HR: 08:45h
AN: S41A-04    [PDF]
TI: The Seismogenic Coupling Zone in Central Chile - Amphibious Experiments SPOC (Subduction Processes Off Chile)
AU: * Krawczyk, C M
EM: lotte@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Stiller, M
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Mechie, J
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Lueth, S
AF: FU Berlin, Malteser Str. 74-100, Berlin, 12249 Germany
AU: Wigger, P
AF: FU Berlin, Malteser Str. 74-100, Berlin, 12249 Germany
AU: Oncken, O
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Reichert, C
AF: BGR Hannover, Stilleweg 2, Hannover, 30655 Germany
AU: Bataille, K
AF: Universidad de Concepcion, Departamento Ciencias de la Tierra, Concepcion, xxxxx Chile
AB: Nearly all interplate megathrust earthquakes occur in the seismogenic coupling zone between converging plates. In the area of the 1960 Chile earthquake (Mw = 9.5), we aim at a quantitative understanding of the seismicity and its relation to processes operating at depth and at the surface. As a first step, the offshore experiment SPOC with RV SONNE was combined with an onshore-offshore, active-passive seismic experiment between 36\deg and 39\deg S, crossing the rupture area of the 1960 Chile earthquake. The campaign comprised: (1) a 2-D wide-angle component recording chemical shots and airgun pulses along three consecutive E-W onshore profiles; (2) a seismic reflection experiment in the onshore-offshore transition; and (3) a 3-D component which recorded both active and passive sources. Offshore, the upper plate is split into many segments with pronounced forearc basins and a narrow accretionary wedge. A thick subduction channel seems to cause a non-frontally accreting subduction mode. Along the westernmost part of the southernmost E-W refraction seismic line, the profile spread of the active reflection seismic survey at 38\deg 15' S was 54 km long, and also recorded the airgun shots of the marine profile with the first 18 km of its spread. Different mainly eastward dipping reflection bands are observed. Between 5-25 km depth the internal structure of the Palaeozoic accretionary wedge is described. Reflections between 16-42 km correlate with Wadati-Benioff seismicity and are interpreted as imaging the top of the downgoing plate. In the central part of the profile a break in reflectivity located below the axis of the coastal cordillera more or less coincides with the intersection between the oceanic plate and the continental Moho. This break in reflectivity also approximately correlates with the downdip end of the seismogenic plate interface as defined by geodetic modelling. These new seismic data provide the geometry of the subduction zone in the area, and hence we suggest the relocation of the 1960 Chile earthquake at 73\deg 05' W.
DE: 7230 Seismicity and seismotectonics
DE: 8102 Continental contractional orogenic belts
DE: 9360 South America
SC: Seismology [S]
MN: 2003 Fall Meeting