Geoscience Reference
In-Depth Information
Earthquake Effects on Nature and Macroseismic
Intensity Scales
J. Vogt
†
Foreword
Earthquake effects on nature are very important macroseismic phenom-
ena, which can be of relevant use for assessing the level of shaking. For that reason,
they have been traditionally incorporated into intensity scales, despite the fact that
such effects are not homogeneous with the ones commonly used for assessing inten-
sity degrees, such as effects on humans and buildings (damage). Problems arise for
five main reasons; (i) these effects are not peculiar to one degree, but can take place
at strengths of shaking that the intensity scales relate to a wide number of degrees;
(ii) they often happen in a few instances (in many cases just single ones), while
modern intensity scales have a statistical “philosophy”; (iii) the effects are often
highly dependant on pre-existing vulnerability states that are usually unknown; (iv)
some effects are not strictly related to strength of shaking at all, and only appear
to be correlated with intensity for indirect reasons; (v) they mostly take place out-
side the localities where intensity is assessed on the base of damage and effects on
humans, and often the corresponding shaking is referred, wrongly, to the nearest
locality. EMS-98 tackled this problem by assigning to geological effects a side role.
Geological effects have been related to intensity degrees through a table, where it
is clear that they are not correlated one to one. Most of the preparatory work was
performed by Jean Vogt, who retrieved a lot of data from his personal and partly
still unexploited archive. It must be said he was never fully happy with the final
table, a hard-to-reach compromise, the development of which can be traced through
a number of letters.
After the publication of the EM-92 intensity scale, which later became EMS-98,
the table was published with some comments by Vogt et al., 1994. At the same time
Jean Vogt prepared a draft of this paper which was completed in the present shape
in 1993 and then waited for an opportunity to be published.
We present the paper mostly as it stands, in spite of the fact that some parts are
still draft, because we do not want to change the original flavour. Most references
have been tracked by P. Albini, A.A. Gomez Capera and P. Migliavacca; a few are
still lacking.
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