HR: 0800h
AN: T11D-1295    [Abstracts]
TI: Validation of a Kinematic Semi Empirical Approach to Calculate Seismic Hazard Scenarios
AU: Pettenati, F
EM: fpettenati@ogs.trieste.it
AF: O.G.S., Borgo Grotta Gigante, 42C, Sgonico, TS 34010 Italy
AU: * Sirovich, L
EM: sirovich@ogs.trieste.it
AF: O.G.S., Borgo Grotta Gigante, 42C, Sgonico, TS 34010 Italy
AB: After validating some source inversions of the regional patterns of intensities of earthquakes in the Greater Los Angeles Region (B.S.S.A., Vol. 93, pp. 47-60; B.S.S.A., 2004, Vol. 94, 5, in press), and in NE Italy (J.G.R., 2004, Vol. 109, in press), in the present work we use our kinematic "KF" approach to produce some regional seismic hazard scenarios in NE Italy. We do this by using the KF formula in the direct mode, and by applying a Montecarlo technique to its eleven source parametres. We remind that KF considers the nucleation coordinates, the seismic moment, the fault plane solution, the lengths of the line source and rupture velocities both along-strike and antistrike. In so doing, we obtain 62.325 sources to calculate the scenario for the M=5.8-6.2 Bosco Cansiglio, 1936 earthquake, and 20.625 sources for an hypothetical destructive earthquake caused by the so-called "Montello" tectonic structure (tentative origin of two earthquakes in 1695, and in 778 A.D.), WSW of the Cansiglio area. Both sources have an Alpine dip-slip mechanism. The Cansiglio scenario starts from i) the fault retrieved by intensity inversion, from ii) the Database of potential sources in Italy, of INGV, and iii) from neotectonic evidence. Both scenarios are obtained by mapping the mean values of intensities, and the corresponding standard deviations, all over the region. Note that in the former case a validation is feasible by comparing the theoretical scenario with the experimental intensities reported by the Italian DOM4.1 catalog. Thus, 44 out of 103 site intensities (within the 55x55 km study area) were forecasted exactly; in 39 sites the deviation between the mean scenario intensities and the reference intensities is $<=$0.5 in real numbers, and the difference is 1.5 in only 5 cases. The means plus 1 standard deviation are conservative when referred to the intensities observed in 1936. Taking the 1936 earthquake as reference event, we compared the fitness of our KF scenario and of a traditional scenario produced by an accredited empirical "attenuation law" (Grandori et al., 1987; however, similar results are obtained with other empirical isotropic relations). The fitness criterion was the sum S of the squared residuals r, with r equal to the intensity observed at each site minus the intensity calculated there. The KF scenario scored S=50.5, the empirical "attenuation" scored S=104.6. Regarding the "Montello" scenario, it starts from a causative fault based on the TRANSALP deep seismic traverse, and on neotectonic evidence. Interestingly, it seems that the only intensity datum available for the 778 A.D. earthquake (VII-VIII degree at Treviso) has a low compatibility with the aforementioned Montello tectonic structure; thus, this fault seems to be an unrealistic source for the VIII Century event.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7260 Theory and modeling
DE: 8123 Dynamics, seismotectonics
DE: 3260 Inverse theory
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting