Oct – Dec 2013
the
Wasatch Front – 7.0 Quake
SALT
LAKE CITY — Scientists say Utah's Wasatch Front faces a 1-in-7 chance of being
hit by a magnitude-7.0 earthquake
sometime in the next 50 years. By Lee Davidson, Deseret
News
If it hits
at the worst-possible time — in the middle of a winter night — government
computer models estimate that it could kill about 3,000 people, injure another
42,000, damage more than a third of all buildings and cause at least $35
billion in economic loss.
More than
60,000 people would need public shelter during freezing temperatures. Most
power, water and communications would be out initially, and may not be restored
in some areas for months. Fires could be widespread.
Police and
firefighters would be so overwhelmed that they could not reach many people for
days, so neighbors would need to rely on each other for help.
QUAKE ODDS
"It's
been about 1,300 years — plus or minus 650 — since the Salt Lake City segment (of
the Wasatch fault) had an earthquake of that magnitude," said University
of Utah seismologist Jim Pechman.
He said the
probability of a large quake on the Salt Lake City segment of the Wasatch fault
(one of 10 independent segments of that fault system) is somewhere between
1-in-10 to 1-in-7 in the next 50 years. "If you look at the Wasatch Front
as a whole, it would be higher," he said, about 1-in-7 odds overall.
QUAKE DESCRIPTION
Scientists
say a worst-case scenario quake in Utah would be centered in mid-Salt Lake
Valley, and would be felt in seconds from Brigham City in the north to
Santaquin in the south, and from Tooele in the west to Coalville in the east.
It would affect 80 percent of Utah's population.
Shaking in
Salt Lake County would be so severe that no one would be able to stand without
falling. Unsecured hot-water heaters would shake loose in many homes, and
broken gas lines would start fires. Bookcases, furniture and debris would fall
and injure many. Some people trying to run out of buildings would be killed by
falling debris. Collapsing buildings would kill many.
A 7.0 quake
would quickly create a ledge or "scarp" that could stretch for nearly
30 miles along the main fault — roughly following Wasatch Drive in the south
valley, and following Highland Drive and 1300 East in the
central and northern parts of the valley.
Pechman said
that scarp, or ledge, would be about 3 feet high — but would be up to 9 feet
tall in places. As the scarp forms, it could snap utility lines and block
transportation across it, and topple houses around it.
Bob Carey, earthquake preparedness director for the Utah Division of
Homeland Security, says two small valley faults would likely also shake
"in sympathy" with the larger Wasatch fault, and also form smaller
scarps.
The
Taylorsville fault roughly follows I-215 northward from 4700 South to Rose
Park. The Granger fault runs diagonally from a point near 2700 West and 5400
South to near North Temple and 5600 West.
Besides the
three scarps blocking east-west traffic and relief efforts, Carey said lands
along the Jordan River are expected to "liquefy" or act like
quicksand in the quake, meaning bridges may collapse. "As a planning
strategy, we're not counting on any of the bridges across the Jordan to be accessible,"
Carey said.
CASUALTIES
Computer
models developed by the state and the Federal Emergency Management Agency
estimate quake damage — and predict that casualties could vary greatly
depending on the time of day that a big quake hits.
Carey said a
7.0 quake hitting in the middle of the night, for instance at 2 a.m., would
cause the most casualties: an estimated 2,920 dead, another 1,480 with
life-threatening injuries, another 9,360 with non-life-threatening injuries but
still needing hospitalization, plus 31,430 with "Band-Aid" injuries.
He said
fatalities would be greater during the night because many older homes in Utah
are "unreinforced masonry buildings," made of bricks on bricks
without reinforcing steel. The brittle structures don't flex well in quakes and
can snap like chalk. Upgrades — such as better attaching of roofs to walls —
can make them safer.
In
comparison, a quake that hits during drive-time rush hour, say 5 p.m., "is
safer because a larger portion of the population is in transit and not in
buildings," Carey said. Models predict fatalities then would be down by 16
percent compared to a middle-of-the-night quake, and other injuries would be
down by 20 percent.
The safest
time for a big quake may be during the workday because more people would be
inside commercial buildings that "tend to be newer, which means they were
built to a higher seismic code," Carey said.
DAMAGE
Carey said
models predict that 38 percent of all buildings in the area would suffer at
least moderate damage. He said they predict that economic losses from damage to
buildings and their contents would be more than $34 billion.
Models also
predict that more than 62,000 people would need public shelter — which could be
dire if an earthquake hits during freezing temperatures in winter. Nearly 100,000
households would be displaced here in a 7.0 quake, but not all would need
public shelter as they huddle with friends or family.
Carey
expects all cell phones and landline phones to go down initially. "Whether
it's due to damage or overuse, they always go down," he said.
"The
power is still going to go down. That's going to be for eight to 12 hours. And
then when it does come back, it's going to be spotty," Carey said, adding
that 80 percent of areas should have it restored within 30 days — a time frame
that should be similar for restoring telephone systems.
"Water
systems will take longer," he said. "We could see some areas without
water for three months." Sewer systems take even longer. He said he
expects natural gas "to perform a little better" because of upgrades
to pipes and systems recently.
PLANNING
Carey said
police and firefighters would likely be overwhelmed in a 7.0 quake, and
neighbors will likely need to depend on each other for help for the first hours
and days. That is why the state has encouraged neighborhoods to form Community
Emergency Response Teams. Many local cities offer CERT training.
Carey said
personal and family preparedness is also wise. For example, officials have said
that in a 7.0 quake, residents may need to depend on their "72-hour"
kits of supplies for five days or more for food, water and other basics. A book
by the state on earthquake dangers and how to prepare is available online at quake.utah.edu.
