摘要
苏鲁超高压变质带的研究对了解发生在地幔深处的大陆动力学作用具有重要意义.近年来在此带中进行了大陆科学钻探和以深反射地震为主导的详细的综合地球物理调查,为研究超高压变质带地壳上地幔组构提供了难得的基础资料.根据大陆科学钻探工程的安排,在钻探取心,测井和地面三维地震观测的同时,还在5000m的钻孔中用三分量数字检波器,对地表激发传播到井中的地震波场作垂直地震剖面(VSP)观测,目的是将传感器放在钻孔内,近距离、高精度和高分辨率地观测井周围由于超高压变质带的构造特征和岩石岩性特征引起的波场变化.通过零偏移距和非零偏移距VSP调查,我们首次在超高压变质带取得了深度达5000m的精细的横波速度和泊松比等地球物理属性数据,作出了钻井岩心柱、测井、VSP纵波速度、横波速度和纵横波速度比、VSP上行波和地面地震资料的桥式综合对比图,使不同尺度的地质和地球物理调查资料互相连接在一起.零偏和非零偏VSP观测可以标定主孔地质剖面各深度地质体的地震反射特性、井旁地震剖面上各个同相轴的地质属性,并对井旁局部地质构造作精细成像.由此观测取得的横波速度资料,成为建立孔区横波速度模型主要的资料来源,这种模型也是地面多波观测数据处理不可缺少的.因此,建议在进行大陆科学钻探时尽可能安排VSP地震调查.
The research on the Sulu ultra-high-pressure metamorphic belt has great significance for understanding the continental geodynamic processes that occurred in the deep mantle. In recent years,Chinese Continental Scientific Drilling and detailed comprehensive geophysical investigation including deep seismic reflection have been carried out. These offered rare basic data for the research of ultrahigh-pressure metamorphic belt,the earth's crust and upper mantle fabrics. The drill-hole cores offered the direct data of composition,structure and construction of deep rocks,in which feature scale is merely a few centimeters. However,drill-hole and well-logging can only survey in one dimension. Therefore three dimensional seismic data should be calibrated with both spatial and time sampling scales for comparing drill-core and well-logging data. The survey of offset and non-offset vertical seismic profile serves to provide good links between the cores and well-logging data with seismic reflection events,show their geological attributes,and imaging structural details of around-hole rocks. In addition,the VSP data provide S-wave velocity profile along the hole that is the primary source for building the S-wave velocity. Besides,as a result of using digital three-component geophones,various information of structure and rock properties in drilling area was obtained,such as shear wave velocity model in the scientific drilling area,which is pre-required in the data processing of multi-wave exploration. In conclusion,this work suggests VSP investigation be carried out in continental scientific drilling project in crystalline rock areas, it seems possible and feasible.