北天山上地幔各向异性研究

SEISMIC ANISOTROPY ON THE UPPER MANTLE IN NORTHERN TIANSHAN

利用新疆地震台网记录到的远震波形数据,对北天山地震带上的15个台站记录到的58次地震进行剪切波偏振分析,采用最小能量法和旋转相关法,计算台站下方介质的各向异性分裂参数,即快慢波延迟时间和快波的偏振方向。研究结果表明,在沿准噶尔盆地西南和东南边缘,台站下方各向异性快波方向呈NWW向,与天山造山带的走向基本一致,其慢波延迟时间基本在0.7-1 s,而在南北天山交汇区附近,台站下方各向异性方向转为与天山山脉走向垂直的NE—NEE向,这种变化可能是与坚硬的塔里木块体和准噶尔及哈萨克斯坦块体双向俯冲,导致岩石圈缩短变形,产生了复杂各向异性结构。

Using teleseismic wave data in Xinjiang seismic network, writers carried out shear wave splitting analysis in 15 seismic stations for 58 earthquakes along northern Tianshan tectonic zone. It calculated the anisotropic parameters beneath those seismic stations, the fast wave polarization direction and delay time, taking both minimum energy and rotation correlation method. The result indicated that along the southwest and southeast of Dzungarian basin the delay times varied from 0.7 s to 1 s, and the direction of fast wave was nearly NWW direction, which had similar trend with Tianshan foldbelt. Nearby the intersection of southern Tianshan and northern Tianshan, the direction turned into NE-NEE direction which was vertical with the strike of Tianshan. Writers considered this complex anisotropy which related to shortening of lithosphere caused by the subduction of stiff Tarim block and Dzungarian block.