AbstractThe focal depths and the rupture processes of four moderate earthquakes, which occurred in central Italy during 1997 and 1998, are investigated using broadband teleseismic data. The earthquakes, the largest with MW = 6.0, caused significant damage in the epicentral area and are part of an unusual sequence of moderate-sized earthquakes to strike the central Apennines. For three of the events, the waveforms are found to be consistent with seismic ruptures confined to the top 5 to 7 km of the crust. Directivity effects are evident in the waveforms of the largest earthquake, and waveform inversion suggests an upward rupture with a horizontal component oriented toward the north. One earthquake (MW = 5.2) is confirmed from waveform modeling to have occurred at 50 km depth. This is the first event of this magnitude to have been located in the mantle beneath the Apennines. |