2-D MAGNETIC INTERPRETATION USING THE VERTICAL INTEGRAL

摘要

A magnetic interpretation method is presented which numerically computes the vertical integral of the observed total-field anomaly along a profile. This transformed field is fitted by the vertical integral (also computed numerically) of the total-field anomaly of an interpretation model using a standard, nonlinear, least-squares estimation routine. The vertical integral transformation used here is similar to using a spatial domain pseudogravity operator after reducing the magnetic anomaly to the pole. The difference is that the reduction to the pole is not needed, so that the knowledge of the magnetization direction is not required. This method estimates the depth to a weakly magnetized basement that is intruded by strongly magnetized rocks. This method is best suited for the case where sills cut the overlying sediments and interfere with the magnetic signal from basement. Attempts to interpret isolated anomalies of stocks in the basement should take into account this kind of interference. The proposed method attenuates the effect of the shallow sources and produces a better lateral resolution than the upward continuation filter. Synthetic examples show that in interpreting the total-field anomaly, the presence of shallow sources leads to underestimated depths to the basement. By using the vertical integral of the total-field anomaly, on the other hand, depth estimates closer to the true values are obtained the method is applied to aeromagnetic data from Amazon Basin, Brazil, and produces estimates for the basement depths that are consistent with the geological knowledge and with previous magnetic interpretations. [References: 23]