2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis GEOLOGY AND SOILS Faults The nearest mapped active fault to the project area is the Newport Inglewood Fault in Huntington Beach, approximately 6.2 miles southwest of the project area. Other active faults in the region include the Whittier Fault, approximately 12.9 miles to the north; the Chino Fault, approximately 19.5 miles to the northeast; and the Palos Verdes Fault Zone, approximately 17 miles southwest offshore in the Pacific Ocean (CGS 2013; see Figure 5.42, Fault Mali). An uncertain location of an unnamed fault, not classified as active, crosses Harbor Boulevard northwest southeast approximately 0.2 mile south of the southern project boundary. A second uncertain location of an unnamed fault, also not classified as active, extends north south approximately 0.9 mile west of the segment of Harbor Boulevard in the project area (see Figure 5.41, Geolog*Map). Historical Earthquakes in the Region Historical earthquakes that caused substantial ground shaking in the region include: • Wrightwood Earthquake of 1812 (magnitude 7.5 [estimated]; San Andreas [probable]); • Elsinore Earthquake of 1910 (magnitude 6, Elsinore Fault) • San Jacinto Earthquake of 1918 (magnitude 6.8, San Jacinto Fault) • North San Jacinto Fault Earthquake of 1923 (magnitude 6.3, San Jacinto Fault) • Long Beach Earthquake of 1933 (magnitude 6.4; Newport Inglewood Fault); • San Fernando Earthquake of 1971 (magnitude 6.6, San Fernando Fault) • Landers Earthquake of 1992 (magnitude 7.3; several faults); • Northridge Earthquake of 1994 (magnitude 6.7; Northridge Thrust) (SCEDC 2013). Ground Shaking Ground shaking in the project area with a 10 percent probability of exceedance in 50 years, that is, an average return period of 475 years, is estimated between 0.3 g and 0.4 g where g is the acceleration of gravity. That intensity corresponds to intensity VII to VIII on the MMI scale. Liquefaction Liquefaction is a loss of strength and stiffness in soil due to ground shaking; it typically occurs within 50 feet of the surface, in saturated, loose, fine- to medium grained sandy to silty soils. Liquefaction can substantially damage structures and can cause structures to sink or tilt. Three conditions are needed for liquefaction: ground shaking with acceleration of about 0.2 g or greater; loose, unconsolidated sediments; and saturated soil within approximately 50 feet of the surface. The entire project area is in a zone of required investigation for liquefaction designated by the California Geological Survey (CGS 1998x, 1998b). Most of the project area is also mapped as an area of potential liquefaction in Exhibit 5, Potential Liquefaction Areas, of the City's General Plan. Page 5.44 PlaceWorkr