Earthquake scientists have spent years peppering continents and islands with seismometers and other instruments to clock the movement of Earth's fissures around the globe. Trouble is, this network covers but a small fraction of the planet.
With roughly 70 percent of Earth's surface underwater, scientists need a way to place their sensitive instruments at the foot of the volcanoes and valleys that crisscross the the ocean floors. A network of retired deep-sea telephone cables may help them accomplish just that.
One cable, located 16,400 feet beneath the Pacific Ocean between California and Hawaii, now functions as the lifeline for the first permanent US sea-floor observatory. Built as a cooperative project by the Incorporated Research Institutions for Seismology (IRIS), the University of Hawaii, and the Woods Hole Oceanographic Institution, the Hawaii-2 Observatory will eventually be a hub for numerous scientific instruments to take the pulse of the ocean floor, giving researchers up-to-the-minute data on seismic activity in the deep.
"[The observatory] is a foot in the door for us to get data about the ocean in real time," said Alan Chave, senior scientist in geology and geophysics at Woods Hole.
The Hawaii-2 Observatory, or H2O, represents 10 years of study on building a truly global seismic network. The work began as a cooperative effort between IRIS program manager Rhett Butler and AT&T in 1987, when the telephone company began to retire thousands of miles of old deep-sea cables in both the Atlantic and Pacific. Some had lost their functionality while others were being discarded in favor of newer fiber-optic technology. These old cables still had the ability to provide power down to the sea and to transmit data, however, which suited the needs of a communications network nicely.
But for the network to move from communications to seismology, Butler knew he needed to find a way to get the instruments to the ocean floor and hooked up to the cables. While scientists like Butler must rely on standard research vessels and work on a relatively small budget, a company like AT&T has the ships and the tools to do the job.
"We're not installing a revenue-generating technology [like AT&T does]," said Butler, who heads the global seismic network project for IRIS. "Ours is for study, so our equipment and budgets are different."
Technical issues also blocked the way. To survive at those depths, Butler knew the instruments would have to withstand immense fluid pressure -- as much as 500 Earth-atmospheres worth -- as well as the harsh elements of the ocean environment that cause materials to corrode. And then there was the tricky task of attaching cable to instrument.
Butler's quest eventually brought him to work with the Japanese who, as residents of an island nation surrounded by volcanoes, fault lines, and other reminders of Earth's shaky activity, understood the need for getting instruments under the sea. Several years of working on an observatory stationed between Guam and Japan taught Butler that simplicity was the key: Instruments needed just to plug into the network.
The Hawaii-2 Observatory is basically one large extension cord with an outlet into which instruments can be plugged and unplugged with the use of an ocean floor rover, such as Woods Hole's Jason, which explored the wreck of the Titanic. Scientists used Jason to cut the cable and then bring the ends aboard the ship. Termination was added topside, then the cable was resubmerged and Jason installed the giant outlet.
"[Installing the outlet] was the most challenging thing to do at sea," Butler said. "We had to do much of the work twice to get it to work."
The effort paid off, said Butler. The outlet, a junction box built from titanium to protect against corrosion, can provide 400 watts of power for instruments to gather and transmit data in real time. In all, it can accommodate more than eight instruments. Devices can be daisy-chained in much the same way that consumers hook up machines such as printers, scanners, and extra hard disks to their computers.
The cable, like computer networks, will allow scientists to conduct two-way communications with their instruments on the sea floor, enabling them to program and troubleshoot from the confines of their laboratories. Chave believes this will advance ocean science generally and add to the understanding of quake activity specifically, a view Butler endorses.
Prior to H2O, for example, scientists studying quake activity along California's San Andreas Fault could only obtain data from north, south, and east of the epicenter. Missing was vital information to the west, where much of the fault lies in the Pacific. "You can now study quakes as they happen and get a full picture of a large event instantly and see if other faults [offshore] are involved," noted Butler.
Because of its permanent nature, the observatory can and will be used to monitor other events that can cause the ocean floor to stir, including nuclear blasts and tsunamis.
The idea of receiving a continuous picture of oceanic activity is attractive to other researchers, too. Until now, information could only be obtained from on-the-spot observations or by dragging instrumentation through the water. Even then, the data was spotty, Chave said, since it could only represented a given moment and did not account for changes due to weather, season, or time of day.
H2O should change all this, Chave said.
Earth and ocean scientists have also resorted to space. NASA's NIMBUS-7 and its current effort with the Sea-viewing Wide Field-of-View Sensor satellite help give near real-time information about the Earth and its oceans. But the information about the ocean is limited to the surface, said Chave. "You get only a centimeter of depth, we want to know about the biology and physical oceanography of the sea floors."
