SALT LAKE COUNTY PUBLIC WORKS DEPARTMENT
PLANNING AND DEVELOPMENT SERVICES DIVISION
COUNTY GEOLOGIST
2001 South State Street #N3600
Salt Lake City, UT 84190-4050
(801) 468-2070
Geologic Hazards Ordinance - Chapter 19.75 Appendix B
LIQUEFACTION : 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
This pamphlet was prepared to help answer some of the common
questions about liquefaction and Salt Lake County’s Geologic Hazards
Ordinance as well as provide a guide to performing liquefaction analyses
in 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 term
liquefaction refers to the physical change that occurs when certain soils are
shaken and transformed from solid ground capable of supporting a
structure to a quicksand-like liquid with a greatly reduced ability to bear the
weight 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 are
transferred through the foundation into underlying soils. If you were to
closely examine soil in the ground, you would see it is composed of many
sediment particles which form a framework of grains in contact with one
another 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 undergoes
oscillatory straining (shaking) which can cause the individual soil particles
to shift into a tighter framework. If the space between the grains is filled
with groundwater, as the particles readjust into a closer “packing”
arrangement, the pressure in the pores between the grains is increased. If
the pore pressure increases enough and the water cannot easily drain away,
gravity loads are transferred from the sediment framework to the pore
water. This process of sediment losing load carrying ability to the pore
water is called liquefaction. Liquefaction results in a greatly diminished
capacity for the ground to support the weight of overlying structures. In
dry, 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 the
intensity and duration of shaking needed to cause liquefaction-induced
damage in areas with susceptible soils.
Because liquefaction occurs beneath the ground surface, there is often
no apparent evidence to indicate where liquefaction has occurred in the
past. Sometimes construction excavations will reveal disturbed, convoluted
sedimentary layers that suggest prehistoric earthquake-induced
liquefaction. In some cases, surficial evidence of liquefaction will appear in
the form of sand boils (or sand volcanoes), ground settlement, and fissures
(FIGURE 1). These surface features are not always created during
liquefaction, and when formed, they can be quite easily eroded and seldom
preserved. Therefore their absence from a site does not indicate that
liquefaction has not occurred in the past.
FIGURE 1 - Sand “boils” formed during the 1934 magnitude 6.6 Hansel Valley earthquake
(courtesy University of Utah Marriott Library Special Collections.
LIQUEFACTION ON THE BEACH
You 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 body
weight represents the weight of a building, with the sand’s sediment
framework supporting you. As a wave comes in it will saturate the sand,
filling the pore spaces between sand grains with water. If you rapidly shift
your weight from one foot to the other, simulating seismic waves, you can
pressurize 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 LIQUEFACTION
Three 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. For
liquefaction to occur, all three factors must be present at the same time; for
example, neither a loosely compacted, dry sand, or a saturated, densely
compacted sand would be prone to liquefaction because one of the three
critical liquefaction elements is missing.
The Liquefaction Potential Map for Salt Lake County shows that the
most liquefaction-prone areas (the High and Moderate areas) are located
along the valley floor, tributary stream channels, and near the Great Salt
Lake. Soils in foothill areas are generally less susceptible to liquefaction
because they are coarser, and not saturated by shallow groundwater.
LIQUEFACTION: A GUIDE TO LAND USE PLANNING
SALT LAKE COUNTY, UTAH
PAGE 2
Ground Water - Sediments must be saturated with ground water in order to
liquefy during an earthquake. A shallow “perched” water table will
contribute to liquefaction conditions and should not be disregarded or
confused with deeper water levels recorded in culinary water well logs.
Fluctuations in the shallow ground water level will also affect liquefaction
conditions. Seasonal or cyclical “wet” periods often cause ground water
levels to rise, saturating shallower sediments, and perhaps increasing the
liquefaction potential in an area.
Grain Size - The size of the sediment particles controls the size of the pore
spaces. This is critical in clay and fine silt grains (those less than 1/32 of an
inch in diameter) because, although water can fill the small pore spaces, the
flow of water between pores becomes so restricted that liquefaction becomes
difficult.
Gravel particles (larger than 1/5 of an inch in diameter) pose a different
situation. Due to the much larger mass of the grains and generally higher
porosity, the great intensity and duration of ground shaking that is required
to induce liquefaction rarely occurs, except in the largest earthquakes.
Generally, only sands and coarse silts combine the optimum grain mass
and pore-space geometry to liquefy, given the intensity of shaking expected
in a moderate to large Wasatch Front earthquake. The sands and silts must
also be relatively “clean” for liquefaction to occur. This means that
liquefaction is most likely to occur in sands and coarse silts with a uniform
grain size. A clayey-sand, for example, would have a reduced liquefaction
potential because the clay-sized particles fit between the sand grains,
“tightening” up the framework and increasing soil cohesion.
FIGURE 2 - Tilting and settlement of apartment buildings due to soil bearing capacity
failure during the 1964 magnitude 7.5 Niigana, Japan earthquake (Photo by G.W.
Housner).
Soil Density - Loose compaction of the soil also contributes to the
liquefaction potential. The more densely the grains are compacted in the
framework, the greater the earthquake-shaking intensity, or acceleration,
needed to raise pore pressures enough to shift the grains. It is unlikely that
a typical Wasatch Front earthquake could provide sufficient shaking to
induce 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 their
density. Historically, liquefaction has been observed mainly in sediments
less than 45 feet below the ground surface.
WHY IS LIQUEFACTION A CONCERN ?
Liquefaction poses a real, identifiable hazard to structures built on the
ground or buried beneath the surface. Damage to buildings caused by
liquefaction can result in structural collapse and loss of life or injuries.
Loss of the soil’s capacity to support the weight of a structure can have
disastrous effects. This type of ground failure, generally termed a bearing
capacity failure, could result in differential subsidence, where parts of the
building might sink, tilting the building severely to one side, and breaking
it into segments or presenting a threat of structural collapse. In the case of
buried structures (a fuel tank or utility pipeline, for example), the structure
may either float or sink depending on its relative buoyancy compared to the
surrounding liquified material (FIGURES 2 and 3).
Another type of liquefaction ground failure results in a lateral spread
landslide. If a structure is built near a steep embankment, or even gently
sloping ground, and sediments beneath the building liquefy, the building
and surrounding ground could slide downslope in shallow landslide blocks
(FIGURES 4 and 5). Sliding and rotational movement of the landslide blocks
can break a building into pieces and also cause structural collapse. Lateralspread landslides can occur on slopes with grades as gentle as one-half of
one percent, but are rare on slopes greater than 5 percent
Liquefaction-induced structural damage is more likely to occur in
buildings that place heavy loads on their foundations (high rise office or
apartment buildings), or buried structures with significant density contrasts
from sediments in which they are buried (utilities). Buildings with only
lightly loaded foundations- like a single-family home, or those that spread
the load over a larger area, are less susceptible to damage.
FIGURE 3 - Liquefaction and loss of bearing strength in soil can cause large buildings to
tilt as happened in Niigata, Japan in 1964. Drawing from Youd (1984).
The damaging effects of liquefaction were dramatically displayed
during the October 17, 1989 Loma Prieta earthquake. This magnitude 7.1
event triggered soil liquefaction over a wide area, but particularly in the
Marina district of San Francisco about 50 miles from the epicenter (FIGURE
6). Many buildings were damaged or destroyed due to foundation failure
and thousands of homes were left without gas or water when buried utility
lines ruptured due to liquefaction-induced lateral spreading. Natural gas
from ruptured gas lines ignited and consumed a block-wide area. Firefighting 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, for
example) should understand the liquefaction potential of any property. The
well-informed real estate buyer can obtain this data before making a
purchase decision. Owners of existing property may want to consider
liquefaction potential when building, remodeling, or selling property.
LIQUEFACTION: A GUIDE TO LAND USE PLANNING
SALT LAKE COUNTY, UTAH
PAGE 3
FIGURE 4 - This wrecked Anchorage, Alaska school building
demonstrates the type of damage caused by liquefaction induced lateral
spread landslides (1964 magnitude 8.6 “Good Friday” earthquake).
FIGURE 6 - Three story building damaged because of liquefaction during 1989 magnitude
7.1 Loma Prieta earthquake. What is seen is the third story.
Although it is impossible to predict the date or location of the next
earthquake along the Wasatch Fault, geologic evidence has shown that the
liquefaction threat along the Wasatch Front is significant. Thus, a prudent
strategy is to assume that an earthquake may occur at any time, and to be
prepared by understanding the risks involved and building accordingly.
FIGURE 5 - Diagram illustrating a lateral spread landslide. Arrows indicate direction of
flow. Drawing modified from Youd (1984).
Buildings located in a High or Moderate Liquefaction Potential area are
not certain to be damaged during an earthquake, because the liquefaction
potential map is based on generalized geological conditions and does not
consider the type or quality of building construction. A well designed, well
constructed building in a liquefaction prone area may suffer much less
damage than an inadequately designed or poorly constructed building
located over non-liquefiable soils. This is because not all sediments in the
valley floor are likely to liquefy and the lateral accelerations from
earthquake ground shaking affect buildings everywhere, regardless of the
liquefaction potential area. In general, unreinforced masonry structures are
considered 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 liquefaction
occurrence is directly related to the frequency of earthquakes. The Wasatch
Fault has not experienced a major earthquake since the first settlers began
keeping records in about 1847. Looking farther back in time, geologic
studies of the Wasatch Fault Zone have found that the last major earthquake
occurred about 1,300 (+200) years ago, with an average time interval
between large, surface fault rupturing earthquakes (magnitude 6.5-7.5) of
about 1,350 years (±200 years; Black and others, 1992l). This data suggests
that we are within the time frame where we should anticipate a major
earthquake at any time.
Liquefaction can also result from moderate-sized earthquakes
(magnitude 5.0 or greater), which have a much higher probability of
occurring. In addition to the Wasatch Fault, many other potential
earthquake sources exist throughout Utah and Idaho (central Intermountain
Seismic Belt) that are capable of generating moderate earthquakes. The
average return interval for a magnitude 5.0 or greater earthquake
somewhere in the Wasatch Front region is 10 years.
THE LIQUEFACTION POTENTIAL MAP - SALT LAKE COUNTY
For 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 information
about what could be done to help reduce the hazards. The U.S. Geological
Survey recognized this problem, and in the early 1980's funded a period of
intense geological research along the Wasatch Front as part of the National
Earthquake Hazards Reduction Program (NEHRP).
One NEHRP product was the Liquefaction Potential Special Study Area
Map (Salt Lake County, 1989) prepared by Anderson and others (1986). This
liquefaction study looked at subsurface soil conditions from previous
building site investigations and supplementary exploratory drill holes and
computed levels of ground shaking needed to induce liquefaction in
susceptible soils under existing conditions. The amount of shaking that
would cause liquefaction was termed the critical acceleration. The
liquefaction potential at each location was then classified as high, moderate,
low, or very low based on the probability that the needed critical
acceleration would occur in a 100 year period (TABLE 1). Sample sites
having similar liquefaction potential ratings were grouped together to
create the Liquefaction Potential Special Study Area Map for Salt Lake
County. This map is published by, and available through, Salt Lake County
Planning and Development Services Division.
It is important to remember that the Liquefaction Potential Map is based
on a regional-scale investigation of the valley floor and not every parcel in
the county was sampled. Therefore, while the map serves as a good
reference tool for pointing out areas that warrant further investigation prior
to building, the liquefaction potential at a specific site may indeed be
different (higher or lower) than that suggested by the map. The canyons are
not included on the map because of difficulty in characterizing sediments
in mountain areas. Canyon areas are generally assumed to have a low
potential for liquefaction and no special liquefaction studies are typically
required. A site-specific investigation involving soil sampling is the only
definitive method for determining the true liquefaction characteristics of a
site.
LIQUEFACTION: A GUIDE TO LAND USE PLANNING
SALT LAKE COUNTY, UTAH
PAGE 4
TABLE 1 - LIQUEFACTION POTENTIAL RATING SYSTEM
LIQUEFACTION POTENTIAL
APPROXIMATE PROBABILITY
HIGH
> 50 %
MODERATE
10 - 50 %
LOW
5 - 10 %
VERY LOW
<5%
1) Soil Liquefaction Analysis
This report is focused on site-specific soil data and a liquefaction
analysis. The Liquefaction Potential Map is a regional scale map, and it is
possible that the actual liquefaction potential at a particular project site may
be different than that depicted on the map. A site-specific liquefaction
assessment, performed by a geotechnical engineer or engineering geologist,
will address the actual liquefaction potential of the soils at the site. If a
geotechnical soils and foundation report is prepared for the project, the
liquefaction analysis is usually included with the geotechnical report.
REQUIREMENTS FOR DEVELOPMENT
In May 1999, the Salt Lake County Commissioners approved the
Natural Hazards Ordinance (Chapter 19.75 of the County’s Zoning
Ordinance in response to an increased understanding of the potential for
damage due to geologic hazards, and a realization that there were no
existing development guidelines to help ensure the health and safety of
citizens and their property in geologically sensitive areas. This ordinance
was revised in 2001 as the Geologic Hazards Ordinance, and this document
was incorporated by reference as Appendix B of the ordinance.
Although the liquefaction map covers the entire valley area in Salt Lake
County, the County’s regulations apply only to the unincorporated area.
Liquefaction regulations may vary in incorporated cities. City or county
planning 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 the
land-use/liquefaction potential matrix shown in Table 2.
TABLE 2 - IS A LIQUEFACTION REPORT REQUIRED ?
LIQUEFACTION POTENTIAL AREA
PROPOSED LAND USE
(Type of Facility)
WHAT IS A LIQUEFACTION REPORT ?
Some general guidelines have been developed to aid in the preparation
of the liquefaction report. There are three basic approached that can be used
for the liquefaction study, depending mainly on the type of structure
proposed.
HIGH and
MODERATE
LOW and
VERY LOW
CRITICAL FACILITIES
(As defined in Section 19.75.020)
YES
YES
INDUSTRIAL & COMMERCIAL
BUILDINGS
(1 story and < 5,000 sq. ft.)
NO
NO
RESIDENTIAL SUBDIVISIONS (>9
lots), MULTI-FAMILY RESIDENCES
( 4 or more units/acre) and ALL OTHER
INDUSTRIAL and COMMERCIAL
YES
NO
SINGLE LOTS, RESIDENTIAL
SUBDIVISIONS (<9 lots), and
MULTI-FAMILY DWELLINGS
(Less than 4 units/acre)
NO *
NO
* Although no special study is required, disclosure is required
Most commercial and industrial uses will require studies in high and
moderate liquefaction potential areas. Special studies are also required for
multi-lot subdivisions in moderate and high liquefaction areas. No special
studies are required for single family homes, smaller subdivisions, or light
industrial buildings, however, disclosure of the liquefaction potential by the
property owner is mandated. Because of the importance of ensuring safety
for a critical facility (a hospital, for example) and the recognition that the
map data are regional in scale, liquefaction analysis is required at any
proposed critical facility site.
The preferred method for assessing liquefaction potential follows the
NCEER (1997), which compares the predicted cyclic stress ratio that would
be induced by a given design earthquake (magnitude 7.5 is typically used)
with that required to induce liquefaction. Soil data for this analysis can be
obtained from borings using the standard penetration resistance of the soils.
Borings must penetrate a minimum of 45 feet below final ground surface.
Highest seasonal ground-water levels must be considered.
The
methodology used must be referenced, and liquefaction calculations must
be included in the report.
Additional protocol for liquefaction
investigations is provided in SCEC, 1999.
If liquefaction-prone soils are found, the report must provide estimates
of expected ground settlement, and recommend measures to reduce the
hazard (see “What Can Be done About Liquefaction”). An assessment of the
potential for lateral spread must also be performed for sites potentially at
risk. A stamped letter from the project structural engineer or architect
acknowledging receipt of the report, proposed design measures, and the
expected behavior of the structure during an earthquake with respect to life
safety, is required. Some techniques for liquefaction hazard reduction are
discussed in the next section. A notice disclosing the availability of the
liquefaction report for public review will be required to be completed by the
owner prior to approval.
This type of liquefaction investigation would be warranted for critical
facilities, high occupancy or multi-story commercial or residential
buildings, certain other commercial and industrial structures, and some
large subdivision projects as shown in Table 2.
2) Liquefaction Hazard Reduction
A liquefaction investigation may be waived if liquefaction hazard
reduction measures are to be included in the design and construction of the
structure. This option assumes that liquefaction is likely to occur at the site
and hazard reduction steps will be taken without first confirming the
subsurface conditions. Such an approach would be warranted for some
industrial, commercial, or high-occupancy residential buildings in areas
near where past studies have already shown liquefaction-prone sediments
are present.
A stamped letter from the project structural engineer or architect stating
the proposed design measures and the expected behavior of the structure
during an earthquake with respect to life safety, is required. Some
techniques for liquefaction hazard reduction are discussed in the next
section. A disclosure notice referencing this letter will be required to be
completed by the owner and filed with Salt Lake County prior to approval.
3) Inherent Structural Liquefaction Resistance
The subsurface investigation may be waived if a structural engineer or
architect prepares a signed, stamped statement that special liquefaction
hazard reduction measures do not need to be implemented because of the
type or design of the structure (even though liquefaction-prone sediments
may be present). The letter must explain what hazard reduction measures
are included in the structure, or explain why none should be required. Risk
to the occupants and potential damage to the structure must be addressed,
but the applicant must demonstrate that the life safety of occupants will be
preserved should liquefaction occur. Types of buildings suitable for this
method would be well-connected, low-rise wood frame structures with low
footing and foundation bearing pressures, i.e., single family residences and
some simple, low-occupancy commercial and industrial structures.
Recording a formal disclosure notice referencing this document is required.
LIQUEFACTION: A GUIDE TO LAND USE PLANNING
SALT LAKE COUNTY, UTAH
PAGE 5
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 of
structure and careful cost-benefit analysis. Critical or high-occupancy
structures may warrant more expensive hazard reduction techniques, while
some small, lightweight structures, such as single-family homes, may
possess 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 it
usually isn’t feasible to relocate a project to a site without liquefaction risks.
The liquefaction map is a very useful tool for developers seeking sites
for future development as well as for individual home buyers. The
liquefaction implications of each site, including costs for special studies
and/or hazard reduction measures and individual risk preferences, should
be 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 with
drains or pumps, densification of the soils by dynamic compaction or
vibration, 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 additional
foundation, wall, and roof ties is common. Foundation support
redistributed through the use of piles or caissons which extend through the
liquefiable layers can help reduce liquefaction induced damage. Specially
designed mat foundations have also been used in some buildings in Salt
Lake 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 risk
provided that disclosure is insured for future owners. Single-family homes
are an example. In these cases, the owners may want to consider earthquake
insurance 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 past
damaging geologic events (the September 1991 mudslide in North Ogden
is a good example), property owners were angered because, although
geologic-hazard maps had been prepared and were available, they were not
aware of this information or the potential risks and felt deprived of critical
information needed to make an informed purchase decision.
Salt Lake County’s Geologic Hazards Ordinance requires a formal
disclosure document to be recorded with the legal property description for
all new development in High and Moderate liquefaction areas as part of the
approval process. Disclosure is not retroactive to existing projects approved
prior to enactment of the ordinance. The owners record the completed
Disclosure form, along with the parcel legal description, at the County
Recorders Office, and then return the form to the County Geologist.
ACKNOWLEDGMENT AND DISCLOSURE FORMS
There are two types of “Acknowledgment and Disclosure” forms
(FIGURE 7).
The yellow “Acknowledgment and Disclosure” form is required in cases
when no special liquefaction report is required, such as for new small
subdivisions or single-family homes. This is a simple disclosure which only
informs owners that their parcel is within a Moderate or High liquefaction
area. No special liquefaction report is required because 1) the expense of
preparing a report for only one residence is burdensome, and 2) single
residential units typically have some inherent hazard reduction
characteristics (low foundation bearing weight and resilient wood frame
construction, for example).
FIGURE 7 - Formal disclosure documents are used to notify owners in High and
Moderate Liquefaction Potential areas and to inform of any special study reports
available.
The green “Acknowledgment and Disclosure” form is used in cases
where a liquefaction report addressing the liquefaction potential has been
prepared. This form references the file number in the County Geologist’s
Hazards Library where the site-specific liquefaction report is available for
inspection. Reports submitted to Salt Lake County become public
information 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 automatic negative “red flag”. Indeed, if a liquefaction report has
been completed for a project and concluded either a low liquefaction
potential exists, or recommended hazard reduction techniques, the report
and disclosure should be considered a favorable sign. Many developers
have found the liquefaction report and disclosure a useful marketing tool
to show potential buyers that they have created a safe development.
If a report was not required, however, for example, a single-family
home, the disclosure should not be considered as a negative aspect.
Disclosure is meant to inform owners of a potential for liquefaction, not an
indication that future damage will occur. The design, type, and quality of
building construction must be considered in assessing possible liquefactioninduced damage. Although lightweight, frame dwellings offer some
inherent liquefaction damage resistance, it is impossible to predict the
performance of a building without individual site and structural analysis.
Individual risk preference must play a part in determining what steps
the owner will take in a Moderate or High Liquefaction area. Some may
choose to carry earthquake insurance, others may only feel secure after a
liquefaction report has been done, while still others may be willing to
simply accept the risk and be prepared for possible damage.
DISCLOSURE AND REAL ESTATE SALES
There is no specific statutory requirement in Utah for real estate agents
to formally disclose geologic hazards information to potential buyers, unlike
California where potential hazard areas are disclosed in the earnest money
agreement. A conscientious real estate agent, however, will research and
disclose to buyers the liquefaction potential and any pertinent special
studies available. The Liquefaction Potential Map and other information is
available from the County Geologist.
LIQUEFACTION: A GUIDE TO LAND USE PLANNING
SALT LAKE COUNTY, UTAH
PAGE 6
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 Lake
County a safer place to live, work and play. If you have questions regarding
liquefaction, or other aspects of development and geologic hazards, please
contact us.
REFERENCES
Earthquake Video Programs:
ARABASZ, W. J., PECHMAN, J. C., and BROWN, E. D., 1987, Observational
seismology and the evaluation of earthquake hazards and risk in the
Wasatch Front Area, Utah: U. S. Geological Survey Open-File Report 87-585,
Vol. I, pp. D1-D58.
The Planning and Development Services Division has two excellent video
tapes available for home viewing. If you are interested in borrowing one or
both of these videos please call our office at 468-2000. There is no charge to
check out either program.
Earthquake Awareness and Hazard Mitigation is a 22-minute
introduction to the earthquake hazards we all face living along the Wasatch
Front. This program, jointly produced by Utah State University and the Salt
Lake County Planning Division, describes the types of seismic hazards
found in Salt Lake County and provides ideas about what can be done to
minimize the effects of a major earthquake. This program is very
appropriate to show to larger groups.
Surviving the Big One is a 58-minute program dealing with how to
prepare for a major earthquake. This is a very good program to watch with
your family. The tape was produced by KCET (Los Angeles) and is narrated
by Henry Johnson, a Los Angeles fire fighter and earthquake preparedness
expert. Johnson visits the sites of past major earthquakes from California to
Alaska 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 will
show you how to be prepared !
Other Sources of Earthquake and Preparedness Information
In addition to the Salt Lake County Planning and Development Services
Division, other sources of earthquake hazard and preparedness information
can be obtained from:
Salt Lake County Emergency Services
440 South 300 East
Salt Lake City, Utah 84111
(801) 535-5467
ANDERSON, L. R., KEATON, J. R., SPITZLEY, J. E., and ALLEN, A. C.,
1986, Liquefaction potential map for Salt Lake County, Utah: Utah State
University and Dames and Moore, Final Report for U. S. Geological Survey
Earthquake Hazards Reduction Program, scale 1:48,000.
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 the
Wasatch Fault Zone at the South Fork Dry Creek and Dry Gulch Sites, Salt
Lake County, Utah, Utah Geological Survey Special Study 92.
MACHETTE, M. N., PERSONIUS, S. F., and NELSON, A. R., 1991, The
Wasatch 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 Liquefaction
Resistance of Soils; Youd, T.L., and Idriss, I.M., eds. Technical Report
NCEER 97-0022.
NATIONAL RESEARCH COUNCIL, 1985, Liquefaction of Soils During
Earthquakes: National Academy Press, Washington D. C., 240p.
PLAFKER, George, and GALLOWAY, J. P. (editors), 1989, Lessons Learned
from the Loma Prieta, California Earthquake of October 17, 1989: U. S. Geological
Survey Circular 1045, 48p.
SALT LAKE COUNTY, 1989. Surface Fault Rupture and Liquefaction
Potential 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 Publication
117, Guidelines for Analyzing and Mitigating Liquefaction Hazards in
California, University of Southern California, Los Angeles, California,
March 1999.
Utah Geological Survey
2363 Foothill Boulevard
Salt Lake City, Utah 84109-1491
(801) 467-7970
YOUD, T. L., 1984, Geologic Effects - Liquefaction and Associated Ground
Failure, in Proceedings of the Geologic and Hydrologic Hazards Training
Program: U. S. Geological Survey Open-File Report 84-760, pp. 210-232.
Utah Comprehensive Emergency Management Agency
Room 1110 Sate Office Building
Salt Lake City, Utah 84114
(801) 538-3400
YOUD, T.L., Hansen, C.M., and Bartlett, S.F., 1999, Revised MLR Equations
for Predicting Lateral Spread Displacement, Proceedings, 7th U.S.-Japan
Workshop of Earthquake Resistant Design of Lifeline Facilities and
Countermeasures Against Liquefaction, Seattle, Washington,
Multidisciplinary Center for Earthquake Engineering Research Technical
Report MCEER-99-0019, p. 99-114.
U. S. Geological Survey
Earth Science Information Office
125 South State Street, Room 8105
Salt Lake City, Utah 84138-1177
(801) 524-5652