Stress state and its anomaly observations in the vicinity of a fault in NanTroSEIZE Expedition 322

Hung Yu Wu, Saneatsu Saito, Masataka Kinoshita

Research output: Contribution to journalArticlepeer-review


To better understand the stress state and geological properties within the shallow Shikoku Basin, southwest of Japan, two sites, C0011A and C0011B, were drilled in open-ocean sediments using Logging While Drilling (LWD) and coring, respectively. Resistivity image logging was performed at C0011A from sea floor to 950 m below sea floor (mbsf). At C0011B, the serial coring was obtained in order to determine physical properties from 340 to 880 mbsf. For the LWD images, a notable breakout anomaly was observed at a depth of 615 m. Using resistivity images and a stress polygon, the potential horizontal principal stress azimuth and its magnitude within the 500-750 mbsf section of the C0011A borehole were constrained. Borehole breakout azimuths were observed for the variation by the existence of a fault zone at a depth of 615 mbsf. Out of this fracture zone, the breakout azimuth was located at approximately 109° ± 12°, subparallel to the Nankai Trough convergence vector (300-315°). Our calculations describe a stress drop was determined based on the fracture geometry. A close 90° (73° ± 12°) rotation implied a 100% stress drop, defined as a maximum shear stress drop equal to 1 MPa. The magnitude of the horizontal principal stresses near the fracture stress anomaly ranged between 49 and 52 MPa, and the bearing to the vertical stress (Sv = 52 MPa) was found to be within the normal-faulting stress regime. Low rock strength and a low stress level are necessary to satisfy the observations.

Original languageEnglish
Pages (from-to)4422-4432
Number of pages11
JournalGeochemistry, Geophysics, Geosystems
Issue number12
Publication statusPublished - 2015 Dec

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology


Dive into the research topics of 'Stress state and its anomaly observations in the vicinity of a fault in NanTroSEIZE Expedition 322'. Together they form a unique fingerprint.

Cite this