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Abstract

The availability of a high-sensitivity digital aeromagnetic survey over the U.S. Atlantic continental margin and new graphical color-display techniques enabled us to compile residual maps of total magnetic intensity, and of its second-vertical-derivative and wavelength-filtered maps, which show structural elements that are not obvious in the original aeromagnetic maps.

A regional tilt in the original total-intensity map was removed by fitting a quadratic surface to the data. The resultant residual map reveals broad positive anomalies over the Baltimore Canyon trough, Carolina trough, and Blake Plateau basin. A regional negative anomaly overlies the Georges Bank basin and Long Island platform.

The visual effect of the second-vertical-derivative map is to emphasize the gradients, thereby sharpening and resolving anomalies of small areal extent; the high frequencies are enhanced. The low-frequency anomalies define the major basins that are presently being explored for petroleum resources, such as the Georges Bank basin, Baltimore Canyon trough, Carolina trough, and Blake Plateau basin, as well as a number of smaller basins. The second-vertical-derivative map indicates complex structure associated with the East Coast Magnetic Anomaly (ECMA). For example, two positive lineaments between 36° and 37°30' N suggest that although a simple edge effect associated with the oceanic crust may account for a large part of the total anomaly of 200-600 nT, more complex structures are also present. We compiled a map showing tectonic elements of the continental margin from the second-vertical-derivative map.

High-pass filters of 60-, 40-, and 20-km wavelength illustrate successively shallower sources of anomalies and provide a useful first approximation of depth to magnetic basement.

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