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Geologic Hazards Ordinance - Chapter 19.75 Appendix BLIQUEFACTION : A GUIDE TO LAND USE PLANNING

By Craig V Nelson; Revised April 2002 by Darlene Batatian

A foolish man ... built his house upon the sand. - Matthew VII. 26

SALT LAKE COUNTY PUBLIC WORKS DEPARTMENTPLANNING AND DEVELOPMENT SERVICES DIVISION

COUNTY GEOLOGIST2001 South State Street #N3600Salt Lake City, UT 84190-4050

(801) 468-2070

This pamphlet was prepared to help answer some of the commonquestions about liquefaction and Salt Lake Countys Geologic HazardsOrdinance as well as provide a guide to performing liquefaction analysesin areas subject to liquefaction hazards.

WHAT IS LIQUEFACTION ?Liquefaction is a common earthquake hazard related to ground shaking

that accompanies earthquakes, typically magnitude 5.0 or greater. The termliquefaction refers to the physical change that occurs when certain soils areshaken and transformed from solid ground capable of supporting astructure to a quicksand-like liquid with a greatly reduced ability to bear theweight of a building.

HOW DOES LIQUEFACTION OCCUR ?Liquefaction occurs when seismic waves generated by a large

earthquake pass through unconsolidated sediments near the ground surface.When a structure is built, the weight of the structure and its contents aretransferred through the foundation into underlying soils. If you were toclosely examine soil in the ground, you would see it is composed of manysediment particles which form a framework of grains in contact with oneanother with a small amount of void space (or pore space) between them,similar to a bucket filled with marbles.

As seismic waves pass through an area, the ground undergoesoscillatory straining (shaking) which can cause the individual soil part iclesto shift into a tighter framework. If the space between the grains is filledwith groundwater, as the particles readjust into a closer packingarrangement, the pressure in the pores between the grains is increased. Ifthe pore pressure increases enough and the water cannot easily drain away,gravity loads are transferred from the sediment framework to the porewater. This process of sediment los ing load carrying ability to the porewater is called liquefaction . Liquefaction results in a greatly diminishedcapacity for the ground to support the weight of overlying structures. Indry, unsaturated sediments where the void spaces are filled with air,liquefaction does not occur because the air in the pore space is easily

compressed and the sediment framework sustains the load.Although any source of strong ground motion, such as an explosion, can

trigger liquefaction, only moderate to large earthquakes generally create theintensity and duration of shaking needed to cause liquefaction-induceddamage in areas with susceptible soils.

Because liquefaction occurs beneath the ground surface, there is oftenno apparent evidence to indicate where liquefaction has occurred in thepast. Sometimes construction excavations will reveal disturbed, convolutedsedimentary layers that suggest prehistoric earthquake-inducedliquefaction. In some cases, surficial evidence of liquefaction will appear inthe form of sand boils (or sand volcanoes), ground settlement, and fissures(FIGURE 1). These surface features are not always created duringliquefaction, and when formed, they can be quite easily eroded and seldompreserved. Therefore their absence from a site does not indicate thatliquefaction has not occurred in the past.

LIQUEFACTION ON THE BEACHYou can experiment with liquefaction the next time you visit a sandy

beach. Find a spot of wet sand within the reach of small waves. Your bodyweight represents the weight of a building, with the sands sedimentframework supporting you. As a wave comes in it will saturate the sand,filling the pore spaces between sand grains with water. If you rapidly shiftyour weight from one foot to the other, simulating seismic waves, you canpressurize the sediments under your foundation. If conditions are right,as you shift your weight you will slowly sink into the sand, because the

liquified sand is no longer capable of supporting your weight.

CONDITIONS FOR LIQUEFACTIONThree critical factors must be present for sediments to be prone to

liquefaction. The sediment must be 1) saturated with ground water, 2)composed of sand or silt-sized particles, and 3) compacted fairly loose. Forliquefaction to occur, all three factors must be present at the same time; forexample, neither a loosely compacted, dry sand, or a saturated, denselycompacted sand would be prone to liquefaction because one of the threecritical liquefaction elements is missing.

The Liquefaction Potential Map for Salt Lake County shows that themost liquefaction-prone areas (the High and Moderate areas) are locatedalong the valley floor, tributary stream channels, and near the Great SaltLake. Soils in foothill areas are generally less susceptible to liquefactionbecause they are coarser, and not saturated by shallow groundwater.

FIGURE 1 - Sand boils formed during the 1934 magnitude 6.6 Hansel Valley earth(courtesy University of Utah Marriott Library Special Collections.


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LIQUEFACTION: A GUIDE TO LAND USE PLANNING SALT LAKE COUNTY, UTAH

FIGURE 2 - Tilting and settlement of apa rtment buildings due to soil bearing cafailure during the 1964 magnitude 7.5 Niigana, Japan earthquake (Photo by GHousner).

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Ground Water - Sediments must be saturated with ground water in order toliquefy during an earthquake. A shallow perched water table willcontribute to liquefaction conditions and should not be disregarded orconfused with deeper water levels recorded in culinary water well logs.Fluctuations in the shallow ground water level will also affect liquefactionconditions. Seasonal or cyclical wet periods often cause ground waterlevels to rise, saturating shallower sediments, and perhaps increasing theliquefaction potential in an area.

Grain Size - The size of the sediment particles controls the size of the porespaces. This is critical in clay and fine silt grains (those less than 1/32 of aninch in diameter) because, although water can fill the small pore spaces, theflow of water between pores becomes so restricted that liquefaction becomesdifficult.

Gravel particles (larger than 1/5 of an inch in diameter) pose a differentsituation. Due to the much larger mass of the grains and generally higherporosity, the great intensity and duration of ground shaking that is requiredto induce liquefaction rarely occurs, except in the largest earthquakes.

Generally, only sands and coarse silts combine the optimum grain massand pore-space geometry to liquefy, given the intensity of shaking expectedin a moderate to large Wasatch Front earthquake. The sands and silts mustalso be relatively clean for liquefac tion to occur. This means thatliquefaction is most likely to occur in sands and coarse silts with a uniformgrain size. A clayey-sand, for example, would have a reduced liquefactionpotential because the clay-sized particles fit between the sand grains,tightening up the framework and increasing soil cohesion.

Soil Density - Loose compaction of the soil also contributes to theliquefaction potential. The more densely the grains are compacted in theframework, the greater the earthquake-shaking intensity, or acceleration,needed to raise pore pressures enough to shift the grains. It is unlikely thata typical Wasatch Front earthquake could provide sufficient shaking toinduce liquefaction in very densely compacted soils.

Soil density generally increases with the age and depth of deposits.Sediments tend to compact over time and with burial, increasing theirdensity. Historically, liquefaction has been observed mainly in sedimentsless than 45 feet below the ground surface.

WHY IS LIQUEFACTION A CONCERN ?Liquefaction poses a real, identifiable hazard to structures built on theground or buried beneath the su rface. Damage to buildings caused byliquefaction can result in structural collapse and loss of life or injuries.

Loss of the soils capaci ty to support the weight of a structure can havedisastrous effects. This type of ground failure, generally termed a bearingcapacity failure, could result in differential subsidence, where parts of thebuilding might sink, tilting the building severely to one side, and breakingit into segments or presenting a threat of structural collapse. In the case ofburied structures (a fuel tank or utility pipeline, for example), the structuremay either float or sink depending on its relative buoyancy compared to thesurrounding liquified material (FIGURES 2 and 3).

Another type of liquefac tion ground failure results in a lateral spreadlandslide. If a structure is built near a steep embankment, or even gentlysloping ground, and sediments beneath the building liquefy, the buildingand surrounding ground could slide downslope in shallow landslide blocks(FIGURES 4 and 5). Sliding and rotational movement of the landslide blockscan break a building into pieces and also cause structural collapse. Lateral-spread landslides can occur on slopes with grades as gentle as one-half ofone percent, but are rare on slopes greater than 5 percent

Liquefaction-induced structural damage is more likely to occur inbuildings that place heavy loads on their foundations (high rise office orapartment buildings), or buried structures with significant density contrastsfrom sediments in which they are buried (utilities). Buildings with onlylightly loaded foundations- like a single-family home, or those that spreadthe load over a larger area, are less susceptible to damage.

The damaging effects of liquefaction were dramatically displayedduring the October 17, 1989 Loma Prieta earthquake. This magnitude 7.1event triggered soil liquefaction over a wide area, but particularly in theMarina district of San Francisco about 50 miles from the epicenter (FIGURE6). Many buildings were damaged or destroyed due to foundation failureand thousands of homes were left wi thout gas or water when buried utilitylines ruptured due to liquefaction-induced lateral spreading. Natural gasfrom ruptured gas lines ignited and consumed a block-wide area. Fire-fighting was hampered because of the disabled water system.

Because of the possibility for injury and structural damage, owners,occupants, and those with financial interests (mortgage holders, forexample) should understand the liquefaction potential of any property. Thewell-informed real estate buyer can obtain this data before making apurchase decision. Owners of existing property may want to considerliquefaction potential when building, remodeling, or selling property.

FIGURE 3 - Liquefaction and loss of bearing strength in soil can cause large buildtilt as happened in Niigata, Japan in 1964. Drawing from Youd (1984).


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FIGURE 5 - Diagram illustrating a lateral spread landslide. Arrows indicate direction of flow. Drawing modified from Youd (1984).

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Buildings located in a High or Moderate Liquefaction Potential area arenot certain to be damaged during an earthquake, because the liquefactionpotential map is based on generalized geological conditions and does notconsider the type or quality of building construction. A well designed, wellconstructed building in a liquefaction prone area may suffer much lessdamage than an inadequately designed or poorly constructed buildinglocated over non-liquefiable soils. This is because not all sediments in thevalley floor are likely to liquefy and the lateral accelerations fromearthquake ground shaking affect buildings everywhere, regardless of theliquefaction potential area. In general, unreinforced masonry structures areconsidered to have the highest risk for earthquake damage.

HOW OFTEN DOES LIQUEFACTION OCCUR ?Liquefaction is caused by ground shaking during moderate to large

earthquakes (magnitude 5 or greater). So the frequency of liquefactionoccurrence is directly related to the frequency of earthquakes. The WasatchFault has not experienced a major earthquake since the first settlers begankeeping records in about 1847. Looking farther back in time, geologicstudies of the Wasatch Fault Zone have found that the last major earthquakeoccurred about 1,300 (+200) years ago, with an average time intervalbetween large, surface fault rupturing earthquakes (magnitude 6.5-7.5) ofabout 1,350 years (200 years; Black and others, 1992l) . This data suggeststhat we are within the time frame where we should anticipate a majorearthquake at any time.

Liquefaction can also result from moderate-sized earthquakes(magnitude 5.0 or greater), which have a much higher probability ofoccurring. In addition to the Wasatch Fault, many other potentialearthquake sources exist throughout Utah and Idaho (central IntermountainSeismic Be lt) that are capable of generating moderate earthquakes. Theaverage return interval for a magnitude 5.0 or greater earthquakesomewhere in the Wasatch Front region is 10 years.

Although it is impossible to predict the date or location of the nextearthquake along the Wasatch Faul t, geologic evidence has shown that theliquefaction threat along the Wasatch Front is significant. Thus, a prudentstrategy is to assume that an earthquake may occur at any time, and to beprepared by understanding the risks involved and building accordingly.

THE LIQUEFACTION POTENTIAL MAP - SALT LAKE COUNTYFor many years earthquake hazards (including liquefaction), although

recognized as possible, were largely ignored in development in Salt Lake

County, perhaps due to a lack of acceptable hazard maps and informationabout what could be done to help reduce the hazards. The U.S. GeologicalSurvey recognized this problem, and in the early 1980's funded a period ofintense geological research along the Wasatch Front as part of the NationalEarthquake Hazards Reduction Program (NEHRP).

One NEHRP product was the Liquefaction Potential Special Study AreaMap (Salt Lake County, 1989) prepared by Anderson and others (1986). Thisliquefaction study looked at subsurface soil conditions from previousbuilding site investigations and supplementary exploratory drill holes andcomputed levels of ground shaking needed to induce liquefaction insusceptible soils under existing condit ions. The amount of shaking thatwould cause liquefaction was termed the critical acceleration. Theliquefaction potential a t each location was then classified as high, moderate,low, or very low based on the probability that the needed criticalaccele ration would occur in a 100 year period (TABLE 1). Sample siteshaving similar liquefaction potential ratings were grouped together tocreate the Liquefaction Potential Special Study Area Map for Salt LakeCounty. This map is published by, and available through, Salt Lake CountyPlanning and Development Services Division.

It is important to remember that the Liquefaction Potential Map is basedon a regional-scale investigation of the valley floor and not every parcel inthe county was sampled. Therefore, while the map serves as a goodreference tool for pointing out areas that warrant further investigation priorto building, the liquefaction potential at a specific site may indeed bedifferent (higher or lower) than that suggested by the map. The canyons arenot included on the map because of difficulty in characterizing sedimentsin mountain areas. Canyon areas are generally assumed to have a lowpotential for liquefaction and no special liquefaction studies are typicallyrequired. A site-specific investigation involving soil sampling is the onlydefinitive method for determining the true liquefaction characteristics of asite.

FIGURE 4 - This wrecked Anchorage, Alaska school buildingdemonstrates the type of damage caused by liquefaction induced lateralspread landslides (1964 magnitude 8.6 Good Friday earthquake).

FIGURE 6 - Three story building damaged because of liquefaction during 1989 mag7.1 Loma Prieta earthquake. What is seen is the third story.


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TABLE 1 - LIQUEFACTION POTENTIAL RATING SYSTEM

LIQUEFACTION POTENTIAL APPROXIMATE PROBABILITY

HIGH > 50 %

MODERATE 10 - 50 %

LOW 5 - 10 %

VERY LOW < 5 %

REQUIREMENTS FOR DEVELOPMENTIn May 1999, the Salt Lake County Commissioners approved the

Natural Hazards Ordinance (Chapter 19.75 of the Countys ZoningOrdinance in response to an increased understanding of the potential fordamage due to geologic hazards, and a realization that there were noexisting development guidelines to help ensure the health and safety ofcitizens and their property in geologically sensitive areas. This ordinancewas revised in 2001 as the Geologic Hazards Ordinance, and this documentwas incorporated by reference as Appendix B of the ordinance.

Although the liquefaction map covers the entire valley area in Salt LakeCounty, the Countys regulations apply only to the unincorporated area.Liquefaction regulations may vary in incorporated cities. City or countyplanning offices can help determine which jurisdiction a parcel falls within.

WHEN IS A LIQUEFACTION STUDY REQUIRED ?The Geologic Hazards Ordinance requires a site-specific liquefaction

investigation to be performed prior to approval of a project based on theland-use/liquefaction potential matrix shown in Table 2.

TABLE 2 - IS A LIQUEFACTION REPORT REQUIRED ?

LIQUEFACTION POTENTIAL AREA

PROPOSED LAND USE(Type of Facility)

HIGH andMODERATE

LOW andVERY LOW

CRITICAL FACILITIES(As defined in Section 19.75.020) YES YES

INDUSTRIAL & COMMERCIALBUILDINGS(1 story and < 5,000 sq. ft.)

NO NO

RESIDENTIAL SUBDIVISIONS (>9lots), MULTI-FAMILY RESIDENCES( 4 or more units/acre) and ALL OTHERINDUSTRIAL and COMMERCIAL

YES NO

SINGLE LOTS, RESIDENTIALSUBDIVISIONS (


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WHAT CAN BE DONE ABOUT LIQUEFACTION ?Several alternatives exist for dealing with liquefaction hazards. The

method of hazard reduction selected usually depends on the type ofstructure and careful cost-benefit analysis. Critical or high-occupancystructures may warrant more expensive hazard reduction techniques, whilesome small, lightweight structures, such as single-family homes, maypossess some inherent structural hazard reduction factors.

1) Avoid liquefaction-prone areas.Perhaps the simplest method of dealing with liquefaction is to locate

new development in areas that do not have liquefiable soils. However,because much of the Salt Lake Valley, including many commercial,industrial, and residential zones fall within High or Moderate areas itusually isnt feasible to relocate a project to a site without liquefaction risks.

The liquefaction map is a very useful tool for developers seeking sitesfor future development as well as for individual home buyers . Theliquefaction implications of each site, including costs for special studiesand/or hazard reduction measures and individual risk preferences, shouldbe part of any parcel purchase decision.

2) Soil mitigation.Problems with liquefaction may be mitigated by altering the site soil

characteristics. Examples include lowering the ground water table withdrains or pumps, densification of the soils by dynamic compaction orvibration, installation of stone columns, and grouting.

3) Structural mitigation.The damaging effects of liquefaction is most frequently reduced using

structural techniques. Strengthening the structure using additionalfoundation, wall, and roof ties is common. Foundation supportredistributed through the use of piles or caissons which extend through theliquefiable layers can help reduce liquefaction induced damage. Speciallydesigned mat foundations have also been used in some buildings in SaltLake County

4) Understand the potential hazard and accept the risk.In some cases, when the risk of damage and injury are low, it may be

acceptable for individual, informed owners to choose to accept the riskprovided that disclosure is insured for future owners. Single-family homesare an example. In these cases, the owners may want to consider earthquakeinsurance to protect their investments and reduce the need for government(taxpayer) assistance following a damaging earthquake event.

WHAT IS A LIQUEFACTION DISCLOSURE ?The purpose of disclosure is to help make liquefaction information

available to the public, particularly potential buyers. After some pastdamaging geologic events (the September 1991 mudslide in North Ogdenis a good example), property owners were angered because, althoughgeologic-hazard maps had been prepared and were available, they were notaware of this information or the potential risks and felt deprived of criticalinformation needed to make an informed purchase decision.

Salt Lake Countys Geologic Hazards Ordinance requires a formaldisclosure document to be recorded with the legal property description forall new development in High and Moderate liquefaction areas as part of theapproval process. Disclosure is not retroactive to existing projects approvedprior to enactment of the ordinance. The owners record the completed

Disclosure form, along with the parcel legal description, at the CountyRecorders Office, and then return the form to the County Geologist.

ACKNOWLEDGMENT AND DISCLOSURE FORMSThere are two types of Acknowledgment and Disclosure forms

(FIGURE 7).

The yellow Acknowledgment and Disclosure form is required in caseswhen no special liquefaction report is required, such as for new smallsubdivisions or single-family homes. This is a simple disclosure which onlyinforms owners that their parcel is within a Moderate or High liquefactionarea. No special liquefaction report is required because 1) the expense ofpreparing a report for only one residence is burdensome, and 2) singleresidential units typically have some inherent hazard reductioncharacteristics (low foundation bearing weight and resilient wood frameconstruction, for example).

The green Acknowledgment and Disclosure form is used in caseswhere a liquefaction report addressing the liquefaction potential has beenprepared. This form references the file number in the County GeologistsHazards Library where the site-specific liquefaction report is available forinspection. Reports submit ted to Salt Lake County become publicinformation and copies of liquefaction reports can be obtained for a nominal

photocopying fee.A liquefaction disclosure attached to a parcel should not be perceived

as an automat ic negative red flag. Indeed, if a liquefaction report hasbeen completed for a project and concluded either a low liquefactionpotential exists, or recommended hazard reduction techniques, the reportand disclosure should be considered a favorable sign. Many developershave found the liquefaction report and disclosure a useful marketing toolto show potential buyers that they have created a safe development.

If a report was not required, however, for example, a single-familyhome, the disclosure should not be considered as a negative aspect.Disclosure is meant to inform owners of a potential for liquefaction, not anindication that future damage will occur. The design, type, and quality ofbuilding construction must be considered in assessing possible liquefaction-induced damage . Although lightweight, frame dwellings offer someinherent liquefaction damage resistance, it is impossible to predict theperformance of a building without individual site and structural analysis.

Individual risk preference must play a part in determining what stepsthe owner will take in a Moderate or High Liquefaction area. Some maychoose to carry earthquake insurance, others may only feel secure after aliquefaction report has been done, while still others may be willing tosimply accept the risk and be prepared for possible damage.

DISCLOSURE AND REAL ESTATE SALESThere is no specific statutory requirement in Utah for real estate agents

to formally disclose geologic hazards information to potential buyers, unlikeCalifornia where potential hazard areas are disclosed in the earnest moneyagreement. A conscientious real estate agent, however, will research anddisclose to buyers the liquefaction potential and any pertinent specialstudies available. The Liquefaction Potential Map and other information isavailable from the County Geologist.

FIGURE 7 - Formal disclosure documents are used to notify owners in High anModerate Liquefaction Potential areas and to inform of any special study repoavailable.


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WHERE CAN I GET MORE INFORMATION ?The Salt Lake County Geologist is dedicated to helping inform county

residents about earthquake and other geologic hazards to make Salt LakeCounty a safer place to live, work and play. If you have questions regardingliquefaction, or other aspects of development and geologic hazards, pleasecontact us.

Earthquake Video Programs:The Planning and Development Services Division has two excellent videotapes available for home viewing. If you are interested in borrowing one orboth of these videos please call our office at 468-2000. There is no charge tocheck out either program.

Earthquake Awareness and Hazard Mitigation is a 22-minuteintroduction to the earthquake hazards we all face l iving along the WasatchFront. This program, jointly produced by Utah State University and the SaltLake County Planning Division, describes the types of seismic hazardsfound in Salt Lake County and provides ideas about what can be done tominimize the effects of a major earthquake. This program is veryappropriate to show to larger groups.

Surviving the Big One is a 58-minute program dealing with how toprepare for a major earthquake. This is a very good program to watch withyour family. The tape was produced by KCET (Los Angeles) and is narratedby Henry Johnson, a Los Angeles fire fighter and earthquake preparednessexpert. Johnson visits the sites of past major earthquakes from California toAlaska and shows how the key to survival is knowing what to do before,during and after a major quake. Our BIG ONE is coming This tape willshow you how to be prepared !

Other Sources of Earthquake and Preparedness InformationIn addition to the Salt Lake County Planning and Development Services

Division, other sources of earthquake hazard and preparedness informationcan be obtained from:

Salt Lake County Emergency Services440 South 300 EastSalt Lake City, Utah 84111(801) 535-5467

Utah Geological Survey2363 Foothill BoulevardSalt Lake City, Utah 84109-1491(801) 467-7970

Utah Comprehensive Emergency Management AgencyRoom 1110 Sate Office BuildingSalt Lake City, Utah 84114(801) 538-3400

U. S. Geological SurveyEarth Science Information Office125 South State Street, Room 8105Salt Lake City, Utah 84138-1177(801) 524-5652

REFERENCES

ANDERSON, L. R., KEATON, J. R., SPITZLEY, J. E., and ALLEN, A. C.,1986, Liquefaction potential map for Salt Lake County, Utah: Utah StateUniversity and Dames and Moore, Final Report for U. S. Geological SurveyEarthquake Hazards Reduction Program, scale 1:48,000.

ARABASZ, W. J., PECHMAN, J. C., and BROWN, E. D., 1987, Observat ionalseismology and the evaluation of earthquake hazards and risk in theWasatch Front Area, Utah: U. S. Geological Survey Open-File Report 87-585,Vol. I, pp. D1-D58.

BLACK, B.D., LUND. WR., SCHWARTZ, D.P., GILL, H.E., AND MAYES,B.H., 1992, Paleoseismic Investigation on the Salt Lake City Segment of theWasatch Fault Zone at the South Fork Dry Creek and Dry Gulch Sites, SaltLake County, Utah, Utah Geological Survey Special Study 92.

MACHETTE, M. N., PERSONIUS, S. F., and NELSON, A. R., 1991, TheWasatch Fault Zone, Utah - segmentation and Holocene earthquakes:

Journal of Structural Geology, Vol.13, No. 2, pp. 137-149.

National Center for Earthquake Engineering Research (NCEER), 1997,Proceedings of the NCEER Workshop on Evaluation of LiquefactionResistance of Soils; Youd, T.L., and Idriss, I.M., eds. Technical ReportNCEER 97-0022.

NATIONAL RESEARCH COUNCIL, 1985, Liquefaction of Soils DurinEarthquakes: National Academy Press, Washington D. C., 240p.

PLAFKER, George, and GALLOWAY, J. P. (editors), 1989, Lessons Learne from the Loma Prieta, California Earthquake of October 17, 1989: U. S. GeologicalSurvey Circular 1045, 48p.

SALT LAKE COUNTY, 1989. Surface Fault Rupture and LiquefactionPotential Special Study Areas, Salt Lake County, Utah, adopted March 31,1989 and revised March 1995 (Map).

SOUTHERN CALIFORNIA EARTHQUAKE CENTER (SCEC) 1999.Recommended Procedures for Implementation of DMG Special Publication117, Guidelines for Analyzing and Mitigating Liquefaction Hazards inCalifornia, University of Southern California, Los Angeles, California,March 1999.

YOUD, T. L., 1984, Geologic Effects - Liquefaction and Associated GroundFailure, in Proceedings of the Geologic and Hydrologic Hazards TrainingProgram: U. S. Geological Survey Open-File Report 84-760, pp. 210-232.

YOUD, T.L., Hansen, C.M., and Bartlett, S.F., 1999, Revised MLR Equationsfor Predicting Lateral Spread Displacement, Proceedings, 7 th U.S.-JapanWorkshop of Earthquake Resistant Design of Lifeline Facilities andCountermeasures Against Liquefaction, Seattle, Washington,Multidisciplinary Center for Earthquake Engineering Research TechnicalReport MCEER-99-0019, p. 99-114.

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