Abstract
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.