Orientation of In Situ Stresses in the Pacific Plate: Deep Sea Drilling Project Hole 597C

Abstract

The analysis of borehole televiewer records from DSDP Hole 597C has provided an estimate of the orientation of the near-surface horizontal principal stresses at a site in the oceanic crust about 1800 km west of the East Pacific Rise at 19°S. The televiewer data reveal wellbore breakouts with a consistent orientation of N31E ± 25°. This orientation indicates an average maximum horizontal compression direction of N121E magnetic, which, when corrected for magnetic declination at the site, results in a maximum horizontal compression direction of N110E ± 25°. This direction is parallel to both the relative and absolute motion vectors for the Pacific Plate. It is also parallel to the orientation of the P axes of focal mechanism solutions of intraplate earthquakes located near the site, and it is consistent with an interpretation of a dominant ridge-push force acting at the site.