Hydrofracturing in-situ stress measurement in Hanzhong Basin, Shaanxi Province

Hanzhong basin is located at the end of northeastern section of Longmenshan fault zone. After the Wenchuan M_S8.0 earthquake, the earthquakes tend to occur mainly in the northeastern section of the Longmenshan fault and migrate towards NE direction. In order to study the stress state after the mainshock and analyze the seismic risk in Hanzhong basin region，two drillings were arranged to conduct hydrofracturing in-situ stress measurement on the western margin of Hanzhong basin. Both drillings have a depth of 300 m，the distance between the two drillings is 33 m. The results of stress measurement are perfect. Based on a comprehensive analysis of the stress measurement results，the following conclusions are drawn： ① On western margin of Hanzhong basin within 300 m depth，the maximum horizontal principal stress is 5.69—19.52 MPa，the minimum horizontal principal stress is 3.81—10.90 MPa，and the vertical principal stress is 1.25—7.03 MPa. The horizontal principal stress plays a dominant role and the minimum principal stress is vertical. The stress state is in favor of thrust fault movement. ② The present maximum horizontal principal stress in Hanzhong basin is in WNW-ESE orientation or in EW. ③ Since the occurrence of Wenchuan M_S8.0 earthquake，the tectonic stress in Hanzhong basin and its western neighbour region has been in an adjustment phase and being stable generally.