秦岭造山带及其两侧区域地壳剪切波分裂

Shear-wave splitting in Qinling Orogen and its both sides

本文分析了陕西区域地震台网2006年1月到2015年7月的近震波形资料,采用剪切波分裂系统分析方法(SAM),获得了秦岭造山带及两侧区域17个台站的快波偏振方向和慢剪切波时间延迟.结果显示,剪切波分裂参数具有明显的分区特征.鄂尔多斯内部和渭河盆地的台站表现出NE-SW和NEE-SWW向的快波偏振方向,与华北地块区域主压应力方向一致;鄂尔多斯西南部,处于多个地块过渡区,积累了大量的应变,该区快波偏振方向较为复杂,反映了该区复杂的区域构造;南秦岭以勉略缝合带为界,北部为秦岭微板块,南部为扬子地块北缘.秦岭微板块地区台站快剪切波优势偏振方向为NWW-SEE向,与华南地块应力方向一致;扬子地块北缘地区台站表现出NE-SW向的快波优势偏振方向,可能受到青藏高原向东北扩张的影响.本文得到的快剪切波优势偏振方向与秦岭造山带被商丹缝合带和勉略缝合带分割的构造划分方案一致.研究区内,扬子地块北缘地区慢剪切波时间延迟最大,可能反映该区各向异性强于其他区域.本文的研究结果为进一步了解区域应力场特征和动力学过程提供了重要参考.

In this study, the polarization of fast shear waves （PFS） and time delay of slow shear-wave beneath the 17 stations in this area were computed by shear-wave Splitting Analysis Method （SAM） based on the seismic data during January 2006 to July 2015, recorded by Shaanxi Regional Digital Seismic Network. The parameters of shear-wave splitting have a striking regional division character. In the basin of Ordos and Weihe Basin, the PFS exhibits NE-SW and NEE-SWW direction, which agree with the direction of pressure stress in North China block. In the region adjacent to South-West of Ordos basin, which is located in a transition zone and accumulates a lot of strain, the dominant direction of PFS is complex. The south Qinling orogen is separated by Mianlue belt, the north region is Qinling micro-plate and the south region is located in north of Yangtze plate. The dominant PFS in Qinling micro-plate is in NWW-SEE direction, which is according with the direction of pressure stress in South China block. In north of Yangtze plate, the dominant direction of PFS is NE-SW, which may be affected by the northeastward movement of Tibetan Plateau. The results of PFS are coincident with the division of the tectonics that Qinling orogen is separated by Shangdan suture belt and Mianlue suture belt. The time delay of slow shear-wave is the biggest in north of Yangtze plate, which probably means that the anisotropy is stronger than that of other areas in this study. The results provide a very important basis for the further understanding of the compressive stress and kinetic processes of the study area.