Seamount structure from seismic tomography and gravity inversion

Seismic tomography and gravity inversion are used to model the velocity and density structure of an intraplate seamount. Rugged, deeply submerged terrain makes seamounts difficult subjects for conventional, high-resolution geophysical experiments. New techniques are explored for imaging the interior of seamounts and structural comparisons are made between mid-size seamounts, the immense Hawaiian volcanoes, and crust generated at mid-ocean ridges.; The refraction tomography experiment utilized Ocean Bottom Seismographs and seafloor shots to image two sections of Jasper Seamount (30{dollar}spcirc{dollar} 27{dollar}spprime{dollar}N, 122{dollar}spcirc{dollar} 44{dollar}spprime{dollar}W). Average compressional (P) and shear (S) velocity models suggest that seamount construction is dominated by extrusives and is fundamentally different than that of mid-ocean ridges. The {dollar}Vsb{lcub}P{rcub}{dollar}/{dollar}Vsb{lcub}S{rcub}{dollar} data indicate that Jasper Seamount has a high average porosity. The average Jasper P-velocities are similar to those within Kilauea. A spectral tomographic inversion was used to model the {dollar}Vsb{lcub}P{rcub}{dollar} structure of the two sections. High velocity anomalies extend deep beneath major seamount ridges, suggesting intrusive rift structure. The seamount summit and non-rifted flank are characterized by low velocities that suggest extrusive construction from shallow, explosive eruptions.; A gravity inversion algorithm was developed to select the simplest or most nearly uniform density model that fits the data within a specified misfit. The inversion was applied to shipboard gravity data collected over Jasper Seamount. The low density models are consistent with the high porosities predicted by the velocity models. Very small non-uniform structure was required to fit the data, however, increasing density beneath Jasper's western flanks may correspond to intrusions associated with the NW and SW rift zones. The inversion was also applied to shipboard gravity data collected over Axial Volcano. The resulting density model was integrated with short-wavelength density structure modeled from seafloor gravity data.; The velocity and density models of Jasper Seamount are consistent with the results of magnetic, petrologic and dating analyses. The Jasper Seamount model suggests the structure of intermediate-size seamounts resembles shallow Hawaiian structure--not a scaled down version of an entire Hawaiian volcano.