Source of Moderate Size Events during the 1997 Umbria-Marche Seismic Crisis
The temporal network that operated from Sept. 28th to Oct. 24th
during the Umbria-Marche crisis recorded more than 2000 earthquakes
on 3-component digital stations. We focused on the events of
magnitude larger than 3.7 and applied different techniques to
retrieve the main parameters of their source.
We first considered a point-source approximation and applied a
simple source inversion technique at short distances in an
Theoretical seismograms used in the inversion included intermediate
and near field contributions. A grid search was performed to
determine the focal mechanism and the seismic moment which
minimize the error between the observed and the synthetic
This procedure gave fast and quite robust estimation of source
parameters when the point source approximation hypothesis could
be considered as valid.
For the largest earthquakes, an extended source definition was necessary to fit the waveform recorded. We applied a trial and error approach to retrieve the main parameters of the rupture (directivity, fault dimensions). Green's functions were obtained by Empirical Green's function technique when possible, or were computed by a reflectivity method in an heterogeneous media.