SAFER Testsite: Athens

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SAFER Test-site Athens

• Partners NOA, NKUA, NORSAR

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1995 6.2
1999 5.9
1981 6.8, 6.4, 6.3
Corinth rift fast opening 1cm/y, high
seismicity M 7 good azimuthal coverage, close
to Athens
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NKUA/NORSAR

• Development of instrumentation with the aim to
  apply
• Tnow network based location approach.
• Tc and Pd on-site calculation approach.
• Array based processing approach.

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NOA

• Development of the algorithm FORMA for the near
  real-time recognition of changes in the states of
  seismicity.
• Retrospective performance in strong Greek
  earthquake sequences.
• Application in swarm activities in Corinth Gulf.
• Criteria for the discrimination between
  foreshocks and swarms in Corinth Gulf.

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Corinth rift is very prone to foreshock and swarm
activity Papadopoulos et al. (2000)
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• Foreshock sequences
• n37 , d81 days

• Swarms
• n64 , d86 days

11 Feb 1984
18.03.01
12.06.01
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Criteria for swarm identification

• Minimum number of events 10 (Mogi criterion)
• b-value swarm b-value background
• Seismicity rate swarm seismicity rate
  background
• Probability for the occurrence of n events by
  chance
• ? lt 110-3

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Determination of background seismicity rate

• Earthquake catalogue was declustered by a Greek
  version of the Gardner and Knopoff (1974)
  algorithm (Latoussakis and Stavrakakis, 1992)

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January 2009 onset of swarm activity in Corinth
rift
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January 2009 onset of swarm activity in Corinth
rift
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January 2008 termination of swarm activity in
Corinth rift
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Conclusions

• 1.Algorithm FORMA performs well enough not only
  in stronmg earthquake sequences but also in
  swarm-type activity.
• 2.Identification of swarm activity is of great
  importance for reducing false alarms based on
  wrong foreshock determination.