Goal A of the 2008 NEHRP Strategic Plan is to “improve understanding of earthquake processes and impacts.” Earthquake processes are difficult to observe; they involve complex, multi-scale interactions of matter and energy within active fault systems that are buried in the solid, opaque earth. These processes are also very difficult to predict. In any particular region, the seismicity can be quiescent for hundreds or even thousands of years and then suddenly erupt as energetic, chaotic cascades that rattle through the natural and built environments. In the face of this complexity, research on the basic physics of earthquake processes and impacts offers the best strategy for gaining new knowledge that can be implemented in mitigating risk and building resiliency (NRC, 2003).
The motivation for such research is clear. Earthquake processes involve the unusual physics of how matter and energy interact during the extreme conditions of rock failure. No theory adequately describes the basic features of dynamic rupture and seismic energy generation, nor is one available that fully explains the dynamical interactions within networks of faults. Large earthquakes cannot be reliably and skillfully predicted in terms of their location, time, and magnitude. Even in regions where we know a big earthquake will eventually strike, its impacts are difficult to anticipate. The hazard posed by the southernmost segment of the San Andreas Fault is recognized to be high, for example—more than 300 years have passed since its last major earthquake, which is longer than a typical interseismic interval on this particular fault. Physics-based numerical simulations show that, if the fault ruptures from the southeast to the northwest—toward Los Angeles—the ground motions in the city will be larger and of longer duration, and the damage will be much worse, than if the rupture propagates in the other direction (Figure 3.1). Earthquake scientists cannot yet predict which way the fault will eventually go, but credible theories suggest that such predictions might be possible from a better understanding of the rupture process. Clearly, basic research in earthquake physics will continue to extend the practical understanding of seismic hazards.
To move further toward NEHRP Goal A and improve the predictive capabilities of earthquake science, the National Science Foundation (NSF) and the U.S. Geological Survey (USGS) should strengthen their current research programs on the physics of earthquake processes. Bolstering research in this area will “advance the understanding of earthquake phenomena and generation processes,” which is Objective 1 of the 2008 NEHRP Strategic Plan. Many of the outstanding problems can be grouped into four general research areas: