羌塘盆地中部地区地壳S波速度结构及构造意义  

Waveform inversion of S-wave velocity model in the central Qiangtang in North Tibet and its geological implications

作　　者：吴蔚[1] 刘启元[2] 贺日政[1] 曲中党 

机构地区：[1]中国地质科学院地质研究所国土资源部深部探测与地球动力学重点实验室,北京100037 [2]中国地震局地质研究所地震动力学国家重点实验室,北京100029

出　　处：《地球物理学报》2017年第3期941-952,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41574086;41274095);国家重点研发计划(2016YFC0600301);中国地质调查局项目(12120115027101);国土资源部公益行业基金项目(201011013;201011044)资助

摘　　要：羌塘盆地是我国最大的海相盆地.本文根据在羌塘盆地内布设的27个宽频带地震观测台站记录的远震波形数据,利用非线性复谱比反演算法得到各台站下方100 km深度范围内S波速度结构.结果表明.羌塘地区Moho深度较为平缓,平均深度为61 km;北羌塘地壳内低速层广泛分布;北羌塘具有两个较大的沉积盆地,龙尾错和白滩湖坳陷,沉积厚度分别有10 km和15 km.尽管北羌塘下地壳受到强烈的新生代火山岩作用改造,但是这种深部岩浆热作用会加速烃源岩中有机质的热演化历程.北羌塘两个盆地具有很好的油气前景.与北羌塘低速层分布相比,南羌塘下低速层更深,可能与班公怒江洋于中生代的俯冲消减及拉萨地体北向俯冲有关.The Qiangtang basin is the largest Mesozoic-to-Cenozoic marine sediment basin in China. The central metamorphic belt in central Qiangtang divides it into South Qiangtang basin and North Qiangtang basin. This study conducted a series of teleseismic receiver functions across the Qiangtang basin. The teleseismic data came from a temporary seismic array in Qiangtang basin. High-quality receiver functions were picked up from 738 teleseismic traces of 338 teleseismic events recorded by 27 stations along 88.5°E in 2009-2010. 1-D S-wave velocity model was calculated by the nonlinear inversion of conjugate gradients algorithm for the complex spectrum ratios of receiver function. Because the method made full use of amplitude ratio between the vertical and radial components of the receiver function in time domain, the final model from the method is completely independent of the initial model parameters. The velocity model indicated that the Moho beneath Qiangtang area rises slowly from south to north. The South Qiangtang basin has an average Moho depth of 68 kin. In the North Qiangtang basin the average Moho depth is 60 km, which are in accordance with H-~ stack and deep seismic reflection results. There is a continuous low velocity layer beneath the North Qiangtang basin. While in the South Qiangtang basin the low velocity area is discontinuous, which causes hot springs along thrust faults. The sedimentary thickness was determined by deep seismic reflection and Poisson＇s ratio. There is one large sedimentary basin in the South Qiangtang basin and two in the North. Geological survey suggested that the two depressions in North Qiangtang, Longwei Co and Baitan Lake, have pretty good outlook in petroleum exploration.

关 键 词：羌塘盆地 沉积坳陷 接收函数非线性反演 地壳厚度 壳内低速层 

分 类 号：P315[天文地球—地震学]