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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS004 Oral Presentation 1900
Assessing the completeness of an active fault database: the Italian case
history
Dr. Roberto Basili
Sara Scrivieri, Gianluca Valensise, Diss Working Group
For most applications a fault database is effective only to the extent that it ensures a certain level of
completeness, i.e. if all existing fault zones are captured and correctly described. For this reason, and in
addition to mapping the potential sources of individual large earthquakes, the new version of the Italian
Database of Individual Seismogenic Sources (DISS, v. 3.0.2: http://www.ingv.it/DISS/) describes the
countrys earthquake potential in terms of a new category of potential sources, the Seismogenic Areas.
These are narrow, elongated portions of the territory that are intended to represent the surface
projection of active and potentially seismogenic fault systems capable of earthquakes of M 5.5 and
larger. Seismogenic Areas were designed to combine the historical record with a number of lines of
geologic and tectonic evidence that are normally insufficient to determine the existence of potential
sources of individual earthquakes. For this reason Seismogenic Areas are described using the same
geometric and kinematic parameters as the standard sources, but are more loosely defined and are not
internally segmented. More importantly, they aim at a complete description of the earthquake potential
that may allow them to be used in new generation SHA schemes. How can the completeness of
Seismogenic Areas be tested We subdivided Italy into eight zones that are believed to be relatively
homogeneous from the geodynamic point of view. For each zone we calculated two earthquake moment
rates, respectively from all 81 Seismogenic Areas and from over 300 historical earthquakes having M ≥
5.5 (http://emidius.mi.ingv.it/CPTI/) that fall within it. The results show that for six zones the moment
rate from Seismogenic Areas justifies the rate derived from seismicity: in one case it exceeds it, and in
the last case it underestimates it. This suggests that the Seismogenic Areas are already reasonably
complete, although at this stage we cannot exclude that large real uncertainties within a given zone
might compensate among them and simulate a good match. This and other limitations of the test
should be overcome when Seismogenic Areas will be tested against the strain rates derived for the
whole country using a finite-element geodynamic model currently in preparation (see Barba et al., this
session).
Keywords: seismogenesis, database