SEA-FLOOR TECTONIC FABRIC FROM SATELLITE ALTIMETRY

Ocean floor structures with horizontal scales of 10 to a few hundred k ilometers and vertical scales of 100 m or more generate sea surface gr avity anomalies observable with satellite altimetry. Prior to 1990, al timeter data resolved only tectonic lineaments, some seamounts, and so me aspects of mid-ocean ridge structure. New altimeter data available since mid-1995 resolve 10-km-scale structures over nearly all the worl d's oceans. These data are the basis of new global bathymetric maps an d have been interpreted as exhibiting complexities in the sea floor sp reading process including ridge jumps, propagating rifts, and variatio ns in magma supply. This chapter reviews the satellite altimetry techn ique and its resolution of tectonic structures, gives examples of intr iguing tectonic phenomena, and shows that structures as small as abyss al hills are partially resolved. A new result obtained here is that th e amplitude of the fine-scale (10-80 km) roughness of old ocean floor is spreading-rate dependent in the same way that it is at mid-ocean ri dges, suggesting that fine-scale tectonic fabric is generated nearly e xclusively by ridge-axis processes.