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.