number of programs ranging from earthquake prediction and earthquake
engineering to risk assessment and damage mitigation.
The programs are diverse, but the goals remain the same: to lessen the
risk posed by major earthquakes.
Earthquake Hazards Mapping
Major earthquakes seem to be occurring with more frightening regularity,
says Macari ,and they are causing much more damage and loss of life
than in the past. A recent quake in Russia, for example, caused billions
of dollars in property damage and claimed 2,000 lives. The earthquake
that struck Kobe, Japan, early this year, killed more than 5,000,
injured more than 26,000, and left some 300,000 homeless.
Damage estimates topped $200 billion.
"We can't stop earthquakes from occurring," says Macari, "but we can come
up with effective ways of reducing the risk and mitigating the damage. "
Common geotechnical hazards that occur during earthquakes include soil
liquefaction, ground motion amplification and landslides," says Macari.
"Soil liquefaction occurs when water-saturated, sandy soil is shaken
during an earthquake. The intense vibrations disrupt the normal
character of the soil, transforming it from a solid to a fluid state.
In essence, liquefaction turns the ground into quicksand, causing
building foundations lose their footing and sink."
Ground amplification occurs when the surrounding soil goes into resonance,
thereby magnifying the intensity of earthquake-induced vibrations. Mexico
City offers a classic example.
"Mexico City was buiit on top of an old lake bed," says Macari. "The
underlying sediments can be compared to a huge bowl of gelatin. When
you shake this 'bowl' at the bottom, the lake bed can resonate, substantially
increasing the vibrational amplitude at the surface. So even a small
earthquake can have devastating consequences to the buildings located above."
This article was published in Research Horizons at Georgia Tech
on May 8, 1996: http://www.gtri.gatech.edu/rh-sf95/quake.htm
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