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Bottom-simulating reflector variability at the Costa Rica subduction zone and corresponding heat flow model

UTIG Seminars

Bottom-simulating reflector variability
at the Costa Rica subduction zone
and corresponding heat flow model

Shannon Cavanaugh
MS student, UTIG

When: Friday, Dec. 2, 2011, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
Where: Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758
Host: Charles Jackson, UTIG

Live broadcast

We use 3D seismic reflection data acquired in April - May 2011 by the R/V Marcus G. Langseth to extract heat flow information using the bottom-simulating reflector across the Costa Rica convergent margin. These data are part of the CRISP Project, which will image the Middle America subduction zone in 3D. The survey was conducted in an area approximately 55 x 11 km, to the northwest of the Osa Peninsula, Costa Rica. For the analysis presented here, 3D seismic data were processed with Paradigm Focus software through post-stack time migration.

The bottom-simulating reflector (BSR)-a reverse polarity reflection indicating the base of the gas hydrate phase boundary-is imaged very clearly in two regions within the slope-cover sediments in the accretionary prism. In deep water environments, the BSR acts as a temperature gauge revealing subsurface temperatures across the margin. We predict BSR depth using a true 3D diffusive heat flow model combined with IODP drilling data and compare results with actual BSR depth observations to constrain where heat flow anomalies exist. Uniform heat flow in the region should result in a deeper BSR downslope toward the trench, however our initial results indicate the BSR shoals near the trench to approximately 96 m below the sea floor, suggesting elevated heat flow towards the toe. Landward, the BSR deepens to about 333 m below the sea floor indicating lower heat flow. Both BSR segments display a trend of deepening landward from the trench, however the further landward BSR's depth below the sea floor is greater overall than the toe segment. We suggest two regimes with differing heat flow exist across the margin that likely represent two separate fluid flow regimes - one from recently accreted sediments near the prism toe and the other through the older materials making up the prism.