Estimation of Minimum Principal Stress from an Extended Leak-off Test Onboard the Chikyu Drilling Vessel and Suggestions for Future Test Procedures

To understand the physics of faulting and rupture propagation for the great M8-class Nankai earthquakes that recur approximately every 100 years, a comprehensive drilling project is underway: the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE; Tobin and Kinoshita, 2007), which is part of the Integrated Ocean Drilling Program (IODP). Stress levels along seismogenic faults must be known in order to understand processes controlling the timing, energetics, and extent of earthquake ruptures. For scientific drilling projects such as NanTroSEIZE, it is very important to determine the in situ stress state at the decollement and the mega splay fault in the Nankai Trough