The Correspondence of Altimetric Gravity Texture to Abyssal Hill Morphology

We examine the possible relationship between altimetric and abyssal hill textures along the flanks of Southeast Indian Ridge, where previous studies observed a progressive west-to-east increase in abyssal hill roughness and scales. Such a relationship is often considered unlikely because abyssal hills are typically smaller than upward continuation filter scales. Nevertheless our analysis, which carefully avoids inclusion of fracture zones and major propagator psuedofaults, also demonstrates a west-to-east increase in gravity rms roughness and scale. The rms exhibits the most well resolved variations. Characteristic scales and aspect ratios also increase to the east, although less resolvably. At the roughest gravity textures, ∼ridge-parallel lineaments can be resolved, suggesting that this texture is directly responding to abyssal hill morphology. We suggest that the westernmost gravity texture samples, adjacent to axial high regions, represent a base noise level. The rms roughness of these data is ∼4 mgals with a characteristic scale of ∼9 km. We demonstrate, using synthetic realizations, how a filtered product such as altimetric gravity could be responsive to variations in the unfiltered substrate from which it was derived at scales smaller than the length of the filter. We first compare the roughness and characteristic scales from filtered and unfiltered profiles. Filtered profile scales are weakly dependent on unfiltered scale where the latter are smaller than the filter size, but possibly resolvable enough so the lineated fabric of larger abyssal hills could be evident in the altimetry data. The roughness of the filtered profiles is found to be strongly dependent on both the roughness and scale of the unfiltered profiles. Altimetric roughness may thus be very sensitive to gross changes in abyssal hills, even those too small to be directly resolved. A reduction in the noise level by future altimetry missions would greatly enhance this response. Our follow-up investigations will focus on predictions of altimetry texture based on upward continuation of 2-D abyssal hill morphology and realistic renderings of altimetric noise.