Assessing Site Response Complexity Using Single Station HVSR: Mexico City Case Study.
Pontrelli, Marshall.
2019
-
Sedimentary basins
with high impedance contrasts can lead to significant shaking due to local site response
during earthquakes and, as a result, pose a significant risk to infrastructure and local
populations. The site response transfer function is most often modeled as the response
of a soil column to a forcing function assuming vertically propagating shear waves
through horizontal, laterally ... read morehomogenous soil systems. In real soil systems, however,
these assumptions tend to collapse due to wave scattering through heterogenous
materials, significant attenuation, non-vertical incidence, and other complexities in
the subsurface. In work by Thompson et al. (2012), the authors develop a taxonomy using
surface-downhole spectral ratios from weak ground motions for classifying a site's
resonant behavior referenced to the SH1D condition. We attempt to apply this taxonomy to
single station recordings in Mexico City, a case study where basin effects are well
documented, by using the horizontal to vertical spectral ratio (HVSR) (Nakamura, 1989)
as a first estimate of the site empirical transfer function (Lermo and
Chávez-Garcia, 1994b), and using a theoretical transfer function derived from
inversion. The HVSR clearly identifies a fundamental resonance peak and even higher
resonance modes at some stations in the basin; however, the shape of the HVSR changes
from the transition zone (at the edge of the basin) into the lake bed sediments (within
the basin). The inverted theoretical transfer function also exhibits limitations mapping
onto the HVSR. We extend the taxonomy by proposing a set of statistics describing the
shape of the HVSR to assess site response complexity: the number of significant peaks,
and the frequency, amplitude, half power bandwidth and interevent variability of the
fundamental peak. We observe that these statistics vary spatially across the extent of
the Mexico City basin in quantifiable patterns, reflecting variations in subsurface
properties and providing indications of complex site
response.
Thesis (M.S.)--Tufts University, 2019.
Submitted to the Dept. of Civil Engineering.
Advisor: Laurie Baise.
Committee: Richard Plumb, Juan Pestana, and Jonathan Lamontagne.
Keywords: Geophysical engineering, Civil engineering, and Geological engineering.read less - ID:
- wh2476293
- To Cite:
- TARC Citation Guide EndNote
