AGU 2008
HR: 0800h
AN: T41A-1944
TI: Wide-Angle Seismic Experiment Across the Oeste Fault Zone, Central Andes, Northern Chile.
AU: * Lorenzo, J M
AF: Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA 70803-4101, United States
AU: Yáñez, G A
AF: CODELCO-CHILE, Teatinos 258 Piso 8, Santiago, 0000, Chile
AU: Vera, E E
AF: Universidad de Chile, Departamento de Geofísica Facultad de Ciencias Físicas y Matemáticas, Santiago, 0000, Chile

AU: Sepúlveda, J
AF: GEODATOS, SAIC, Román Díaz 773 Providencia, Santiago, 0000, Chile
AB: From December 6-21, 2007, we conducted a 3-component, radio-telemetric, seismic survey along a ~ 15-km wide E-W transect in the Central Andes, at a latitude of ~ 22.41° S, centered north of the city of Calama (68.9° W), Chile. The study area is sandwiched between the Central Depression in the west and the Andean Western Cordillera of Chile. Recording stations, nominally spaced at intervals of either 125 or 250 m collected up to 3.5 s of refracted seismic arrivals at maximum source-receiver offsets exceeding 15 km. Ten shothole sources, spaced 2-6 km apart focused energy on the shallow (0-3 km), crustal, Paleogene-age structures. Preliminary, tomographic inversions of refracted first arrivals show the top of a shallow (< 1km), high- velocity (VP, ~5 km/s) crust, deepening sharply eastward to at least 2 km. At the surface, this central basement step correlates to a regionally extensive (> 600 km), strike-slip fault zone known as the Oeste fault. Turning ray densities suggest the base of the overlying velocity gradient unit (VP, 2-4 km/s) dips inwardly from both east and west directions toward the Oeste fault to depths of almost 1 km. Plate reorganization commencing at least by the latter half of the Oligocene led from oblique to more orthogonal convergence between the South American and the Nazca (Farallon) Plates. We interpret previously mapped, older, minor faults as being generated within the right-lateral, orogen-parallel, Oeste strike-slip fault zone, and postdated by Neogene, N-S striking thrust faults. In this context we also interpret that the spatial distribution of velocity units requires an period of extensional activity that may (1) postdate the transpressional strike slip fault activity of the Neogene, (2) be related to a later releasing bend through the translation and interaction of rigid blocks hidden at depth or even (3) be the consequence of inelastic failure from the result of flexural loading.
DE: 0935 Seismic methods (3025, 7294)
DE: 7270 Tomography (6982, 8180)
DE: 8104 Continental margins: convergent
DE: 8111 Continental tectonics: strike-slip and transform
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: 2008 Fall Meeting