Andaman Sea magnetic and gravity profiles: Depth and structure analysis

Abstract

Second vertical derivative processing can be useful in magnifying and separating near-surface f atures by increasing the power of the depth dimension in the denominator. A relationship exists between a second erivative map and a residual map in that curvature is actually measured. Areas of large curvature are related to smaller scale structures. Figure 3 gives the results of a second vertical derivative solution. The Piney Creek lineament can be seen to correspond to a linear region of negative curvature, which compares well with the shape of the processed anomaly shown in Figure 2. This negative curvature anomaly appears to disrupt he east-west rend associated with folding and faulting. A second derivative computed in this manner has the resolving power of a downward continuation of several levels. However, derivative anomalies have a lesser quantitative value and are most useful in locating extrema and inflection points. The discussion thus far has been concerned with the filtering of low frequency effects in order to enhance local anomalies. An upward continuation accomplishes the reverse of this process. Figure 4 gives an upward continuation of 3 km (1.86 miles) of the test area. The effect shown is that of emphasizing a regional field arising from a southward-deepening basin. The dashed contours in Figure 4 are taken from a regional gravity map and correspond well with the upward continuation. Note the manner in which the northeast-trending Piney Creek lineament symmetrically divides the continued field. This trend is interpreted to have regional significance as a fracture zone caused by forces which deformed the basin. In this way, evidence is given for a previously unrecognized northeast-trending structural grain in this region of the Arkoma basin.