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Fault Line Missing From Map
SEE UPDATE! Fault Found! -- Deseret News article of 1/8/99
Sunday, December 7, 1997
BY LEE SIEGEL 1997, THE SALT LAKE TRIBUNE
When a building sits directly on a fault line, a major earthquake not only will shake it, but
also literally can rip the structure apart. Salt Lake City and County have banned new
buildings on fault lines since the 1980s. So accurate maps of faults are important.
But a branch of Utah's Wasatch fault was wiped off maps of downtown Salt Lake City
because of breakdowns in the system of checks and balances intended to protect buildings
and lives.
Those failures allowed the Salt Palace to be rebuilt between 1994 and 1996 without the
required ``special study'' to learn if the fault passes directly under the $85 million
convention center.
(See Fault Found! - Deseret News article of January 8, 1999)
If a fault is found by such a study, called a ``fault- rupture hazard investigation,'' a
proposed building must be redesigned so it doesn't straddle the fault. That's expensive if
construction has begun.
Yet consultants never did such a study for the Rose Wagner Performing Arts Center on
Broadway (300 South). They looked for and didn't find the fault beneath the LDS Church's
planned 21,000-seat Assembly Building, Zions Securities' 19- floor Gateway Tower West at
South Temple and Main Street, and the adjacent parking garage under Main.
They didn't include fault investigations in geotechnical reports submitted before excavation
or construction began on those three projects.
``That's irresponsible,'' said engineering geologist Bruce Kaliser, a former Utah Geological
Survey official. ``These geotechnical professionals must know a horse comes before the
cart. Professionals can get away with a half-assed job here in Utah that would never fly in
California 20 years ago.''
``Everyone is trying to do the right thing, but we need to take a close, hard look at the
system,'' said Craig Nelson, who was Salt Lake County's geologist during 1985-1992 and
reoccupied the job Nov. 1. ``It's not working right.''
University of Utah geologist-geographer Don Currey said it is ``a departure from
responsible planning'' that the Warm Springs branch of the Wasatch fault vanished from
downtown on Salt Lake County's 1997 geologic hazards map when it was present on the
1989 version of the map.
``The best case is it was an unintentional mistake,'' Currey said. ``The worst-case scenario is it is revisionist geology to accommodate somebody.''
Disappearance of the downtown fault shows independent geologists should review changes
to earthquake hazard maps, said U. seismologist Walter Arabasz, chairman of Utah's
Seismic Safety Commission.
He said there also must be a ``clear mechanism'' to ensure fault investigations are
conducted by qualified consultants and reviewed independently before construction starts.
No one knows the fault's exact location downtown. Nelson said within six months he will
revise the map to make it more accurate.
Until then, he urged Salt Lake City to use the 1989 map when deciding where to require
preconstruction fault investigations for new buildings, otherwise buildings could be erected
directly on the fault line.
During a single magnitude-7 earthquake, ground on one side of the Wasatch fault rises 6
feet to 9 feet relative to ground on the other side, which drops downward. Thousands of
major quakes during millions of years uplifted the Wasatch Range.
In the south half of the Salt Lake Valley, the Wasatch fault intersects the ground at the
base of the Wasatch Range and dips westward beneath the valley. But in the north half of
the valley, the fault line is farther west, such as where it runs along 1300 East near the U.
The valley's northernmost part of the Wasatch fault is even farther west. It was named the
Warm Springs fault after thermal springs north of downtown Salt Lake City near Beck
Street.
When Nelson published the county's first geologic hazards map in 1989, solid lines
represented the Warm Springs fault's known location running north to south along the
west flank of Capitol Hill. Dashed lines, which were based on 1960s and 1970s maps,
depicted two possible forks of the fault extending farther south beneath downtown. An
eastern fork of the fault ran along the base of Capitol Hill, then south through the
Assembly Building site, Temple Square and Crossroads Plaza. A nearly parallel western
fork ran under the Salt Palace and almost to 400 South.
When the 1997 version of the map was issued in February by Brian Bryant -- county
geologist from 1992 until last August -- the fault lines had vanished from downtown.
Instead, the Warm Springs fault stopped at 700 North, well north of downtown.
The map was incomplete. A 1990 study had found the fault came at least three blocks
farther south, running beneath Washington Elementary School. Bryant said he heard of
the study, but never got a copy to consider when he changed the county map.
At the school, geologists found that during prehistoric quakes, ground on the Capitol Hill
side of the fault had moved upward 14 feet to 40 feet relative to ground on the other side.
So much ``offset'' does not occur where a fault is tapering out. So the fault must continue
farther south toward or into downtown.
The large offset also shows why planners must consider the risk of buildings being torn
apart by earthquake fault rupture. No building sitting on a fault line can withstand more
than about 4 inches of vertical offset, even if designed to withstand strong shaking.
Danger Zones: Fault lines on the 1989 and 1997 county maps show where fault rupture
might happen. Fault locations are uncertain, so the maps also show shaded zones called
Special Study Areas extending up to 500 feet from fault lines.
Before a structure is built in a Special Study Area, county ordinance requires developers to
hire a qualified geotechnical consultant to conduct a fault-rupture hazard investigation.
Such investigations involve digging trenches, drilling holes or using other methods to
determine if a fault passes through the property. Fault investigations range from $1,500 for
a home to $5,000 or more for a large building. If a fault is found, the proposed building
must be redesigned so it is set back from the fault.
After the downtown fault lines and Special Study area evaporated on the 1997 county map,
four geologists and engineers at AGRA Earth & Environmental consultants in Salt Lake
wrote Bryant complaining the disappearance was ``a significant error.''
AGRA, operating under a previous name, found the fault at Washington School in 1990.
The letter from AGRA's Greg Schlenker, Jennifer Helm, Jeff Keaton and Bill Gordon said
the fault must extend even farther south.
The letter noted the shrunken Warm Springs fault on the 1997 county map was based on a
similar shortened fault on a 1992 map prepared by Stephen Personius and William Scott of
the U.S. Geological Survey (USGS).
But when Personius was contacted by AGRA, he said his 1992 map showed only where the
fault was obvious on the surface. He and Scott never looked for underground evidence of
possible extensions into downtown.
``We were conservative in a scientific sense but not in a public-hazard sense,'' Personius
said recently. ``It's obvious what's on this map and what's not on this map is very
important for development. Those considerations we didn't take into account.''
Personius said he and Scott did their fieldwork for the 1992 map in 1989, and never knew the fault was later found under Washington School.
Because Capitol Hill rose upward along the fault during prehistoric quakes, Schlenker
believes the fault may extend at least to the bottom of the hill, or North Temple Street.
Personius and Utah Geological Survey geologist Gary Christenson agree.
That could place the fault under the Assembly Building site -- although it hasn't yet been
found there -- or perhaps west of it. If the fault is west of that block, it might extend
beneath the Salt Palace, depending on how far south it goes.
Capitol Hill once extended farther south than it does today, but its lower end was buried by
sediments deposited by prehistoric City Creek -- sediments on which downtown sits. So the
fault may follow the buried base of Capitol Hill south of North Temple and through much
of downtown.
Three decades ago, Kaliser mapped the fault under downtown based on that premise. A
few years ago, he discovered a spa had been located on 200 South between Main and West
Temple in the 1800s -- more evidence the fault lurks downtown. Hot springs bubble
upward along faults.
Bryant, who quit as county geologist to teach high-school science in Lancaster, Calif., said
reconstruction of the county-owned Salt Palace triggered his decision to shrink the fault on
the 1997 county map.
On March 25, 1994, after the old Salt Palace was demolished, Salt Lake City
development-review supervisor Larry Butcher wrote county officials: ``Salt Palace is
located in a known fault area. Ordinance does not allow a structure to be placed over a
fault line. Please provide documentation that building will not be located over a fault.''
Four days later, Salt Palace geotechnical engineer Ralph Rollins of Provo's RB&G
Engineering told county officials that because Personius' 1992 USGS map ``indicates that
the Warm Springs fault does not pass through the Salt Palace area, we recommend Salt
Lake City allow the construction to proceed as scheduled.'' The county passed Rollins'
reply to Butcher. Construction proceeded.
Rollins is an engineer and was not qualified to make such a judgment about the fault
hazard, Kaliser and Nelson said. Rollins said his firm includes geologists.
The geotechnical report for the new Salt Palace included only soil studies aimed at
designing the foundation. There was no fault-rupture investigation, Bryant and
Christenson said.
``It should have been done,'' Christenson said. Rollins replied: ``No one asked for a fault
investigation.''
Even though the Salt Palace was in a Special Study Area where fault investigations would
be required if the county had jurisdiction, Butcher said city officials felt the requirement
was satisfied when Rollins said the 1992 USGS map showed the fault wasn't nearby.
Bryant said he became convinced proper procedure was to use the most recent map -- the
1992 map. Kaliser scoffed: ``All previous mapping must be consulted.''
Christenson said he and other geologists gave the Salt Palace excavation an ``eyeball''
inspection. ``To the extent we could look, we didn't see any obvious faulting. It doesn't
mean it wasn't there.''
Bryant said he then decided, as a matter of fairness, to revise the county hazard map to
shrink the fault as it was on the 1992 USGS map. If the county used the 1992 map to justify
rebuilding the Salt Palace without a fault investigation, ``then developers and private firms
should also be able to use it.''
New Map, Old Map: Bryant finally issued the new county map last February. Until then,
the 1989 county map still applied. Indeed, Butcher, Salt Lake City building services
director Roger Evans and zoning administrator Randolph Taylor all insist they still are
using the old map to require fault investigations before issuing building permits in the
downtown Special Study Area.
But geotechnical reports for the Assembly Building, Gateway Tower and the adjacent
parking garage all lack fault investigations. When shown the reports, Butcher
acknowledged that after the 1994 Salt Palace incident, the city was satisfied if geotechnical
reports on proposed buildings simply addressed the fault issue.
Nelson replied city officials ``don't understand a two- line paragraph in a consultant's
report can totally dismiss the hazard. Unfortunately, there are too many consultants who
are willing to easily dismiss these hazards.''
He said that is why cities should ask the county geologist or some other independent
geologist to review geotechnical reports by developers' consultants, who too often put their
clients' projects above public safety.
Les Youd, civil-engineering chairman at Brigham Young University, said: ``I'm not sure
anyone was trying to pull a fast one, but once one person said, `We don't have to look for it
[the fault]' and gave a justification, it became a standard practice'' not to include fault
investigations in preconstruction geotechnical reports.
``We were aware somebody waved their hands and the Salt Palace fault disappeared,'' said
Gordon, a vice president of AGRA. As a result, he said AGRA did not do a fault study on
the Rose Wagner Performing Arts Center, a block south of the Salt Palace.
In 1996, AGRA's Gordon wrote geotechnical studies for Gateway Tower West and the
underground parking garage. Each report contained a sentence noting the 1989 county
map ``indicates potential active faulting in the site area,'' but adding AGRA's studies of
other parcels suggested the fault wasn't under the tower or garage.
Nelson said: ``More should have been done than one sentence dismissing the fault without
any evidence.''
Gordon said AGRA found no evidence of faulting when drilling to design Gateway Tower's
foundation, but didn't mention it in the geotechnical report. ``I don't know why. We should
have.'' He said he later looked at the excavation ``and there was no evidence of faulting.''
Project Under Way: A fault investigation also was not included in the geotechnical report
for the LDS Church's Assembly Building site north of Temple Square. The report was
written last April, after the county hazard map was revised. So the building was no longer
in the Special Study Area and a fault investigation technically wasn't required.
U. geologist Currey said: ``The responsible thing for them to have done is a full
geotechnical investigation'' before excavation began.
Church officials and consultants have searched for the fault since Assembly Building
excavation started. So far, they have looked at 80 percent of the site and ``we have not seen
any indication there's a fault that goes through the property,'' said Jim Nordquist of
Applied Geotechnical Engineering Consultants.
The northwest corner of the Assembly Building site remains to be examined next spring.
Nordquist and Tom Hanson, Assembly Building project manager, said they doubt they will
find the fault.
If they do, ``we would recommend they stop the project pending further investigations to
determine the nature of the faulting,'' said Christenson of the Utah Geological Survey. ``It
wouldn't necessarily kill the site.''
The Assembly Building is being constructed to exceed even California-style building codes,
which are tougher than Utah's, said Hanson and architect Kerry Nielsen. If the fault is
found beneath the site, ``we'd have to evaluate the structure and what it could handle,''
Nordquist said.
BYU's Youd said the Utah Geological Survey should take ``an independent look'' for any
faulting at the Assembly Building excavation. He also recommended making the foundation
even stronger.
Arabasz and Youd said geologists should search downtown to find the fault's precise
location. Christenson and State Geologist Lee Allison, said that would be difficult and
expensive because downtown has been excavated repeatedly by 150 years of construction,
geologists can't dig where buildings exist and the fault likely is buried by sediments.
So Utah residents may not learn the fault's path downtown ``until the big one occurs,''
Christenson said.
That could be any time. Studies found major quakes on the Wasatch fault in the Salt Lake
Valley happened an average of every 1,350 years in prehistoric times. It has been about
1,300 years since the last one. The Utah Geological Survey estimates such a quake could kill
up to 7,600 people, injure 44,000 others and cause $12 billion in damage.
Updated on January 12, 1999