Science Opportunities - Basic Research Opportunities in Earth Science - page 54

studies of rock friction and theoretical models of stress transfer to clarify how
stress interactions among active faults affect the sequencing of large earthquakes
( Figure 2.12 ). Excellent progress has also been made in understanding the
shorter-term, smaller-scale processes that control earthquake nucleation and
rupture dynamics. Combining this information with simulations of seismic wave
propagation through complex geological structures is leading to significant
improvements in the ability to forecast damaging ground motions— information
crucial to seismic hazard analysis and earthquake engineering.
FIGURE 2.11 Geodetically determined (GPS) velocities, relative to stable
interior North America, for southern California and adjacent regions of Nevada,
Arizona, and Mexico. Stations located on islands in the Pacific Ocean move
approximately with the Pacific plate, at ` 5 0 mm per year northwest. In the
northern portion of the diagram the zone of active strain between the Pacific
plate and North America is several hundred kilometers in width, while in the
southern portion of the diagram, most of the strain is localized within a zone 50
km wide and occurs on or near the San Andreas Fault. Comparison of actively
accumulating deformation obtained from geodetic measurements yields
important insights into seismic risk.