Abstract by Benjamin Barton
Using HVSR and MASW to determine saprolite thickness on Oahu, Molokai, and Hawaii islands.
With millions living in tropical regions of the world with volcanic substrates, understanding how basalts weather into a lateritic Critical Zone is vital to these areas. Hawaii is an excellent natural analog to study chemical weathering due to the uniform bedrock composition, but with large variations in precipitation and ages across the islands.
In this study, the rapid non-invasive horizontal-to-vertical spectral ratio (HVSR) method was employed using 3-component seismometers to collect seismic soundings on the islands of Oahu, Molokai, and Hawaii for the purpose of determining saprolite thickness. The multichannel analysis of surface waves (MASW) method was used to obtain characteristic shear wave velocity values for saprolite. Calibration of the HVSR method to MASW profiles well logs data was performed to guide forward modeling. In some areas, especially Molokai, MASW data show that featureless HVSR spectra are due to gradational weathering rather than sharp saprolite-bedrock boundaries seen in Oahu and parts of Hawaii.