Regional Moment Tensors of the 2009 L'Aquila Earthquake Sequence

Broadband waveform inversion of ground velocities in the 0.02-0.10 Hz frequency band is successfully applied to 181 earthquakes with M-L >= 3 of the April 2009 L'Aquila, Italy, earthquake sequence. This was made possible by the development of a new regional crustal velocity model constrained by deep crustal profiles, surface-wave dispersion and teleseismic P-wave receiver functions, and tested through waveform fit. Although all earthquakes exhibit normal faulting, with the fault plane dipping southwest at about 55 degrees for the majority of events, a subset of events had much shallower dips. The issue of confidence in the derived parameters was investigated by applying the same inversion procedure by two groups who subjectively selected different traces for inversion. The unexpected difficulty in modeling the regional broadband waveforms of the mainshock as a point source was investigated through an extensive finite-fault modeling of broadband velocity and accelerometer data, which placed the location of major moment release up-dip and about 4-7 s after the initial first-arrival hypocentral parameters.