琼西北地区的基底速度图象

IMAGE RECONSTRUCTION OF VELOCITY ON THE CRYSTALLINE BASEMENT IN HAINAN ISLAND

利用人工地震测深纵剖面和非纵剖面的资料,对琼西北地区P_g波的走时进行了层析反演,对比了代数重建法和同时迭代重建法的效果.综合了纵剖面的模型后,在三维弯曲界面上重建了基底速度图象,探讨了用射线椭圆评价分辨的途径. 层析成象结果给出了许多有价值的信息,揭示琼西北的结晶基底存在三条北东向断裂和两条北西向断裂,后者是继承性的活动断裂,控制着新生代次级断块的发展与火山活动.地表所推断的东西向王五—文教深大断裂,在该处只呈断续隐伏状显示.该区的基底存在儋县、临高和光村三个高速区,主要反映着基性岩体或花岗侵入体.基底整体性最好的是在儋县—王五地区,破碎程度最严重的是在王五—中和—光村以西的地区.

In 1984 the field work of a deep seismic sounding was performel in the northwestern part of the Hainan Island. Three reversed in-line profiles and broadside seismic refraction and reflection data are ready to be used. Such technique of spatial seismic refraction recording produces a superabundance of common ray interseciions at the target horizon. The reversed in-line refraction data gives the control on the velocities, while the broadside refraction yields the detailed velocity distribution of crystalline basement over the area of interest. From the travel time of Pg wave, ART and SIRT algorithms are adopted to reconstruct the velocity image on the curved surface of basement. The distribution of ray ellipses is used to estimate the resolution of the image.The results inlicate that there exist three important faults striking NE and two of NW. The faults of NW strike are active and conTol Cenozoic block faulting and volcanic activity. Wangwu-Wenjiao fault, a huge deep fault zone oriented along east-west inferred from the observation on the surface has an interrupted and blind feature. Three high velocity areas in the crystalline basement around Danxian, Lingao and Guangchen, reflect the basic rock and intrusive body.of granite. The most homogeneous and compact basement is located in Dan-xian-Wangwu, while serious fractured basement is to the west of Wangwu-Zhonghe-Guangchen.