Low-frequency and broad-band source models for the 2009 L'Aquila, Italy, earthquake

The 2009 L’Aquila, Italy, earthquake (Mw 6.3) produced an unprecedented number of seismologicalrecords for a normal faulting event, and hence represents an important case studyof damaging moderate magnitude earthquakes occurring in densely inhabited areas. We haveinvestigated the source process of the 2009 L’Aquila earthquake in both the low- and broadbandfrequency ranges by analysing the teleseismic and strong motion data. A low-frequency(<0.5 Hz) source model has been determined by waveform inversion of teleseismic and nearfieldstrong motion data, yielding slip distributions with a major asperity located about 8 kmsoutheast of the hypocentre. The broad-band (0.2–10 Hz) source characteristics were estimatedusing the empirical Green’s function method providing the strong motion generation area ofabout 42 km2 located southeast of the hypocentre below the village of Onna. This coincideswith the location of the asperity from the inversion analysis, indicating that the low-frequencyand broad-band ground motions produced during the earthquake were generated at similarlocations on the fault plane. The position of the strong motion generation area also correlateswell with the distribution of observed macroseismic (MCS) intensities reported by INGV. Themaximum macroseismic intensities of IX–X were reported southeast of the epicentre, withan intensity of X measured in Onna. The source properties of the 2009 L’Aquila mainshockreveal the estimated size of the strong motion generation area to be in agreement with predictionsmade using empirical source scaling relation for inland crustal earthquakes, implying astress drop of approximately 10MPa. This further indicates that the 2009 L’Aquila earthquakeinvolved a stress drop similar to that of previously recorded earthquakes in the Central andSouthern Apennines.