Las Cruces
KEEPING your ear to the ground could give you early warning of an approaching
tornado. Now an electronic ear that will do the job for you and should cost less
than $50 is in prospect.
In 1989, a tornado swept through the small town of Huntsville, Alabama, and
killed 29 people. Afterwards, people told Frank Tatom, head of the local company
Engineering Analysis, that they felt vibrations in the ground before the tornado
reached them. Tatom calculated that a large tornado can transfer energy to the
ground equivalent to half a tonne of TNT exploding every second鈥攁nd that
seismometers could detect the shock waves.
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Tatom started working with Stanley Vitton of Michigan Technological
University, who specialises in soil mechanics, to produce a prototype detector.
鈥淲e are now designing detectors that could alert cities, or individual
home-owners, to approaching tornadoes,鈥� says Tatom.
Vitton began by modelling the type and magnitude of the seismic signals.
鈥淣ormally, signals given off by a tornado would be at a higher frequency than
traditional seismometers are programmed to detect,鈥� says Vitton. Seismometers
filter out relatively high frequency vibrations to avoid interference with the
earthquake tremors. 鈥淥ur devices, which are similar to simple seismometers, look
for those signals instead,鈥� says Vitton.
Working with seismologist Jim Dorman of the University of Memphis, Tatom and
Vitton discovered that tornadoes also cause the Earth鈥檚 surface to tilt as they
touch the ground. 鈥淲e believe that a tornado works like a plunger trying to lift
up or press down on the Earth鈥檚 surface, and this can cause the Earth鈥檚 crust to
tilt slightly,鈥� Tatom says.
Tatom鈥檚 company has made six small instruments that can detect both the shock
waves and tilt signals. They will be tested this year by tornado chasers. 鈥淲e
hope to take the data they collect and make our next generation of detectors
smarter,鈥� says Tatom. He foresees both a network of detectors that provides
public warnings of tornadoes and individual alarms for homes. 鈥淐ities in
tornado-prone areas now rely on weather forecasts and human spotters, but this
combination is not perfect,鈥� he says.
Many tornadoes never touch the ground so they cause no damage. But the
weather forecasters鈥� radar picks up all tornadoes. The large number of false
alarms causes many people to ignore tornado warnings.
鈥淲e think a network of sensors, in a circle about 30 kilometres from a city,
could provide at least five to ten minutes鈥� warning鈥攁nd not have the high
false-positive rate.鈥� Tatom and Vitton also hope to develop a $50 alarm
for home-owners that provides five minutes鈥� warning, 鈥渆nough time to get to a
basement or at least to the safest part of the house,鈥� says Tatom.
