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IV. Environmental Impact Analysis D. Geology and Soils IV. Environmental Impact Analysis D. Geology and Soils 1. Introduction This section of the Draft EIR analyzes the proposed Project’s potential impacts with regard to geology and soils. The analysis includes an evaluation of the potential geologic hazards associated with fault rupture, seismic ground shaking, liquefaction, landslides, inundation, other geologic conditions, and underlying soils. The analysis is based on the Geotechnical Engineering Evaluation prepared by Geotechnologies Inc., which is provided in Appendix D of this Draft EIR. 2. Environmental Setting a. Existing Conditions (1) Regional Geologic Setting The Project site is located in the northern portion of the Peninsular Ranges Geomorphic Province. The Peninsular Ranges are characterized by northwest-trending blocks of mountain ridges and sediment-floored valleys. The dominant geologic structural features are northwest trending fault zones that fade out to the northwest or terminate at east-trending reverse faults that form the southern margin of the Transverse Ranges. The Los Angeles Basin (Basin) is located at the northern end of the Peninsular Ranges Geomorphic Province. The Basin is bounded to the east and southeast by the Santa Ana Mountains and San Joaquin Hills and to the northwest by the Santa Monica Mountains. Over 22 million years ago, the Basin was a deep marine basin formed by tectonic forces between the North American and Pacific plates. Since that time, over five miles of marine and non-marine sedimentary rock as well as intrusive and extrusive igneous rocks have filled the basin. During the last two million years, defined by the Pleistocene and Holocene epochs, the Basin and surrounding mountain ranges have been uplifted to form City of Los Angeles USC Development Plan SCH. No. 2009011101 May 2010 Page IV.D-1 WORKING DRAFT - Not for Public Review IV.D. Geology and Soils the present day landscape. Erosion of the surrounding mountains has resulted in deposition of unconsolidated sediments in low-lying areas by rivers such as the Los Angeles River. Areas that have experienced subtle uplift have been eroded with gullies.1 (2) Local Geologic Setting (a) Fault Rupture A fault is defined as a fracture along which rocks on one side have been displaced with respect to those on the other side. The California Geological Survey (CGS) categorizes faults within the earth’s crust as active, potentially active, or inactive. Active faults are those that have shown evidence of surface displacement within the past 11,000 years (i.e., Holocene). Potentially active faults are those that have shown evidence of surface displacement between 11,000 and 1.6 million years ago (i.e., Pleistocene). Inactive faults are those that have not shown evidence of surface displacement within last 1.6 million years before the present.2 Additionally, there are blind thrust faults, which are low angle reverse faults with no surface exposure. The southern California region is crossed by numerous active and potentially active faults and is underlain by several blind thrust faults as shown in Figure IV.D-1 on page IV.D-3. Fault rupture is the visible breaking and displacement of the earth's surface along the trace of a fault during an earthquake. As further discussed below, the Alquist-Priolo Earthquake Fault Zoning Act requires the State Geologist to establish and map fault rupture zones (called earthquake fault zones).3 These zones, which generally extend from 200 to 500 feet on each side of a known active fault, identify areas where potential fault rupture along an active fault could prove hazardous and identify where special studies are required to characterize hazards to habitable structures. As indicated in the geotechnical report prepared for the Project site, no known active or potentially active faults underlie the Project site or within 500 feet of the Project site.4 Thus, the Project site is not located 5 within a State-designated Alquist-Priolo earthquake fault zone. 1 Geotechnologies, Inc., “Geotechnical Engineering Evaluation for the Proposed University of Southern California Master Plan Area,” May 14, 2009, page 5. (Available in Appendix D of this Draft EIR) 2 California Geological Survey, Special Publication 42: Fault Rupture Hazard Zones in California, Interim Revision, 2007. 3 Earthquake fault zones were formerly called “Special Studies Zones” until 1975. 4 Geotechnologies, Inc., “Geotechnical Engineering Evaluation for the Proposed University of Southern California Master Plan Area,” May 14, 2009, page 16. (Available in Appendix D of this Draft EIR) 5 Ibid. City of Los Angeles USC Development Plan SCH. No. 2009011101 May 2010 Page IV.D-2 WORKING DRAFT - Not for Public Review 36 35 40 34 1 San Cl em en t e Fau l t 37 32 29 41 2 Pal os Verd es Fau l t 38 3 Ro se Can y o n Fau l t 31 4 Newport-Inglewood Fault 39 21 5 Whittier Fault 25 42 44 33 6 Santa Cruz Fault 43 45 30 19 7 Malibu Coast Fault 26 8 San t a M o n i ca Fau l t 47 28 46 9 Raymond Hill Fault 24 10 Sierra Madre Fault 48 20 50 51 23 22 11 El si n o r e Fau l t 49 8 27 12 Superstition Mountain Fault 9 10 17 13 Superstition Hills Fault 6 7 5 14 Imperial Fault 15 18 4 Page IV.D-3 15 Banning Fault 16 San Jaci n t o Fau l t 34 So. Death Valley Fault 16 2 17 Pi n t o Mou n t ai n Fau l t 35 Panamint Valley Fault PROJECT SITE 18 Blue Cut Fault 36 Sierra Nevada Fault 11 19 Ludlow Fault 37 Kern Front Faul t 13 20 Pi sg ah Fau l t 38 Whit e Wolf Fault 21 Cal i co Fau l t 39 Pl ei t o Fau l t 3 14 22 West Calico Fault 40 Rinconada Fault 12 23 Em er so n Fau l t 41 San Ju an Fau l t 24 Cam p r o ck Fau l t 42 Ozena Fault 1 25 Lockhart Fault 43 San t a Yn ez Fau l t 26 Lenwood Fault 44 Bi g Pi ne Faul t 27 Old Woman Springs 45 Pine Mountain Fault 0 100 km 28 Helendale Fault 46 San Cayetano Fault 29 Si erra Front al Faul t 47 San Gab r i el Fau l t 30 San An d r eas Fau l t 48 Arroyo Parida Fault 31 Harper Fault 49 Oakridge Fault 32 Bl ackw at er Faul t 50 San t a Su san a Fau l t 33 Garl ock Faul t 51 Nort h Front al Faul t Figure IV.D-1 Regional Faults in Southern California Source: California Geological Survey IV.D. Geology and Soils In addition, the City of Los Angeles General Plan Safety Element designates fault rupture study areas extending along each side of active and potentially active faults to establish areas of hazard potential due to fault rupture. The Project site is not located within a City-designated fault rupture study area.6 Based on the above, the potential for fault rupture to occur on the Project site is very low. (b) Seismic Groundshaking As previously stated, the southern California region is crossed by numerous active and potentially active faults and is underlain by several blind thrust faults. As such, the region is susceptible to strong seismic groundshaking. Approximately 45 known active and potentially active faults are located within a 60-mile radius of the Project site.7 Table IV.D-1 on page IV.D-5 lists the 12 closest faults to the Project site. As shown in Figure IV.D-1 on page IV.D-3, the Newport-Inglewood Fault and Hollywood Fault8 are located approximately 4.7 miles and 6.0 miles, respectively from the Project site. These two faults can produce an earthquake with a 7.1 and 6.4 moment magnitude (Mw), respectively.9 In addition, the Raymond Fault is located approximately 7.5 miles to the northeast and can produce a maximum 6.5 Mw magnitude earthquake. Another notable nearby fault is the Whittier Fault which is located approximately 15 miles to the east, and extends in a west-northwest direction for a distance of 20 miles from the Santa Ana River to the terminus of the Puente Hills. The Whittier Fault can produce an earthquake with a maximum earthquake magnitude of 6.8 Mw. At its closest point, the well-known San Andreas Fault system is located approximately 30 miles northeast from the Project site. The San Andreas Fault system has had a long history of inferred and historic earthquakes. Large historic earthquakes caused by this fault system include earthquakes at Fort Tejon in 1857, Point Reyes in 1906, and Loma Prieta in 1989. Based on single- event rupture length, the maximum magnitude earthquake is expected to be 8.25 Mw. The southern portion of the fault system is suspected of producing a large earthquake every 100 to 200 years. 6 City of Los Angeles General Plan Safety Element, Exhibit A, adopted by the City Council, November 26, 1996. 7 Geotechnologies, Inc., “Geotechnical Engineering Evaluation for the Proposed University of Southern California Master Plan Area,” May 14, 2009, Table I – Faults in the Vicinity of the Site. (Available in Appendix D of this Draft EIR) 8 The Hollywood Fault can be considered a westward extension of the Raymond Fault. 9 The moment magnitude (Mw) is based on the moment of the earthquake, which is equal to the rigidity of the earth multiplied by the average amount of slip on the fault and the size of the area that slipped.
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