Validation of a kinematic and parametric approach to calculating intensity scenarios

We employ our semi-empirical kinematic model for shear body waves (KF) [Sirovich L. A simplealgorithm for tracing out synthetic isoseismals. Bull Seism Soc Am 1996;86(4):1019–27; Sirovich L.Synthetic isoseismals of three earthquakes in California-Nevada. Soil Dyn Earthquake Eng1997;16:353–62] to back-predict and then validate the regional intensity scenario of a destructiveearthquake (Loma Prieta, California,Ms7.1, October 17, 1989). Only the pre-1988 geological andseismotectonic knowledge was used to set the 11 source parameters ofKF(in this sense, our procedurewas deterministic). Then, the ranges of the pre-1988 uncertainties were explored by grid search andthe parametric combination produced 59,049 sources. The quality of our prediction was measured usingthe field intensities of 1989 by the US Geological Survey (in the MMI scale). The squared scenarioresiduals are: 73 for the meanKFscenario and 123 for the best available empirical attenuation of MMIintensity. We stress that, before usingKFin the forward mode, its automatic inverse application hasalready been validated by refinding a series of earthquake sources [Gentile F, Pettenati F, Sirovich L.Validation of the automatic nonlinear source inversion of the US geological survey intensities of theWhittier Narrows, 1987 Earthquake. Bull Seism Soc Am 2004;94(5):1737–47; Pettenati F, Sirovich L.Intensity-based source inversion of three destructive California earthquakes. Bull Seism Soc Am2007;97(5):1587–606; Sirovich L, Pettenati F. Source inversion of intensity patterns of earthquakes: adestructive shock in 1936 in northeast Italy. J Geophys Res 2004;109:B10309, doi:10.1029/2003JB002919:1–16]. If our technique had been available at the time, the 1989 pattern of damagesouth of San Francisco would have been conservatively foreseen even from 1983 on.