LSMSA and LIGO-LA (Laser Interferometric Gravitational wave Observatory- Livingston, Louisiana) have collaborating on a study of microseisms. There are many causes of microseisms, many of them man-made, but we are presently interested in the low frequency seismic signals from tropical storms in the Gulf of Mexico.
Adam Bray, graduate from LSMSA now at Yale, and Grant Belgard, senior, are helping investigate the correlation between the wave activity due to passing storms, measured by buoys of the National Buoy Data Center, and the seismic signals recorded at Livingston.
To do this we have Fourier transformed seismic time-series data to extract the frequency content and constructed seismograms stretching over periods of days to weeks. The wave signal is usually around 0.10 Hertz increasing in intensity when a storm is off the Louisiana coast. When a storm comes on-land or goes up on the shelf off-shore there is an increase in the "double frequency" signal intensity -- roughly in the 0.15-0.3 Hertz band.
For an example, Bill passed directly over LIGO on July 1:
Low res of original from GOES archives at NCDC
Bill was a relatively low intensity storm that produced some rain bands and flooding, but quickly went inland and fell apart. The seismic records produced the following seismogram (all times in UTC):
frequency (Hz)
Note the low frequency, below 0.05 Hz, signals. Many of these are earthquakes, especially the ones stretching from low to high frequencies around 0.1 Hz that decay away in a few hours. The times of these events were compared to known earthquakes at this site run by the USGS (only earthquakes in the last week or in the last 8-30 days are listed unless the earthquake was "significant." None of the earthquakes in this graph counted as significant!).
This is only a sample of the work we have done and I will update this site as time permits. Check back soon! J.S.