PEER has just published Report No. 2014/12 titled “Reference-Rock Site Conditions for Central and Eastern North America: Part II – Attenuation (Kappa) Definition” as a new addition to the PEER Report Series. It was authored by Kenneth W. Campbell, Youssef M.A. Hashash, Byungmin Kim, Albert R. Kottke, Ellen M. Rathje, Walter J. Silva, and Jonathan P. Stewart.
This report presents the results of a comprehensive literature search and limited additional studies that support the recommendation of a probability distribution for the shear-wave (S-wave) site attenuation parameter K0, or site kappa, associated with a reference-rock site condition in central and eastern North America (CENA). This study was conducted as part of the Geotechnical Working Group (GWG) activities of the Next Generation Attenuation for Central and Eastern North America (NGA-East) Project conducted by the Pacific Earthquake Engineering Research Center (PEER). The recommended reference-rock site condition, which is documented in a separate GWG report, is defined as a hard-rock site with an S-wave velocity (Vs,ref) of 3000±300 m/sec [Hashash et al. 2013]. The recommended distribution of the reference-rock site kappa K0,ref for this reference-rock site condition is lognormal, with a median value of 0.006 sec, an aleatory standard deviation of 0.43, and epistemic standard deviations of 0.12, when uncertainty in source, path, and site-amplification effects are included in simulations used to develop ground motion prediction equations, and 0.20, when they are not. This distribution is intended to represent the center, body, and range of the technically defensible interpretations of the wider scientific community as defined in the Senior Seismic Hazard Analysis Committee (SSHAC) guidelines [Budnitz et al. 1997; NRC 2012] for a SSHAC Level 3 study. The reference-rock site conditions defined in this study and in Hashash et al.  represent a reference for determining site amplification for other types of site conditions in CENA, a companion activity of the GWG that is being conducted outside of the SSHAC process. One of the major limitations of the study is that most of the data used to estimate K0 come from southeastern Canada and the northeastern U.S., and are not necessarily representative of other regions of CENA.