音频大地电磁测深反演南沙新区地下空间岩性构造特征

Study on Lithology-Structure Characteristics of Underground Space in Nansha New Area by Inversion of Audio Magnetotelluric Sounding

查明区域地下空间岩性构造特征,可反映下伏岩性变化、断裂空间分布,对基础地质研究、地下空间开发建设均有较大意义。借助音频大地电磁测深(AMT)技术,采用点测观测方式,通过后期二维反演,可获取连续的研究区二维地电断面结果。通过对广州南沙新区实测的2条长剖面数据进行噪音剔除、静态效应校正,并利用SCS2D软件进一步精细处理反演,结果如下:(1)万顷沙下伏空间存在岩性从晚三叠世花岗岩(T3ηγ)过渡到莘庄村组(E1x)砂砾岩,再出现晚三叠世花岗岩(T3ηγ)发育的过程,局部莘庄村组砂砾岩埋深超过500 m未见底,有较大范围砂砾岩红层覆盖在花岗岩顶部;(2)推断了2处隐伏断裂(F1、F2),均为东西走向,断裂位置与区域地质资料较为吻合;(3)利用SCS2D反演软件能较好反应剖面整体电性特征、突出局部异常,对断裂构造、岩性变化有较准确的刻画;(4)采用AMT作为勘探万顷沙地区特殊地形地貌的地球物理手段,具备测点布置灵活、勘探深度大、反演分辨率高等优点,能快速查明该区地下空间岩性、构造特征。

Finding out the lithology-structure characteristics of regional underground space can reflect the underlying lithology changes and spatial distribution of faults,which is of great significance to the basic geological research and the development and construction of underground space.With the aid of the audio magnetotelluric sounding(AMT)technology,continuous two-dimensional geoelectric section results in Nansha New District,Guangzhou City can be obtained by using point observation method and two-dimensional inversion.Through the noise elimination and static effect correction of the two measured long profile data,and further fine processing inversion by using the SCS2D software,it is concluded that:(1)In the underlying space of Wanqingsha area,there is a process of lithology transition from granite of Late Triassic to sandstone conglomerate of Xinzhuangcun Formation,and then the occurrence of granite of Late Triassic.The burial depth of local sandstone conglomerate of Xinzhuangcun Formation is more than 500 m,and there is a large range of red sandstone conglomerate layer covering the top of granite;(2)It is inferred that the two buried faults(F1 and F2)are in E-W trend,and the location of the faults is consistent with the regional geological data;(3)The SCS2D inversion software can better reflect the overall electrical characteristics of the profile,highlight local anomalies,and accurately describe the fault structure and lithology changes;(4)AMT,as a geophysical means to explore the special topography of Wanqingsha area,has the advantages of flexible layout of survey points,large exploration depth,high inversion resolution,and can quickly identify the lithology and structure characteristics of underground space.