The mapping of tectonic features in the ocean basins from satellite altimetry data

Satellite altimetry data provide information on the height variations of the sea surface. The angle between a line perpendicular to the sea surface and a vertical line between the satellite and the sea surface is referred to as the deflection of the vertical and is equal to the first derivative of the sea surface. This study examines two theoretical models describing the relationship between the deflection of the vertical data and the bathymetry 1) across a fracture zone in a large age-offset, fast-spreading regime and 2) across a fracture zone in a small age-offset, slow-spreading regime. The models are respectively compared to the observed relationship 1) across the Mendocino Fracture Zone which is in a large age-offset, fast-spreading regime and 2) across the DuToit Fracture Zone which is in a medium age-offset, slow-spreading regime. The strong agreement between the theoretical models and the observed relationships suggests that the models can be used with the deflection of the vertical data to locate fracture zones in known regimes. The angle between the trend of a feature and the trend of the satellite track affects the deflection of the vertical signal. As the angle becomes smaller, the amplitude of the deflection of the vertical signal, which varies with the sine of this angle, decreases and the wavelength of the signal increases. Once the feature is parallel to the track, there is no deflection of the vertical signal. The deflection of the vertical signal is also affected by the direction the satellite travels. If the feature trends between the ascending and descending tracks of the satellite, then the satellite will cross the feature from opposite directions and the ascending and descending signals will be opposite to each other. If the feature does not trend between the ascending and descending tracks, then the satellite will cross the feature from the same side and the deflection of the vertical signal will be similar for both the ascending and descending data sets. A third factor affecting the deflection of the vertical signal is the latitude at which the feature is located. The trend of the satellite track varies as a function of latitude, ranging from 18° at 0° latitude to 64.6° at 70° latitude. Because the trend of the satellite track varies, not only does the angle between the trend of a feature and the trend of the satellite track vary with latitude, but the amplitude of the deflection of the vertical signal varies with latitude as well.