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Abstract The research area，in Lizhou district，Guanyuan City in the northwest Sichuan Basin，is located between the central faults and front faults of north section of Longmenshan fault belt. The major geological structural units in the research area are semi-platform unit and thrust nappe unit. The lithology is mainly mudstone and silt mudstone formed during the lower Silurian era，which are present almost all over the research area. In order to meet the requirements of one engineering establishment，the in-situ stress measurements by hydraulic fracturing method in four boreholes were accomplished；and the measurement time span was up to 23 years. The measured results indicated that：the in-situ stress state did not change in the past 23 years；the dominant orientation of the horizontal principal stresses in the research area was N24.4°W；and the stress gradients of the maximum and minimum horizontal principal stresses vs. depth were 0.036 and 0.025，respectively. The four feature parameters，kH max，kh min，?m and R，calculated through measured principal stresses，did not change during the 23 years. The research area is in the foot wall of the central faults of the Longmenshan fault belt，and is a passive wall. At the same time，the activities of fault movements and seismic events in the research area are extremely weak. Such a specific regional geodynamic conditions have determined the very stable stress field of this area. Comparing with the other research findings，the calculated ?m reflects the stress accumulative capability of the regional crust in this area，i.e. the magnitude of ?m reflects the strength of regional faults from the point of stress accumulation. Such a finding is consistent with the others′. In the future research，it is possible to use ?m values determined with the measured stresses and the corresponding data from the analysis of activities of fault movements and seismic events to evaluate the earthquake risk of one certain area.
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Received: 31 March 2012
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2012, Vol. 31 
