Abstract: Seismic tomography has been applied to seismology as a new technique. The application of the technique,however,is sometimes limited by the incomplete projection and parameter coupling of the models used in geosciences. In this paper,a method of reconstructing the velocity image of sedimentary basement or Moho discontinuity based on head wave data is developed.This method can also be used to correct further the depth of hypocenter. In the computation,the algebraic reconstruction technique (ART) is adopted and modified. In order to improve the computation stability and convergence of ART and SIRT algorithms,a reasonable weighting factor is suggested. The corresponding resolution and variance of different algebraic reconstruction algorithms are also analysed through numerical estimation.Using P₈ wave data from Profile Ⅰ and Ⅱ of deep seismic sounding in Hainan Island,the velocity image of the basement in the region is reconstructed. The result shows that two low velocity zones are well consistent with the important Chunjiang-Zhonghe and Ganchong-Mutang surficial fault zones,indicating that the two fault zones cut through the sedimentary basement. In addition,the segmentation features of the fault zones are well reflected on the basement velocity image.

Key words: Seismic Tomography technique, Head wave, Fault zone, Hainan Island

摘要： 地震层析技术(SeismicTomography)正在作为一种新技术引入到地震学的研究中^[1],但由于地学中存在着非完全投影和模型参数间的耦合,使得该技术的应用受到了限制。本文讨论了用首波走时资料作为投影数据,重建基底或莫霍界面的速度图象的方法,同时亦可利用该方法对震源深度做进一步的修正。计算中采用了代数重建法,并就改善ART和SIRT这两种算法的稳定性及收敛速度,提出了较合理的权因子。通过数值模拟还对分辨和方差的影响进行了分析。利用海南岛人工爆破地震Ⅰ、Ⅱ测线非纵剖面的P₈波走时资料,初步得到了该区基底面的速度图象。结果表明,基底的低速区分布与地表的两条断裂带吻合得较好,说明北东向的春江-中和断裂与干冲-木裳断裂穿过了基底。断裂带内的分段特征也在图象中有所表现。

关键词: 地震层析技术, 首波, 断裂带, 海南岛