NSF PR 98-24 - April 24, 1998
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Global Seismic Network Now Extends to the Deep Oceans
Ocean Drilling Program's New Technology
to Open Exploration of Earth's Interiors
This month, scientists with the Ocean Drilling Program
(ODP) will install one of many planned Geophysical
Ocean Bottom Observatories (GOBO), in which a permanent
seismograph station will be established on the sea
floor for monitoring earthquake activity. ODP is funded
in large part by the National Science Foundation (NSF).
"Installing a seismic station in an ocean basin will
be like filling in missing portions of a mirror or
lens in a telescope," says Bruce Malfait, director
of ODP at NSF. "It will allow us to examine regions
of the earth's interior that are only poorly imaged
at present by stations on a few islands, or the 30%
of the earth's surface occupied by continents."
The global network of on-land seismic stations provides
sufficient earthquake monitoring capabilities for
large parts of the earth's surface in continental
regions and on some islands. However, oceanic regions
that cover approximately 70 percent of the earth's
surface remain largely unmonitored, creating large
"holes" in worldwide data coverage for low magnitude
earthquakes and for earth's deep interior.
Scientists aboard the research vessel JOIDES Resolution
will drill into the oceanic basement of the Indian
Ocean, a region of the world where there is a lack
of ocean-bottom seismograph stations. The expedition,
referred to as ODP Leg 179, began when the ship departed
Cape Town, South Africa, on April 21. It concludes
with a port call in Darwin, Australia, on June 6.
"During the past 10 years our knowledge of deep earth
interior processes has greatly improved with the development
of new generations of global seismic monitoring networks,"
says John Casey of the University of Houston, co-chief
scientist for the expedition. "The need for ocean-bottom
observatories is driven by the lack of observations
in large tracts of the world ocean where neither continents
nor islands are available to place observatories."
Before laying the groundwork for the new seismic observatory,
ODP will test a new drilling system designed to drill
large-diameter casing into hard fractured rock on
the sea floor. The new drilling system, called water
hammer drilling, uses a percussion drill similar to
a jackhammer but is driven by fluid rather than air.
If the tests are successful, reentry systems will
be placed on the boreholes, allowing scientists to
return to these locations to conduct future experiments.
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