HR: 13:40h
AN: S43D-01 INVITED     [Abstracts]
TI: The Relation Between Tectonics, Fluid Flow and Seismogenesis at Convergent Erosional Margins
AU: * Ranero, C R
EM: cranero@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3,, Kiel, 24148 Germany
AU: Weinrebe, W
EM: wweinreb@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3,, Kiel, 24148 Germany
AU: Grevemeyer, I
EM: igrevemeyer@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3,, Kiel, 24148 Germany
AU: von Huene, R
EM: rhuene@mindspring.com
AF: IFM-GEOMAR, Wischhofstrasse 1-3,, Kiel, 24148 Germany
AU: Reichert, C
EM: Christian.Reichert@bgr.de
AF: BGR, Bundesanstalt f�r Geowissenschaften and Rohstoffe, Stilleweg 2, Hannover, 30655 Germany
AB: The integration of seismic reflection images, multibeam bathymetry, sidescan sonar images, seafloor observations, heat flux measurements and well-located microearthquakes show the relationship between tectonics, fluid flow and seismic activity at the erosional Middle America convergent margin. Seismic images show that the plate boundary is characterized by large amplitude reflections under the continental slope. The amplitude of plate-boundary reflectivity rapidly decreases inboard, beneath the continental shelf. Temperatures calculated at the plate boundary indicate that large amplitudes occur where dehydration reactions (~60 C to ~160 C) release chemically-bound water of subducting sediment. The rapid decrease in plate boundary reflectivity parallels the predicted decrease in dehydration-related fluid release with increasing temperature ($>$160 C). Thus, seismic images give the qualitative distribution of fluids along the plate boundary. Above the area of high fluid release, the overriding plate is traversed by numerous faults that link the hydrological system of the plate boundary with the seafloor. Fluids rising across the upper plate vent across the continental slope at fault scarps and mud diapirs with carbonate crust and chemosynthetic fauna indicative of active fluid flow. The association between areas of higher fluid release, strongly deformed upper plate and venting at the seafloor is observed to correspond to the continental slope for hundreds of km along the margin. Underneath the continental shelf, the upper plate is comparatively little deformed and the plate boundary has little fluid. Here, large earthquakes nucleate and microearthquakes indicate stronger mechanical coupling of the plates. We hypothesize that progressive changes in plate boundary fluid content influence faulting mechanisms, and that changes in upper plate strength control the amount of elastic energy that can be stored. Those two parameters may be key for earthquake generation.
DE: 7230 Seismicity and seismotectonics
DE: 8150 Plate boundary--general (3040)
DE: 7209 Earthquake dynamics and mechanics
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting