISMOTECTONIC CHARACTERISTICS AROUND THE ARICA BEND, CENTRAL ANDES (16$\deg$S-20$\deg$S): PRELIMINARY RESULTS
AU: * Comte, D
EM: dcomte@dgf.uchile.cl
AF: Dpt. Geophysics, University of Chile, Blanco Encalada 2085, Santiago, 6511227 Chile
AU: Tavera, H
EM: jtavera@geo.igp.gob.pe
AF: Instituto Geofisico del Peru, Marquez de Calatrava Lt 10, Lima, 3747 Peru
AU: David, C
EM: d.claire@dgf.uchile.cl
AF: Dpt. Geophysics, University of Chile, Blanco Encalada 2085, Santiago, 6511227 Chile
AU: Legrand, D
EM: denis@dgf.uchile.cl
AF: Dpt. Geophysics, University of Chile, Blanco Encalada 2085, Santiago, 6511227 Chile
AU: Dorbath, L
EM: louis@eost.u-strasbg.fr
AF: Institut de Recherche pour le Developpement, 5 rue Rene Descartes, Strasbourg, 67084 France
AU: Gallego, A
EM: agallego75@hotmail.com
AF: Dpt. Geophysics, University of Chile, Blanco Encalada 2085, Santiago, 6511227 Chile
AU: Perez, J
EM: josperez@esfera.cl
AF: Dpt. Geophysics, University of Chile, Blanco Encalada 2085, Santiago, 6511227 Chile
AU: Glass, B
EM: bglass@uta.cl
AF: Centro Sismologico, Universidad de Tarapac , Campus Saucache, Arica, 7-D Chile
AU: Haessler, H
EM: henri@topkapi.u-strasbg.fr
AF: Institut de Physique du Globe de Strasbourg, 5 rue Rene Descartes, Strasbourg, 67084 France
AU: Correa, E
EM: ecorrea@uta.cl
AF: Centro Sismologico, Universidad de Tarapac , Campus Saucache, Arica, 7-D Chile
AU: Cruz, A
EM: acruz@uta.cl
AF: Centro Sismologico, Universidad de Tarapac , Campus Saucache, Arica, 7-D Chile
AB: The Arica bend region corresponds to the main along strike geometrical change observed in the western South America subduction zone. As a first step, one could think that the geometry of the underlying subduction plate could be symmetric respect with an axis oriented along the direction of convergence between the Nazca and South American plates and passing through the Arica bend. However, the situation is different. The topography of the Altiplano and the characteristics of the subduction do not exhibit the same symmetry north and south of the Arica bend, suggesting that the tectonic of the Central Andes depends strongly on the dynamics of subduction. The Arica bend acted in the past as a geometrical barrier that stopped the ruptures of the large earthquakes of the southern Peru and northern Chile regions. The historical sequence of large earthquakes occurring along the interplate contact of southern Peru and northern Chile compromised different segments of the area associated with the largest earthquakes reported. The 2001 earthquake is not equivalent with the large previous one that occurred in 1868, the analysis of macroseismic parameters suggests that the 2001 earthquake is similar to the 1784 one. The southern segment of the 1868 seismic gap, the Ilo-Tacna (South Peru) segment, remains still intact, joint with the northern Chile seismic gap. In order to better understand the seismotectonic characteristics of the subduction process in the Ilo-Tacna segment and compare them with that observed in northern Chile, we deployed 27 short period three component stations from the U. of Chile-IRD-France around the Arica bend, between November 2002 and March 2003, from the coastline to the Altiplano. 19 stations of the temporary network were installed in southern Peru and 8 of them in northern Chile, that complemented the coverage area of the 13 stations of the permanent seismic network that is in operation there since 1994, through a joint project with the IPG-Strasbourg, IRD-France, the University of Tarapac  and the University of Chile. The about 3000 microearthquakes recorded by the seismic networks permitted a detailed definition of the Wadati-Benioff zone in southern Peru and northern Chile region, around the Arica bend. The average dip angle of the subducting slab observed in northern Chile is similar with that obtained in southern Peru, however, the interplate contact seems less active in the Arica bend with respect to that observed north and south of it. The intracontinental seismicity beneath the Chilean and the Peruvian forearc, joint with shallow seismicity beneath the magmatic arc can be also observed in southern Peru, as well as in northern Chile; those earthquakes are located between the surface up to 60 km depth, suggesting a lineament almost perpendicular to the dip of the subducting slab. This intracontinental seismicity is in agreement with previous results of the lithospheric characteristics of the Central Andes related with the reological, thermal behaviour and the depth of the Moho, and could be interpreted as a result of local tilting deformation, accommodating the elevation of the Altiplano.
DE: 7200 SEISMOLOGY
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting