Regional attenuation models in Central and Eastern North America using the NGA-East database

Abstract

The anelastic attenuation term found in ground motion prediction equations (GMPEs) represents the distance dependence of the effect of intrinsic and scattering attenuation on the wavefield as it propagates through the crust and contains the frequency-dependent quality factor, $Q(f)$ , which is an inverse measure of the effective anelastic attenuation. In this work, regional estimates of $Q(f)$ in Central and Eastern North America (CENA) are developed using the NGA-East regionalization. The technique employed uses smoothed Fourier amplitude spectrum (FAS) data from well-recorded events in CENA as collected and processed by NGA-East. Regional $Q(f)$ is estimated using an assumption of average geometrical spreading applicable to the distance ranges considered. Corrections for the radiation pattern effect and for site response based on $V_{s30}$ result in a small but statistically significant improvement to the residual analysis. Apparent $Q(f)$ estimates from multiple events are combined within each region to develop the regional models. Models are provided for three NGA-East regions: the Gulf Coast, Central North America, and the Appalachian Province. Consideration of the model uncertainties suggests that the latter two regions could be combined. There were not sufficient data to adequately constrain the model in the Atlantic Coastal Plain region. Tectonically stable regions are usually described by higher $Q(f)$ and weaker frequency dependence ( $\eta$ ), while active regions are typically characterized by lower $Q(f)$ and stronger frequency dependence, and the results are consistent with these expectations. Significantly different regional $Q(f)$ is found for events with data recorded in multiple regions, which supports the NGA-East regionalization. An inspection of two well-recorded events with data both in the Mississippi embayment and in southern Texas indicates that the Gulf Coast regionalization by Cramer in 2017 may be an improvement to that of NGA-East for anelastic attenuation. The $Q(f)$ models developed serve as epistemic uncertainty alternatives in CENA based on a literature review and a comparison with previously published models.