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

We derive the relative moment rate function for the main shocks in the Fall 1997 Central Italy seismic sequence (M-W=5.7; 6.0; 5.6) by applying an emp irical Green function method. By using three conveniently placed broadband MedNet stations we obtain clear source time functions indicating directivit y effects for all of the three earthquakes, with southeastward rupture prop agation for the two southernmost events and an opposite direction for the o ther and largest one. Taking a simple source model, forward modeling is uti lized for determining fault parameters such as length, rupture propagation velocity and direction and slip distribution.