EARTHQUAKE HAZARD ALONG THE WASATCH FRONT
Question 1 – What potential problems do I see in terms of the spatial distribution of hospitals, police
stations and fire station in Salt Lake County compared to the fault lines and potential liquefaction zones?
How about transportation networks? How would that affect emergency response crews?
After reading the material provided and speaking with the local fire, police departments and local hospitals
in my area, I have arrived at the following conclusions. There is a plan in place regarding the instance of
earthquake that takes into account the location of all emergency facilities and locations. There are
hospitals, police and other emergency centers such as IHC insta-care facilities spaced appropriately through
the valley in Salt Lake County. The Wasatch Fault, which is the fault in my area (Holladay) is
approximately 240 miles long and runs from southern Idaho, through northern Utah near the area where I
live and ends in central Utah. To give some background to the Wasatch Fault, the fault is made up of
several segments, each about 20 to 25 miles long, and it is possible for each of the sections to
independently produce earthquakes as powerful as local magnitude 7.5 which is something I never knew
and is to say the least, a little disturbing. The Wasatch Fault is a vertical motion fault which forms the
eastern boundary of the Basin and Range geologic province which comprises the geographic Great Basin.
To explain the Basin and Range, this province is characterized by abrupt changes in elevation, alternating
between narrow faulted mountain chains and flat valleys. The region covers most of the western United
States and extends into northwestern Mexico and is mostly dry desert. The geo system of the province is
the result of tectonic extensions that began around 17 million years ago in Early Miocene time. The
Wasatch Mountains have been uplifted and tilted to the east by movement of the fault. The average rate of
uplift along the Wasatch fault is approximately 1 mm per year. There are indications that more rapid slip
has occurred in the past few thousand years. The fault does not continually slowly slip; instead, it remains
locked for hundreds to thousands of years until approximately 1 to 4 meters of slip occurs rapidly,
producing a strong earthquake. An area hundreds of feet wide can be affected, called the zone of
deformation, which occurs chiefly on the downthrown side of the main fault and can cause multiple minor
faults, cracks, local tilting, and down dropped blocks between faults. Buildings in the zone of deformation
would be damaged, particularly those straddling the main fault. Also, anything crossing the fault, such as
highways, transportation corridors, utilities, and other lifelines, both underground and above ground, can be
damaged or broken. The ground can be dropped below the water table on the down-dropped side, resulting
in local flooding. Surface fault rupture can also cause tectonic plate movement, which is the broad,
permanent tilting of the valley floor down toward the fault scarp. Tilting can cause flooding along lake and
reservoir shorelines nearest the fault; along altered stream courses; and along canals, sewer lines, or other
gravity-flow systems where slope gradients are lessened or reversed.
Due to the location of the Wasatch Fault line and the location of emergency venues, there is no real way to
predict what could or would happen. There are plans and procedures in place with alternate routes
available. Additionally, the highways run west of the fault in my area. There are several highways, 201, I
215, I 15 as well as side streets that could be affected were a major earthquake to occur. There are plans in
place to take alternate routes if one or another were broken down or destroyed. Again, emergency services
are equipped to deal with problems of that nature. The problems I see would be electricity to hospitals and
the need for plenty of generators. I see problems with communication between the emergency services
using cell phones, electronic devices and GPS sources for vehicles, etc. I believe the transportation would
simply be whatever was not damaged and extensive maps and route systems would be available if
communication lines were available.
Question 2 – How close (in miles) do I live, work or go to school near a fault line and what liquefaction
zone am I in? What potential hazards might I expect during or following an earthquake along the Wasatch
Front.
I live in Holladay, Utah. I am literally within a few miles of the Wasatch Fault area. However, per the
attached Liquefaction Potential Map I have attached at the bottom of this page, I am within the “very low”
liquefaction zone in Salt Lake County. If I lived closer to the Jordan River I would be in a much more
serious circumstance.
Soil liquefaction describes a phenomenon whereby a saturated earth it’s strength and stiffness due to an
applied stress or event, usually an earthquake, shaking or other sudden change in stress condition, causing it
to behave like a liquid. In soil mechanics, the term "liquefied" was first used by Hazen in reference to the
1918 failure of the Calaveras Dam in California. He described the mechanism of flow liquefaction of the
embankment dam as follows: If the pressure of the water in the pores is great enough to carry all the load,
it will have the effect of holding the particles apart and of producing a condition that is practically
equivalent to that of quicksand; the initial movement of some part of the material might result in
accumulating pressure, first on one point, and then on another, successively, as the early points of
concentration were liquefied. This event is most often observed in saturated, loose, low density or un
compacted sandy soils. Utah has soil that is of this consistency. Loose sand has a tendency to compress
when a load of some sort is applied; dense sands by contrast tend to expand in volume. If the soil is
saturated by water, as exists when the soil is below the ground water table or sea level, then water fills the
gaps between soil grains. In response to the soil compressing, this water increases in pressure and attempts
to flow out from the soil to zones of low pressure or upward towards the ground surface. However, if the
loading is rapidly applied and large enough, or is repeated many times as in earthquake shaking, such that it
does not flow out in time before the next cycle of pressure is applied, the water pressures may build to an
extent where they exceed the contact stresses between the grains of soil that keep them in contact with each
other. These contacts between grains are the means by which the weight from buildings and overlying soil
layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil
structure causes it to lose all of its solidity and it may be observed to flow like a liquid - hence
'liquefaction'.
Utah is certainly in the running for liquefaction to occur. The building codes in many developed countries
require engineers to consider the effects of soil liquefaction in the design of new buildings and
infrastructure such as bridges, embankment dams and retaining structures. If an earthquake were to occur
along the Wasatch Front there would certainly be slipping possible in the mountainous area. The pictures I
attached on my e-portfolio site, in my area of interest have already experienced some movement over the
years.
The hazards to be expected would be gas leaks, power outages, destruction of roads and transportation
venues as outlined previously in the above paragraph. Injuries, deaths and a lot of fear would also be
expected. The best preparation, should a major earthquake occur in the Salt Lake area would be to be
prepared in advance. Always have enough supplies to last ones family for 3 days. Keep radios tuned in for
any local information assuming radio stations are able to operate. Stay in contact with churches, schools as
well as the emergency venues to be certain to receive current and updated information. And always just be
calm. There are emergency plans out there that have been prepared and are constantly updated by the Red
Cross, hospitals, police departments and fire stations. Certainly the best preparation for any disaster is to
just be aware of potential hazards and do your best to protect yourself and help those around you in any
emergency event.
In conclusion, I hope there is not a major earthquake along the Wasatch Fault in my area. If there is, I feel
confident that the emergency departments have things in line, the Salt Lake Chapter of the Red Cross and
FEMA will be able to handle the emergencies that arise here. Additionally, I am prepared for my 3 days in
the event of a disaster.