Uranium-thorium disequilibrium dating is gaining importance in both neotectonic and paleoseismic studies. Coral heads uplifted during paleoseismic events in Vanuatu have been dated with errors of just a few years, and similarly precise timings have been made for the uplift and submergence during large earthquakes of the Sumatran subduction zone, the long-term deformation along low-latitude coastlines, and the glacial low stands and interglacial high stands of sea level in the tropics (87). The latter provide a basis for inferring the ages of deformed coastal deposits and surfaces at high latitudes.

Knowing the age of ground surfaces can be critical to quantifying the rate of deformation of a fold, the rate of tilt of a surface, or the rate of slip across a fault, but surfaces have been notoriously difficult to date, especially beyond the 50,000-year range of radiocarbon analysis. Surface-exposure dating by cosmogenic isotopes, especially 10Be, 26Al, and 36Cl, has resolved some of these problems, and these techniques have been applied to faulting caused by the Indian-Asian collision, normal fault scarps in limestone in the eastern Mediterranean, and California marine terraces (88). The last were revealed to be tens of thousands of years younger than previously thought, implying that earthquakes such as the 1989 Loma Prieta event must be far more frequent.

Neotectonics

Although plate tectonics furnishes the first-order framework for understanding global seismicity, most tectonically active plate boundaries exhibit significant second-order complexities that are responsible for a large percentage of the destructive earthquakes of the twentieth century (see Chapter 2). Placing the resulting diversity of fault structures in a consistent kinematical framework is the program of neotectonics.

Maps of Active Faults and Folds Active faults and folds have been mapped at a scale of 1:1,000,000 to 1:10,000,000 for Japan, Turkey, the United States, New Zealand, China, and many other regions (89). These maps are commonly derived from interpretations of aerial photographs, satellite imagery, or bathymetry verified by field mapping and sampling. Despite this progress, no global map of active faults and folds has been compiled at even these coarse scales (90). Furthermore, such maps seldom are in the digital formats that allow ready access to a full range of geologic information.

More detailed maps and databases of active regions reveal the geometric and kinematic data necessary to forecast future behavior and explain past seismicity. These larger-scale maps, such as for the North Anatolian fault or the Nankai trough in Japan, often include features



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