Publication Date:
2017-04-04
Description:
In August 2000 and July 2001 two seismic sequences, characterized by mainshocks with Ml (local magnitude)
respectively 5.1 and 4.8, occurred in the Monferrato region (Italy). The regional seismic network of North-western
Italy (RSNI) recorded more than 250 foreshocks and aftershocks. The routine locations, obtained from the Hypoellipse
code, show a seismic activity concentrated in a circular area, of a radius of about 15 km, located near Acqui
Terme, and randomly distributed in depth. Location errors, due to an uneven azimuthal station distribution of the
regional seismic network, prevent recognition of the geometry of the active zone. Waveform analysis revealed the
presence of several multiplets. In order to discriminate and successively relocate them, an automatic cross-correlation
procedure was applied. Normalized cross-correlation matrixes, for the RSNI stations which recorded almost 90% of
considered events, on the basis of a signal to noise ratio analysis, were computed using only S wave time windows.
The use of a relocation procedure, based on the double-difference method which incorporates ordinary absolute
travel-time measurements and/or cross-correlation differential travel-times, allowed us to overcome the constraints
of the uneven distribution of stations giving a quite different frame of seismicity. The improved locations showed
that the seismic activity is mainly arranged along a NE-SW oriented volume, at a depth range of 8–20 km, involving
the basement crystalline units. This orientation is confirmed by the analysis of the focal mechanisms: most focal
solutions show a strike slip component with one of the nodal planes consistent with the main orientation of the
seismic events.
Description:
Published
Description:
1-22
Description:
JCR Journal
Description:
reserved
Keywords:
earthquake clusters
;
waveform
;
04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
