Intensity Measure Correlations Observed in the NGA-West2 Database, and Dependence of Correlations on Rupture and Site Parameters

This manuscript reports ground motion intensity measure ( IM) correlations for a number of IM types, as measured from the NGA-West2 database. IMs considered are Spectral Accelerations with periods from 0.01 s to 10 s, Peak Ground Acceleration, Peak Ground Velocity, and Significant Duration (for 5–75% and 5–95% definitions). Results are shown for correlations of both maximum-direction and geometric mean spectral acceleration values, given the need for such maximum-direction correlations in a new ASCE 7-16 procedure. Additionally, the potential magnitude-, distance- and site-condition-dependence of IM correlations are evaluated. The results are practically important as IM correlations are increasingly used in a range of engineering and seismic hazard calculations. We find that maximum-direction spectral correlations are comparable to correlations for other spectral acceleration definitions, and that the correlations have no practically significant dependence on magnitude, distance or site conditions. These results support the collective understanding that IM correlations are stable across a range of conditions, and as a result, that existing correlation models are generally appropriate for continued use in engineering calculations.