ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

tors when studying the mechanism through which precipitation
is transformed into river runoff. On the basis of the
analysis of lithological and hydrogeological conditions and
chemical contents of surface water, it was possible to distinguish
components of the runoff in the Kluda and describe
the hydrological system of the catchment.
The stream water of the Kluda catchment belongs to the
calcium-bicarbonate type. It is characteristic of young-glacial
lakeland areas built of tills rich in calcium carbonate.
Worth noting are the waters of basins without outlets that
can be found throughout the catchment, which are largely
of the calcium sulphate type. The range of variation in
physical-chemical parameters of those waters reveals considerable
differences in the properties of surface water in the
catchment. A grouping procedure and principal components
analysis, carried out on the basis of 10 physical-chemical
parameters characterising the measurement sites,
produced four (A, B, C, D) hydrochemical groups. The
groups mainly reflect the influence of the lithology, pattern
and character of soil processes and water pathways in the
catchment.
The established routes of water circulation in the slope system
and their importance for the supply of solutes to the
channel system provided a basis for distingnishing four
morphodynamic zones in the catchment (a divide, a hillslope,
a plateau escarpment, and a valley). These zones make
different contributions of water and solutes to the river
channel from the watershed area. Their spatial distribution
is an indicator of feature of present tendencies in the relief
development of young-glacial areas.
ENRICO MAZZINI 1, KAZUMI SUWABE2 & KOHEI TANAKA 1
Geographic Information System (GIS) reliability
in earthquake-induced landslides simulation,
a case studied: Irozaki area, Izu Peninsula, Japan
1 National Research Institute for Earth Sciences and Disaster Prevention,
3-1 Tennodai, Tsukuba, Ibaraki 305, Japan
2 Asia Air Survey Co. Ltd., Asahi Seimei BId. IF,
8-10 Tamura-cho, Atsugi-shi, Kanegawa-ken 243,Japan
In the last decades a growing number of spatial landslide
hazard models has been developed. These modelling approaches
aim at the identification of areas with specific
probability for future landslide events, which means to
evaluate spatial probability of future slope instability. The
Gis techniques have demonstrated, in such kind of studies,
to be a useful tool for their capabilities in treating a huge
amount of multidisciplinary data pertaining to large areas.
The present work demonstrates and discusses the results
achieved from the application of Gis in earthquake-induced
landslide prevision.
The main purpose of the suggested methodology is to determine
the reliability of hazard scenarios obtained by a
computer modelling technique, coupled with a Gis and
properly tailored, for determining the instability proneness
of slopes due to earthquake shaking.
The algorithm of the programme for the stability analysis is
based on the known equation for the calculation of the critical
acceleration in pseudo-static conditions, for an infinite
slope model, proposed by Wilson & Keefer (1985). The
algorithm considers the following parameter: slope angle,
soil/rock specific weight, depth of the slipping surface,
friction angle and cohesion mobilised along the slip surface
and the seismic acceleration. As concerning the epicentre
of the seism, it has been possible to test the applicability
of the model using a two dimensional scaling function
for the ground seismic acceleration.
The application of this algorithm resulted in hypothetical
or theoretical distribution maps of landslides induced by
the project earthquakes. These maps have been compared
to the ones obtained directly from the interpretation of aerial
photographs, and showing the actual landslides distribution.
The application was carried out over the Izu Peninsula,
located few dozens of kilometres southern of
Tokyo area, where the intersection of the three lithospheric
plates that are involved in the tectonic evolution of the
Japanese arc-trench system is found. This area is widely
known for its seismicity; in fact, in the recent past, it has
been the theatre of many earthquake sequences as well as
spectacular volcanic eruptions. These natural hazards have
had a very strong impact both on the people and on the
morphological evolution of the territory. Of particular interest,
two earthquakes set off in 1974 and 1978, known as
«Izu-Hanto-Oki» and «Izu Oshimae-Kinkai» respectively,
were studied thoroughly and it was possible to relate a
great number of mass movements directly to the main
earthquake shocks. The availability of good aerial photograph
coverage, conducted over the area immediately after
the occurrence of the earthquakes, has allowed the construction
of maps showing the distribution of seismicallytriggered
landslides.
The effectiveness of the scenarios obtained from the
performed simulations has been judged by the superimposition
of both simulation and actual distribution maps. In
this way, a reliability index was developed. This index is
based on the percentage and position of landslide areas
that are exposed in both the simulation and distribution
maps.
Achieved results seems to be realistic and confirm a good
level of reliability of the simulation model herein presented.
The calibration of the model consents to apply it in
the evaluation of the landslide hazard due to earthquakes
in other parts of Izu Peninsula. However, the authors propose
that such a model should be used as a starting point
for the development of more complex simulation models
that could consider the contemporary influence of severe
rainfall events.
Finally, a number of conclusions have been formulated
concerning landslide movement direction in relation to the
orientation of both seismic source areas and slopes.
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