Geophysical Investigations of Near-Surface Structure on the Earth and Mars

• Main Author: Selvans, Michelle Marie
• Format: Thesis
• Language: English
• Published: California Institute of Technology 2011
• Subjects: Mexico; north polar layered deposits; Guadalajara; Mars; triple junction; radar; sediment; earthquake cycle; finite-difference method; Moho; Geophysics; FOS Earth and related environmental sciences; Middle America Trench; Planum Boreum; basement; reflection; Adare Basin; crustal thickness; Jalisco; Antarctica; FD model; continental shelf; stratigraphy; velocity model; refraction; Northern Basin; rift; basal unit; seismic; tectonics; subsurface structure; Ross Sea; North Pole; Adare; Antarc*
• Online Access: https://dx.doi.org/10.7907/078p-0c05; https://resolver.caltech.edu/CaltechTHESIS:05252011-161906788

I use remote sensing and active seismic methods to investigate near-surface structure on the Earth and Mars. These studies provide insight into styles of crustal deformation acting on continental margins in regions of extension, as well as paleoclimates that shaped the polar ice caps on Mars. I map the overall structure of the ice-rich Planum Boreum deposit at the north pole of Mars using 178 orbits of Mars Advanced Radar for Subsurface and Ionosphere Sounding data, and find no deflection of the lithosphere beneath the ice load. Bright, laterally extensive subsurface reflectors in the radargrams define the surface underlying Planum Boreum, as well as the interface between the two main units, the stratigraphically older Basal Unit and the stratigraphically younger North Polar Layered Deposits. The volumes of these units, and the overall edifice, are determined to the greatest accuracy possible to date. On Earth, I use a GPS campaign network in the state of Jalisco to investigate tectonic motion and interseismic deformation in the area. The consistent magnitude and direction of station velocities on the Jalisco Block suggest that it is moving rigidly with respect to North America. We constrain extension across the bounding fault zones of the block to values that are slow compared to relative rates of motion at nearby plate boundaries. I study another continental rift zone, in the Ross Sea, Antarctica, with refraction seismic data collected during research cruise NBP0701. I construct velocity models from 71 sonobuoys that detect deep structure in the oceanic crust of the Adare Basin and the crust of the Northern Basin, which lies to the south on the continental shelf. We demonstrate the importance of using multi-channel seismic data to correct for ocean currents and changes in ship navigation, the finite-difference modeling techniques necessary for accurately determining 1D velocity profiles for each sonobuoy, and for tying true velocities to the multi-channel seismic images of subsurface structure. We construct 2D velocity profiles using widely spaced sonobuoys in the Adare Basin, and using overlapping sonobuoys along some lines in both basins, and across the shelf break, to investigate crustal structure in the region. Detection of the Moho at 5.5 km below the seafloor by one sonobuoy suggests relatively thin oceanic crust in the Adare Basin, and flat velocity contours across the margin suggest continuity in crustal structure between the two basins.