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| Titel |
Limits on nucleation and some pre-seismic phenomena from continuous strain in the near field of the 2009 L'Aquila earthquake. |
| VerfasserIn |
Luca Crescentini, Antonella Amoruso |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039426
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| Zusammenfassung |
| Several phenomena have been proposed as diagnostic precursors of earthquakes, including
strain-rate changes, changes in seismic wave velocities, electromagnetic signals, changes in
groundwater levels and flow, radon anomalies, and acoustic emissions. Moreover,
laboratory studies and models suggest that fault failure is preceded by subsonic
pre-seismic slip. Most, if not all, those phenomena should produce an associated
strain field detectable by close strain meters. Till now, most observations of crustal
strain have not detected any pre-seismic deformation, thus constraining the size and
strength of the pre-seismic phenomenon source. The constraint strictness depends
on the time interval considered and on the distance of the strain meter from the
source.
Two crossed 90-m long laser extensometers are operating in the Gran Sasso underground
observatory (Central Italy) since several years. The instruments are characterized by very
high sensitivity, wide frequency band (from DC up to hundreds of Hz), large dynamic range,
and long-term stability (years).
Here we show the results from the analysis of strain recorded in the two years preceding
the 2009/04/06 L’Aquila earthquake. No anomalous signal is clearly visible and thus we can
limit the maximum strength of some possible pre-seismic phenomena. In particular, our
analysis indicates that
the seismic moment of the pre-rupture nucleation slip in the hypocentral region
was less than 5Ã10-4 M0 (5Ã10-7 M0) in the two days (two seconds) preceding
the main shock, M0 being the seismic moment of the main shock itself;
the volume of the dilatant zone was smaller than few km3 in the month preceding
the main shock, for a 10% change of the elastic moduli (5% change of seismic
velocities);
change in tidal response was not greater than about 1% in amplitude and 10 in
phase.
Our results confirm what previously obtained by others, e. g. for the 2004 Parkfield
earthquake, and put lower limits on the size of pre-seismic phenomena capable to generate a
strain field, at least in the case of the 2009 L’Aquila earthquake. |
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