Project 2: Risk assessment for
geohazards
Project Manager: Unni Eidsvig (NGI)
Subproject 3:
Hazard zonation, vulnerability and losses
Two studies are
presented within this subproject:
- Quantitative
Estimation of Regional-Scale Vulnerability to Landslides
- Hazard zonation in
Møre og Romsdal
Quantitative
Estimation of Regional-Scale Vulnerability to Landslides
A methodology for
scenario-based, quantitative estimation of regional-scale vulnerability
is proposed. The vulnerability model parameterises the severity of
landslide action (landslide intensity) and the capacity of vulnerable
elements to withstand an action of a given degree of severity
(susceptibility of vulnerable elements) is proposed here:
V = I · S
in which V indicates
vulnerability; I indicates landslide intensity and S indicates the
susceptibility of elements at risk.
Susceptibility refers
to the lack of inherent capacity of the elements in the spatial
extension under investigation to preserve their physical integrity and
functionality in the course of the physical interaction with a generic
sliding mass. The susceptibility defined herein is independent of the
characteristics of the acting agent, i.e. the landslide.
The susceptibility S
of any category of elements at risk ranges from 0 (no susceptibility) to
1 (maximum susceptibility). A general susceptibility model is
proposed:
in which ξi
is the i-th of ns susceptibility factors (each defined in the range
[0,1]) contributing to the category susceptibility. Such factors
are category-dependent, and may be defined on the basis of existing
literature or by other criteria set by the user. Tentative models for
the calculation of the susceptibility for a number of categories of
elements at risk are proposed i.e. susceptibility of buildings and
susceptibility of persons. The quantification of susceptibility of
persons includes: Susceptibility of persons in open spaces and vehicles
(considering population density, income and age) and Susceptibility of
persons in structures.
Figure 1
Susceptibility model for persons in structures, (SSTR = susceptibility
of structures, SPST = susceptibility for persons in structures)
Landslide intensity
Hungr (1997) concisely
and effectively defined landslide intensity as “a set of spatially
distributed parameters describing the destructiveness of a landslide”.
While such qualitative definition of intensity can be readily accepted,
a univocal quantitative definition is not available at present.
Landslide intensity has been addressed and defined quantitatively using
a variety of parameters. Hungr (1997) reports use of maximum velocity,
total displacement, differential displacement (relative to points
adjacent to the point under consideration), depth of the moving mass,
depth of deposits after the movement ceases, depth of erosion, unit
discharge, kinetic energy per unit area, maximum thrust, impact
pressure, maximum normal or shear strain at or below ground surface.
A composite landslide
intensity parameter, accounting for kinetic and kinematic
characteristics of the interaction between the sliding mass and the
reference area is proposed.
Kinetic
characteristics are related to the kinetic energy of the sliding mass,
i.e. to the damage caused by impact on the vulnerable elements.
Kinematic intensity accounts for the effects of size-linked features of
a reference landslide. The damage caused by a slow-moving landslide on a
building is mainly due to the displacement (i.e. kinematic parameter),
while kinetic characteristics could be predominant in case of a rapid
movement.
Any kinetic intensity
parameter may be defined by the user provided it is defined in the range
[0,1] with unit values indicating maximum intensity. Models for kinetic
intensity (as function of landslide velocity) and kinematic intensity
(as functions of displacements) are proposed.
Figure 2 Proposed
kinetic intensity function
Hazard zonation in Møre og Romsdal
The
purpose of this study is to apply the grid based GIS techniques for
Landslide Susceptibility Mapping to the Romsdal region (Norway).
The scope includes the preparation of Landslide Susceptibility map and,
the comparison of the Landslide Susceptibility map with the previously
occurred landslide points.
Figure
3 Study region
Here
susceptibility expresses the likelihood that a landslide will occur in
an area on the basis of the local terrain conditions. Return period or
annual probability of occurrence is not considered. The main difference
between susceptibility and hazard is therefore that the latter considers
the temporal factor, by estimating the probability of occurrence of the
phenomenon within a specified period of time.
Method of study
An empirical approach was used to map and evaluate landslide
susceptibility. In this approach a grid based Geographic information
system (GIS) was used to construct a landslide hazard map for east part
of Norway Romsdal region. Five layers of data with 30 × 30 m resolution
grid were superimposed to create the landslide susceptibility map. Slope
was given the most emphasis, followed by, topological index, density of
vegetation, density of lineament and proximity to road networks. A
numerical rating system was applied and each of the five factors was
grouped into three categories, and each category was assigned a value
between 1 and 3, with 1 being least susceptible and 3 most susceptible
to landslides.                               
Figure 4 The
method of the study
Figure 5 Example of
resulting susceptibility map. Previous landslides are with red dots.
The picture above
shows a resulting susceptibility map. Comparison with previous
landslides shows that most of the previous landslides (70% - 95%) are
within the high or medium susceptible areas.
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