A Study On Bounding Problem Using Gravity Data In The Geological Mapping

Geological mapping is an integrated basic geological method for improving landand resources survey. Geophysical data contains abundant underground geologicalinformation, especially deeper hidden geological information, so geologicalmapping's information would be greatly improved by using geophysical methods atthe overlaid area. This paper is aimed at some problems about geophysical methodsapplied in geological mapping, mainly is how to accurately delimitate geologic body'sboundary. Gravity data applied in geologic body's boundary locating has been studiedsystematically in the paper. The main results of the study are as below:1. Some applied conditions on boundary locating methods have beensystematically studied. By a lot of forward calculating geophysical parameters as ?g,?gx , ?gzz , ?gzx in 2D models and ?g, ?g horizontal gradient nodule,?gz horizontalgradient module,?gzz in 3D models and their combined models ,based on the gravityanomalies characteristic value, the boundary locating errors have been statisticallyanalyzed, and finally the applied conditions about each method of boundary locatinghave been summarized.2. The boundary locating errors of inclined step and inclined tabular body inbottom infinitely deep have been theoretical calculated. The ?gxx formula of inclinedstep is developed, so the relation of the boundary locating errors of inclined step withits dip angle and the depth of its upper interface is given.3. ?gz horizontal gradient module, for the first time, is used to delimitate the3D geologic body's boundary, ?gzx is used to delimitate the 2D tabular body'sboundary. Compared with conventional methods, these methods have more accurateand wider applicable extension.4. The reasons why it has undesirable effects that gravity data is used todelimitate the geologic body's boundary have been analyses. The first is the problemsof the gravity data itself. The survey grid spacing determines that the gravity anomalywhich width is more than 25 kilometers can be used for inversion in 1:200000 gravitydata. The second is the applied problems of gravity interpretation methods. Theapplied condition of each method is ignoring. For example, one method or onetechnique parameter uniformly processes large region gravity data. The inversionmethods in relation to 2a/h ratio and dip angle, in principle, it is difficultly to controland evaluate the precision of their inversion results, etc.5. The approach of improving boundary location precision of gravity data ingeology mapping is put forward. Based on survey grid spacing and gravity resultantaccuracy, the anomaly of using quantitative interpretative methods can be chosen, bythe regional correction then local anomalies are separated from the anomaly, and usedin half-quantitative inversion or 3D auto inversion, finally the results are carried outinteractive man-computer 3D inversion method.