The Influence of Local Site Conditions on the Significant Duration of Strong Ground Motions

Abstract

The influence of local site conditions on the significant duration of strong ground motions for shallow crustal earthquakes was evaluated using a database of 2,610 strong ground motions recorded in the United States and Taiwan. Motions recorded with the closest distance to the causative fault, R_RUP, between 10 and 100 km with moment magnitude, M_W, between 4 and 7.6 were considered in the analysis. Values for the significant duration, D_5-95, the time between the arrival of 5% and 95% of the strong motion energy at the site, were downloaded from the strong motion database maintained by the Pacific Earthquake Engineering Research Center in the U.S. The associated values of M_W, R_RUP, and the average shear wave velocity for the top 30 m of the site, (V_S)₃₀, were also downloaded from this database. The data was separated into Site Classes A (hard rock) through E (soft soil) as defined based upon (V_S)₃₀. A functional form relating D_5-95 to M_W developed in previous studies was employed in the analysis. The data set was analyzed in aggregate and then separately for the recordings from the U.S. and Taiwan. The results of the analysis show the importance of considering the site class and tectonic setting when evaluating the duration of strong ground motion.