Rupture directivity of the major shocks in the 1997 Umbria-Marche (Central Italy) sequence from regional broadband waveforms

Abstract

We derive the relative moment rate function for the main shocks in the Fall 1997 Central Italy seismic sequence (Mw=5.7; 6.0; 5.6) by applying an empirical Green function method. By using three conveniently placed broad-band MedNet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes, with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one. Taking a simple source model, forward modeling is utilized for determining fault parameters such as length, rupture propagation velocity and direction and slip distribution. Copyright 1999 by the American Geophysical Union.