Abstract by Isaiah Spring
Geophysical Measurements of Weathering Profiles Thickness in the Hawaiian Islands
Understanding weathering processes is an important issue in tropical regions especially in areas with volcanic substrates. Hawaii is composed of basalt and has a tropical climate with variable precipitation driving weathering, making it an excellent location to study weathering processes. This study sought to measure the thickness of alteration and the boundary between basaltic bedrock and saprolite through measuring geophysical differences in the substrates. Seismic soundings were taken on three Hawaiian Islands using 3-component seismometers. Saprolite thicknesses were estimated using the Horizontal-Vertical Spectral Ratio (HSVR) method. A method for determining boundaries was developed by comparing known shear wave velocities of basalt and saprolite from prior studies. The boundaries between altered and unaltered rock were not uniform across the islands, those older than 2 million years showed a distinct geophysical boundary between altered and unaltered rock whereas younger islands have largely gradational boundaries.