Correlation of spectral values in worldwide subduction zone earthquakes

Ground motion prediction equations (GMPEs) have been developed to predict the mean and standard deviation of the logarithm of spectral acceleration for a wide variety of earthquake types and locations. An example is the PEER NGA-West1 and West2 GMPEs, which were developed for shallow, crustal events typical of locations such as California. Many researchers have extended these models by determining the correlation between response spectral values at different periods. These results can be used to develop conditional spectra (CS) and conditional mean spectra (CMS), which are becoming more commonly used for ground motion selection and scaling. Currently, correlation coefficients developed considering only shallow, crustal events are commonly used to develop CS and CMS. Whether or not these correlations and corresponding equations are valid for other tectonic regimes, such as subduction zones, is currently unknown. This paper evaluates the response correlation values from a large database of worldwide subduction zone earthquakes, comprising over 4400 events recorded in worldwide subduction regimes, including the recent Tohoku, Japan (Mw 9.0, 2011), Maule, Chile (Mw 8.8, 2010), and Sumatra, Indonesia (Mw 9.1, 2004) earthquakes. The results are then compared to the correlations observed for shallow, crustal events. The results of this study can be used to develop CS and CMS in worldwide subduction tectonic zones, such as those found in South and Central America, Japan, and the Pacific Northwest of North America.