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William Shermerhorn Thesis Final

April 23 @ 4:00 pm - 5:00 pm MDT

William Shermerhorn

FUNDAMENTAL RESONANT FREQUENCIES DERIVED FROM SHALLOW SEDIMENT PROPERTIES FOR THE CHARLESTON, SOUTH CAROLINA AREA

For the Charleston, South Carolina area, predominant peaks in the acceleration response spectra match fundamental periods of many existing buildings. Spectral characteristics above one Hz are driven mostly by soil thickness and shallow shear wave velocities (Vs). Boise State University acquired 14 km of seismic land streamer data, in profile, to derive these properties. Unconsolidated, mostly saturated late Quaternary sediments lie directly upon more competent carbonate Tertiary rock. Previous studies show little velocity-depth dependence within Quaternary strata, and our results are consistent with this observation. Using a grid search approach and rock physics relationships, I obtain Vs models that minimize the misfit between observed and calculated dispersion, then derive seismic impedance and fundamental resonant frequencies (Fn) from these data. I compare >2700 Vs profiles to regional seismic cone penetrometer measurements, surficial geology, and detailed stratigraphic logs that identify a top of Tertiary boundary and provide additional constraints. I find consistent Vs and Quaternary layer thickness estimates between each dataset, allowing us to develop a regional relationship of Fn to soil thickness for the greater Charleston region. I compare my regional correlations to mapped faults identified with my seismic reflection data and to liquefaction features documented from the 1886 earthquake. Where shallow Vs measurements are well calibrated to the local geology, I suggest that my approach to estimating Fn may be applicable for other areas within the Atlantic Coastal Plain, when in the presence of a similar shallow high impedance boundary.

Advisor: Lee Liberty

Co-Advisors: Brittany Brand, Dylan Mikesell

When: April 23, 2021
Time: 3:00 PM
Where: ZoomMeeting ID: 952 6534 0108