nological investments accelerate progress? This chapter presents the committee consensus on these issues in nine key areas where better knowledge is needed. The order of topics reflects the organization of the earthquake research effort laid out in Chapters 3 through 5 and is not intended to imply a prioritization.

6.1 FAULT CHARACTERIZATION

Almost all destructive earthquakes are generated by the sudden slippage of faults near the Earth’s surface. Most dangerous faults in the continental crust (i.e., those that slip at average rates greater than a few millimeters per year) can be identified through a combination of geologic, geodetic, and seismologic measurements. New technologies in all three fields have enhanced the ability to locate active faults and assess their seismogenic potential (Chapter 4). These advances now warrant a substantial expansion in regional data gathering, including the densification of seismic and geodetic monitoring systems and more intense efforts to mine the geological record of fault activity. The goal should be a comprehensive catalog of fault information.

Goal: Document the location, slip rates, and earthquake history of dangerous faults throughout the United States.

Fault characterization at the detail required for comprehensive seismic hazard analysis will require nationwide efforts to improve capabilities in the three main observational areas of seismology, geodesy, and geology:

  • a national seismic network capable of recording all earthquakes down to moment magnitude (M) 3 with fidelity across the entire seismic bandwidth and with sufficient density to determine the source parameters, including focal mechanisms, of these events; the location threshold for regional networks should reach M 1.5 in areas of high seismic risk;

  • geodetic instrumentation for observing crustal deformation within active fault systems with enough spatial and temporal resolution to measure all significant motions, including aseismic events and the transients before, during, and after large earthquakes; and

  • programs of geologic field study to quantify fault slip rates and determine the history of fault rupture over many earthquake cycles.

Major programs for augmenting seismic and geodetic instrumentation have been proposed by the NEHRP science agencies. The Advanced National Seismic System (ANSS), to be deployed by the U.S. Geological



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