Wednesday, December 10, 2003

Ike Shake:

Apparently there was a magnitude 4.5 earthquake just before 4 p.m. yesterday, but I didn't feel a thing. I was probably either walking around, or I am on a floor in my building that was a node for the dominant frequency.

Here's the USGS webpage for this event.

The epicenter was nearer to Richmond, and occurred in a known area of seismic activity that can just be made out on this map of seismic activity in the U.S.:

The event was very shallow, only about 5.0km. Western earthquakes are often between 10 and 150 km deep.

It's actually very hard to get away from a fault if you are on land - the maximum distance between faults is about 5 miles in the U.S., a fact that makes siting nuclear power plants very hard, since seismic hazards are important to safety. The key factor is how active the fault is - and most faults are pretty much quiescent. The hazard map above takes that into account with the "2% Probability of Exceedance in 50 years" statement.

Note the hotspots in the East - the Arkansas-Missouri area, South Carolina, Massachusetts, and the St. Lawrence - all places where there have been very large, but rare, movements: the New Madrid earthquake in 1811 (M=7.58), Cape Ann in 1755, Charleston in 1886 (M=7.3), and Massena, NY in 1944 (M=5.80).

Yesterday's quake released about 100,000 tons of TNT-equivalent energy. I happened to come across this fact while looking over data for the "Atoms for Peace Program," which was announced by Pres. Eisenhower fifty years ago on December 8.

How is this related?

Ike's announcement led to the Plowshare program which explored the use of nuclear power to dig large holes for use in construction. There were a total of 35 shots in this series, the first of which was Gnome under Operation Nougat, forty-two years ago today.

The most famous Plowshare shot is probably Sedan, carried out on July 6, 1962 which created a crater over 300 feet deep. Tours of the Nevada Test Site stop here. Here it is in action:

The Sedan explosion had a yield of 104 kilotons - about the same energy as yesterday's earthquake. There are about 13,000 of these light earthquakes a year worldwide.

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