Empirical equations for the prediction of PGA and pseudo spectral accelerations using Iranian strong-motion data

Abstract

A recently compiled, comprehensive, and good-quality strong-motion database of the Iranian earthquakes has been used to develop local empiri- cal equations for the prediction of peak ground acceleration (PGA) and 5%-damped pseudo- spectral accelerations (PSA) up to 4.0 s. The equa- tions account for style of faulting and four site classes and use the horizontal distance from the surface projection of the rupture plane as a distance measure. The model predicts the geometric mean of horizontal components and the vertical-to-horizontal ratio. A total of 1551 free-field acceleration time histories recorded at distances of up to 200 km from 200 shallow earthquakes (depth < 30 km) with mo- ment magnitudes ranging from Mw 4.0 to 7.3 are used to perform regression analysis using the ran- dom effects algorithm of Abrahamson and Youngs (Bull Seism Soc Am 82:505–510, 1992), which considers between-events as well as within-events errors. Due to the limited data used in the develop- ment of previous Iranian ground motion prediction equations (GMPEs) and strong trade-offs between different terms of GMPEs, it is likely that the pre- viously determined models might have less preci- sion on their coefficients in comparison to the cur- rent study. The richer database of the current study allows improving on prior works by considering additional variables that could not previously be adequately constrained. Here, a functional form used by Boore and Atkinson (Earthquake Spect 24:99– 138, 2008) and Bindi et al. (Bull Seism Soc Am 9:1899–1920, 2011) has been adopted that allows accounting for the saturation of ground motions at close distances. A regression has been also per- formed for the V/H in order to retrieve vertical components by scaling horizontal spectra. In order to take into account epistemic uncertainty, the new model can be used along with other appropriate GMPEs through a logic tree framework for seismic hazard assessment in Iran and Middle East region.