南襄盆地及邻区地壳厚度与泊松比研究

Study on Crustal Thickness and Poisson's Ratio in Nanxiang Basin and Its Adjacent Area

摘要:

利用河南、湖北、陕西地震台网共27个固定台站记录到的2014~2016年远震波形的接收函数，通过叠加获得了南襄盆地及邻区26个台站下方的地壳厚度和泊松比，结合该区地形地貌特征、断裂分布和地震活动，得出以下结论：①南襄盆地及邻区的地壳厚度与地形变化关联紧密，呈现出由NE向SW方向增厚的趋势，地壳厚度为30~41km；②泊松比高值集中在房县-兴山附近，为0.31~0.34，这可能与区域内大量出露寒武-奥陶系的辉长岩、苏长岩等铁镁质基性岩相关；低值为0.18~0.24，分布在商南-西峡-淅川一带，与区域内存在大量的长英质岩有关，它们与南襄盆地内的新生代沉积地层形成整合接触关系。由此可推断，在淅川、西峡一带存在因介质的较大差异而导致地震射线在传播过程中出现反射的可能。

Abstract:

In this paper,the receiver functions of the teleseismic waveforms from 2014 to 2016 recorded by 27 fixed seismic stations of Henan Digital Seismic Network,Hubei Digital Seismic Network,and Shanxi Digital Seismic Network were used to obtain the crust thickness and Poisson's ratio of the stations below the 26 seismic stations in the Nanxiang Basin and its adjacent area,which combined with the fracture distribution,seismicity,and topographic features of the area,has reached the following conclusions:(1)The crust thickness of the Nanxiang Basin and its adjacent areas is closely related to terrain change. It shows a trend of thickening from the northeast to the southwest,and the crust thickness is 30-41km.(2)The high value area of Poisson's ratio is located in the vicinity of Fangxian and Xingshan,the value of which is from 0.31 to 0.34. It may be associated with a large number of mafic rocks in the Cambrian-Ordovician,such as gabbro and sulphite. The range of low value is from 0.18 to 0.24,and the area distributes in Shangnan and Xixia,and is related to a large number of felsic rocks. They formed an integrated contact with Cenozoic sedimentary strata in the Nanxiang Basin. From this,it can be inferred that there is a possibility of reflection of seismic rays during the propagation process due to large differences in the medium between the Xichuan and Xixia areas.