Southern California Earthquake Center
Studying earthquakes and their effects in California and beyond
A sequence of large earthquakes along the Aleutian arc and Kurile-Kamchatka trench from 1952 to 1965 released interplate stresses accumulated over a much longer period prior to the sequence. The subsequent evolution of postseismic deformation of the Pacific lithosphere has been predicted using a viscoelastic coupling model consisting of a purely elastic oceanic lithosphere overlying a viscoelastic asthenosphere with viscosity = 5 $\times$ 1017 Pa s. Southward propagation of both postseismic strain and velocity fronts is consistent with patterns of (apparently triggered) earthquake occurrence along western North America over the past 30 years, including accelerations in California seismicity from about 1979 to 1994. The model is consistent with observed anomalous velocity of broadly distributed Pacific geodetic sites and suggests that stress redistribution following earthquakes may produce tangible effects over a spatial scale of 1000's of km.
Find recent or historic earthquakes, lists, information on selected significant earthquakes, earthquake resources by state, or find webservices.
While most recorded earthquakes are consistent with expectations based on current understandings of plate tectonics, and with simplifying assumptions about the earthquake source, there are a number of very interesting exceptions. Earthquakes with non-double couple focal mechanisms, or which contain a non-zero isotropic component, may be the result of source processes other than slip on a planar fault surface. Earthquakes which occur outside of well-defined bands of seismicity, or which display focal mechanisms at odds with the stress regimes we believe to exist in a given region, may cause us to revise our understanding of regional tectonics, or of deformation processes in general. The Unusual Earthquakes research effort studies a small number of events in detail, by a variety of methods, in an effort to gain a more thorough understanding of source processes and tectonics which differ from accepted standard models.
The USGS monitors and reports on earthquakes, assesses earthquake impacts and hazards, and conducts targeted research on the causes and effects of earthquakes. We undertake these activities as part of the larger National Earthquake Hazards Reduction Program (NEHRP), a four-agency partnership established by Congress.
Seismic activity at Yellowstone Lake in Yellowstone National Park increased in late December 2008. As of January 8, 2009, the seismic activity has markedly decreased.