Stress state estimation by geophysical logs in NanTroSEIZE Expedition 319-Site C0009, Kumano Basin, southwest Japan
Article first published online: 21 SEP 2012
©2012. American Geophysical Union. All Rights Reserved.
Geophysical Research Letters
Volume 39, Issue 18, September 2012
How to Cite
2012), Stress state estimation by geophysical logs in NanTroSEIZE Expedition 319-Site C0009, Kumano Basin, southwest Japan, Geophys. Res. Lett., 39, L18303, doi:10.1029/2012GL053086., , and (
- Issue published online: 21 SEP 2012
- Article first published online: 21 SEP 2012
- Manuscript Accepted: 14 AUG 2012
- Manuscript Revised: 9 AUG 2012
- Manuscript Received: 11 JUL 2012
- Grant-in-Aid for Scientific Research on Innovative Areas, MEXT. Grant Number: 21107006
 To understand the stress regime in the shallow portion of the Nankai Trough seismogenic zone, we carefully investigated the resistivity image logs at IODP Site C0009 that penetrated to 1600 meters below the sea floor (mbsf) in the central Kumano forearc basin. During the riser drilling, several downhole measurements were run including image logs, caliper and comprehensive geophysical logs sets. Borehole resistivity images obtained by a wireline-logging tool were reprocessed in order to eliminate image artifacts generated by sticky tool movements, etc. The constraints on the possible magnitude and orientation of horizontal principal stresses are provided from the borehole images, rock strength, and logging data. The absence of borehole breakouts above 1285 mbsf represents a small difference (<10 MPa) between horizontal principal stresses and reflects the normal faulting and strike–slip faulting stress regimes. A stable, continuous breakout was observed in the resistivity image logs suggest that the stress state is in a strike–slip faulting and tending to reverse faulting regime below 1285 mbsf. The differential horizontal stress (up to 15 MPa) is significantly larger than in the shallow portion of the borehole (SHAMX ≫ Sv > Shmin).