Expedition 314 Summary Expedition 314 Sept Nov 2007

Expedition 314 Summary Expedition 314: Sept - Nov, 2007 Logging-While-Drilling dedicated holes at 5 sites forearc basin accretionary prism y a l p s ega m to ent m e s a ng b i t c u d b p of su Philippine Sea plate

Logging While Drilling

LWD (Logging-While-Drilling) 1 -2 rot/sec Bulk density/Porosity/Caliper Vp by check shot Data transfer/annular P Sonic velocity Resistivity image Drill bit

Site Overview forearc basin accretionary prism y a l p s ega m to ent m e s a ng b i t c u d b p of su Philippine Sea plate

Site C 0002: Kumano Forearc Basin and Underlying “inner wedge”

Site C 0002 LWD log summary

Checkshot data for C 0002

Site Overview forearc basin accretionary prism y a l p s ega m to ent m e s a ng b i t c u d b p of su Philippine Sea plate

Sites C 0001 and C 0004: Mega-splay thrust sheet

C 0001 Log Summary

Borehole Breakouts: Indicators of Principal Stress Orientations SHmax Shmin LWD Resistivity Image log Walls of the borehole fracture or “break out” perpendicular to the direction of horizontal maximum compressional stress SHmax

Site C 0001 Synoptic view: large horizontal exaggeration Breakouts welldeveloped from 60 -550 mbsf Deeper interval has rare breakouts, abundant tensile fractures

Shmax ~ 336˚ normal to thrust strike suggests thrust stress state … but convergence obliquity must be taken up elsewhere Convergence at 310˚ 315˚ SHmax � Shmin � SHmax �

Site C 0003 - stuck and abandoned LWD string

Sites C 0001 and C 0004: Mega-splay thrust sheet

Site C 0004 Thrust fault zone at 250 -292 mbsf Breakouts cross this interval with no significant change in azimuth

Site C 0004 SHmax ~ 320˚

C 0004 main splay fault interval

Site Overview forearc basin accretionary prism y a l p s ega m to ent m e s a ng b i t c u d b p of su Philippine Sea plate

Site C 0006 - toe of wedge

Site C 0006 SHmax ~ 330˚

Site Overview forearc basin accretionary prism y a l p s ega m to ent m e s a ng b i t c u d b p of su Philippine Sea plate

Site C 0002: Kumano Forearc Basin and Underlying “inner wedge”

Site C 0002 Breakouts are welldeveloped to 1400 m depth Mean azimuth = 134°

forearc basin C 0002 prism toe C 0001 C 0004 C 0006

These observations are consistent with: • a compressional and/or transpressional stress state in the outer wedge SHmax = 1 • an extensional stress state in the Kumano basin AND the underlying inner wedge, at least to 1400 mbsf. SHmax = 2 This does not require a rotation of principal stress axes, only a change in their relative magnitude. Upper 950 m: forearc basin Lower 450 m: prism

Faulting Stress Regimes Thrust

Stress Regimes from Breakouts extensional compressional +/- strike-slip • Horizontal principal stress axis change is sharp, lies between Sites C 0001 and C 0002 • Consistent with change in relative magnitude of principal stresses

Future Work 1. Constrain stress magnitudes through strength testing of core samples 2. Drill deeper at C 0002 (forearc basin site) Will stress axes flip/rotate with depth?