For regions without adequate strong ground motion records, a method is developed to establish strong ground motion attenuation relationships, based on the stochastic method. Sendai area of Japan (N36°~40°, E138°~143°) is selected as the target, since there are enough data from seismographic observation for calculation, and those from strong ground motion observation and some empirical relationships for result testing.
Three parameters related to regional source and crustal medium are inversed by the micro-Genetic Algorithm. Total of 240 records from 77 small events (Mw=3.5~4.5, focal depth≤30 km) in two directions, recorded by F-net, are adopted for the inversion. Fourier spectra are adopted as the objective function. These parameters are then taken into the stochastic method to estimate the root-mean-square acceleration and velocity (Arms and Vrms) and the peak factor (γm), PGA or PGV is the product of Arms or Vrms and γm.
The regional ground motion attenuation relationships, for PGA and PGV, are compared with strong ground motion records from K-NET (Mw≥4.5, focal depth≤30 km, equivalent shear-wave velocity≥500 m/s) and empirical relationships. There is a great agreement, which can illustrate the reliability of this method.