The Mark at Eugene January 6, 2026 <br />Seismic Hazard Study 7 Project No.: 2251077 <br />Eugene, Oregon Landmark Construction, LLC <br />Additional research suggests multiple repeated M8 earthquakes might have occurred <br />along the southern portion of the CSZ (including the southern Oregon coast) between <br />the larger, M9 earthquakes, which are thought to rupture the entire length of the CSZ <br />(Frankel et al., 2015). <br />CSZ Intraplate Earthquakes. There have been no documented intraplate earthquakes in <br />Oregon. However, the Puget Sound region of Washington State has experienced three <br />intraplate events in the last ±76 years, including a surface wave magnitude (Ms) 7.1 <br />event in 1949 (Olympia), a Ms 6.5 event in 1965 (Seattle/Tacoma) (Wong and Silva, <br />1998), and a Mw 6.8 event in 2001 (Nisqually) (Dewey et al., 2002). <br />Crustal Earthquakes. Crustal earthquakes dominate Oregon's seismic history. Only two <br />historic crustal events in Oregon have reached Richter local magnitude (ML) 6 (the <br />1936 Milton-Freewater ML 6.1 earthquake and the 1993 Klamath <br />Falls ML 6.0 earthquake) (Wong and Bott, 1995). The majority of Oregon’s larger <br />crustal earthquakes are in the ML 4 to 5 range (Wong and Bott, 1995). <br />Table 2D summarizes earthquakes with a M of 4.0 or greater or Modified Mercalli <br />Intensity (MMI) of V or greater, that have occurred within a ±50-mile radius of Eugene <br />in the last ±192 years (Johnson et al., 1994; USGS, 2013). Note that the referenced <br />earthquake catalogs are a composite of different earthquake catalogs and seismic <br />networks; therefore, data errors may exist. Complete historic earthquake records may <br />not yet be included in the referenced earthquake catalogs. Therefore, it is possible <br />some earthquakes may not be included in Table 2D. <br />Table 2 D. Historic Earthquakes Within a ± 50 -mile Radius of Eugene (1) <br />Year Month Day Hour Minute Latitude Longitude Depth <br />(miles) <br />Magnitude or <br />Intensity (2) <br />1921 02 25 20 00 44.4 -122.4 unknown MMI = V <br />1942 05 13 01 52 44.5 -123.3 unknown MMI = V <br />1961 08 19 04 56 44.7 -122.5 unknown M = 4.5 <br />2015 07 04 15 42 44.1 -122.8 5.0 ML = 4.1 <br />2022 10 07 12 52 44.5 -122.6 8.2 ML = 4.4 <br />(1) The site is located at Latitude 44.0464, Longitude -123.0811. <br />(2) M = unspecified magnitude, Mb = compressional body wave magnitude, Mc = primary coda magnitude, Md = duration <br />magnitude (also known as coda magnitude), ML = local Richter magnitude, and MMI = Modified Mercalli Intensity at or <br />near epicenter. <br /> <br />Seismic events in Oregon were inconsistently documented until 1928 (Wong and Bott, <br />1995). Earthquake epicenters located in Oregon from 1928 to 1962 were limited due <br />to the number of and the distance between seismographs, the number of recording <br />stations, and the uncertainty in travel times (PNSN, 2004). Therefore, information <br />recorded during that time suggests only earthquakes with magnitudes >5 would be <br />recorded in Oregon (Bela, 1979). Oregon State University (OSU) likely had the first <br />station installed in 1946, and the first modern seismograph was installed at OSU in