深圳市中生代巨型花岗岩体浅部速度结构

Shallow shear wave velocity structure of huge mesozoic granitic pluton in Shenzhen from ambient noise tomography

利用南方科技大学2017年12月至2018年2月在深圳市布设的41个流动地震台站数据,通过背景噪声层析成像方法得到研究区域内0.5~5 s周期范围的瑞利波相速度,并对研究区地下0~8 km深度范围内的S波速度结构进行了反演.结果表明,浅部速度结构与地表地质构造有很好对应关系.这些在浅部呈水平展布的高速异常体与地表出露的巨型中生代花岗岩体很好对应.研究区在4 km深度以下主要存在两块高速异常体:西南部南山区和福田区沿海平原区域下方的大范围高速体和东北部神仙岭区域的高速体.地表这两块巨型中生代花岗岩体的下方,在浅部呈水平展布的高速异常体,和深部4 km以下的两块高速异常体形成了侧向连接关系.该结果刻画了深圳地区地表大面积出露的花岗岩体在地下的展布形态,显示了中生代岩浆通过主控断层上涌侵入,对地壳浅部形成改造的图像.本研究也展示了短周期密集台阵在城市地下波速结构研究中的应用潜力.

Employing the seismic data observed by 41 temporary seismic stations deployed by South University of Science and Technology in Shenzhen City from December,2017 to February,2018,we first obtain Rayleigh wave phase velocity of 0.5~5 s period by Ambient Noise tomography method in this region,then invert S-wave velocity structure from Earth′s surface to 8 km depth.Results show that the velocity structures near the Earth′s surface are well correspond to local tectonics.A salient feature is that high and low velocity staggered distribution exist in all depths,and the demarcations of high and low velocity anomalies are consistent with faults exposed.High velocity zones horizontally located at different depths are well connected via fault zones and obviously contact with the exposed areas of volcanic-intrusive mass on the Earth′s surface,interbedded with low velocity anomaly sheets.Deep rising high anomaly zones are correspond with areas lacking of low velocity anomalies at shallow depths,where Mesozoic granites exposed,usually hills.This phenomenon implies that deep hot material intruded in Mesozoic via faults and flooded between sedimentary rock layers,deforming the crust structure.The results show that velocity structure and exposed geological tectonic features are consistent in this region;also show potential for well studying the Earth′s deep structure in urban areas by employing densely deployed short-period seismic array data.