The agencies discussed in this section are not part of NEHRP. Yet two of them contribute significantly to earthquake research because of their technological focus on the sea (National Oceanic and Atmospheric Administration, NOAA) and space (National Aeronautics and Space Administration, NASA). There are, of course, many informal working relationships between these agencies and NEHRP, but the lack of formal structure can lead to a lack of focus. Nonetheless, both NOAA and NASA have managed to make critical contributions to an understanding of earthquakes and earthquake-hazard mitigation.
NOAA is part of the Department of Commerce, which until the early 1970s was the only government department, through the U.S. Coast and Geodetic Survey and the National Weather Bureau, with a federal mandate to study earthquakes. After a battle with the USGS for primacy in earthquake funding, the Department of Commerce withdrew from the field in the early 1970s, and the USGS took over, as discussed earlier in this chapter. This might have been a reason NOAA was excluded from NEHRP in 1977.
NOAA is the principal federal agency responsible for tsunami hazards (see Chapter 9). Earthquake and tsunami data are distributed through its National Geophysical Data Center in Colorado. NOAA also provides real-time tsunami warnings for the United States and its territories through tsunami warning centers in Alaska and Hawaii (described in Chapter 9). After a tsunami generated by the 1992 Cape Mendocino Earthquake was detected on the northern California coast, Congress gave NOAA additional funds and responsibilities and established the National Tsunami Hazard Mitigation Program, designed to reduce risks from tsunamis. NOAA is the lead federal agency in this initiative, with participation by FEMA, USGS, and NSF (Chapter 9).
The U.S. Navy has declassified arrays of hydrophones (called SOSUS) on the seafloor that were used during the Cold War to monitor military ship traffic in the oceans and has allowed these hydrophones to be used by NOAA. These hydrophones, in addition to recording ship engine noise and whale calls, monitor earthquake waves transmitted directly through water, called T-phase waves. These waves locate earthquakes on the seafloor with much higher accuracy and to a much lower magnitude threshold than is possible from land-based seismographs. Furthermore, NOAA has located many times the number of earthquakes on the deep ocean floor than the landbased seismograph network.
Just as the USGS is responsible for topographic mapping on land, NOAA is responsible for mapping the topography (or bathymetry) of the seafloor using a ship-borne mapping device called SeaBeam. Earlier mapping techniques relied on individual soundings of water depth followed later by profiles of the seafloor by depth recorders mounted in the hulls of passing ships. SeaBeam and similar technologies developed by the British, French, and Japanese map a swath of seafloor based on the echoes of sounds transmitted from several locations mounted in the ship’s hull. NOAA swath bathymetry results in topographic maps of the sea bottom comparable in accuracy to topographic maps of dry land constructed by the USGS.
Once thought to be a barren, featureless landscape, the seafloor is now known to be marked by canyons, great faults, volcanoes, landslides, and active folds (Figures 2-4, 4-4, and 8-14). Tectonic features of the deep ocean floor are not altered by erosion to the degree that land structures are. The bathymetry is recorded digitally so that it can be displayed as a computer model in which the water has been stripped away, as shown in Figures 4-4 and the offshore part of Figure 8-14. (Similarly, the USGS has digitized its land topographic maps permitting a new and revealing perspective on the tectonic forces that produce the topography above sea level, as illustrated in Figures 4-5, 6-11, 6-24, 6-25 and the onshore portion of Figure 8-14.) SeaBeam bathymetry directs submersibles with observers and remote-controlled robotic vehicles to observe and map faults on the seafloor. An active research program involving submersibles, funded by NOAA’s National Undersea Research Program (NURP), has led to new detailed information on the Cascadia Subduction Zone and active faults and folds on the continental shelf and slope.
Because NOAA is not part of NEHRP, programs such as NURP earthquake hazards research and SeaBeam bathymetric mapping are at risk from budget cutters because except for tsunamis, earthquake hazard research is not a primary mission of NOAA.