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.
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