物探方法对已知岩溶陷落柱的对比试验效果

CONTRAST TEST RESULT ON KNOWN KARST COLLAPSE BRECCIA PIPE USING GEOPHYSICAL METHODS

选择磁偶源频率测深法与地震折射波法,在岩溶陷落柱已被查明的河下矿区进行试验效果对比,证明利用低阻、低速带确定岩溶陷落柱是可行的。使用该两种方法相互配合可以互补,从而提高推断解释之准确性。这对于在条件相似的华北地区进行岩溶陷落柱的调查具有一定指导意义。

Magnetic dipole frequency sounding and seismic refraction methods are used to make comparative study on existing karst collapse breccia pipes and country rocks . It is proved to be feasible to delineate collapse body by the use of low resistivity and velocity zone. Magnetic dipole frequency sounding was performed with 200-300m dipole moment and 10 different frequencies. Test data were shown on frequency curve. For each frequency three components Hz,Hx,Ey were observed. Apparent resistivity was calculated from the formula of electric and magnetic field ratio. For seismic refraction survey , time-distance curve observation system was applied. Measuring line was 230m long with detector intervals of 10m, And 6 shotpoints were distributed on each line. The tests brought us a good result. For collapse body, average apparent resistivity (ρ) is 16. 7-30. 0Ωm and wave velocity is 2174-2666m/s. And for its surrounding rock the values are 39. 3-82.6Ωm and 2900-4500m/s respectively, There are distinctive difference between two methods. Magnetic dipole frequency sounding used low resistivity zone determines the location and shape of collapse breccia pipe, and all-frequency explanation method estimates its underground extension. To eliminate topotgraphical effect, equal T substraction method was applied on time-distance curve to get velocity values. Complete elimination of topographical effect still needs further study.