Understanding the period from the present to about 500,000 yr ago (the late Quaternary) forms the best basis for analyzing active tectonics of concern to society. To study this period of time calls for a special mix of geologic, seismological, geophysical, and geodetic techniques, many of which need major research efforts to achieve their full potential. Some of the most critical needs are highlighted in this Overview. Detailed discussions of recent advances in understanding active tectonic processes and their rates appear in the authored chapters that follow this Overview.

Many research programs that can provide background for the study of active tectonics have been considered in earlier reviews by the National Research Council, including such reports as Geophysical Predictions (1978), Earthquake Research for the Safer Siting of Critical Facilities (1980), Geodetic Monitoring of Tectonic Deformation—Toward a Strategy (1981), Effective Use of Earthquake Data (1983), Seismographic Networks: Problems and Outlook for the 1980s (1983), Explosive Volcanism: Inception, Evolution, and Hazards (1984), and Seismological Studies of the Continental Lithosphere (1984). Research needs in, for example, seismological and geodetic techniques of importance to active tectonics are well formulated in these documents. The present study makes no attempt to review all these previous analyses but builds on them and specifically endorses some previous recommendations. For the most part, the previous reports have not addressed the premodern part of the time frame of the past few hundred thousand years, which must be understood to evaluate ongoing tectonic activity fully.

Some potentially powerful techniques that should be developed by accelerated research are considered in this study. The recently emerging subdiscipline of paleoseismology—in which geologic techniques are used to identify and evaluate prehistoric earthquakes—has provided some of the most important recent advances in earthquake prediction. Similar techniques have also permitted evaluation of seismic hazards for urban areas and for critical facilities such as dams and nuclear reactors. Essential to such geologic research and evaluations are the ages of geologic units. Only by having the geologic history calibrated by known dates can we calibrate the (1) recurrence intervals of earthquakes and volcanic eruptions and (2) continuing rates and changes of rates of all tectonic processes. The determination of rates of processes and means of dating materials of late Quaternary age (past 500,000 yr) thus are considered of high priority for research attention.

Among other facets of geology that have been underused in studying active tectonics is geomorphology. Landforms are everywhere; they are extremely sensitive to active tectonics; and geomorphic analysis has the potential for providing insights into active tectonic rates, styles, and patterns of deformation available through almost no other approach. Serious efforts are needed to accelerate research in quantitative geomorphology.

The need is recognized for improving geodetic measurements of active tectonics through new land-based instruments, such as two-color laser distance-measuring devices, and space-related techniques, such as the Global Positioning System (GPS). Regional seismic networks are considered essential to track the patterns of ongoing strain release, to assist in mapping the activity of faults, and to assist in tracking the movement of magmas under volcanoes. Rapid data gathering, processing, and analyses are imperative. Great volumes of data from regional seismic networks and a variety of strain meters and geodetic networks must be handled quickly if useful forecasts (with lead times up to a few weeks) of earthquakes, volcanic eruptions, and landslides are to be made successfully.

In summary, this study addresses tectonic processes, their rates, and methods of identifying and evaluating active tectonics by analysis of events, especially in the time frame from the present to about 500,000 yr ago. Except for brief comments, the socioeconomic and engineering accommodations for coping with the problems created by

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