Regional Basic Professional Training Course in Korea

determine their liquefaction potential according to the following scheme:
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5. SITING CONSIDERATIONS
Evaluation of shear stresses from earthquakes regarded as plausible, represented by
a number of loading/unloading cycles;
Laboratory determination of the shear strength of the soil;
Comparison of the two studies to determine a margin of safety (at least 1.3 to 1.5).
5.3.1.5. The problem of volcanic risk
Volcanic risks are peculiar in being often very severe where they exist at all, but also in
being localized very narrowly in well‐defined areas of the globe (the zones affected by
volcanoes account for only 1 to 2 % of submerged land). Their study belongs to the
highly specialized field of volcanology, which it would be very difficult to treat
adequately in a general text.
It will suffice to say that, when it is impossible to avoid locating a site in a volcanic
region, there are methods of analysis to evaluate the various contingencies. The effects of
volcanoes are characterized first of all by their great diversity. They include the emission
of effusive products, lava and mudslides, the projection of materials, bombs and ashes,
and explosive phenomena like hot clouds.
The starting point for the evaluation of this type of risk is, once again, careful mapping of
the volcano(es) in question to determine the various risks incurred and their geographical
distribution. Dating can give a better idea of the frequency of the phenomena and, in
favorable cases, identify an activity cycle. Concurrently, the installation of a microseismic
observation network and other geophysical instruments yields an idea of the current state
of the volcano.
The current techniques of investigation are starting to bear fruit, and while placing a