Seismic reflectivity anomalies in sediments at the eastern flank of the Juan de Fuca Ridge; evidence for fluid migration?

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doi: 10.1029/1999JB900061
Author(s): Zühlsdorff, Lars; Spiess, Volkhard; Hübscher, Christian; Breitzke, Monika
Author Affiliation(s): Primary:
Univerity of Bremen, Department of Geosciences, Bremen, Federal Republic of Germany
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 104(B7), p.15,351-15,364. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 34 refs.; illus., incl. 2 tables
Summary: A high-resolution seismic survey was carried out in the vicinity of Ocean Drilling Program (ODP) Leg 168 drill sites at the eastern flank of the Juan de Fuca Ridge. Three seismic systems with different source frequencies up to 4000 Hz were used simultaneously along each seismic line. The data sets were combined to provide the best possible resolution at any given depth level. An integrated interpretation of narrow zones of low reflection amplitudes is presented, which are related to basement highs but are independent of seafloor topography. The effect is most pronounced above a buried basement ridge in the vicinity of ODP Sites 1030 and 1031, where higher porosity values are present. Higher porosities can reduce seismic impedance contrasts and may therefore cause the observed low reflection amplitudes. In addition, Biot-Stoll's [Biot, 1956a, b; Stoll, 1989] model suggests that attenuation coefficients are porosity dependent and reflection amplitudes are further decreased at higher seismic frequencies when porosity increases. Since zones of higher porosities are potential pathways for fluids, they may be associated with hydrothermally driven fluid discharge, which was previously predicted above the buried basement ridge. It is therefore proposed that the observed seismic amplitude reduction in the vicinity of ODP Sites 1030 and 1031 indicates zones of upward fluid migration. Copyright 1999 by the American Geophysical Union.
Year of Publication: 1999
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Crust; East Pacific; Fluid phase; Geophysical methods; Geophysical surveys; Juan de Fuca Ridge; Leg 168; Migration; North Pacific; Northeast Pacific; Ocean Drilling Program; Ocean floors; Oceanic crust; Pacific Ocean; Plate tectonics; Sea-floor spreading; Seismic methods; Spreading centers; Surveys
Coordinates: N475000 N475600 W1283000 W1285000
Record ID: 1999061002
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