ABYSSAL HILL SEGMENTATION - QUANTITATIVE-ANALYSIS OF THE EAST PACIFICRISE FLANKS 7-DEGREES-S-9-DEGREES-S

The recent R/V Maurice Ewing EW9105 Hydrosweep survey of the Fast Paci fic Rise (EPR) and adjacent flanks between 7-degrees-S and 9-degrees-S provides an excellent opportunity to explore the causal relationship between the ridge and the abyssal hills which form on its flanks. Thes e data cover 100% of the flanking abyssal hills to 115 km on either si de of the axis. We apply the methodology of Goff and Jordan (1988) for estimating statistical characteristics of abyssal hill morphology (rm s height, characteristic lengths and widths, plan view aspect ratio, a zimuthal orientation, and fractal dimension). Principal observations i nclude the following: (1) the rms height of abyssal hill morphology is negatively correlated with the width of the 5- to 20-km-wide crestal high, consistent with the observations of Goff (1991) for northern EPR abyssal hill morphology; (2) the characteristic abyssal hill width di splays no systematic variation with position relative to ridge segment ation within the EW9105 survey area, in contrast with observations of Goff (1991) for northern EPR abyssal hill morphology in which characte ristic widths tend to be smallest at segment ends and largest toward t he middle of segments; (3) abyssal hill rms heights and characteristic widths are very large just north of a counterclockwise rotating ''nan noplate'', suggesting that the overlap region is being pushed northwar d in response to microplate-style tectonics; and (4) within the 7-degr ees-12'S-8-degrees-38'S segment, abyssal hill lineaments are generally parallel to the ridge axis, while south of this area, abyssal hill li neaments rotate with a larger ''radius of curvature'' than does the EP R axis approaching the EPR-Wilkes ridge-transform intersection.