Understanding Active Fault Hazard

 

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There are three, well defined, different processes associated with the activity of a seismogenic fault:

  • ground shaking;
  • surface deformation;
  • surface rupture.

These three processes are the primary cause for damage to buildings and infrastructures. A survey of 50 major earthquakes occurred between 1989 and 2003 around the world (Bird and Bommer, 2004) shows that the primary cause for building collapse is ground shaking in 98% of the cases, followed by liquefaction (32%), slope failure (28%), tsunami (10%), and fault rupture (10%).

Ground Shaking

  • occurs always but is transient;
  • affects the widest area;
  • is responsible for most of the damage;
  • may trigger other geological effects (liquefactions, landslides, secondary ruptures);
  • requires mapping at 1:200k-1M.

Ground Shaking

Surface Deformation

  • occurs always and is permanent;
  • affects a wide area (fault size x2);
  • produce limited damage (critical facilities);
  • may trigger other geological effects (stream avulsions, slope instabilities, secondary ruptures, tsunamis);
  • requires mapping at 1:200k-1M.

Surface Deformation

Surface Rupture

  • occurs when faults "daylight" and is permanent;
  • affects a limited area (smaller than fault length);
  • may produce significant damage;
  • may trigger other geological effects (water ponding, damming);
  • requires mapping at 1:1k-10k.

Surface Rupture

References

  • Bird J.F. and Bommer J.J. (2004), Earthquake losses due to ground failure, Engineering Geology, 75(2), 147-179, doi:10.1016/j.enggeo.2004.05.006.

 



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