Dense local seismographic networks, together with computerized data-analysis facilities, are absolutely essential if detailed studies of earthquake-related active tectonics are to be carried out in a given area. Ideally, the distance between seismometers should be roughly comparable to the average depth of earthquakes in the area if good hypocentral locations (including focal depth) are to be obtained.
Modern techniques of seismic analysis, particularly as related to the understanding of fault mechanics, are increasingly dependent on improved instrumentation, such as wideband, digitally recording seismometers. Particularly for the studies of worldwide large earthquakes, which represent our best “window” to contemporary tectonic processes, it is essential that support be obtained and continued for the proposed new Global Seismographic Network (NRC Committee on Seismology, 1983; Incorporated Research Institutes for Seismology, 1984), which will effectively replace the 23-year-old World Wide Standardized Seismographic Network, which has served its purpose well but is now clearly outmoded.
Every effort should be made to increase the number of strong-motion accelerographs in areas—anywhere in the world—where large earthquakes are most likely to occur (NRC Committee on Earthquake Enginering Research, 1982). Despite the many years of recording, engineers and seismologists have obtained very few records of the actual ground motion in the close vicinity of a truly great earthquake, and thus we are still deficient in our knowledge of active-tectonic processes in the “near field” of such an event.
In the area of paleoseismology, perhaps our greatest need is simply for more trenches across active faults where significant results might be obtained. But it is also critical that we improve our basic understanding in several of the following areas:
Soils are among the geologic features most often disturbed by faulting and earthquakes, but our knowledge of the ages of soils and their rates of development in different climatic environments leaves much to be desired. Furthermore, slow gravity-induced downhill movements of soils (soil “creep”), even on very gentle slopes, can sometimes cause numerous deformational features remarkably similar in appearance to those due to sudden earthquake movements; a better understanding of this phenomenon is important.
The most common problem in paleoseismological investigations is that of dating the strata involved, particularly those of an alluvial nature that still defy most of the traditional methods of absolute age dating. Carbon-14 dating, for example, requires the collection of organic materials that are typically rare in alluvial deposits. Improved geochemical techniques of dating young materials are critical, as well as the further development of other promising techniques such as those based on paleomagnetism.
Insofar as many prehistoric earthquakes have been associated with the formation of geomorphic features such as fault scarps that are still preserved on the landscape, an improved understanding of the erosional degradation of such features is important if we are to understand their ages of formation. Recent research work in quantitative geomorphology (e.g., Hanks et al., 1984) has been encouraging in this regard and deserves continued vigorous support.
Detailed field studies of recent earthquakes, such as the 1980 Algerian disaster (e.g., Philip and Meghraoui, 1983), indicate that many types of surficial deformation other than primary fault scarps may occur in the epicentral area. These features, too, may become buried in the geologic section and be recognizable at a later date, so it is important to understand their origins and possible mechanisms of preservation. Only by studying contemporary earthquakes in the field in great detail will we learn to recognize what is important in identifying and interpreting “fossil” earthquakes.
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