广东地区地壳地震波速不均匀性研究

A Study on the Inhomogeneity of Crustal Seismic Wave Velocity in Guangdong

利用广东"十五"区域测震台网自2007年以来的324个地震的直达Pg波及绕射Pn波(共8821个)走时资料,采用遗传算法在广东省范围内联合反演获得走时残差最小的整个研究区的一维速度结构(水平分层),以及上述324个地震的发震时刻和震源位置。在此基础上,缩小范围,同时考虑到地震台站和震中分布的实际情况,将整个研究区域分成7个小区,对每个小区域内传播的射线再次进行拟合迭代获得该小分区内走时残差最小的反演结果,最后通过对不同分区速度结构的"拼接"、"对比"以探索研究区内的三维速度结构和发生地震的深部构造背景。由此得出研究区域的地壳厚度为31.09 km,各层地壳厚度:沉积层为0.9 km、上地壳为13.3 km、中地壳为8.3 km、下地壳为8.6 km。从而总结出广东及其邻省的地震大多发生在上地壳层,即在14.2 km以上,有少数在中地壳层(14.2～22.5 km)。反演结果也表明,大多数地震震源位于高低速度体的过渡区域。

Derived from Guangdong ＂10th Five＂ regional digital seismometry network since 2007, direct Pg waves and diffracted Pn waves travel time data （8821 in total） of 324 earthquakes, are used in genetic algorithms along with joint inversion within Guangdong province to acquire the one-dimensional velocity structure （horizontal layer） with minimum residual, as well as seismic origin time and location of the 324 earthquakes mentioned above. With this basis and narrowed range, considering the actual circumstances of the distribution of seismic stations and epicenters, the entire study region can be divided into seven areas. The transmission ray of each area will be fitted and iterated a second time to obtain the inversion result with minimum travel time residual. Finally, through ＂stitching＂ and ＂comparison＂ of velocity structures of all seven areas, the regional three-dimensional velocity structures and the deep structures may be explored and studied. In addition, it＇s simultaneously obtained that the crust thickness of the study region is 31.09 km; Crustal thicknesses of each layer： sedimentary 0.9 km, the upper crust 13.3 km; the middle crust 8.3 km and the lower crust 8.6 km. Thus concluding that most earthquakes in Guangdong and its neighboring provinces occurs in the upper crust, e.g. 14.2 km above, and there are a few in the middle crust （14.2-22.5 km） .The inversion results also show that most earthquake sources are located in the transition zone of high and low velocity bodies.