This document is one in a series of three topical reports compiled by the Pacific Northwest National Laboratory to summarize technical information on selected topics important to the performance of a probabilistic seismic hazard analysis of the Hanford Site. The data used to compile this report are based on scientific studies and a search of the literature current through 2008. The purpose of this report is to summarize available data and analyses relevant to the Yakima Fold Belt (YFB) that may bear on the question of whether or not the YFB behaves as a single seismotectonic province in which activity along one fold structure is representative of behavior along all other fold structures. This topic has met with a fairly high level of contention in the expert community and has the potential to result in significant impacts on an evaluation of seismic hazard at the Hanford Site. This report defines the alternative conceptual models relevant to this technical issue and the arguments and data that support those models. It provides a brief description of the technical issue and principal uncertainties; a general overview on the nature of the technical issue, along with alternative conceptual models, supporting arguments and information, and uncertainties; and, finally, suggests some possible approaches for reducing uncertainties regarding this issue. v Acronyms and Abbreviations ACM alternative conceptual model BP before present CLEW Cle Elum-Wallula deformed zone CRBG Columbia River Basalt Group DOE-ORP U.S. Department of Energy Office of River Protection GMA ground motion attenuation ka kilo-annum; one thousand years ago (age) kyr kiloyear(s); one thousand years (time interval) LiDAR light detection and ranging Ma mega-annum; millions of years before present NGA next generation attenuation (model) OWL Olympic-Wallowa lineament PNNL Pacific Northwest National Laboratory PSHA probabilistic seismic hazard analysis RAW Rattlesnake-Wallula alignment SSC seismic source characterization SSHAC Senior Seismic Hazard Analysis Committee TI technical integrator TR topical report WFZ Wallula fault zone YFB Yakima Fold Belt vii Glossary of Terms probability of activity-The probability of activity is the likelihood that a given structure is seismogenic, or active, within the present tectonic regime and will, therefore, localize seismicity above the rates occurring randomly within the region (Geomatrix 1996, p. 3-11). The assessment of activity generally is made based on such factors as association with historical seismicity, evidence for late Quaternary fault displacements, geomorphic evidence for geologically recent deformation, association with neighboring structures showing evidence for Quaternary activity, pre-Quaternary history of deformation, and orientation relative to the present stress field. CLEW-The Cle Elum-Wallula (CLEW) deformed zone is a segment of the Olympic-Wallowa lineament that passes through the central Yakima Fold Belt (Reidel et al. 1989, p. 248). coupled model-The coupled model, sometimes referred to as the...