There was an interesting paper in Science some years back that showed a 
fairly convincing correlation between certain wavelength atmospheric 
disturbances (harmonic order in the 20s or so) and a seismically 
detectable excitation in the Earth at the same wavelengths. Another 
paper in Nature showed annual modulation of Landers aftershocks with 
activity peaking in September. I think there is pay dirt there, but 
I've not followed the developments...some times these claims are even 
retracted after further analysis and thought. Some current paradigms on 
seismicity, e.g. chaos theory, might suggest that every little factor 
can have an effect on seismicity (like the butterfly effect).

Here are the refs:

Gao, S.S., P.G. Silver, A.T. Linde, and I.S. Sacks, Annual Modulation 
of Triggered Seismicity Following the 1992 Landers Earthquake in 
California, Nature, vol. 406: 500-504, Aug. 3, 2000.

Kiwamu Nishida, Naoki Kobayashi, and Yoshio Fukao, Resonant 
Oscillations Between the Solid Earth and the Atmosphere, Science 2000 
March 24; 287: 2244-2246.

Cheers!
John

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