THE SHALLOW ATTENUATION STRUCTURE OF THE FAST-SPREADING EAST PACIFIC RISE NEAR 9-DEGREES-30'N

Direct measurements of Q values in the shallow crust are difficult to obtain due to the lack of energy turning in this region. We analyze a unique data set consisting of seven refraction experiments carried out with both the source and receiver near the seafloor. This experimenta l geometry allows us to resolve the shallow compressional wave attenua tion structure of young crust at the East Pacific Rise. All models dep ict a low-Q layer 2A (apparent Q=11-22), and several models resolve a layer 2B with a much higher Q (apparent Q >70). This structure is cons istent with a layer 2A composed of extrusives overlying a layer 2B com posed of sheeted dikes.