The L'Aquila, Central Italy earthquake, occurred on April 6, 2009 at 01:32:40 UTC time. This Mw 6.3 (Global CMT) event caused large damages to the city of L'Aquila and surrounding villages of the Abruzzi region. Event was followed by a significant aftershock activity that extended over the length exceeding 30 km in NW-SE direction. According to the moment tensor solution, the earthquake was generated by a normal faulting on a fault system running parallel to the axis of the Apennine mountains. The aftershock distribution (Amato et al., 2009) and the previous studies of the active faults in the area (e.g., Salvi et al., 2003) suggest that the fault activated during the mainshock is a NW-SE oriented structure dipping towards the southwest. The updated epicenter location is reported by INGV, Rome to be 2 km away from the city of L'Aquila. A detailed study of the source process of this event is essential for understanding the observed macrosesmic effects and the relation between the causative fault and the aftershock activity. We develop a rupture model for the L'Aquila event by analyzing the teleseismic waveform data of IRIS-DMC and strong motion records from the Italian Strong Motion Network (RAN). To estimate the general pattern of the source rupture area and determine the hypocentral depth, we have performed the moment tensor analysis as well as the source inversion of broadband teleseismic records using the methods developed by Kikuchi and Kanamori (1982, 1991), Kikuchi et al. (2003), and Yoshida et al. (1996). Based on the aftershock study, we assumed that the rupture occurred on the SW dipping fault plane with the dimensions of 25 km in length by 15 km in width. We also assumed strike = 148 deg and dip = 44 deg, based on the residuals of the point source analysis and the aftershock distribution. The optimal depth that maximizes the waveform fit was found to be 6 km. The total seismic moment corresponds to 3.10 x 10**18 Nm. The inverted slip model shows one main asperity located in the upper shallow part of the fault close to the hypocenter, and a rupture extension towards the southeast. We further performed a waveform inversion of strong motion data recorded at RAN stations using the method of Yoshida et al. (1996) and fault parameters from the teleseismic waveform inversion. We constructed the velocity structure of the area by the 1D model derived from Di Luzio et al. (2009). According to the results of the inversion, the strong motion records at near-source stations can be fully explained by the asperity located in the northern part of the fault above the hypocenter. The southeast extension of the slip area is necessary in order to explain the observations from the strong motion stations at larger distances. This is in agreement with the model from teleseismic data. The inversion also suggests an optimal hypocenter depth and the need of a more detailed velocity model.
Rupture Process of the 2009 L’Aquila, Italy, Earthquake Inferred from the Inversion of Multiple Seismological Datasets
VUAN A;
2009-01-01
Abstract
The L'Aquila, Central Italy earthquake, occurred on April 6, 2009 at 01:32:40 UTC time. This Mw 6.3 (Global CMT) event caused large damages to the city of L'Aquila and surrounding villages of the Abruzzi region. Event was followed by a significant aftershock activity that extended over the length exceeding 30 km in NW-SE direction. According to the moment tensor solution, the earthquake was generated by a normal faulting on a fault system running parallel to the axis of the Apennine mountains. The aftershock distribution (Amato et al., 2009) and the previous studies of the active faults in the area (e.g., Salvi et al., 2003) suggest that the fault activated during the mainshock is a NW-SE oriented structure dipping towards the southwest. The updated epicenter location is reported by INGV, Rome to be 2 km away from the city of L'Aquila. A detailed study of the source process of this event is essential for understanding the observed macrosesmic effects and the relation between the causative fault and the aftershock activity. We develop a rupture model for the L'Aquila event by analyzing the teleseismic waveform data of IRIS-DMC and strong motion records from the Italian Strong Motion Network (RAN). To estimate the general pattern of the source rupture area and determine the hypocentral depth, we have performed the moment tensor analysis as well as the source inversion of broadband teleseismic records using the methods developed by Kikuchi and Kanamori (1982, 1991), Kikuchi et al. (2003), and Yoshida et al. (1996). Based on the aftershock study, we assumed that the rupture occurred on the SW dipping fault plane with the dimensions of 25 km in length by 15 km in width. We also assumed strike = 148 deg and dip = 44 deg, based on the residuals of the point source analysis and the aftershock distribution. The optimal depth that maximizes the waveform fit was found to be 6 km. The total seismic moment corresponds to 3.10 x 10**18 Nm. The inverted slip model shows one main asperity located in the upper shallow part of the fault close to the hypocenter, and a rupture extension towards the southeast. We further performed a waveform inversion of strong motion data recorded at RAN stations using the method of Yoshida et al. (1996) and fault parameters from the teleseismic waveform inversion. We constructed the velocity structure of the area by the 1D model derived from Di Luzio et al. (2009). According to the results of the inversion, the strong motion records at near-source stations can be fully explained by the asperity located in the northern part of the fault above the hypocenter. The southeast extension of the slip area is necessary in order to explain the observations from the strong motion stations at larger distances. This is in agreement with the model from teleseismic data. The inversion also suggests an optimal hypocenter depth and the need of a more detailed velocity model.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
