The Chilean Subduction Zone at 38.2° S: Implications for the Seismogenic Coupling Zone and the Subduction Channel
Abstract
The crustal structure of the subduction zone in south central Chile was revealed with high-resolution reflection seismic imaging within project TIPTEQ (from The Incoming Plate to mega-Thrust EarthQuake processes). The near-vertical incidence reflection seismic profile spans across 140 km from the coast of the Pacific Ocean to the Central Valley. The downdip end of the seismigenic coupling zone and the hypocenter of the great Chilean earthquake of 1960 (Mw = 9.5) lie in the center of the seismic section. Here, we show the structural inventory of the Chilean fore-arc at 38.2°S. The downgoing oceanic plate can be traced from 27-55 km depth. The oceanic crust has a varying reflectivity. A smooth increase in reflectivity below 30 km depth may be caused by the release of fluids because of the porosity collapse in the oceanic basalt. A zone of high Vp/Vs ratio supports this observation. A clear structurally imaged continental Moho could not be found, but it may be inferred together with constraints from gravimetrical modelling. Strong reflectivity above the plate interface may be associated with a subduction channel with a varying thickness of 2-5 km. Local seismicity possibly defines its upper boundary. The segmented crust of the overriding plate has two great seismically transparent zones, devided by the crustal Lanalhue Fault Zone. The eastern transparent zone may be caused by the Coastal Batholith which is covered by sediments in the Central Valley. A nearsurface first-break tomography of the TIPTEQ data set revealed the subsurface continuation of the batholith and a sediment thickness of ca. 1 km in the western part of the Central Valley. The seismic depth section is discussed in an integrated interpretation with magnetotelluric, gravimetrical and seismological findings along the TIPTEQ transect at 38.2°S.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T23A1994M
- Keywords:
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- 7230 Seismicity and tectonics (1207;
- 1217;
- 1240;
- 1242);
- 7240 Subduction zones (1207;
- 1219;
- 1240);
- 8104 Continental margins: convergent;
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413)