| dc.description.abstract | It is well known that the use of an incorrect density in constructing Bouguer gravity map will cause abnormal results. To reconstruct a Bouguer gravity map in the Miao-Li area, average rock density was investigated in this study. For optimization of gravity result, the density for the Bouguer correction and terrain correction of gravity was derived from N-method, g-H relations, and the method of Bouguer density and terrain density in this study.
In addition, gravity data are often acquired over long periods of time using different instruments and various techniques, resulting in data sets of non-uniform accuracy. In order to obtain more precise gravity data, the Kriging technique of geological statistics was employed to determine Bouguer anomaly value exactly. With the feature of least variance and the best linear unbiased estimator, Kriging technique could take into account station accuracy and decrease interpolation error. The Kriging technique was also applied to the simulation of geological structure.
The general procedure to determine geological structure is as fallows. Density structures of three cross-sections perpendicular to strike of the surface geology were obtained from modeling of well strata. We compared calculation result from modeling with observed values, which were judged by traditional correction of gravity. Moreover, the density structures of the model were fixed until the anomaly curves trend to coincide each other.
After processing, however, the new method for determination of density has two advantages. First, since the density was computed with the function of the latitude, longitude, elevation, and observed gravity value of the station, the new method can save more time and has smaller error than the previously direct measured method. Second, the density of any region can be obtained form database immediately without reconstructing station data. Besides, the surface density structures obtained from modeling of three cross-sections indicated that the formations in west-northwestern side are uplift. This feature can be recognized by a step in decollement of a deep thrust in the base of Miocene formations. The fault-bend folding mountain belt in eastern side shows that deformation of the Miao-Li area was caused by the northwestward compressive force which was possible the results of the orogeny of early Pleistocene. In general, the gravity results between observed and modeling are consonance except for mountain area. | en_US |