岩溶区利用地震速度成像研究地下地质结构及特征

在场地狭窄,电性干扰严重的浅覆盖岩溶区,不利于电探方法来探查地下地层的岩溶发育特征。推荐采用地震纵波速度成像、横波速度剖面来综合探查地下的基岩起伏、地质结构和岩溶发育特征。在野外采用同一个排列保持道距不变的情况下,很容易获得这两种方法的地震记录。两种方法研究结果表明,多道噪音记录的折射微动面波法在探测基岩起伏方面具有较高的分辨率但探测深度浅;多炮点纵波速度成像对基岩面有平滑作用但探测深度较深。钻探资料证实,纵波速度成像中的相对低速区反映基岩内岩溶裂隙发育,是寻找地下水的有利靶区。多道记录,炮点—检波点射线高密度覆盖,可保证获得可靠的速度资料。两种方法联合探测地下岩溶特征具有一定的优势。

Study on underground geological structures and characteristics in Karst areas by using seismic velocity tomography

It is unfavorable to use electrical methods to detect underground Karst characteristics in the shallow covered Karst areas owing to the field limitation and high electromagnetic interference. It is recommended that the seismic longitudinal wave velocities tomography and transverse wave velocities profile could be used to explore the bedrock relief, geological structure and Karst development. It is not difficult to get the seismic records by using the two methods in the field while keeping the spacing unchanged within a single array. The results show that the refraction microtremor method with multichannel noise records is of higher resolution but only for small prospecting depth in detecting bedrock relief, however, the longitudinal velocity tomography with muhichannel shots is favorable in penetrating a bigger depth with the tendency of smoothing bedrock surface. It is confirmed by borehole data that the low longitudinal velocity zone within high velocity indicates the Karst area with rich fissures in bedrock, which is the good target to find underground water. It is guaranteed that both the multichannel records and the covering with the high shot-geophone ray density can gain the reliable longitudinal wave velocities. The combination of the two methods has some superiority to detect underground Karst features.