Geologists
test area land for earthquake impact
FOX 7 On Your Side,
Evansville IN Nov. 17, 2003
Reporter: Casey Stegall
Evansville, IN November 18 -- An earthquake can be both damaging and
frightening. But some scientists think the Midwest could actually be
prone to more earthquake damage than other parts of the country.
We all know the Tri-State is close to New Madrid fault line. That,
mixed with silty and loose soil in this area, causes experts to fear
this terrible combination if a big one hits.
A truck plays a key role in figuring out where damage is most likely to
occur. It plunges a probe 40 feet into the earth's surface, collecting
important data along the way. The idea is to get a feel for what the
ground is made of.
"If you have looser material, the more devastation," explained
geologist Richard Harrison.
One theory is the ground will actually liquify if a big enough
earthquake hits. "When you have loose soil mixed with water, the ground
becomes unsteady," said Thomas Noce of the U.S. Geological Survey.
Their findings, so far, indicate parts of the Midwest have very loose
soil, which could have unimaginable consequences. "Buildings will sink,
pipes will break," Noce said.
The testing truck travels the country taking measurements. The
information is then crunched and mapped for use in picking the best
spots for building new roads and major structures.
The truck will be in Evansville over the next few weeks. They'll test
about 40 sites total while they're here. It will be some time before
their official findings are released.
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Quake's impact on
local soil studied
By HERB MARYNELL Courier & Press staff writer
November 17, 2003
Testing being conducted over the next few weeks should determine if a
major earthquake could cause liquefaction under Evansville, causing
foundations to break and structures to sink.
The testing is being done by scientists from Indiana, Kentucky and U.S.
Geological Survey organizations.
Roger Lehman, city-county building commissioner and president of the
Southwest Indiana Disaster Resistant Community Corp. (DRC), said this
is the first time such extensive testing has been done on the possible
liquefaction of the ground under the city's center.
Liquefaction is where the ground turns to "soup" or quicksand.
The work comes as the city kicks off Earthquake Awareness Week today.
Christine Martin, DRC executive director, said the core of the city is
built on silt.
"If we have a very hard earthquake," she said, "there's a high
potential for liquefaction and the Downtown sliding into the river."
Lehman said whether liquefaction occurs depends on the underground
water table at the time of a major earthquake. "We've got plenty of
water," he added.
The scientists from the three geological survey organizations will use
a high-tech, 20-ton cone penetration testing truck for the tests. The
truck is equipped with a cylinder that uses hydraulics to shove a metal
cone into the ground to a depth of at least 60 feet, Lehman said.
The equipment measures the resistance of the ground to the cone, giving
an indication of how much load bearing capacity the ground has, he
said.
The testing also determines the type of soil and how fast shock waves
move through it, he said.
The test equipment will give officials "additional information about
liquefaction that we don't have," Lehman said. The scientists also will
review sediments and evidence of liquefaction from previous
earthquakes.
The study should indicate areas most subject to liquefaction, whether
existing building codes are adequate and assist in land-use and public
safety decisions and plans in the future, Lehman and Martin said.
Engineers also can incorporate the data into design plans for
developments to reduce the impact or likelihood of building failures in
major earthquakes, Lehman said.
Lehman said most significant structures built in the previous 25 years
have pilings that go down past the 60 foot level.
The silt found in portions of the city comes from water runoff from the
last glacier that reached to the northern edge of today's Vanderburgh
County 10,000 or more years ago.
Lehman said the theory is that the glacier pushed a pile of debris
miles ahead. As the glacier melted and receded, water could have become
trapped between the glacier and the debris field, creating a possible
lake in what is now Evansville.
"Now we will find out if that is true" from the tests, he said.
The scientists will be here three or four more weeks conducting tests
generally in an area bordered by Franklin Street, Pigeon Creek, Morgan
Avenue and U.S. 41, he said.
Tests also are being completed on the city's far East Side to determine
how extensive silt under the surface may be, he said.
Earthquakes are not rare in the Tri-State area. The last notable
earthquake was in June 2000 and was a 5.0 magnitude, Lehman said.
Massive earthquakes in 1811 and 1812 along the fault in New Madrid,
Mo., caused the Mississippi River to run upstream, church bells to ring
in Boston and created Reelfoot Lake in Tennessee. Those earthquakes
later were estimated at a magnitude of 8.4 to 8.7.
Lehman said the goal is to find ways to protect the public from
earthquakes in the magnitude range of 7.0 to 7.5.
Mayor Russ Lloyd Jr. will read a proclamation today for Earthquake
Awareness Week and outline events planned this week by the local
Disaster Resistant Community group.
This will include unveiling of a new three-dimensional seismograph at
Harrison High School.
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Quake scientists
mapping area before 'serious shaking'
By MARK WILSON Courier & Press
staff writer
November 19, 2003
Thousands of years before Native Americans or early pioneer settlers
made their dwellings here, the seeds of the potential destruction of
the structures were already planted deep beneath the Earth's surface.
"It has always been here. The Wabash Valley Seismic Zone is a zone of
major faulting at depth. It has been around many years," said geologist
Norm Hester on Tuesday.
Hester, a former director of the Indiana Geological Survey at Indiana
University, is working with the U.S. Geological Survey and the Central
U.S. Earthquake Consortium in a five-year program to assess the
earthquake hazards in the greater Evansville area.
The effort will eventually yield three-dimensional earthquake hazard
maps that will provide better guidance for building codes, setting
insurance rates, siting and designing buildings and implementing
emergency response and mitigation plans.
The hazard has not increased, but as the area has grown, the risk to
its population has grown, too.
"The risk we have is because of the built environment," Hester said.
"Nobody has intentionally built in harm's way but you have to build
somewhere. There are lots of good reasons to build in a river area."
Recent field work has shown that a major earthquake has already
happened in the Wabash Valley fault zone in the past several thousand
years, Hester said. The chances that it will happen again are good.
"The USGS has gone on record that there is a 25 percent to 40 percent
chance that a 6.0 or greater earthquake will occur in the next 50
years," he said. "It's going to do some serious shaking."
About 30 counties in Illinois, Indiana and Kentucky could be affected,
Hester said, and there is potential for serious damage to unreinforced
buildings.
Although geologists know there is no way to say with any certainty when
an earthquake might happen, there is significant opportunity to
understand where it is likely to hit the hardest and use that
information to curb the risk. As our understanding of the hazards
beneath us increases, Hester said, so does our capability to build
structures that can better withstand earthquake damage.
"People want to know more, and they need to know what kind of risk they
are looking at," said Roger Lehman, Evansville-Vanderburgh County
building commissioner.
Such engineering decisions, Lehman said, are currently based on much
more generalized national hazard maps.
"It is like looking at a map of the United States where one inch equals
a thousand miles and trying to plan where you want to put something,"
he said. "At least this will be area and region specific. We have been
trying to get better information for 20 years."
Much of the Tri-State rests on a thick bed of saturated sediment,
sometimes as deep as 100 feet, above the bedrock. The geologists are
working to understand how greatly these geologic features will amplify
the shaking of a major earthquake and the potential for soil
liquefaction - a process by which water-saturated sediment temporarily
loses strength and acts as fluid.
Tom Noce, a USGS geologist helping on the project, is using in the
Evansville area the same technology he has put to work around Memphis,
Tenn., and Oakland, Calif., in recent years to determine the properties
of soils in the areas. The information will be used to help create the
maps.
It is done using a special Cone Penetration Testing truck. The 23-ton
truck, weighed down with the addition of 14 tons of lead, uses the
truck's weight to help push sensors into the ground down to depths of
170 feet.
The hollow steel tip of the probe contains about $4,000 worth of sensor
technology, Noce said, that will relay data back to a computer in the
truck. That data is displayed in graph form on a monitor and printed
out. It is also stored so that it can be injected into computer models
to determine the effect of earthquakes of different magnitudes on the
soil conditions.
Noce has spent the last two weeks taking readings from the flood plain
between Evansville and the Ohio River. Starting Tuesday near Epworth
Road in Warrick County, he began an effort to take readings from across
the northern part of the Evansville area.
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