HR: 1340h
AN: S13A-1033    [Abstracts]
TI: Identifying Asperities: Correlating b-value and Isostatic Residual Anomaly Maps
AU: Meyer, U
EM: umeyer@gfz-potsdam.de
AF: BGR Hannover, Alfred-Bentz Haus, Stilleweg2, Hannover, 30655 Germany
AU: * Sobiesiak, M
EM: polar@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Schmidt, S
EM: sabine@geophysik.uni-kiel.de
AF: University of Kiel, Institute for Geophysics, Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Goetze, H
EM: goetze@geophysik.uni-kiel.de
AF: University of Kiel, Institute for Geophysics, Otto-Hahn-Platz 1, Kiel, 24118 Germany
AU: Krawczyk, C
EM: lotte@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AB: Asperity structures influence the rupture propagation of large earthquakes and cause inhomogeneously distributed concentrations of high moment release or slip on the fault plane. Considering this capacity and its significance for future earthquakes, identification of asperities and the investigation of their nature is of some importance in terms of hazard assessment. Within the framework of a collaboration between the German Task Force for Earthquakes and the German Collaborative Research Project 267 ("Deformation Processes in the Andes"), we investigated relations between the spatial distribution of the seismic b-value derived from the aftershock sequence of the 1995 M=8.0 Antofagasta earthquake, Northern Chile, and the isostatic residual anomalies computed from regional gravity data. Despite some limiting factors in resolution of both mapping methods, the positive correlation between patches of high b-values (b>0.9) and high isostatic residual anomalies (delta g>50mGal) is significant. In a previous study we were able to link also coseismic high moment release to high b-value patches (Sobiesiak, 2000). In our interpretation, the isostatic residual structures are caused by high density batholitic bodies located in the upper crust which are locally connected to the seismogenic zone of the subduction interface. In addition, buoyancy and shear forces of the subducting Nazca plate are directed upward in the area of the seismogenic zone causing isostatic anomalies and local stress sources. From these coinciding observations, we deduce that the batholites in conjunction with the buoyant and shear forces of the subducting plate are responsible for the genesis of the asperities in the Antofagasta region. These features employ long-term steady-state conditions with a life time of geological time scales. This yields the hypothesis that the asperities around Antofagasta are stationary features capable to survive several seismic cycles and thus are able to rupture repeatedly.
DE: 1734 Seismology
SC: Seismology [S]
MN: 2004 AGU Fall Meeting