. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography McGregor et al.: Magnetics Mid-Atlantic Ridge 233. Fig. 3. Residual magnetic anomalies with a 50-y contour interval, negative. Dashed line is topographic axis of the rift valley. 44'15' Shaded areas are an average magnetization along an axial dipole field direction. Over the last 3 the sea floor in this study area has not moved appreciably, so that constant direction of magnetization is a reasonable assumption. Recent Deep-Sea Drilling Project
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography McGregor et al.: Magnetics Mid-Atlantic Ridge 233. Fig. 3. Residual magnetic anomalies with a 50-y contour interval, negative. Dashed line is topographic axis of the rift valley. 44'15' Shaded areas are an average magnetization along an axial dipole field direction. Over the last 3 the sea floor in this study area has not moved appreciably, so that constant direction of magnetization is a reasonable assumption. Recent Deep-Sea Drilling Project analyses of lavas from west of the Azores Plateau, however, showed that the mag- netic intensity and polarity of the volcanic sequence varied greatly with depth in the sequence [Ade-Hall et al., 1975]. Simplifying assumptions for the model may introduce some departures from reality, but as more drilled samples become available, the model can be adjusted. Ten profiles across the ridge crest approxi- mately 4 km apart (Figure 2) were analyzed with a computer program written by R. L. Parker and S. P. Huestis of the Institute of Geophysics and Planetary Physics, University of California at San Diego (Figure 4). Bathymetry and magnetic anomaly values were selected every km. The sloping line at the end of each profile repre- sents artificial data to reduce the contamination of the computed magnetization by replications introduced by the Fourier transform [Parker. 1973]. The measured magnetic anomaly, the cal- culated magnetization, and the bathymetry are plotted for each profile. The solution of the inverse problem given the set of assumptions outlined above is still nonunique. To the solution of the equation which gives the ob- served magnetic anomaly, one may add any amount of the solution which causes no external field [Parker and Huestis, 1974]; the latter magneti- zation function is called the annihilator. In each of the profiles of Figure 4 the amount of annihilato
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