A. Michelini et al., The 1997 Umbria-Marche (Italy) earthquake sequence: Tomographic images obtained from data of the GNDT-SSN temporary network, J SEISMOL, 4(4), 2000, pp. 415-433
We present some preliminary images of the 3-D P-wave velocity model and of
the relocated seismicity obtained from the data collected by the GNDT-SSN t
emporary network installed in the epicentral area of the earthquake sequenc
e that followed the 26 September, 1997, Central Italy main shock (M-w = 6.0
). This network consisted of a total of 15 stations, was deployed in the so
uthern part of the area affected by the earthquake sequence and operated fo
r a total of 17 days starting on 10/18/97. Our results indicate that 1) the
P-velocity structure displays a pattern of lateral variations consistent w
ith the general NW-SE trend of the Apennines in the area; 2) the aftershock
foci distribute, in the southern part of the sequence, on distinct and wel
l defined SW dipping planes which surface intersections match previously re
cognized active normal faults; 3) a distinct zone of aftershock quiescence
is observed in correspondence of the 10/12 (M-L = 5.3) and 10/14/97 (M-L =
5.7) hypocenters near Sellano; 4) the seismicity at the southern end is ver
y shallow and it is unclear the relationship between the 1997 and the 1979
Norcia sequences.