Foreshocks, Aftershocks, and Earthquake Swarms with Special Reference to Normal Seismic Activity in and Near the Japanese Islands

  1. Leon Knopoff,
  2. Charles L. Drake and
  3. Pembroke J. Hart
  1. Norio Yamakawa

Published Online: 18 MAR 2013

DOI: 10.1029/GM012p0051

The Crust and Upper Mantle of the Pacific Area

The Crust and Upper Mantle of the Pacific Area

How to Cite

Yamakawa, N. (2012) Foreshocks, Aftershocks, and Earthquake Swarms with Special Reference to Normal Seismic Activity in and Near the Japanese Islands, in The Crust and Upper Mantle of the Pacific Area (eds L. Knopoff, C. L. Drake and P. J. Hart), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM012p0051

Author Information

  1. Seismological Laboratory, Meteorological Research Institute, Japan Meteorological Agency, Suginami, Tokyo, Japan

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 20 APR 2012

Book Series:

  1. Geophysical Monograph Series

Book Series Editors:

  1. Waldo E. Smith

ISBN Information

Print ISBN: 9780875900124

Online ISBN: 9781118663738

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Keywords:

  • Abnormal seismic activity;
  • Earthquake swarms;
  • Focal mechanism;
  • Foreshocks and aftershocks;
  • Japanese islands;
  • Seismicity;
  • Thompson method;
  • Utsu-Seki and modified Omori formulas

Summary

To study foreshocks, aftershocks, and earthquake swarms, it is fundamentally important to give a clear definition of what is tentatively called ‘abnormal seismic activity.' A definition based on the Thompson method is proposed. This method is applied to distinguish abnormal seismic activity from background seismic activity in active regions in and around the Japanese islands. The goodness of fit of the modified Omori formula for frequency decrease of aftershocks and the Utsu-Seki formula for aftershock area is also discussed from the geophysical point of view. The focal mechanism and areal concentration of energy of foreshocks, aftershocks, and earthquake swarms are also discussed with some reference to crustal deformation.