Insun Song 1, Chandong Chang 2, and Hikweon Lee 1 (1) Korea Institute of Geoscience and Mineral Resources (2) Chungnam National University, Korea

Location of study area and tectonic setting

Geologic profile

Breakouts and in situ stress  hmin  hmax IODP EXP 314 NanTroSEIZE report    (MPa)  º  HH rock strength bb bb

Strength vs. sonic velocity Depth (mbsf) V P (m/s) UCS (MPa) Counts V P (m/s) C0002A mbsf Ave.=1784.4m/s (Chang et al., 2009)

   (MPa)  º  HH bb BB Height (m) BB C0002A ( mbsf) Counts UCS (MPa) C0002A mbsf Determination of far-field stress magnitudes bb  hmax breakout BB

Average strength vs. average breakout width Stress (MPa)  ( o ) Average strength Average width

Strength distribution vs. breakout width distribution Stress (MPa)  ( o )

In situ stress determination algorithm Counts UCS (MPa) For S h = 26 MPa  S H = 0.05 MPa Integration of all misfits S H = 28.5 MPa BB For S h = 26 MPa  S H = 0.05 MPa Cumulated density in height (m) Cumulated probability Assume Gaussian distribution of UCS(P) and  i = 0.6 (Song et al., 2010) Using the M-C failure criterion with probability, calculate the probability function of breakout width for given far-field stresses (S hmax and S hmin ) Compare the probability with breakout density in height Select the far-field stress with the minimum misfit

Examples of grid searching method 335 mbsf 484 mbsf 1295 mbsf 1172 mbsf 845 mbsf S hmin from LOT 875 mbsf

Stress profiles  s =0.6 hydrostatic Lithostatic (Chang et al., 2009) unconformity LOP

Stress polygon C0002A LOP

Conclusions Using the distributions of rock strength and breakout width instead of their averages, we were able to determine both S hmin and S Hmax simultaneously. In normal faulting stress regime, S hmin is insensitive to error and becomes more sensitive as it goes to the strike-slip faulting stress regime. In Kumano forearc basin in situ stress is very close to the limit equilibrium condition for normal faulting. Underneath the unconformity the stress condition becomes stable and goes to the strike-slip fault stress regime with increasing depth.

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