Ground-Motion Amplitudes for Earthquakes in Puerto Rico

Abstract

We explore ground-motion amplitudes for earthquakes in Puerto Rico using the Referenced Empirical approach. The technique is based on the use of residual analysis to model discrepancies between ground-motion observations for Puerto Rico and a reference ground-motion prediction equation (GMPE). The refer- ence GMPE is that of Boore and Atkinson (2008) for shallow crustal earthquakes in active tectonic regions (as modified by Atkinson and Boore (2011) to improve the fit for small-to-moderate events). Amplitudes are examined for both shallow (depth < 34 km) and deep (35-200 km) earthquakes in Puerto Rico. Overall, we conclude that ground motions in Puerto Rico are consistent in attenuation rates with those in other active regions, for shallow events. Amplitude levels appear to be lower than those predicted by Boore and Atkinson (2008), but the discrepancy is magnitude dependent, decreasing to a near-zero bias near M 6. We thus postulate that amplitude levels may be considered equivalent for the magnitude-distance range of engineering interest, allowing GMPEs for other active regions to be used for Puerto Rico. Furthermore, deeper events have amplitudes that also appear consistent with typical GMPEs for shallow events, if the greater distance of the events due to their depth is considered.