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The Mark at Eugene January 6, 2026 Seismic Hazard Study 4 Project No.: 2251077 Eugene, Oregon Landmark Construction, LLC Seismic Setting and Local Faulting We reviewed information pertaining to the CSZ and nearby crustal faults to evaluate the seismic setting and identify the potential seismic sources. The US Geological Survey (USGS) website includes an interactive deaggregation tool, which allows evaluation of the contribution of the various seismic sources to the overall seismic hazard (USGS, 2014b). The USGS interactive deaggregation indicates the seismic hazard at the site is dominated by the CSZ (USGS, 2014b). A discussion of these earthquake sources is provided below. Cascadia Subduction Zone (CSZ). Eugene is located ±110 miles inland from the surface expression of the CSZ. It is estimated that the average rate of subduction of the Juan de Fuca plate under the North American plate is ±37 mm/year northeast, based on Pacific and Mid-Ocean Ridge velocities, geodetic studies of convergence, and magnetic anomalies of the Juan de Fuca plate (Personius and Nelson, 2006; DeMets et al., 2010). Available information indicates the CSZ is capable of generating earthquakes along the inclined interface between the two plates (interface) and within the descending Juan de Fuca plate (intraplate) (Weaver and Shedlock, 1996). Intraplate (Intraslab or Wadati-Benioff Zone) earthquakes occur at depths of ±21 to 43 miles (Petersen et al., 2014). The fault rupture may occur along a segment or the entire length of the CSZ (Weaver and Shedlock, 1996). The estimated maximum magnitude of a CSZ interface earthquake is up to a moment magnitude (Mw) 9.3 (Petersen et al., 2014). The maximum estimated magnitude of an intraplate earthquake is about Mw 7.5 (Petersen et al., 2014). Crustal Faults. Crustal faults are fractures within the North American plate. Earthquakes on crustal faults occur within the North American plate, typically at depths of ±6 to 12 miles. The estimated maximum magnitude of a crustal earthquake in the Willamette Valley and adjacent physiographic regions is about Mw 7.0 (Petersen et al., 2014). Numerous crustal faults are shown on local and regional geologic maps. However, not all faults are considered to be active. Because the historical earthquake record is so short, active faults are identified by geologic mapping and seismic surveys. The USGS has defined four fault classifications based on evidence for displacement within the Quaternary (<1.6 million years) in their US fault database (Palmer, 1983; Personius et al., 2003). The fault classes are defined as follows: