stantial warnings of impending eruptions. However, they cannot predict the severity of eruptions, so it is difficult to make evacuation plans. By quantifying the magnitude of eruptions in the geological record, it will be possible to improve estimates of the likelihood and styles of future eruptions.

Groundwater contaminated by nuclear and chemical waste represents a growing hazard. Research is growing, too, but it is not clear that the full expertise of the solid-earth science community is being involved on a large enough scale.

The potential health hazards of such materials as asbestos and radon need to be evaluated in terms of levels of acceptable risk, taking into account the expertise of mineralogists and other appropriate scientists. There is a risk that legislation based on extrapolation of unreliable data could place large (and avoidable) financial burdens on the country. This is given high-priority in Priority Theme D, the environment.

There is a small but real possibility that an asteroid or comet could strike the Earth in the next century. Anything larger than the small objects that fall as meteorites could cause substantial damage, and a larger body could generate a global catastrophe.

Top-Priority, Theme C: Define and Characterize Regions of Seismic Hazard

Hazard reduction requires better understanding of where and how earthquakes occur. Progress toward predicting when they are likely to occur emerges from this understanding.

The establishment of two NSF-supported technology centers, one in earthquake research and the other in earthquake engineering research, the development of the NEHRP program, and a variety of other activities following the Loma Prieta earthquake have helped to bring seismic hazard activity to the forefront. New ideas are emerging that challenge some of the old assumptions about the very mechanisms by which earthquakes originate and propagate, particularly the role of chaotic behavior in the seismic cycle. At the same time, our experience in the probabilistic assessment of seismic risk is growing. There is a growing need for integrated approaches, including seismic networks, space geodesy, geology, neotectonics, and paleoseismology. Paleoseismology has a special need for the excavation of trenches across fault zones to characterize past seismic activity.

Other High Priorities

For Priority Theme C Table 7.12 lists two high-priority research areas: defining and characterizing areas of landslide hazard and defining and characterizing potential volcanic hazard; both are considered in Chapter 5. Landslide hazards arise from the association, in a small area, of a variety of phenomena such as steep slopes, wet conditions, and weak surficial rocks. Understandably, the integration of disparate data using geographic information systems has been found useful. The distribution and timing of ancient landslides can be an important guide to the hazard, and this information is also important for understanding aspects of past global change.

Volcano hazard research has been stimulated by the occurrence first of the Mount St. Helens explosive events, by the substantial loss of life at Nevada de la Ruiz, and the destruction resulting from Mount Pinatubo. Volcanologists are beginning to make excellent and informed use of the opportunities provided by these and other events to focus their efforts in the directions most useful to society.

Programs and Infrastructure

Federal agencies are actively involved today in assessing these geological hazards. The USGS, the NSF (both the Division of Earth Sciences and the Directorate for Engineering), FEMA, and the National Institute of Standards and Technology have lead roles in NEHRP and represent a national commitment in this direction. Other agencies, such as DOE and the Nuclear Regulatory Commission, have mission-oriented roles in seismic hazard analyses. The existence of the two NSF centers related to earthquake studies is a good indication of the importance the federal government attaches to such hazards.

National and regional seismic networks, with real-time monitoring capabilities where appropriate, are needed. Seismotectonic regionalization is not yet adequate and should be improved using seismic, strong-motion, and paleoseismic (especially trenching) techniques.

Priority Theme D: To Minimize and Adjust to the Effects of Global and Environmental Changes

The aim of the last priority theme is to mitigate and remediate the adverse effects produced by

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