Paleoseismology

Abstract

Paleoseismology is a subdiscipline of seismology that provides observational data on large earthquakes over millennial timescales through the application of geologic methods. Paleoseismic data can provide constraints on models of fault behavior, fault interaction, and tectonic processes and insights into the likely impacts of future earthquakes and the probability of extreme events. With few exceptions, earthquakes are generated by the movement of faults, so paleoseismic research is directly or indirectly a study of faults and their coseismic surface expression. Paleoearthquakes, or paleoseismic events, are recognized by detailed observations and analyses of geologic or environmental conditions within fault zones or in seismically active regions. Paleoseismic research involves identifying and cataloging paleoearthquakes through the examination of surface rupture evidence, regional coseismic deformation, and effects of ground shaking such as liquefaction or disturbance of fragile geologic features. Paleoseismic investigations also collect data on slip per earthquake, magnitude of paleoearthquakes, and fault slip rate. Recent developments in airborne and terrestrial digital imaging methods have led to improved recognition of tectonic deformation by enabling high-resolution remote imaging and analysis of fault scarps. Various geochronological methods are applied to determine the ages of paleoearthquakes and rates of fault-induced deformation. Advances in radiocarbon dating and application of Bayesian statistical methods have greatly reduced uncertainty in paleoearthquake ages. Classic models of fault behavior derived from paleoseismic data include segmentation, characteristic earthquake, and time-predictable rupture models. Improvements in the quantity and quality of paleoseismic data have allowed testing of these models on individual faults, with mixed results.