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of events, and a large regional knowledge, first of all of past events, seismological
and geological. We are far from a standard implementing of an intensity scale's
criteria.
Appraisal of liquefaction features in alluvial plains, etc. is considered apart. In
most cases, even in the past, liquefaction is clearly identified by descriptions of hol-
lows, mounds and, above all, projection of water, sand, etc. Outstanding inventories
have been prepared over centuries, for instance for Italy (Berardi et al., 1991), with
deep-dipping correlations with magnitudes, etc. On the other hand, unlike other ge-
ological effects, liquefaction has been discussed in a systematic way from a geotech-
nical point of view (Wang Zhong-qi et al., 1983), with a high theoretical level. So,
at a first glance, no peculiar problem should arise with the use of liquefaction in an
intensity scale.
However it should be emphasized that sources, inventories and geotechnical dis-
cussions mostly deal with impressive cases, either by their scale or their effects. To
some extent correlations and appraisals could be biased. Further the interpretation of
many not so well described “crevices” is not easy. Considering their setting, part of
them could possibly be linked with liquefaction. While not one doubtless example
of liquefaction is known from France, vague descriptions of several “crevices” do
not exclude such a possibility.
Whatsoever, the MSK scale considers liquefaction with degree 9 and, in an im-
plicit way, with higher ones, discussing, although in a more general way, including
other effects, it seems, the width of crevices. Indeed, most inventories agree, on the
whole, with this threshold.
However such a wide agreement should not lead to an indiscriminate use of this
appraisal. Once more careful confrontation with other evidence is needed in each
case. For the 1856 Algerian earthquake, damage to buildings is known only from
Djidjelli, while liquefaction features (as well as rockfalls) are described from the
countryside, rising an arduous problem of location of the epicentre, depending on
the very way liquefaction is interpreted (Gaultier de Claubry, 1856).
Besides acceleration, local conditions should be carefully considered without
giving too much weight to abstract discussions of a more general kind. These con-
ditions are:
seasonal, with the evolution of the water-table, a most important factor;
permanent lithology and geometry, with emphasis on contrasting behaviour
of layers and complex channel systems. Such essential information is not of-
ten provided by geological maps, for reasons either of scale or of doctrine,
with “wholesale” mapping surficial formations, considered a hindrance. While
some preventive research is devoted to potential of liquefaction, background
information is often gathered after an earthquake.
Careful work shows fine examples of liquefaction with degree lower than 9. During
the 1989 earthquakes of coastal Venezuela, such processes occurred with degree 7
(De Santis et al., 1990). During the 1946 British Columbia earthquake, liquefaction
was observed in sensitive settings even with degree 6 (Rogers, 1980). So the range
of degree is the same as for rockfalls and landslides, more or less.
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