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Journal: Science in China: Earth Science  2014 No.6  Share to Sinaweibo  Share to QQweibo  Share to Facebook  Share to Twitter    clicks:813   
Title:
Three-dimensional in situ stress determination by anelastic strain recovery and its application at the Wenchuan Earthquake Fault Scientific Drilling Hole-1 (WFSD-1)
Author: SUN DongSheng, LIN WeiRen, CUI JunWen, WANG HongCai, CHEN QunCe, MA YinSheng, WANG LianJie
Adress: Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
Abstract:

In situ stress state becomes more and more significant with in-depth research on geodynamics and energy development. However, there has not been an economic and effective method developed to determine deep three-dimensional in situ stress. The Anelastic Strain Recovery (ASR) method is a newly developed technique that can determine three-dimensional in situ stresses. After the 12 May 2008 Ms8.0 Wenchuan earthquake, the ASR method was used for the first time in mainland China to measure the in situ stresses in the WFSD scientific boreholes in Sichuan Province, China. In this paper, the basic procedure of the ASR method is introduced in detail and the compliances of ASR for boring cores are investigated. The results show that the maximum principal stress direction was NW64° at a measured depth (MD) of 1173 m (vertical depth 1151 m) in WFSD-1. The ratio of shear mode to the volume mode compliance of ASR was 2.9. And the three principal stresses at 1173 m MD in WFSD-1 are 43, 28 and 25 MPa. Combined with stress measurement results determined using other in situ measurement methods along the Longmenshan fault zone, the directions of the maximum horizontal principal stress changes from E-W to NEE-SWW to NWW-SEE when moving from NE to SW along the Longmenshan fault zone. This change is in agreement with the stress regime of the Longmenshan fault zone of the Wenchuan Earthquake, which supports a stress regime consisting predominantly of thrusts in the southwest and strike-slip in the northeast.

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