Volcanic Seismology

Volume 3 of the series IAVCEI Proceedings in Volcanology pp 223-234

Non-Double Couple Earthquake Focal Mechanisms and the Accretionary Tectonic Cycle

  • Gillian R. Foulger
  • , Roger E. Long

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This chapter discusses the results of recent investigations of small magnitude earthquake activity in geothermal areas in Iceland. Instrument deployment was sufficient to constrain source mechanisms and mixed suites of double couple and non-double couple events were reported. The focal mechanisms of these continuous events allow us to study the cyclic pattern of the stress field with time, close to the accretionary plate boundary. During periods of tectonic quiescence, plate movements build up an extensional stress field close to the boundary and extensional failure occurs. Immediately after rifting, the extensional component is removed. The resulting stress field is roughly triaxially symmetric and variable on a small scale in both magnitude and orientation.