inu-
d in
| the
no-
onic
ins
onic
the
ograd,
Macedonia. Fractural fabric seen in this map differs signi-
ficantly from the LANDSAT-seen picture: the role of the
ancient NNW-oriented fractures on it is much more
accentuated (Fig.4) and the neotectonic NW-SE fractures
are not prominent enough to be perceived for a separate
system and not merely deflecting from the NNW-SSE one. The
Polog depression (8) is conspicuous, same as the Kriva
Lakavica graben (2), but faults striking SW-NE have been
noted on air photographs only partially (e.g. the BoZava
fault, 10). Fig.5 shows the fractures which are common for
both maps.
SEISMOTECTONIC IMPLICATIONS
Two important directions of seismological investigations
are much discussed today: short-term earthquake prediction,
and analysis of seismic risk or seismic zoning. The aim of
the short-term prediction is foreseeing an earthquake in
certain area in a time span sufficient for salvage of popu-
lation and public property. Development of such forecasts,
which is expected in foreseable future, would help enormously
in degreasing the number of victims and the general damage.
But they are of no importance for regional planning, where
forecasts should cover a time span of 101-10° years. What
is needed are the analyses of seismic risk, with the purpose
of classifying the area according to the expected frequency
of seismic shocks, their maximum energy release, and damage
done. Several approaches are attempted, especially the
statistical analysis of earhhquake frequency in space .and
time, and the analysis of geological controls of seismic
activity.
Earthquake statistics is doubtlessly important, being based
on the observed facts and not on hypotheses. Based on the idea
of certain (and rather short-term) periodicity in the energy
release it has, nevertheless, serious limitations. A very
impressive illustration represents the cummulative diagram
of the seismic energy release for Khansu and Northern China
in the last 2000 years (Mei, 1960). In the area, where in
1556 occurred one of the most disastrous earthquakes known,