Earthquakes in the Pacific Northwest

Posted by cdj On November - 8 - 2012

A recent, powerful earthquake off the Pacific coast of British Columbia, Canada (Mw=7.7, depth=12.5 miles) has focused interest on that region’s seismicity and revived interest in North American vulnerability to Pacific Ocean subduction zone earthquakes and tsunamis. The October 27, 2012 earthquake, the largest in Canada since 1949, was not a subduction event but occurred on a strike-slip fault system (Queen Charlotte Fault) which typically does not generate large tsunamis – unlike the region’s great Cascadia Subduction Zone which is capable of creating huge tsunami waves from earthquake vertical displacements in the ocean. The West Coast and Alaska Tsunami Warning Center generated a tsunami warning immediately after the main Mw=7.7 earthquake event; providing a test of the warning system since only a very slight ocean wave resulted from this BC earthquake. The state of preparedness in Western Canada for a large earthquake and tsunami is now being revisited popularly, especially since the devastating Tohoku (Japan) earthquake and tsunami of 2011 and the 2010 Maule (Chile) earthquake and tsunami. Professional seismologists and engineers developing probabilistic seismic hazard analysis (PSHA) calculations for subduction earthquake ground motion prediction equations (GMPE) applicable to the Pacific Northwest, are using the rare strong ground motion data generated by these earlier, large subduction earthquakes in the Pacific Ocean near Japan and Chile. Several researchers reported on this work recently at the 15th World Conference in Earthquake Engineering in Lisbon, Portugal. For three examples, see these papers now in NISEE e-library:

- Regional differences in subduction ground motions. (C.Beauval, F.Cotton, N.Abrahamson, N.Theodulidis, E.Delavaud, L. Rodriguez, F.Scherbaum, A.Haendel) – Lisboa: 15WCEE, 2012.
Comparison of BC Hydro subduction GMPE to data from recent large megathrust earthquakes. (N.J.Gregor, K.O. Addo, N.A. Abrahamson, R.R. Youngs) – Lisboa: 15WCEE, 2012.
- Strong ground motion attenuation relations for Chilean subduction zone interface earthquakes. (V. Contreras & R. Boroschek) – Lisboa: 15WCEE, 2012.

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