西昆仑接收函数反演与构造解析

中法合作布设的青藏高原西昆仑叶城-噶尔(狮泉河)天然地震探测剖面穿越了西昆仑构造的主要构造单元, 通过对36个台站128个远震P波事件的接收函数分析,取得了各台站的接收函数随方位角和震中距变化的趋势, 分析了变化趋势与地壳构造的关系。通过台站平均接收函数的反演拟合,取得了120km深度范围以上的横波速度分布,综合地质构造解释,发现康西瓦断裂地表倾斜渐变为直立并略向南拖曳的现象,塔里木前陆盆地沉积与逆冲构造有比较明显的显示,同时推测了盆地下的滑脱构造。班公湖-怒江断裂也有向北俯冲的显示,得出了印藏碰撞远距离效应在西昆仑受阻,应力通过地表次级断裂释放,同时形成盆地沉积的前陆构造模式。

Receiver function inversion and structural analysis in the West Kunlun

The seismic profile from Yecheng-Gar (Shiquanhe) in the West Kunlun on the Qinghai-Tibet Plateau deployed by the Sino-French joint project traversed major structural units in the West Kunlun tectonic syntax. Through a receiver function analysis of three-component P wave data recorded by 36 stations for 128 teleseismic events, the authon obtained the variation trend of the receiver functions with the azimuth and epicenter distance for these stations and analyzed its relationship with crustal structure. The shear wave velocity distribution in the upper 120 km of the crust and upper mantle was obtained by the inversion of average receiver functions at various stations. On that basis, combined with interpretations of geological structure, the phenomenon that the inclined surface of the Kangxiwar fault becomes gradually nearly upright and then drags southward slightly has been found, which is markedly manifested by sediments of the Tarim foreland basin thruste structures, and in addition it is also inferred that there is decollement beneath the basin. The Bangong Co-Nujiang suture also has traces of northward subduction. So it is deduced that the long distance effect of India-Tibet collision is hindered at the West Kunlun, and the stress is released by subsidiary faults at the surface and a foreland structural model of basin sediments is constructed.