Orientation of in situ Stresses Near the Costa Rica Rift and Peru-Chile Trench: Deep Sea Drilling Project Hole 504B

摘要

Analyses of borehole televiewer (BHTV) records from DSDP Hole 504B have provided an estimate in the direction of horizontal principal stresses in the oceanic crust, which has implications for the relative influence of plate driving mechanisms. Breakouts are borehole elongations caused by perferential spalling at an azimuth perpendicular to the maximum horizontal principal stress direction. DSDP Hole 504B is located about 200 km south of the east-west trending Costa Rica Rift and about 350 km northwest-trending Peru-Chile Trench. Processing of borehole televiewer data from DSD Hole 504B has revealed breakouts that show consistent direction of N114E + or - 16 deg. When corrected for magnetic declination at the site, the breakouts indicate a maximum horizontal principal stress direction of N20E + or - 16 deg. The data imply at this site both the slab pull forces associated with subduction of the Nazca Plate and the ridge push forces from Cocos-Nazca spreading axis contribute to the in situ stress field. (Reprints).