对布设在鄂尔多斯块体及其周缘的固定宽频带地震台网90个台站记录作远震SKS波形资料偏振分析,采用最小切向能量法求得每个台站的SKS快波偏振方向和快慢波时差,获得块体及其周缘上地幔各向异性图像,并结合1999～2007年相对鄂尔多斯块体的GPS水平地壳运动速度场,分析块体及其周缘的各向异性特征和壳幔耦合特征并重新认识块体的运动及周缘断陷带的动力学成因.分析结果认为,块体内部以零分裂为主,表现为各向同性特征；块体周缘台站延迟时间则明显大于块体中部,表现出明显的各向异性特征；快波偏振方向与地质构造走向、水平速度场方向基本一致,表明壳幔之间存在耦合,而个别台站在方向上与周围台站存在差异,可能与早期的块体活动有关.SKS横波分裂结果和现今GPS地壳水平运动场解释了鄂尔多斯块体没有旋转运动,在西南缘六盘山一带存在分叉绕流运动,汾渭断陷带的形成和发展是由于上地幔塑性物质沿挤出方向水平运动和沿裂隙向上入侵、横向扩张的综合演化结果.%Based on the polarization analysis of teleseismic SKS waveform data recorded at 90 broadband stations in Ordos block and adjacent regions, the splitting parameters of fast polarization direction and delay time between the fast and slow shear waves are determined at each station using the minimum transverse energy method, and the image of upper mantle anisotropy was acquired. Combined with the GPS horizontal velocity field relative to the Ordos block during 1999～2007, we analyze the seismic anisotropy as well as the crust-mantle coupling in Ordos block and its adjacent regions. At last, a new understanding of the block movement and the dynamic causes of the adjacent fault zone is achieved. The results reveal that there are nulls in the block which show an obvious isotropic characteristic. The delay time of the adjacent stations is obviously greater than those in the central block, which indicates an obvious anisotropy; the fast polarization directions are compatible with the tectonic strike direction and the horizontal velocity direction, which shows the crust-mantle coupling, however, the differences between the directions at some stations may possibly be explained by early block activities. According to the SKS shear wave splitting results and the current GPS velocity field, we know that the Ordos block does not rotate. Meanwhile, the horizontal and ascending intrusion and the transverse extension of the plastic material in the upper mantle lead to the bifurcated flow along the southwestern margin of Liupanshan. One flow forms the Fenwei graben.
展开▼
