HR: 0800h
AN: G51C-0092    [Abstracts]
TI: Gravity Data Analysis and Forward Modelling Along the Chilean Margin at 36-42\deg S
AU: * Tasarova, Z
EM: zuzana@geophysik.fu-berlin.de
AF: Freie Universitaet Berlin, Institut fuer Geologische Wissenschaften FR Geophysik Malteserstrasse 74-100, Berlin, 12249 Germany
AU: Goetze, H
EM: hajo@geophysik.uni-kiel.de
AF: Christian-Albrechts-Universitaet zu Kiel, Institut fuer Geowissenschaften Abteilung Geophysik Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Schmidt, S
EM: sabine@geophysik.uni-kiel.de
AF: Christian-Albrechts-Universitaet zu Kiel, Institut fuer Geowissenschaften Abteilung Geophysik Otto-Hahn-Platz 1, Kiel, 24118 Germany
AB: The Chilean margin between 36 and 42\deg S is the subject of new geological and geophysical research. The information about this area come from comprehensive gravity database, field geological observations, seismic reflection profiles (amphibious wide-angle seismic experiment across the subduction zone) at 36-38\deg S, and the integrated active and passive seismological experiment ISSA 2000 at 36-39\deg S, including also the receiver function study and the local earthquake tomography model. Based on these constraining data, the 3D density model has been developed within the framework of the German Collaborative Research Center 267 "Deformation Processes in the Andes" (SFB 267, task group F4). The convergent Andean margin, which is subject to some of the earth largest earthquakes, shows pronounced along-strike changes in the tectonic setting, deformation history and its morphological expression. The study area is characterized by much lower (on average less than 2000 meters) and narrower Main Cordillera than in the Central Andes (15-33\deg S), as well as by a thinner crust. The central part of the study region is the site of the large 1960 Valdivia earthquake, which occurred onshore the transition between the oceanic lithosphere generated at two different spreading centers. This region shows no gravity high, whereas a positive Bouguer gravity anomaly is an omnipresent feature along most of the coastline south of 10\deg S. The gravity data, combined under agreements from the oil industry data and other sources, as well as the own measurements, were reprocessed and show clearly a local scale segmentation of the region under study. The results of the forward density modelling show that the position of the Nazca plate and changes in its geometry controls the gravity field. Shallower oceanic plate below the forearc region at 36-39\deg S vs. deeper slab south of 39\deg S might also have its impact on the plate coupling between the subducting and overriding plates. The modelling also indicates a shallow crust beneath the Central Depression, which is observed as well in the earthquake tomography model, together with the high velocity and density anomaly in the mantle below the Central Depression.
UR: http://userpage.fu-berlin.de/~geoinfhb/Welcome.html
DE: 1219 Local gravity anomalies and crustal structure
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting