Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone ...

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B07110 TOMINAGA ET AL.: JURASSIC QUIET ZONE MAGNETIC ANOMALIES B07110 Figure 7. Polarity block model for entire survey, shown for midwater depth ( 3.0 km). Magnetic anomalies have not been deskewed. Top two solid curves show observed magnetic anomalies at sea surface (0 km) and 3 km depth. Dotted curve shows calculated magnetic anomalies. Bottom square wave plots show final combination model based on reconciling the 92 model and the new data. Correlation functions between lines are >0.5 at low offset (Figure 8), indicating a high level of agreement. The worst correlation was in the NORTH survey area, which contains small, difficult-to-correlate anomalies as we had found previously in the 1992 survey (Figure 4). [23] Profiles in the H801 survey, where anomaly amplitudes are mostly 0.5 for lines 2-7 and 2-3, which are 10 km apart, but never >0.2 for lines 2-7 and 3-9, which are 30 km apart (Figures 3, 8). The reasons for the poor correlation are apparent from an inspection of the two profiles (Figure 3); these are probably the most dissimilar lines in terms of anomaly spacing and amplitude. Nevertheless, these two profiles exhibit obvious similarities. For example, for line 3-9 the two main anomalies allowing correlation are the deep low on the north center end of the line (13 km from north end) and the large, double-positive anomaly on the south end (10 km from south end) (Figure 3). In most studies of magnetic anomalies, this degree of correlation would be considered acceptable. Because of the anomaly variations, correlation in the H801 area would be less convincing if only two or three widely spaced profiles were available, a factor to be considered when we interpret other areas of JQZ data. [24] Anomalies in the SOUTH survey have amplitudes of 200 nT (Figure 3). Although we have only two lines (lines 1 and 3-9) located 30 km apart, they display generally good agreement between the large anomaly shapes and locations, albeit with some variation in small features, spacing, and amplitude (Figure 3). The correlation coefficient for these two lines peaks at just under 0.5, but can be increased to >0.6 with small (
B07110 TOMINAGA ET AL.: JURASSIC QUIET ZONE MAGNETIC ANOMALIES B07110 Figure 8. Cross-correlation functions of selected magnetic profiles. Cross-correlation between deeptow profiles shown in upper row of boxes: (left) lines 5-11, 12, 13 in the M34 area; (middle) lines 2-3, 7, and 3-9 in the H801 area; and (right) lines 1 and 3-9 in the SOUTH area. In the latter plot, the solid line shows the improved coherency attained with modified spacing of anomalies on line 1 (see text and Figure 3). Cross-correlation was not plotted for NORTH area lines because the correlation function is small (
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Deep-tow magnetic anomaly study of the Pacific Jurassic Quiet Zone ...

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