接收函数H-k叠加方法在龙门山台阵的应用

H-k stacking of receiver functions and its application in a portable array along the Longmen mountains

龙门山地区的深部构造研究对于龙门山断裂带的深部驱动机制有重要的意义,但由于天然地震太站分布较少,难以获得水平分辨较高覆盖整个龙门山地区的深部构造图像.本文利用最新中德合作在龙门山断裂带两侧布置的天然地震阵列式台站数据,获取了各个台站的接收函数波形数据.通过对H-K叠加方法的研究和改进,并应用到各个台站的实际接收函数数据分析上,获得了断裂带两侧以及沿断裂带的地壳厚度和平均速度比的分布,通过进一步插值形成了覆盖整个龙门山地区的水平分辨20Km的Moho面三维形态.综合对应的速度比和深部物质赋存状态关系的研究,获得以下结论：四川盆地属于平均厚度35-40km冷地壳,松潘和夹金山等山区地壳则属于厚45-50Km的热地壳.而沿断裂带变化比较明显,南段类似高原地区有热而厚的地壳,中段为40-45 km的正常地壳,个别地形突起处深约50 km.北段则逐渐向盆地的冷而薄的地壳过渡,厚度从43-40 km逐渐变化.Moho面的分布特征表明了龙门山断裂带的中部和南部的差异,并推测其间存在一个明显的Moho面异常突起带,与该过渡带的余震的缺失存在一定的关联.

The deep structure survey for Longmenshan area is important to reveal the driving mechanism of Longmenshan Faults.Due to the scarely distributed broadband stations within this area,it is hard to obtain higher horizontal resolution images for whole Longmenshan area.Utilizing the broadband teleseismic data recorded by the stations deployed along both sides of the Longmen mountains by Sino-German cooperations recently,waveforms of receiver functions for each station have been derived.With the aid of a modified H-k stacking technique and its application to the analysis of observed receiver function data for each station,the distribution of Moho depth and the ratio of average compressional to shear wave velocity（Vp/Vs）along as well as on both sides of the Longmenshan fault is presented.After interpolation and ananysis,it forms the whole Moho depth distribution covering Longmenshan Area with 20 km horiztontal resolution.Integrated with correspondent velocity ratio and its relationship with the property of deep materials,we obtain the conclusions：The Sichuan basin has a cold crust with 35-40 km thickness.The Tibetan plateau,Songpan and Jiajin mountains have hot crust with 45-50 km thickness.However,along the fault,the crust varies very obviously.Its southern part has hot and thick crust like the plateau,its middle part has normal crust with 40-45 km thickness except for specific topographic regions where thicknesses of 50 km are obtained and the northern part gradually becomes cold and thin towards the basin with a thickness of 40-43 km.This feature of Moho distribution illustrate the obvious difference between middle part and southern part of Longmenshan Faults,deducing an abnormal bulge of Moho,which might interpretate the absence of aftershocks at that transition zone.