Date of Award

12-2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Civil Engineering

Advisor

Andrus, Ronald D.

Abstract

An updated small-strain shear wave velocity (Vs) model of near-surface sediments is constructed using measurements from over 90 investigation sites in the greater Charleston area. It is constructed by separating the Vs measurements into six major geologic units. The six units are: 1) man-made fills, 2) Holocene and late Pleistocene deposits, 3) the Wando Formation, 4) the Ten Mile Hill beds, 5) the Penholoway Formation and the Daniel Island beds, and 6) Tertiary deposits. Median Vs values for these units in the top 25 m are 145 m/s, 111 m/s, 189 m/s, 176 m/s, 285 m/s and 399 m/s, respectively. For Tertiary deposits in the depth intervals of 25-55 m, 55-75 m and 75-100 m, median Vs values are 435 m/s, 533 m/s and 663 m/s, respectively. These results generally show Vs increasing with geologic age.
Using information from many of the Vs sites and subsurface information from over 200 other sites, a thickness contour map of the Quaternary deposits beneath the Charleston peninsula is also constructed. The thickness of the Quaternary deposits ranges from 6 m to over 24 m, with the thickest sections coinciding with paleochannels incised into the top of the Tertiary sediments.
Based on simple procedures, estimated values of the fundamental ground periods for the Quaternary deposits range from 0.2 s to 0.7 s. The highest values of ground periods occur adjacent to the rivers in the soft Holocene fine-grained deposits. The lowest values of ground periods occur in the stiffer Wando Formation deposits and where the depth to Marl is shallow.
At the time of the 1886 Charleston earthquake building heights ranged from 2.4 m to 22.9 m. Assuming this range of building heights, the estimated range of fundamental building periods is 0.09 s to 0.51 s. Because overlap exists in the building and ground period ranges, a greater percentage of taller buildings (say heights > 11 m) should have suffered more damage than shorter buildings in 1886. This conclusion is supported by the damage statistics summarized by Marciano and Elton, and the spatial distribution of damage intensity mapped by Robinson and Talwani.

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