Na. Pino et S. Mazza, The Umbria-Marche (central Italy) earthquakes: relation between rupture directivity and sequence evolution for the M-w > 5 shocks, J SEISMOL, 4(4), 2000, pp. 451-461
We derive the relative moment rate function for the shocks with M-w > 5 in
the 1997-98 central Italy seismic sequence, started with the M-w = 5.7, 09/
26/97 00:33 event, by applying an empirical Green function method. By using
three conveniently placed broadband MedNet stations we obtain apparent sou
rce time functions indicating clear directivity effects for all of the anal
ysed earthquakes, with rupture propagation generally directed outward from
the epicentral area of the 09/03/97 foreshock sequence. Taking a simple sou
rce model, forward modeling is utilized for determining fault parameters su
ch as length, rupture propagation velocity and direction and, for the three
major events, slip distribution. The effects of the break propagation dire
ctions on the sequence evolution is discussed. A possible inconsistency res
ults for the shallow 04/03/98 shock, which could be avoided if a link with
the deep 03/26/98 event is assumed. Our analysis evidences the importance o
f a quick determination for the fault parameters in order to image the poss
ible induction of fracturing on nearby structures.