中文摘要：

利用基于P波初动和振幅比反演震源机制解的HASH方法,得到鄂尔多斯块体周缘2008-01~2014-06共1 700个ML2.5以上地震的震源机制解,从中选取结果较为可靠的1 581个地震的震源机制解,将研究区域划分为1°×1°的网格,采用阻尼区域应力反演方法（MSATSI软件）获得了研究区域内中小地震震源机制解特征和应力场图像。鄂尔多斯块体周缘震源机制解类型以正断和走滑为主,应力场反演结果表明,鄂尔多斯周缘应力状态以拉张为主,局部区域存在剪切、挤压。块体北缘和西缘的最大水平主应力优势方位为NE向,一致性较好;块体东缘和南缘的最大水平压应力方向与区域内主要活动构造方向基本平行,东缘最大水平主应力方向从南段的近EW向、NEE向逐渐过渡到NE向,南缘是NWW-SEE和近EW向。通过分析研究区域应力状态和最大水平主应力方向认为,银川-吉兰泰南端近NS向活动断裂的剪切应力状态的出现,是由于近NS向活动断裂在NE向挤压应力作用下发生了右旋剪切运动;块体西南缘NEE向的挤压和剪切的应力状态与青藏块体对鄂尔多斯块体的直接作用,以及六盘山断裂带第四纪以来强烈的挤压性质及左旋走滑运动有关;大同盆地出现局部剪切应力状态可能与盆地下方的火山有关。

英文摘要：

The focal mechanism solutions of 1 700 ML2. 5 small to moderate earthquakes which oc- curred in the cireum-Ordos block and its adjacent areas from Jan. 1, 2008 to June 21, 2014 are ob- tained using the HASH method. The stress tensors and the orientations of the maximum horizontal stress of the cireum-Ordos block are determined by the MATLAB package for spatial and temporal stress inversion （MSATSI） using grids, with the damping parameter 1.2 at the 95 % confidence level. The characteristics of the spatial distribution of the focal mechanisms are investigated and their tectonodynamic background is discussed. Main conclusions are drawn as follows. In the rift zone of Yinchuan-Jilantai, Hetao, Shanxi and Weihe, which are located around Ordos block, the main types of the composite focal mechanism are strike-slip and normal types, which reflect the Ordos block suf- fering shear and extension stress field. There are different stress regimes around Ordos. Yinchuan- Jilantai, which is located northwest of Ordos, is a normal stress state which matches well with the re- gional geodynamic mechanisms, but the nearly north-south active fault presents strike-slip regime in the southern part of the northwestern segment which is forced to right-lateral strike-slip shearing from the NE. Three types of the composite focal mechanism are thrust-strike-slip and normal types in the Haiyuan-Liupanshan fault zone located on the SW boundary of Ordos block, which are under the joint action of the NW and NE compressional stress field. The maximum horizontal principal stress orienta- tions are dominanted by NE and NW orientation. That may derive from the NE-directional pushing force from the Qinghai-Tibetan plateau and NW-SE directional extension caused by the uplifting of the deep substance of the Qinghai-Tibetan plateau. The maximum horizontal principal stress orientation seems to rotate slightly anticlockwise in the Shanxi rift, their stress pattern： EW-NE-NEE from south to north, and most of them parallel to the main fault＇s str