JASPER SEAMOUNT STRUCTURE - SEA-FLOOR SEISMIC-REFRACTION TOMOGRAPHY

The velocity structure of Jasper Seamount was modeled using one- and t hree-dimensional inversions of P wave travel times. The results repres ent the first detailed seismic images of a submerged, intraplate volca no. Two seismic refraction experiments were completed on Jasper Seamou nt, incorporating ocean bottom seismometers and navigated seafloor sho ts. The P wave travel times were first used to compute a one-dimension al velocity profile which served as a starting model for a three-dimen sional tomographic inversion. The seamount P velocities are significan tly slower than those observed in typical oceanic crust at equivalent subbasement depths. This suggests that Jasper Seamount is constructed predominantly of extrusive lavas with high average porosity. The veloc ity models confirm morphological predictions: Jasper Seamount is a shi eld volcano with rift zone development. High seismic velocities were d etected beneath the large radial ridges while low velocities character ize the shallow summit and flanks. Comparisons between P velocity mode ls of Jasper Seamount and the island of Hawaii reveal that these two s hield volcanoes are not structurally proportional. Jasper Seamount is far smaller than Hawaii, yet both volcanoes exhibit an outer extrusive layer of similar thickness. This suggests that seamount size influenc es the intrusive/extrusive proportions; density equilibrium between me lt and country rock may explain this behavior.