The Log | School News
From Tiny Quakes, Major Insights into Earth
Peter Malin,
a geology professor, is examining microearthquakes on Montserrat,
Kenya’s Rift Valley and along California’s San
Andreas fault
Duke University scientists are using waves from tiny earthquakes
as geological equivalents of diagnostic X-rays. Emerging from
the ground, the waves can reveal clues about the anatomy of
a West Indian volcano.They can also help in finding geothermal
steam in East Africa, and in zeroing-in on the epicenter of
big earthquakes on the U.S. west coast.
The “microearthquakes” involved are so small
that they may not even register on some sensitive instruments,
the researchers said. Nevertheless they offer useful probes
of the earth’s structure and geological processes because
they occur much more frequently than do larger ones. They
are also located at shallow enough depths for earthquake wave
detectors called seismographs to be installed relatively nearby.
“We have these three major projects that are dovetailing
together,” said Peter Malin, a geology professor at
the Nicholas School. Malin’s seismology group is now
carrying out microearthquake studies on the volcanic island
of Montserrat, in the Rift Valley in Kenya and along the notorious
San Andreas earthquake fault in California.
The true goal of all three efforts is basic science, Malin
said in an interview. “Our group is trying to understand
the relationship between stresses in Earth’s crust and
the generation of these very small earthquakes,” he
said.
In the process, the scientists gain a fringe benefit—information
that is useful to society. The federal government, for example,
has already committed more than $6 million through the National
Science Foundation (NSF) to better understand the San Andreas
fault, the locus of the great San Francisco earthquake as
well as other big and damaging temblors.
The current focus of that project is a $1 million, 7,000-foot
pilot drill hole near Parkfield, Calif. That is where Malin
installed seismometers he helped design—rugged enough
to endure 220 degree Fahrenheit temperatures and pressures
of 300 atmospheres—that will help scientists decide
where to finish drilling the San Andreas Fault Observatory
at Depth (SAFOD).
In Montserrat, a tropical island located in the Caribbean
southeast of Puerto Rico, the question is not when the volcano
will erupt but rather for how long. The Soufriere Hills Volcano’s
latest eruption began in 1995 and has since caused two-thirds
of the population to flee.
This growing mountain continues to belch out not molten lava,
but rather hot boulders that rumble down its slopes. By day,
these big stones look dark like simmering coals, and by night
they glow red. Even more perilous are the occasional explosions
of hot gases that can rush across the hilly terrain faster
than a car can drive. Such a “pyroclastic flow”
killed a group of residents that attempted to farm land within
the government-established danger zone.
“We’re trying to understand the volcano system
better, giving the government the information they need to
know which areas are dangerous to occupy and which are not,”
said Elyan Shalev, a Duke research scientist in seismology.
Towards that end, a NSF-supported scientific team that includes
Shalev and Malin has lowered four different kinds of instruments
down four different 600-foot drill holes. Duke’s contribution
is a set of seismographs that might hint where molten magma
is circulating underneath the summit.
The researchers’ third major project will take place
in Kenya’s Rift Valley, where East Africa is splitting
apart along a line of volcanoes. There, the geologists will
use microearthquakes in attempts to track the location of
underground fluids, in this case not hot magma but hot water.
The goal is to determine where to drill for volcanically derived
steam to fuel Kenya’s next geothermal electric power
plant, which would be the country’s second.
— For the complete article by Monte Basgall of Duke
News and Communications, go to http://www.dukenews.duke.edu/2003/06/microquakes.html
more log > |
