OBJECTIVE CLASSIFICATION OF OCEANIC RIDGE-CREST TERRAINS USING 2-DIMENSIONAL SPECTRAL MODELS OF BATHYMETRY - APPLICATION TO THE JUAN-DE-FUCA RIDGE

An important application of detailed bathymetric mapping is the interp retation of geological processes based on the nature of the fine-scale morphology of the seafloor. This interpretation is usually accomplish ed through qualitative analysis of contour maps. In this paper, an obj ective classification technique, based on a two-dimensional spectral m odel of bathymetry developed by Fox and Hayes (1985) is applied to det ailed Sea Beam data from the Juan de Fuca Ridge. Parameters of the mod el can be directly related to seafloor properties corresponding to 1) isotropic (non-directionally dependent) roughness; 2) anisotropic (dir ectionally dependent) roughness; 3) orientation of the anisotropic com ponent; and 4) spectral roll-off (similar to fractal dimension), by fi tting the model surface to two-dimensional amplitude spectra of bathym etry determined on a regular grid over the study area. A test area was selected which encompasses the southern volcanic rift zone of Axial V olcano and the northern terminus of the Vance Segment. Parameters of t he model clearly define the contrast between the constructional volcan ic terrain (rough, isotropic, with high fractal dimension) and the tec tonic extensional terrain (smoother, anisotropic, with low fractal dim ension). An agglomerative, hierarchical cluster analysis is applied to the data, independent of spatial information, to delineate groups of spectra with similar characteristics. Distinct, mappable regions, corr esponding to volcanic and tectonic provinces, are objectively determin ed. Also, coherent sub-regions of consistent spectral properties occur within the larger volcanic/tectonic divisions. The classification is extended to the Juan de Fuca Ridge system from 44 degrees 30' N to 47 degrees 20'N through combining these results with an a priori techniqu e (K-means clustering). Broad-scale physiographic regions of the Juan de Fuca Ridge are delineated by the technique, which may aid geologist s in the interpretation of crustal accretion processes at seafloor spr eading centers.