derived from stratigraphic data, seismic reflection profiles, seismicity, and tectonic landforms visible in topography, as well as ground-based mapping.

Slip Rates on Active Faults The earthquake production rate is a function of the rate of slip on active faults. At the San Andreas fault, where a 4000-year-old channel and a 14,000-year-old alluvial fan are offset right-laterally, the derived slip rate is about 33 millimeters per year (Figure 4.25). Here, offset during the great earthquake of 1857 was about 9 meters. If this were typical and if earthquakes were periodic, the 1857 event would repeat about every 270 years.

Such simple calculations are a starting point for determining moment-release rates, but strain relief is commonly more complex. Rates of slip along mid-ocean transform faults, for example, can be well constrained by the separation of the magnetic anomalies at the adjacent spreading centers or from globally consistent plate-motion models like NUVEL-1. However, because the rheology of rocks within transform fault zones favors aseismic rupture (91), the rate of production of earthquakes along oceanic transforms is almost always much lower than would be predicted from the slip rate. Cosmogenic exposure dating of surfaces in central Asia, using 10Be and 26Al, has begun to yield reliable slip rates for the great strike-slip faults of the Indian-Eurasian collision (92). Slip rates have been estimated by similar calculations for the growth of folds, blind thrusts, and other reverse faults in many regions of the globe (93).

Variations in sea level on ice-age time scales of 105 to 106 years have produced suites of datable landforms and strata with measurable deformations. Coastal terraces and deposits formed during sea-level highstands about 125,000, 105,000, 82,000, and 5000 years ago have been used widely to determine average rates of uplift and submergence in coastal regions ranging from less than 1 millimeter per year to about 10 millimeters per year (Figure 4.26). The rate for the Corinth fault, as an example, has been about 0.7 millimeter per year over the past several hundred thousand years (Figure 4.21).

Probing the Third Dimension Neotectonics is based on the interpretation of structures and stratigraphy at the surface; however, the extrapolation of active features to depth depends on the integration of surface data with subsurface information from drilling and seismic imaging. Seismic reflection surveys conducted for petroleum exploration and borehole data logged from oil and gas wells have furnished critical information on the three-dimensional structure of the upper crust in seismically active areas (94). The correlation of faults located in the upper 5 to 10 kilometers by these methods with precisely relocated earthquake hypocenters at

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