Attenuation relation for near-field shallow crustal earthquakes using NGA-West2 database with mixed-effect model in comparison with attenuation relations for Iran

This study presents a new empirical equation for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes. This model was developed empirically by regression of the database, which was used by the NGA-West2 GMPE developers with a fault rupture distance less than 60 kilometers. The data set consisted of corrected and processed accelerograms of 1545 strong-motion records of earthquakes between 5.2 and 7.9 Mw. The model was a function of earthquake magnitude, distance of source from site, local average shear wave velocity, nonlinear soil response, sediment depth, rupture dip, faulting mechanism, and hanging wall effect. This equation was derived by a stable algorithm for regression analysis called mixed effect model. The algorithm was used to develop PGA and PSA (T) for periods from 0.01 to 10.0 seconds. Major differences between this model and the recently developed attenuation relations for the world and Iran were observed for large-magnitude ground motions, which were recorded at small-tomoderate distances from seismic source. The results showed that the near-field affected the predicted values, especially in soil sites. Moreover, comparison with the attenuation relations developed by Iranian data set confirmed that the equation in this region was sensitive more to distance than to other parameters.