SPOC Experiment: First Results From Seismological Studies Along the Central Chilean Margin
Abstract
The investigations of the RV SONNE cruise SO161 during the SPOC experiment (Subduction Processes Off Chile) concentrated on the area of the central Chilean margin west off Valparaiso. The main goal of this experiment is to investigate the effects of subducting oceanic seafloor relief on the seismicity of this domain. A marine array of 23 ocean bottom hydrophones and seismometers (OBH/S) was deployed for a period of ten weeks to monitor local earthquakes from this part of the Chilean margin where volcanic structures like the aseismic Juan Fernandez Ridge enter the trench. A strong decrease in dip angle of the subducting plate (flat slab) is observed here, resulting in a segmentation of the margin. The flat slab segment correlates with the absence of Quaternary volcanism and a central valley on the South American plate. It is assumed that a connection between the buoyancy of thickened oceanic crust and the occurrence of shallow subduction earthquakes exists. We present preliminary results of hypocenter determinations, founded on about 300 localisable events based on the OBH/S recordings. The distribution of hypocenters shows a considerable seismic activity within the 15 km - 50 km depth range. The special focus on the transitional domain of the slope allowed us to map in detail the seaward termination of the seismogenic zone. In addition, we used seismological land data, recorded from the Central Chilean Network (CCN) and a number of temporary landstations to supplement the marine data set. Comparative and joint hypocenter analysis from both marine and land data, increases the precision of locations and allows an assessment of systematic errors. We can show the need of both, on- and offshore data sets, to determine offshore earthquake locations with high precision. The seismological investigations are in close collaboration with the active seismic studies carried out during the scope of the SPOC experiment.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.T62B1313T
- Keywords:
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- 8015 Local crustal structure;
- 8105 Continental margins and sedimentary basins;
- 8123 Dynamics;
- seismotectonics;
- 9360 South America