How vulnerable is the US to quakes?

Are We Prepared for an 8.8 Quake?

Excerpts:

Fortunately, we do not expect a magnitude-8.8 earthquakes to be widespread in the United States. Such large magnitude earthquakes require very long faults that are capable of rupturing all at once. Only two such faults appear to have the capability to generate very large earthquakes: the Cascadia subduction zone along the coast of Washington, Oregon, and Northern California and the Aleutian subduction zone along the southern coast of Alaska.

Geologic evidence suggests the Cascadia fault last ruptured in 1700 and generated a 9-magnitude earthquake. In 1964, the Aleutian fault generated a 9.5-magnitude quake. The only other fault of comparable length is the San Andreas fault, but it appears to rupture along shorter segments and generate slightly smaller earthquakes.

Paradoxically, one effect of very long fault ruptures is that the shaking generated at the far end of the fault will be reduced by the time it travels to the other end of the fault. Distance is your friend in the earthquake business. Thus, the threat from these very large earthquakes is duration not strength of shaking. For example, the 1964 Alaskan earthquake lasted more than 4 minutes, whereas the magnitude-6.9 Loma Prieta quake in 1989 lasted less than 10 seconds.

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Beyond California, there are many areas — Oregon, Washington, Utah, the New Madrid region that includes Memphis, the Southeast and Northeast — that are facing major earthquakes and are not doing enough about it. The lack of significant earthquakes in those regions in the modern era has left policymakers with only the possibility of disaster and not a ready example of what can happen.

Of the areas outside of California, the central United States remains my greatest concern. A major earthquake similar to those that occurred in the early 1800’s would devastate the region and have a serious impact on the national economy.

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