台湾海峡西岸地应力特征研究

In Situ Stress Characteristics in the Western Coast of Taiwan Strait

台湾海峡西岸地区受到欧亚板块、太平洋板块和菲律宾板块的共同作用,具有复杂的应力场特征,但本地区现阶段地壳应力状态研究程度较低。为深入了解本区地应力特征,本文采用水压致裂法在福建平潭和广东饶平钻孔中进行了地应力测量,并结合其他实测及震源机制解资料,讨论了台湾海峡西岸构造应力场特征。结果显示平潭和饶平钻孔地应力优势作用方位分别为N19°W和N37°W;由震源机制解资料得到的研究区应力场方向表现为从北向南由NNW方向转向EW方向的扇形分布。地应力状态的水平变化趋势,大致以沙县-南日岛断裂为界,北部为低应力区,南部为高应力区,且南部大致以九龙江下游断裂附近开始,呈现由北向南,地应力水平逐渐降低的趋势。在研究区北部、中部、南部分别选取平潭、泉州、饶平三个钻孔,利用库伦准则对断层活动性进行判断,认为海峡西岸北部地区应力水平较低,断层活动性较弱;泉州所在的海峡西岸中部地区应力已积累到较高的水平,断层失稳滑动的可能性比较大;饶平邻近区域在近期断层失稳滑动的可能性不高。

The west coast of Taiwan Strait has complex stress field characteristics, under the interaction of the Eurasian plate, the pacific plate and the Philippines plate. And in situ stress state in the area is not well researched. In order to further study the in situ stress characteristics, the authors measured the magnitude and direction of in situ stress in Pingtan and Raoping through hydraulic fracturing, and discussed the tectonic stress field characteristics of the western coast of Taiwan Strait on the basis of previous study and focal mechanism data. The study shows that the dominant directions of the maximum principal stress in Pingtan and Raoping are N19°W and N37°W. And analysis based on focal mechanism data suggests that the stress field in the study area has fan-like distribution originated from NNW and expanded to EW. In situ stress state in horizontal direction is roughly divided by Shaxian-Nanridao fault, stress of northern areas is low, but stress of southern areas is high. And in situ stress level gradually decreases from north to south, starting from fault zone in the downstream area of Jiulongjiang. Three boreholes were selected in Pingtan, Quanzhou and Raoping,and Coulomb friction criteria was employed to study the fault activity of these three boreholes. It is considered that fault activity of northern areas of Western Taiwan Strait at low stress level is weak. In situ stresses in middle areas of Western Taiwan Strait, where Quanzhou is located, have accumulated to a high level. Therefore, faults in this area have a high possibility of unstable sliding. Faults in adjacent areas of Raoping is unlikely to slide unstably in the near future.