Two novel methods for studying lowest frequency Earth oscillations   before earthquakes
  Two novel methods, one that is experimental and the other comprising a pair of theoretical types (one component that is mathematically rigorous and the other that is of frequency domain computational type), are being used in concert to study the motion of the Earth at periods in the neighborhood of 1000 s to beyond 10,000 s. Corresponding to frequencies lower than what is routinely measured by commercial seismographs, our observations are yielding new insights into the mysteries of Earth dynamics responsible for earthquakes. 
Randall D. Peters, Michael A. Phillips
physics.gen-ph