HR: 1340h
AN: T33C-0576    [Abstracts]
TI: Repeating Earthquakes in the Outer Rise Offshore Southern Chile
AU: * Tilmann, F J
EM: tilmann@esc.cam.ac.uk
AF: University of Cambridge Bullard Laboratories, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Grevemeyer, I
EM: igrevemeyer@ifm-geomar.de
AF: Leibniz Institut f. Meereswissenschaften IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Gossler, J
EM: jgossler@ifm-geomar.de
AF: Leibniz Institut f. Meereswissenschaften IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Scherwath, M
EM: mscherwath@ifm-geomar.de
AF: Leibniz Institut f. Meereswissenschaften IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Flueh, E
EM: eflueh@ifm-geomar.de
AF: Leibniz Institut f. Meereswissenschaften IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Hofmann, S
EM: Sonja.Hofmann@dkrz.de
AF: Univ. Hamburg Institut f. Geophysik, Bundesstr. 55, Hamburg, 20146 Germany
AU: Dahm, T
EM: dahm@dkrz.de
AF: Univ. Hamburg Institut f. Geophysik, Bundesstr. 55, Hamburg, 20146 Germany
AB: In December 2004-January 2005 two temporary arrays of ocean bottom seismometers and hydrophones (Sonne cruise SO181) were recording the micro-earthquake activity of the outer rise region offshore Southern Chile. The southern array was located offshore the Chonos archipelago (45°S) on very young oceanic plate (6 Ma). No outer rise earthquakes are listed in the global catalogues for this region. The northern array is located off Chiloe island (43°S) on somewhat older plate (14 Ma). Several normal faulting events have occurred in this area in the last 30 years. Nevertheless, during the temporary deployment, the southern region was far more active with several hundred locatable events. Most events located in the crust and the uppermost 1-2~km of the mantle. In contrast, relatively few locatable events (<200) were recorded by the Northern array, with most events lying outside the array. The depth of the few events within the array places them well into the mantle, ~5km deeper than the deepest events in the south. The event set recorded by the southern array is remarkable in that a very high proportion (~0.35) of the events are repeating earthquakes, that is events with a high waveform similarity (correlation coeff. >0.9). They group into 41 clusters of various sizes, with the largest cluster consisting of 24 events. Recurrence times are highly irregular, with repeating earthquakes occasionally being separated by a few minutes only but some sequences stretching over the entire observational period. Repeating earthquakes have been associated with strong patches embedded within weak parts of a fault, with irregularities at the boundary between strong and weak parts, and with systematic changes in pore fluid pressure due to fluid diffusion. We will consider how far each of these models can describe the event sequences at the Outer Rise, where the dominant strain arises due to bending of the oceanic plate.
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8164 Stresses: crust and lithosphere
DE: 9360 South America
SC: Tectonophysics [T]
MN: Fall Meeting 2005