[Axenolith]

I doubt there was 1/5th of those there in the 50’s...

[ErnstStavroBlofeld]

I think we had much more due to the testing at DOE Nevada. We detected the North Korean tests through seismology. I am willing to bet that EG&G had developed the technology. Here is some reading for you:

http://74.125.155.132/search?q=cache:C1w8vCTIhu4J:www.eas.slu.edu/People/LZhu/teaching/eas130/detect.ppt+Nuclear+Seismic+Device&cd=25&hl=en&ct=clnk&gl=us