Physically Parameterized Prediction Equations for Significant Duration in Active Crustal Regions

We develop prediction equations for the median and standard deviation of the significant duration of earthquake ground motions from shallow crustal earthquakes in active tectonic regions. We consider significant duration parameters for 5-75%, 5-95%, and 20-80% of the normalized Arias intensity. The equations were derived from a global database with M 3.0-7.9 events. We find significant noise effects on duration parameters that compel us to exclude some records that had been used previously to develop models for amplitude parameters. Our equations include an M-dependent source duration term that also depends on focal mechanism. At small M, the data suggest approximately M-independent source durations that are close to 1 sec. The increase of source durations with M is slower over the range similar to 5 to 7.2-7.4 than for larger magnitudes. We adopt an additive path term with breaks in distance scaling at 10 km and 50 km. We include site terms that increase duration for decreasing V-S30 and increasing basin depth. Our aleatory variability model captures decreasing between-and within-event standard deviation terms with increasing M.