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| Titel |
"Storms of crustal stress" and AE earthquake precursors |
| VerfasserIn |
G. P. Gregori, M. Poscolieri, G. Paparo, S. Simone, C. Rafanelli, G. Ventrice |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 10, no. 2 ; Nr. 10, no. 2 (2010-02-17), S.319-337 |
| Datensatznummer |
250007937
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| Publikation (Nr.) |
 copernicus.org/nhess-10-319-2010.pdf |
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| Zusammenfassung |
Acoustic emission (AE) displays violent paroxysms preceding strong
earthquakes, observed within some large area (several hundred kilometres
wide) around the epicentre. We call them "storms of crustal
stress" or, briefly "crustal storms". A few case histories are
discussed, all dealing with the Italian peninsula, and with the different
behaviour shown by the AE records in the Cephalonia island (Greece), which is
characterized by a different tectonic setting.
AE is an effective tool for diagnosing the state of some wide slab of the
Earth's crust, and for monitoring its evolution, by means of AE of different
frequencies. The same effect ought to be detected being time-delayed, when
referring to progressively lower frequencies. This results to be an effective
check for validating the physical interpretation.
Unlike a seismic event, which involves a much limited focal volume and
therefore affects a restricted area on the Earth's surface, a
"crustal storm" typically involves some large slab of lithosphere
and crust. In general, it cannot be easily reckoned to any specific seismic
event. An earthquake responds to strictly local rheological features of the
crust, which are eventually activated, and become crucial, on the occasion of
a "crustal storm". A "crustal storm" lasts typically
few years, eventually involving several destructive earthquakes that hit at
different times, at different sites, within that given lithospheric slab.
Concerning the case histories that are here discussed, the lithospheric slab
is identified with the Italian peninsula. During 1996–1997 a
"crustal storm" was on, maybe elapsing until 2002 (we lack
information for the period 1998–2001). Then, a quiet period occurred from
2002 until 26 May 2008, when a new "crustal storm" started, and by
the end of 2009 it is still on. During the 1996–1997 "storm" two
strong earthquakes occurred (Potenza and Colfiorito) – and (maybe) in 2002
also the Molise earthquake can be reckoned to this "storm". During
the "storm", started in 2008, the l'Aquila earthquake occurred.
Additional logical analysis envisages the possibility of distinguishing some
kind of "elementary" constituents of a "crustal storm", which
can be briefly called "crustal substorms". The concept of
"storm" and "substorm" is a common logical aspect,
which is shared by several phenomena, depending on their common intrinsic and
primary logical properties that can be called lognormality and
fractality. Compared to a "crustal storm", a
"crustal substorm" is likely to be reckoned to some specific
seismic event. Owing to brevity purposes, however, the discussion of
"substorms" is given elsewhere.
AE is an effective tool for monitoring these phenomena, and other processes
that are ongoing within the crust. Eventually they result to be precursors of
some more or less violent earthquake. It should be stressed, however, that the
target of AE monitoring is diagnosing the Earth's crust. In
contrast, earthquake prediction implies a much different
perspective, which makes sense only by means of more detailed multiparametric
monitoring. An AE array can provide real physical information only about the
processes that are objectively ongoing inside different and contiguous large
slabs of the crust. The purpose is to monitor the stress propagation that
crosses different regions, in order to envisage where and when it can
eventually trigger a catastrophe of the system. The conclusion is that
continental – or planetary – scale arrays of AE monitoring stations, which
record a few different AE frequencies, appear to be the likely first step for
diagnosing the evolution of local structures preceding an earthquake. On the
other hand, as it is well known, the magnitude of the shock is to be related
to the elastic energy stored in the focal volume, rather than to the trigger
that starts it. |
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