| Space-time TIR anomalies, observed from months to weeks before earthquake
occurrence, have been suggested by several authors as pre-seismic signals.
Up to now, such a claimed connection of TIR emission with seismic activity
has been considered with some caution by scientific community mainly for the
insufficiency of the validation data-sets and the scarce importance attached
by those authors to other causes (e.g. meteorological) that, rather than seismic
activity, could be responsible for the observed TIR signal fluctuations. A
robust satellite data analysis technique (RAT) has been recently proposed
which, thanks to a well-founded definition of TIR anomaly, seems to be able to identify
anomalous space-time TIR signal transients even in very variable
observational (satellite view angle, land topography and coverage, etc.) and
natural (e.g. meteorological) conditions.
Its possible application to satellite TIR surveys in seismically active
regions has been already tested in the case of several earthquakes (Irpinia:
23 November 1980, Athens: 7 September 1999, Izmit: 17 August
1999) of magnitude higher than 5.5 by using a
validation/confutation approach, devoted to verify the presence/absence of
anomalous space-time TIR transients in the presence/absence of seismic
activity. In these cases, a magnitude threshold (generally M<5) was
arbitrarily chosen in order to identify seismically unperturbed periods for
confutation purposes.
In this work, 9 medium-low magnitude (4<Mb<5.5) earthquakes which
occurred in Greece and Turkey have been analyzed in order to verify if, even
in these cases, anomalous TIR transients can be observed.
The analysis, which was performed using 8 years of Meteosat TIR
observations, demonstrated that anomalous TIR transients can be observed
even in the presence of medium-low magnitude earthquakes
(4<Mb<5.5). As far as the research (just started) of possible
correlation among TIR anomalies and earthquake occurrence is concerned, such
a result suggests that: a) in order to identify seismically unperturbed
periods for confutation purposes, a magnitude threshold (at least) lower
than 4 should be used; b) the proposed validation/confutation approach
should be applied in low-seismicity areas in order to find suitably long
seismically quiescent periods. |