Ground Motion Prediction Equation for Lanzhou Region from Small Earthquake Records

Abstract

By small earthquake records from the Gansu broadband digital earthquake network, five regional source and crustal medium parameters, stress drop Δσ, quality factor parameters Q0 and η, geometrical spreading parameters R1 and R2, are inversed for the Lanzhou area. Envelops of Fourier spectra are adopted as the objective function, the values of those parameters are 34.625bars, 95.665, 0.360, 58.188km and 105.650km, respectively. These values are adopted to calculate Fourier amplitude spectra, and complex spectra are formed by combining with random phase spectra. Acceleration time histories can be simulated, and PGAs on different moment magnitude-distance pairs are obtained previously. Compared with several observed strong ground motion data, the result is lower in the case of Mw=5.0, passes through the data in the case of Mw=6.0 and higher than the record of Mw=7.0. It is adopted in regional seismic zonation. Compared with The Zonation Map of Earthquake Ground Motion Parameters in China (GB18306-2001), the result is close to the map when PGA is lower than 0.2g.