3.B. Geology Soils - laschools.org · Mudflows and landslides are the downslope movement of soil and/or rock under the influence of gravity. ... thickness of soil ... downward movement

Los Angeles Unified School District Central L.A. Area New High School No. 11 & Vista Hermosa Park PCR Services Corporation January 2004

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PRELIMINARY WORKING DRAFT – Work in Progress

3B. Geology/Soils

3B.1 INTRODUCTION

This section evaluates potential geologic and soils hazards associated with the proposed project, including, surface rupture, ground shaking, ground failure, liquefaction, landslides, mudflows, and subsidence of the land. The information and findings in this section are summarized from several geotechnical site investigations that have been prepared for LAUSD since 1996. The most recent of these investigations include: the Investigation of Faulting Potential on the Belmont Learning Center Site, Earth Consultants International, Inc., January 2003; and, the Updated Geohazards Evaluation, Belmont Learning Center, URS Corporation, August 5, 2002. These geotechnical investigation reports are summarized along with other relevant studies in Appendix C, and are available for review at the LAUSD Office of Environmental Health and Safety, 355 South Grand Avenue, 15th Floor, Los Angeles, CA 90071.

Surface ruptures are the displacement and cracking of the ground surface along a fault trace. Surface ruptures are visible instances of horizontal or vertical displacement, or a combination of the two, typically confined to a narrow zone along the fault. The effects of ground shaking, the actual trembling or jerking motion of the ground during an earthquake, can vary widely across an area and depend on factors such as earthquake intensity and fault mechanism, duration of shaking, soil conditions, type of building, and other factors. Ground failure results from the cyclical ground acceleration generated during an earthquake, producing landslides, ground cracking, subsidence and differential settlement.

Liquefaction is a seismic phenomenon in which loose, saturated, fine-grained granular soils behave similarly to a fluid when subjected to high- intensity ground shaking. Liquefaction occurs when three general conditions exist: (1) shallow groundwater; (2) low-density, fine, clean sandy soils; and (3) high- intensity ground motion. Studies indicate that saturated, loose and medium dense, near-surface cohesionless soils exhibit the highest liquefaction potential, while dry, dense, cohesive soils exhibit low to negligible liquefaction potential. Effects of liquefaction on level ground can include sand boils, settlement, and bearing capacity failures below structural foundations. Lateral spreading also can occur in areas of sloping ground. Seismic dynamic settlement is a typical term applied to settlement of loose to medium dense granular soils above groundwater.

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Mudflows and landslides are the downslope movement of soil and/or rock under the influence of gravity. Mudflow and landslide processes are influenced by factors such as thickness of soil or fill over bedrock, steepness and height of slope, physical properties of the fill, soil or bedrock materials, and moisture content. These factors may increase the effective force of gravity upon a slope, decrease the ability of the slope to resist gravitational influence or a combination of the two, which can lead to mudflows and landslides.

Subsidence is a localized mass movement that involves the gradual downhill settling or sinking of the earth’s surface, resulting from the extraction of mineral resources, subsurface oil, groundwater, or other subsurface liquids, such as natural gas. Settlement is the gradual downward movement of a structure due to compression of the soil below the foundation. The principal cause of subsidence is the extraction of subsurface liquids, whereas settlement results from the compression of soils due to the weight of the structure or by surcharging following the placement of fill.

3B.2 ENVIRONMENTAL SETTING

3B.2.1 General Site Conditions

The majority of the site has been disturbed by construction activities. Grading for and construction of the structures on the project site was initiated in July 1997, and work on different portions of the site was generally ongoing until work on the then proposed Belmont Learning Center was stopped in January 2000. The Triple Gym, Administrative Center, and Academy House Nos.1 through 4, and a parking structure (all located on the southern portion of the project site) are partially complete. In addition, overall rough grading of the site was about 80 percent complete when work was stopped. Construction activities contoured the site into a series of terraces separated by steep slopes in the middle of the property and at the northern property boundary. The site varies in elevation from approximately 321 feet above mean sea level (amsl) at 1st Street and Beaudry Avenue to 429 feet amsl near the corner of Toluca Street and Colton Street. In undeveloped areas, the surface of the site consists of fill materials generated by the grading and excavation of the site during construction and exposed bedrock consisting of thinly bedded siltstones, sandstones, and claystones.

3B.2.2 Geologic Setting

The project site is located within the southern portion of the Elysian Park Hills, which form the northern portion of the Peninsular Ranges geomorphic province. The Peninsular Ranges province is bounded by the Santa Monica, Raymond, Sierra Madre, and Cucamonga fault zones on the north, the San Jacinto fault zone on the east, the Pacific Ocean coastline on the

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west, and the Mexican border on the south. The province is characterized by elongate northwest-trending mountain ridges separated by straight-sided sediment- filled valleys. The northwest trend is further reflected in the direction of the dominant geologic structural features of the province that are northwest to west-northwest trending folds and faults, such as the nearby Newport-Inglewood fault zone, located approximately 7.2 miles southwest of the project site.24

Figure 3B-1 on page 3-28 illustrates the local geologic materials and features of the project site and its vicinity. Based on previous field investigation and a review of available literature, the on-site geological materials include artificial fill, alluvium, terrace deposits, and sedimentary bedrock units of the Miocene age Puente Formation.

3B.2.3 Faults and Seismically Induced Ground Shaking

Plate Tectonics and Earthquakes in Southern California

In the tens of millions of years that southern California has straddled the boundary of two of Earth’s greatest tectonic plates, it has been fragmented by a myriad of faults. Most of these faults are no longer active and lie embedded and lifeless within the crust. However, many are active and still aid in the inexorable shifting of the North American and Pacific plates past each other. The boundary between these plates is not a narrow, singular fault but, rather, a wide zone of faults that encompasses all of coastal southern California.

Faults are characterized as active, potentially active, or inactive based on the date of last movement. Active faults are defined by the Alquist-Priolo Earthquake Fault Zoning Act (formerly known as the Alquist-Priolo Special Studies Zones Act of 1972) as faults with evidence of surface rupture (displacement) within Holocene time (i.e., within the last 11,000 years). Potentially active faults have evidence of displacement within Pleistocene time (i.e., between 11,000 and 1.6 million years ago), whereas inactive faults do not display evidence of either Holocene or Pleistocene displacement.

The principal active faults of the metropolitan region are shown in Figure 3B-2 on page 3-29. The greatest of these is the San Andreas Fault, approximately 35 miles (55 kilometers) northwest of downtown Los Angeles, on the other side of the San Gabriel Mountains. Several other important active faults lie closer to and even within the populated area of greater Los Angeles. These include the Sierra Madre fault zone, which runs through parts of Altadena and other foothills communities, the Raymond Fault in San Marino, and the Hollywood and Santa Monica Faults along the southern edge of the Hollywood Hills and Santa Monica 24 Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, April 16,

1997.

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Mountains. The Santa Monica-Hollywood fault system, which is located approximately 3.5 miles northwest of the site, is the closest active fault to the project site.

These and other active faults are the sources of damaging earthquakes. For example, the 1971 and 1994 San Fernando and Northridge earthquakes were caused by rupture of two active faults in the northern San Fernando Valley (the red-shaded patches in Figure 3B-2 show the projection of these subsurface fault planes onto the surface). The sudden snapping of these faults produced these two earthquakes, which caused damage at distances up to tens of miles from the faults themselves. The potential for seismic shaking has long been taken into account in the design of buildings in southern California. With each significant earthquake come improvements in understanding how to increase the resistance of structures to damage from shaking.

In 1997, Law/Crandall estimated site-specific peak ground acceleration based on the Upper Bound Earthquake having a 10 percent probability of exceedance during a 100-year time period. The peak ground acceleration, which was estimated by a Probabilistic Seismic Hazard Analysis (PSHA) was estimated to be 0.65g (acceleration of gravity). The PSHA characterized the seismic shaking hazard at the site according to the guidelines outlined in California Geologic Survey (CGS) Note 48. According to URS in 2003, because the groundshaking hazard at the site is dominated by the Elysian Park Thrust, which was assigned a distance of zero kilometers from the site, the recent assumption suggesting that an active fault may exist at the site would not appreciably influence the results of this ground motion evaluation. As such, URS concluded that the PSHA adequately characterized the groundshaking hazard at the site in compliance with accepted professional engineering geologic and geotechnical engineering principles and practices in southern California.25

Fault Rupture at Ground Surface

Faults that intersect the ground surface also have the potential to damage man-made structures directly, by rupture of the ground upon which a structure sits. For example, dozens of homes were damaged when the San Fernando Fault broke beneath them in 1971. This localized but severe damage led to the enactment of the Alquist-Priolo Special Studies Zone Act of 1972 (renamed in 1994 the Alquist-Priolo Earthquake Fault Zoning Act).26 These laws provided for the State Geologist to identify the most important active faults in the State and to create special 25 URS Corporation, Updated Geohazards Evaluation, Belmont Learning Center, Los Angeles, California,

August 5, 2002; Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, First Street and Beaudry Avenue, Los Angeles, California April 16, 1997.

26 Hart, E.W. and Bryant, W.A., Fault Rupture Hazard Zones in California, 1997; California Geological Survey, Special Publication 42: Alquist-Priolo Earthquake Fault Zoning Act with Index to Earthquake Fault Zones Maps, 1999.

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study zones around them. The Act defines an active fault as one that has ruptured the surface of the ground in the past 11,000 years. Under the Act, geologic studies are to be undertaken by landowners prior to certain types of new development. Any active faults discovered within the earthquake fault zones cannot be built across, and a prudent setback from these faults is recommended by the engineering geologist. Although the project site is located in the seismically active southern California region, it is not located within a mapped Alquist-Priolo Earthquake Fault Zone.

Despite the designation by the State Geologist of many earthquake fault zones, many active faults remain unzoned. Prominent examples are the Santa Monica and Hollywood Faults, which run irregularly from the coastline through parts of Santa Monica, Brentwood, Westwood, Beverly Hills, West Hollywood, and Los Angeles. Some of these cities (including Los Angeles) are aware of the potential for ground rupture posed by these faults and require special investigations by developers of properties near them.

Blind Thrust Faults of the Elysian Park Fault System

Not all active faults in southern California intersect the ground surface. Those that do not are called “blind” faults.27 The Whittier Narrows earthquake of 1987 was produced by rupture of one of these blind faults beneath the hills of East Los Angeles.28 In Figure 3B-2 on page 3-29, the small red-shaded patch near the northern tip of the Whittier Fault is the projection of this blind fault onto the surface. The movement of this little, 2-mile–by–2-mile patch of fault approximately 10 miles beneath the Earth’s surface alerted scientists 15 years ago to the fact that there are active blind faults beneath much of the metropolitan area. These faults are called “thrust” faults because they slope gently downward and the overlying block moves upward and over the underlying plate.

Since the 1987 earthquake, geologists have learned that this fault is part of a much larger blind thrust system, commonly called the Elysian Park blind thrust system. There are two principal blind thrust faults within this system, the Las Cienegas blind thrust and the Elysian Park blind thrust. The dashed red lines in Figure 3B-2 on page 3-29 show where these faults would intersect the ground surface if they were not blind but continued all the way up to the

27 Stein, R., and Yeats, R.S., Hidden Earthquakes: Scientific American, Volume 260, 1989. 28 Hauksson, E. and Jones, L.M., The 1987 Whittier Narrows Earthquake Sequence in Los Angeles, Southern

California, Seismological and Tectonic Analysis: Journal of Geophysical Research, Volume 94, 1989.

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ground surface.29 This style of faulting has developed in response to the north-south squeezing of the Los Angeles basin.

Like the entire downtown region, the project site sits atop the active Elysian Park thrust system. This system is blind as it does not break the ground surface. Figure 3B-2 shows that the sediments above the blind thrusts have been warped and tilted, predominantly southward. The exact geometry of the fault or faults that constitute this “blind” north-dipping fault system is not fully defined, but published scientific papers depict it sloping gently northward and lying a couple miles (about 3 kilometers) beneath the project site. Sudden rupture of one of the two faults in the figure would likely produce shaking in the downtown region similar in intensity and duration to that experienced in the northern San Fernando Valley in 1994. Caltech scientists who studied the fault system several years ago concluded that it is capable of generating earthquakes in the range of magnitude 6.2 to 6.7 about every 500 to 1,300 years.30 Thus, the fault is much smaller and less vigorous than the San Andreas Fault, California’s principal fault, which generates a magnitude 7.9 or so every 130 years, on average.31

The downtown region is situated on top the Elysian Park fault system and is expected to move southward a couple yards (meters) when the fault ruptures miles below. The overriding block of ground also is expected to experience very gentle tilts toward the south during these future earthquakes. In fact, it is the accumulation of these very slight tilts over hundreds, if not thousands, of ancient earthquakes that has led to the southward tilts of the bedrock strata beneath the project site and most of the high-rise downtown district. This folding and southward movement has been going on throughout the past three million years.32

Minor Faults Above the Blind Thrusts

Minor faults are commonplace, but not ubiquitous, in rocks that sit atop such thrust fault systems. In the case of a couple of yards (meters) of slip on the underlying blind thrust, a handful of very minor faults above could be expected to slip small amounts. The most conspicuous of these lesser faults manifests itself at the ground surface as a small 30-foot

29 Dolan, J. et.al., Late Quaternary Activity and Seismic Potential of the Santa Monica Fault System, Los Angeles,

California: Geological Society of America Bulletin, 2000. 30 Oskin, M., et.al., Active Parasitic Folds on the Elysian Park Anticline: Implications for Seismic Hazards in

Central Los Angeles, Geological Society of America Bulletin, 2000. 31 Sieh, K., et.al., A More Precise Chronology of Earthquakes Produced by the San Andreas Fault in Southern

California, Geological Society of America Bulletin, 2000. 32 Schneider, C.L., et.al., Structural Evolution of the Northern Los Angeles Basin, California, Tectonics, 1996;

Davis, T.L., et.al., A Cross-Section of the Los Angeles Area: Seismically Active Fold and Thrust, the 1987 Whittier Narrows Earthquake, and Earthquake Hazard: Journal of Geophysical Research, 1989.

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(10-meter) high wrinkle in the ground south of the high-rise district. Comprehensive studies of the escarpment for the Metropolitan Transit Authority’s Red Line concluded that this very minor structure produces 20- to 32-inch (50 to 80-cm) high ruptures about every 2,800 to 3,900 years, probably in association with seismic rupture of the larger Elysian Park Fault.33

Faults at the Project Site

A comprehensive “Special Studies Zone” trenching investigation was conducted at the project site to verify the absence or presence of faults at the project site and, if present, to determine their character (age and potential for surface rupture). The results of the trenching investigation identified a north-south trending “principle minor fault zone” at the project site that passed beneath the existing Administration Center and Academy House No.1. However, the topography of the project site and surrounding property has a long history of modification associated with previous and existing development. Almost all of the young soil or layers that used to overlie these faults were stripped off during grading either for oil recovery early in the past century or during construction of the BLC project beginning in 1997. Without tracing the faults off-site and excavating undisturbed exposures, the age of the last rupture cannot be determined. In addition, the lack of undisturbed, young soils and sediments in the vicinity of the faults precludes determination of the faults’ classification (i.e., active, potentially active, or inactive). All that can be determined with certainty is that the faults at the project site have ruptured after deposition of the ancient sands, silts, and clays that make up the bedrock beneath the site approximately seven million years ago. Because it was not possible to determine whether the fault zone was active due to the disturbance of overlying soils during construction activities, the fault zone is conservatively considered to be active.

3B.2.4 Liquefaction and Seismic-Related Ground Failures

The project site is not located within an area susceptible to liquefaction, as identified in the Safety Element of the Los Angeles City General Plan. However, a small portion of the southeast corner of the site along Beaudry Avenue is within a liquefaction zone as identified by the California Geologic Survey. Due to the scale and general focus of State seismic hazard maps, site-specific studies are necessary as a basis for an accurate determination of the potential for on-site liquefaction. Site-specific studies conducted for the project site by Law/Crandall in 1997 and by URS in 2002 indicate that the site is underlain primarily by interbedded siltstones and sandstones of the Puente Formation that are not prone to liquefaction. Furthermore, the alluvial materials in the area of the site located within the liquefaction zone have been removed,

33 Earth Consultants International, Coyote Pass Escarpment Study, Eastside Light Rail Transit Project, 2001.

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and all buildings are founded on either bedrock or engineered fill.34 Therefore, based on these previous studies and actions taken prior to development in the southeast corner of the site, the potential for liquefaction beneath the site is considered to be low.

The project site is partially located within the Los Angeles City Oil Field. The extraction of water or petroleum from sedimentary source rocks can cause the permanent collapse of the pore space previously occupied by the extracted fluid. However, an investigation conducted by Law/Crandall in 1997 reported that subsidence has not been identified in the Los Angeles City Oil Field based on personal communication with the California Division of Oil and Gas.35

3B.2.5 Slope Stability

The project site is located within a City of Los Angeles Slope Stability Study Zone. The site has hillside terrain that slopes downward from the northwest to the southeast, with a grade change of approximately 125 feet from the highest portion located near the corner of Colton Street and Toluca Street to the lowest portion located near the corner of 1st Street and Beaudry Avenue. However, there are no known landslides at the site, and the site is not in the path of any known or potential landslide. Furthermore, the project site is not located within a landslide hazard zone as identified by the California Geological Survey. In addition, there have been no known mudflow incidents in or near the project area.

3B.2.6 Expansive Soils

Expansive soils swell when they become wet and shrink when they dry out, resulting in the potential for cracked building foundations and, in some cases, structural distress of the buildings. The geologic materials on-site include artificial fill, alluvium, terrace deposits, and sedimentary bedrock units of the Miocene age Puente Formation. These materials consist of finely grained sandy clay and silty clay that are generally stiff and not expansive. However, on-site residual soils and the siltstone material have a high and medium expansion potential, respectively. These materials will shrink and swell with changes in moisture content. Proper engineering practices were implemented during the construction of the existing buildings on the project site to mitigate the adverse effects of expansive soils (i.e., all foundations for the academy buildings and parking structure were extended into the underlying bedrock, and

34 Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, April 16,

1997. 35 Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, First Street

and Beaudry Avenue, Los Angeles, California, April 16, 1997.

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hardscape areas [i.e., floor slabs and walks] were underlain by at least one foot of non-expansive soils).36

3B.3 APPLICABLE REGULATIONS

3B.3.1 California Education Code

California Education Code Section 17212 requires that a geological and soil engineering study be prepared if the prospective school site is located within the boundaries of any special studies zone or within an area designated as geologically hazardous in the Safety Element of the City of Los Angeles General Plan. The geological and soil engineering studies are to provide an assessment of the nature of the site and the potential for earthquake or other geologic hazard damage. The geological and soil engineering studies of the site shall be of such a nature as will preclude siting of a school in any location where the geological and site characteristics are such that the construction effort required to make the school building safe for occupancy is economically unfeasible.

California Education Code Section 17212.5 requires that geological and soil engineering studies, as described above, be prepared for the construction of any school building or if the estimated cost exceeds twenty thousand dollars ($20,000) for the reconstruction or alteration of or addition to any school building for work which alters structural elements. No school building shall be constructed, reconstructed, or relocated on the trace of a geologic fault along which surface rupture can reasonably be expected to occur within the life of the school building.

3B.3.2 California Code of Regulations (CCR)

Title 5 (Education), Section 14010, Standards for School Site Selection, of the California Code of Regulations (CCR) requires that, pursuant to Education Code Sections 17212 and 17212.5, the site not contain an active earthquake fault or fault trace, and that the site is not subject to moderate to high liquefaction or landslides. Regarding earthquake faults pursuant to Education Code Section 17212, the code section specifically prohibits school buildings (rather than sites) from being located on the trace of a geologic fault along which surface rupture can be reasonably expected to occur within the life of the building.

36 URS Corporation, Updated Geohazards Evaluation, Belmont Learning Center, Los Angeles, California,

August 5, 2002; Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, First Street and Beaudry Avenue, Los Angeles, California, April 16, 1997.

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Title 5, Section 14011, Procedures for Site Acquisition—State-Funded School Districts, of the CCR requires that, in compliance with Education Code Sections 17212 and 17212.5, the geological and soils engineering study address all of the following:

a) the nature of the site, including a discussion of liquefaction, subsidence or expansive soils, slope, stability, dam or flood inundation, and street flooding;

b) whether the site is located within a special study zone, as defined in Education Code Section 17212;

c) the potential for earthquake or other geological hazard damage;

d) whether the site is situated on or near a pressure ridge, geological fault or trace fault that may rupture during the life of the school building and the student risk factor; and

e) the economic feasibility of the construction effort to make the school building safe for occupancy.

Title 24, California Building Code, is assigned to the California Building Standards Commission, which, by law, is responsible for coordinating all building standards. Under state law, all building standards must be centralized in Title 24 or they are not enforceable.37 The California Building Code incorporates by reference the Uniform Building Code (UBC) with necessary California amendments. About one-third of the text within the California Building Code has been tailored for California earthquake conditions.

3B.4 IMPACTS AND MITIGATION

3B.4.1 Methodology

The analysis presented below is based on a number of geotechnical, faulting, and structural investigations prepared for the proposed project, many of which involved field investigations and laboratory testing. The findings in these studies, prepared by experts in the geotechnical and structural engineering fields, are based on review of the project relative to its compliance with applicable geotechnical regulations and requirements.

3B.4.2 Criteria for Determining Significance

The criteria used to determine the significance of an impact are based on the model Environmental Checklist Form in Appendix G of the State CEQA Guidelines.

37 Bolt, Bruce, Earthquakes, W.H. Freeman and Company, 1987, 1993 (3rd Ed.).

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The proposed project may result in significant impacts if it would:

Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving:

• rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substant ial evidence of a known fault;

• strong seismic ground shaking;

• seismic-related ground failure, including liquefaction; or

• landslides.

3B.4.3 Project Impacts

Impact B1: The proposed project could expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving an earthquake fault. This is a less than significant impact.

As indicated above, the nearest known active fault is the Santa Monica-Hollywood fault system, which is located 3.5 miles northwest of the project site. The nearest known active tectonic disruption of the ground surface is the Coyote Pass escarpment, located less than one mile south of the project site. In addition, as previously discussed, a north-south trending “principle minor fault zone” was identified at the project site. This principal minor fault zone passes beneath the existing Administration Center and Academy House No.1. Because it is not possible to determine if this on-site fault system has remained inactive over the past 11,000 years, in an abundance of caution LAUSD is assuming that the fault system is active. Further discussion of the potential impacts associated with this fault zone is presented below.

As indicated in Section 3B.3, Applicable Regulations, Education Code Section 17212 states that “No school building shall be constructed, reconstructed, or relocated on the trace of a geologic fault along which surface rupture can be reasonably expected to occur within the life of the school building.” Because LAUSD is conservatively assuming that the mapped fault zone on the site is active and that surface rupture could occur within the life of the project, no occupied buildings are proposed on the principal minor fault zone or within a 50-foot wide buffer zone on both sides of the fault zone, as shown in Figure 3B-3 on page 3-38. Consequently, the project proposes to demolish the existing Academy House No. 1 structure and the Administration Building, the southeastern portions of which overlay the fault zone and the 50-foot wide buffer zone. In addition, a small portion of the northwestern end of the Academy House No. 2 structure

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may require removal or remain unoccupied by any student or faculty due to its proximity to the fault zone (see Figure 3B-3).

The remaining buildings that currently exist on the project site, including Academy House No. 3, Academy House No. 4, and the Triple Gym, would be completed in accordance with all applicable seismic safety requirements as determined by the Division of the State Architect (DSA) prior to approval of final plans. The DSA’s determination of compliance with applicable seismic safety requirements would include consideration of the structural recommendations provided in the structural evaluation report for the BLC prepared in March 2003.38 In addition, two new structures would be constructed to the west of the fault and the 50-foot buffer zone to replace Academy House No. 1 and to provide for a Shared Facilities Building (see Figure 3B-3). These structures also would be completed in compliance with applicable seismic safety requirements pursuant to DSA review and approval. Almost the entire western portion of the project site, proposed for Vista Hermosa Park, is devoid of faults and fractures. Only limited structural development is proposed within the park. Approximately three structures, with an estimated size of 800 square feet each, are proposed to house restroom facilities and a park headquarters building. These structures are proposed to be located outside of the 50-foot wide buffer zone.

Therefore, with all occupied buildings avoiding the principal minor fault zone and the 50-foot wide buffer zone, the proposed project would not expose people or structures to substantial adverse effects involving an earthquake fault and ground rupture, therefore, impacts would be less than significant.

Mitigation Measures

Since impacts due to fault rupture would be less than significant with demolition of the existing buildings (Administration Building, Academy House No. 1, and a potential portion of Academy House No. 2), and adherence to the proposed seismic safety buffer zone, no mitigation measures are necessary.

Residual Impacts

Impacts would be less than significant.

38 Nabih Youssef & Associates, Structural Engineers, Structural Evaluation of the Belmont Learning Complex,

March 18, 2003.

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Impact B2: The proposed project could expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving strong seismic ground shaking. This is a potentially significant impact.

The principal seismic hazard at the project site is strong ground shaking from earthquakes produced by local faults. Modern, well-constructed buildings are designed to resist ground shaking through the use of shear panels and reinforcement. Additional precautions may be taken to protect personal property and reduce the chance of injury, including securing furniture. Similar to development throughout southern California, implementation of the proposed project would expose people on-site to seismic risk associated with ground shaking. However, with regard to potential impacts from seismic ground shaking, all structures on-site would be constructed or completed in accordance with the State’s Uniform Building Code (UBC) and State’s seismic safety standards. The Division of the State Architect would ensure compliance with applicable seismic safety standards prior to their approval of final architectural plans. Furthermore, the gas mitigation and monitoring systems described in Section 3C., Hazards and Hazardous Materials, shall be designed with consideration for seismic safety. These systems will be subject to review and approval of the Department of Toxic Substances Control. Therefore, with implementation of the mitigation measures listed below the project would not cause or accelerate geologic hazards associated with ground shaking.

Mitigation Measures

B-2(a) LAUSD shall secure a licensed architect to design all new buildings in accordance with the California Uniform Building Code and review the existing buildings and facilities to ensure compliance with the California Uniform Building Code. The final design of the new buildings and review of the existing buildings shall be submitted to the Division of the State Architect for approval.

B-2(b) LAUSD shall secure a registered engineering geologist to prepare a geotechnical report which will provide recommendations to the architect for final design and site development. Said report shall be completed to the satisfaction of the Division of the State Architect prior to approval of final design.

Residual Impacts

With implementation of the proposed mitigation measures impacts associated with groundshaking would be less than significant.

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Impact B3: The proposed project could expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving seismic-related ground failure, including liquefaction. This is a less than significant impact.

With regard to seismic-related ground failures, the project site has been determined to have low susceptibility to liquefaction. Furthermore, as previously indicated, the alluvial materials in the area of the site located within a designated liquefaction zone have been removed, and all buildings are founded on either bedrock or engineered fill. Therefore, the proposed project would not expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving seismic-related ground failure, including liquefaction. As such, it is not expected that the proposed project would be exposed to significant impacts from liquefaction.

As discussed in the setting section above, subsidence has not been identified in the Los Angeles City Oil Field, in which the project site is partially located. However, in the event that future subsidence should occur, it would most likely spread over a relatively wide area and in such small magnitude that significant differential settlement is not a potential hazard, minimizing the potential impact to the project.39 As such, potential impacts associated with subsidence are considered less than significant.

Mitigation Measures

No mitigation measures are required.

Residual Impacts

Impacts related to seismic-related ground failure, including liquefaction and subsidence, would be less than significant.

39 Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, April 16,

1997.

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Impact B4: Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving landslides. This is a less than significant impact.

As previously indicated, there are no known landslides at the site, and the site is not in the path of any known or potential landslide. Furthermore, the project site is not located within a landslide hazard zone as identified by the California Geological Survey.

Slope stability analyses and design and construction recommendations for site improvements were addressed in design reports prepared by Law/Crandall in 1996 and 1997.40 Adverse conditions noted in the reports included daylighted bedding components in the bedrock configuration with respect to the final slope geometry. Law/Crandall recommended increased engineering criteria for retaining walls and low angle (2:1 horizontal to vertical) buttressed fill-slopes. Back drains are to be installed behind fill buttresses and walls to relieve potential increased hydrostatic pressure. Consequently, Law/Crandall determined that a sufficient factor of safety was present under the designed final slope conditions. Although the potential for landsliding is low, the need for any modified requirements for retaining walls will be defined in a geotechnical report, as required by Mitigation Measure B-2(b).

Therefore, given the low potential for landslides and engineering requirements to be set forth in a geotechnical report, impacts from landslides are considered less than significant.

Mitigation Measures

No mitigation measures are required.

Residual Impacts

Impacts regarding landslides would be less than significant.

3B.5 CUMULATIVE IMPACTS

Geology and soils impacts are site-specific and are typically addressed and mitigated to acceptable levels on a case-by-case and site-by-site basis. More specifically, impacts associated 40 Law/Crandall, Report of Geotechnical Investigation, Proposed Belmont Learning Complex, First Street and

Beaudry Avenue, Los Angeles, California, October 29, 1996; Law/Crandall, Revised Report of Geotechnical Investigation, Proposed Belmont Learning Center, First Street and Beaudry Avenue, Los Angeles, California, April 16, 1997.

3B. Geology/Soils


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with geologic and seismic issues are typically confined to a project site or within a very localized area and do not affect off-site areas associated with related projects or ambient growth. Cumulative development in the area would, however, increase the overall potential for exposure to seismic hazards by potentially increasing the number of people exposed to seismic hazards. However, all projects are subject to established guidelines and regulations pertaining to seismic hazards. As such, adherence to applicable building regulations and standard engineering practices would ensure that cumulative impacts would be less than significant. Therefore, no cumulative impacts are expected to occur from project implementation.

3.B. Geology Soils - laschools.org · Mudflows and landslides are the downslope movement of soil and/or rock under the influence of gravity. ... thickness of soil ... downward movement

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