鄂尔多斯块体周缘地区现今地壳水平运动与应变

位于青藏块体和华北块体之间的鄂尔多斯块体及其周缘地区是中国大陆构造活动最活跃的地区之一,从1300年至今,在块体周边断陷盆地和西南缘断裂带上发生了五次8级以上的地震.为了了解该地区现今地壳运动、应变状态以及断裂滑动分布,我们收集了中国大陆构造环境监测网络2009—2013年、国家GPS控制网、跨断陷盆地的8个GPS剖面等共527个流动站和32个连续站GPS观测数据,获得了高空间分辨率的地壳水平运动速度场,进一步用均匀弹性模型计算了应变率分布.结果表明,块体内部GPS站点向NEE方向运动,速度变化较小,应变率大多在(-1.0~1.0)×10~(-8)/a之间;山西断陷带构造运动与变形最为强烈,盆地相对于鄂尔多斯块体为拉张变形,应变率为(1.0~3.0)×10~(-8)/a,相对于东部山地则为挤压变形,应变率为(-2.0~-3.0)×10~(-8)/a,盆地西侧断裂(如罗云山断裂、交城断裂)以拉张运动为主,拉张速率为2~3mm·a-1,盆地东侧断裂主要以右旋缩短运动为主,速率为1~3mm·a-1;河套断陷带西部的临河凹陷处于较强的张性应变状态,应变率为(2.0~3.0)×10~(-8)/a;块体西南边缘处于压缩应变状态,应变率为(-1.0~-2.0)×10~(-8)/a,六盘山断裂存在明显的地壳缩短运动,速率约为2.1mm·a-1,速率在断裂附近逐渐减小,反映了断裂处于闭锁状态;相对于鄂尔多斯块体内部渭河断裂带为左旋运动,速率为1.0mm·a-1,盆地处在弱拉张变形状态.

Present-day crustal movement and strain of the surrounding area of Ordos block derived from repeated GPS observations

The surrounding area of Ordos block located between Qinghai-Tibet block and north China block is one of the regions where the tectonic movement is most intensive in China mainland. Five large earthquakes with magnitudes greater than or equal to 8 have occurred in this region since 1300. In order to investigate the crustal movement, strain distribution and fault slip rates in this region, GPS data observed from 2009 to 2013 were collected at 527 campaign-mode and 32 continuously operating GPS stations and used to calculate a precise and high spatial resolution velocity field and strain rate field. The results reveal that GPS sites within Ordos block move towards NEE, the rates of these sites change little, and the strain rates are between (-1.0~1.0)×10^-8/a. Tectonic movement and deformation of Shanxi rift is most intensive. The belt between Shanxi basin and its western mountains is under extension with a strain rate of (1.0~3.0)×10^-8/a. Meanwhile, the belt between Shanxi basin and its eastern mountains is under contraction with a strain rate of (2.0~-3.0)×10^-8/a. The faults at the west boundary of Shanxi basin show 2~3 mm·a^-1 of normal-fault extension. However, the faults at the east boundary of the basin demonstrate right-lateral slip rates of 1~2 mm·a^-1 and contraction rates of 1~3 mm·a^-1. The Linghe depression in the west of Hetao rift shows significant extensional deformation with a strain rate of (2.0~3.0)×10^-8/a. There is a shortening motion of 2.1 mm·a^-1 in the southwest of Ordos block, while the velocity rates change little near Liupanshan fault system. It reveals that the fault system is locked in deep. Weihe fault system shows 1.0 mm·a^-1 of left-lateral slip. Weihe basin is experiencing weak extensional deformation.