Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 17 4 2010 10.5194/npg-17-293-2010 http://www.nonlin-processes-geophys.net/17/293/2010/ http://www.nonlin-processes-geophys.net/17/293/2010/npg-17-293-2010.html http://www.nonlin-processes-geophys.net/17/293/2010/npg-17-293-2010.pdf 293 302 2010-07-02 A simple metric to quantify seismicity clustering N. F. Cho ncho3@uwo.ca K. F. Tiampo S. D. Mckinnon J. A. Vallejos W. Klein R. Dominguez Department of Earth Sciences, University of Western Ontario, London, Canada Department of Mining Engineering, Queen's University, Kingston, Canada Department of Physics, Boston University, Boston, USA Department of Physics, Western Kentucky University, Bowling Green, USA now at: Department of Mining Engineering, University of Chile, Santiago, Chile The Thirulamai-Mountain (TM) metric was first developed to study ergodicity in fluids and glasses (Thirumalai and Mountain, 1993) using the concept of effective ergodicity, where a large but finite time interval is considered. Tiampo et al. (2007) employed the TM metric to earthquake systems to search for effective ergodic periods, which are considered to be metastable equilibrium states that are disrupted by large events. The physical meaning of the TM metric for seismicity is addressed here in terms of the clustering of earthquakes in both time and space for different sets of data. 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