I am a geologist by training, and have lived most of my life in earthquake prone regions (grew up in the PNW, and the last 25 years in Alaska), so I'm kind of interested in this stuff.

I don't wish to minimize the danger of a major earthquake occuring under a major west coast city such as Vancouver BC, Seattle, San Francisco, or LA. However, it is also good to keep in mind that damage and destruction in an earthquake (and resulting tsunami) is generally highly variable over an area. Extrapolating damage from the worst hit area across an entire region can be misleading. At the same time it is prudent not to underestimate the risks.

Damage from an earthquake can occur in a number of ways. The direct ground motion can cause buildings, bridges, and other structures to collapse. The intensity of ground motion depends on how near the epicenter is (map view) and how deep it is. The damage is also highly dependent on local soil and bedrock conditions, and how long the quake lasts. Landslides triggered by the quake can be extremely destuctive, but tend to be localized, depending on topgraphical relief and soil conditions. Structures built directly across a fault which moves will be heavily damaged, but this tends to be a very narrow linear zone. Tsunamis can come from distant earthquakes, or be locally generated. In either case tsunami damage is very dependent on local coastal bathymetry. Some areas are very low risk, and some are high risk.

The 1964 Alaska Earthquake provides a good illustration of this. At 9.2 it is still considered to be the 2nd most powerfull earthquake recorded in modern times. Some of the most graphic images of that earthquake were from Anchorage. But it is well to remember that even in Anchorage, the degree of damage varied dramatically over short distances. The Turnagain area and downtown were severly damaged by landslides, but much of the rest of the city was not. The only deaths directly resulting from the earthquake were the 9 people killed in Anchorage. The other ~124 deaths were elsewhere (16 outside of Alaska), resulting from tsunamis.

Based on actual damage in '64, and more recent geological research, a seismic risk map has been compiled for present day Anchorage: http://www.muni.org/Departments/OCPD/Planning/Planning%20Maps/Anch_Bowl_Seismic_8x11.pdf

The USGS, NOAA, and other agencies attempt to compile similar maps for other threatened cities. For example, in the Seattle area there is a map showing the relationship of earthquake risk to important infrastructure "lifelines" at http://geomaps.wr.usgs.gov/pacnw/lifeline/index.html
For Seattle tsunami hazards see: http://www.pmel.noaa.gov/pubs/PDF/wals2794/wals2794.pdf

Again, I'm not trying to minimize the risks, only to keep them in some kind of realistic perspective.