HR: 0800h
AN: T31A-0267    [Abstracts]
TI: 3D tomographic structure of the north andean subduction zone at the Colombia-Ecuador border
AU: Garcia Cano, L C
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: Garcia Cano, L C
AF: Instituto de Geologia y Mineria (INGEOMINAS), Diagonal 53 No. 34-53, Bogota, 000000, Colombia
AU: Galve, A
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: de la Torre, G
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: de la Torre, G
AF: Instituto Oceanografico de la Armada (INOCAR), Base Naval Sur, av. 25 de Julio, via Puerto Maritimo, Guayaquil, 000000, Ecuador
AU: * Charvis, P
EM: philippe.charvis@geoazur.obs-vlfr.fr
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: Pontoise, B
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: Hello, Y
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: Anglade, A
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AU: Yates, B A
AF: Geosciences Azur, University of Nice Sophia Antipolis, IRD, CNRS, University Pierre and Marie Curie, BP 48, Villefranche-sur-mer, 06235, France
AB: At the latitude of Ecuador - southern Colombia, the Nazca plate converges toward the South American plate along an ~E-W direction at a rate of about 6 cm/yr. Several large subduction earthquakes affected this area during the last century. Near the Ecuador-Colombia border the 500 km long rupture zone of the 1906 event (M = 8.8) was partially reactivated, from south to north, by a sequence of 3 thrust events in 1942 (Mw = 7.8), 1958 (Mw = 7.7) and 1979 (Mw = 8.2). From 1998 to 2005, this zone was the target of five marine geophysical campaigns in order to determine the shallow and deep structure of the margin, its deformation and the possible relation with the rupture zone of the major earthquakes. Bathymetric data, passive and active seismic data were collected off South-Colombia and Ecuador. The data suggest that the interplate earthquakes and the extension of their rupture zone are at least partly controlled by structures on the downgoing and upper plates. To the south the subduction of the buoyant Carnegie Ridge, with a up to 19 km thick crust, is inferred to partially lock the plate interface along central Ecuador. This is illustrated by the rupture zones during the 1942 and 1906 earthquakes that terminated against the subducted northern flank of the ridge. The margin wedge is segmented by transverse crustal faults that correlate with the limits of the earthquake coseismic slip zones at the limit between the 1942 and 1958 rupture zones as well as at the limit between the 1958 and 1979 rupture zones. Furthermore, seaward of the 1958 rupture zone, a 2D profile from the SALIERI experiment (2001) highlights that the margin seems to overthrust a low velocity outer basement high along a splay fault that would decouple the bulk of the margin basement from its frontal part during great earthquake rupture. During, the 3D Esmeraldas experiment, conducted from February to June 2005, 34 3-components portable stations were installed on land and 26 3-components Ocean Bottom Seismometers were deployed offshore on top of the 1958 earthquake rupture zone. This network of seismometers recorded over 19,000 shots, using a 8x16 liters air-gun seismic source, along 25 crossing profiles for a total of ~3,000 km as well as seismic activity during a period of ~3 months. We first constrained a 1-D velocity model that best fits the bathymetry-corrected travel times of Pg and Pn arrivals from OBS located on the margin by forward modeling. This velocity model is used as an initial model for tomographic inversion using the FAST code. Preliminary results of the tomographic inversion provide some new insights of the structure of the margin and of the interplate contact.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 9360 South America
SC: Tectonophysics [T]
MN: 2007 Fall Meeting