A high-resolution technique is developed to image geologic boundaries such as contacts and faults. The outlines of the geologic boundaries can be determined by tracing the maximum amplitudes of an enhanced analytic signal composed of the nth-order vertical derivative values of two horizontal gradients and one vertical gradient. The locations of the maximum amplitudes are independent of the ambient potential field. This technique is particularly suitable when interference effects are considerable and/or when both induced and remanent magnetizations are not negligible. The corresponding depth to each geologic boundary can be estimated from the amplitude ratio of the enhanced and the simple analytic signals, which provides a simple estimation Such a method has been applied to magnetic data acquired in the Ilan Plain of Taiwan located at the southwestern end of the Okinawa Trough. The quantitative analysis shows that the underlying geologic boundaries deepen southward and slightly eastward. The enlargement of the Ilan Plain in the direction of the Okinawa Trough and the existence of north-northwest and west-northwest trending faults near the city of Ilan reveal a discontinuity between the Okinawa Trough backarc extension and the compressional process in Taiwan.