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2. STUDY AREA CHARACTERISTICS TABLE 2.2.3-1 Historical Seismic Events That Have Occurred Within 60t Miles of the MWMC Service Area2 MWMC Facilities Plan, Eugene-Springfield Latitude Longitude Distance Year Month Day (o North) (o West) Magnitude3 Intensity4 (miles) 2004 2 26 45.65 122.75 3.0 IIIF 43.5 1The approximate center of the MWMC service area is located at latitude 45° 05' 00' N, longitude 123° 07' 00" W. 2 Soume: USGS Earthquake Hazards Program (see http://neic.usqs.qov/neis/epic/epic_circ.html). The database search included Significant U.S. Earthquakes 1568 to 1989 and USGS/NEIC (PDE) 1973-Present. The only earthquakes in the database recorded prior to 1953 include two events, in 1892 and 1896. 3 Magnitude values are calculated by the USGS. Magnitude values are Local Magnitudes (LM) and Coda Duration Magnitude (MD). ML magnitude is generally referred to as the true "Richter magnitude." The values are computed for distances less than 600 km with depths less than 70 km. MD estimates are derived from the duration or coda length of earthquake vibrations. Duration or coda magnitude scales are normally adjusted to agree with ML(see http://neic.usgs.gov/neis/epic/code_magnitude.html). 4 Modified Mercalli intensity scale. Dashed line equals no data for that event. Based on information from the USGS database, numerous small earthquakes with magnitudes between 3 and 5 have occurred with 60 miles of the MWMC service area during historical times. The closest earthquakes were magnitude 5.0 and 3.4 events that occurred 12.4 and 13.7 miles from the approximate center of the service area. The largest historical event was an estimated magnitude 5.7 earthquake that occurred in 1993, approximately 21 miles from the center of the service area. As noted above, the two largest earthquakes in recent years in Oregon include the Scotts Mills, (magnitude 5.6) and Klamath Falls quakes (magnitude 5.9 and magnitude 6.0) of 1993 (both earthquakes were beyond the 60-mile radius noted in Table 2.2.3-1) According to the Uniform Building Code Seismic Risk Map of the United States, the Eugene-Springfield metropolitan area (and most counties west of the crest of the Cascades, including the Willamette Valley and the Portland Metro area) are located in Seismic Zone 3 (bBC, 1997). This seismic zone corresponds to an intensity VIII earthquake on the MM Scale. An intensity VIII earthquake can produce slight damage in specially designed structures to considerable damage in ordinary substantial buildings, with partial collapse(see Table 2.2.3.2). An earthquake magnitude of 9.0 was selected as being the controlling event at the Project site (USGS, 2003). The earthquake magnitude selected for the Project site was based on USGS deaggregation seismic hazard mapping for the Eugene-Springfield metropolitan area. The latitude and longitude of the approximate center of the site was entered into the USGS database to obtain seismic magnitude probability for the Project location. The USGS seismic hazard maps present the average magnitude of all potential sources at a given location, and provide the percent contribution at discrete locations of the overall seismic hazard. This magnitude event (9.0) corresponds to a 475-year mean return interval. Seismic ground acceleration for the Project site was determined according to the National Earthquake Hazards Reduction Program (NEHRP) maps for probabilistic ground motion MWMC_2.0_REV23.DOC 2-9