Vs30 Correlations for the Boston Region.
need Vs30 values for use in earthquake design. Currently in Boston, most projects do not
include shear wave velocity (Vs) data due to the high cost of their collection. Vs30 is
time-averaged shear wave velocity in the upper 30 meters of the soil profile. This study
analyzed different methods for regional estimates of Vs30 using surficial geology,
topographic slope, and H/V... read moreestimates. The H/V spectral ratio is a ratio of the spectra
of horizontal and vertical ground motions. The H/V spectral ratio can be used to
estimate the fundamental site period which can then be correlated with Vs30. In Boston,
we had 27 Vs30 values and 560 H/V estimates of Vs30. Elevation and surficial geology
data were also available across the study region. Boston surficial geology is governed
by Pleistocene glaciation, coastal marine sediments, and artificial fill. As a result,
the majority of Vs30 values are in 3 surficial geologic units: artificial fill, ground
moraine/bedrock, and glaciofluvial deposits. In Boston, the topographic slope method for
estimating Vs30 has a strong bias towards NEHRP Class C. Comparatively, the H/V
estimates of Vs30 range from NEHRP Class B to Class D (>760 m/s to 180 m/s) and are
consistent with the measured Vs30. A map of the region was created using the average H/V
estimates of Vs30 by geologic unit. One finding of this work is that an improved
zonation of the Vs30 map could be made with an improved surficial geology map (finer
classifications). For example, the glaciofluvial deposit could be separated into shallow
and deep sediments.
Thesis (M.S.)--Tufts University, 2015.
Submitted to the Dept. of Civil Engineering.
Advisor: Laurie Baise.
Committee: Harold Magistrale, and Christopher Swan.
Keyword: Civil engineering.read less