A Global Perspective on Static vs' Dynamic Earthquake Triggering

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A Global Perspective on Static vs. Dynamic
Earthquake Triggering

• Ellen Mallman - Stanford
• Tom Parsons - USGS

U.S. Department of the Interior U.S. Geological
Survey
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What proportion of triggered earthquakes are hard
to explain with a static model?

• 119 M7 earthquakes from the Harvard CMT catalog
  that have known nodal planes
• Calculate shear stress change on nodal planes of
  all subsequent events

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Are there post-mainshock earthquake rate changes
that are hard to explain with a dynamic model?

• Use the same 119 M7 earthquakes from the Harvard
  CMT catalog
• Look for evidence of post-seismic suppression of
  earthquakes

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Conclusions

• If we assume a static stress model for
  triggering, 40 of M5.5 aftershocks are
  difficult to explain (?at least 40 dynamically
  triggered?)
• 1906-style earthquake suppression is rare on
  global scale (happens 2-3 of the time)
• Significant, long-term (5 yr) post-seismic
  mechanism changes implies that static stress
  changes from M7 earthquakes have measurable
  effects