Page 263 - Numerical Analysis and Modelling in Geomechanics

244 SEISMIC MICROZONING USING NUMERICAL MODELLING
formed by spring water whose chemical content is connected to the activity of
deep faults and fractures; the age of these deposits is from middle Pleistocene up
to the present.
According to the geomorphologic framework of the area, three main
geomorphologic features were taken into account for the site selection:

• Hill tops (mainly on limestones and marly limestones);
• Valley-like morphologies (formed by alluvial deposits, lacustrine deposits or
slope waste deposits and travertine);
• Slopes (slope deposits, travertine or colluvial deposits).

Geologic and geotechnic data

The collection of geologic, geomorphologic and geotechnic data is fundamental
for the site geology reconstruction. The survey aimed to identify the
relationships between lithologic units, to map the main structural features and to
estimate the thickness of surface deposits and their degree of cementation, in
order to assign the proper geotechnic value. Therefore soil columns and data
from geophysic or geotechnic site tests and geotechnic laboratory tests were
always reported on forms, where available. Two-dimensional cross-sections were
drawn to better understand the stratigraphic and tectonic features of each site.
The geomorphologic map was only intended to represent the forms and the
processes acting on the examined landscape.
The lithotechnic map was derived from the geologic map by grouping
geologic units considered homogeneous from the physical and mechanical point
of view; the available data, from laboratory and geophysic tests, allowed to
assign to each lithotechnic unit the geotechnic parameters needed for the
dynamic analyses: the shear wave velocity, the Poisson coefficient, the soil unit
weight, the initial shear modulus and the initial damping coefficient (Table 8.2).
The relationships between shear modulus decay and damping coefficient
variation as a function of the shear strain were also assessed (Figures 8.13 and
8.14).

Analysis

The amplification effects were evaluated in two main steps. First, hazardous
situations were identified for each of the 60 villages and classified according to