Hi All. I found something interesting about “Free Earth Oscillations.” Sorry I was unable to copy and paste the URL. However you can go to the Goggle search engine and type in “Incessant excitation of the Earth’s free oscillations.” That should take you to the link. Be aware that the link may freeze. I have windows XP home edition and it will freeze using it. It is a PDF file.

N. Suda and K. Nawa, Department of Earth and Planetary Sciences, Nagoya University, Nagoya, Japan. Y. Fukao, Earthquake Research Institute, University of Tokyo, Tokyo, Japan.

Earth's free oscillations were considered to be transient phenomena occurring after large earthquakes. An analysis of records of the IDA (International Deployment of Accelerometers) gravimeter network shows that Earth is freely oscillating at an observable level even in seismically inactive periods. The observed oscillations are the fundamental spheroidal modes at frequencies between 2 and 7 millihertz. Numerical modeling indicates that these incessant excitations cannot be explained by stacked effects of a large number of small earthquakes. The observed "background" free oscillations represent some unknown dynamic process of Earth.

They and others continued to research to find the cause or “free earth oscillations” and it now appears they may have found the answer.

Yoshio Fukao and Kiwamu Nishida

Earthquake Research Institute, University of Tokyo,
Tokyo, Japan

Naoki Suda

Graduate School of Science, Hiroshima University,
Higashi-Hiroshima, Japan

Kazunari Nawa

Geological Survey of Japan,
Tsukuba, Japan

Naoki Kobayashi

Earth and Planetary Sciences, Tokyo Institute of Technology,
Tokyo, Japan

Abstract

[1] It has recently been established that the Earth's free oscillations are continuously excited by phenomena other than earthquakes and that these oscillations constitute the background noise in the normal mode band at quiet sites. On the basis of evidence that the excitation source is at or just above the Earth's surface, a normal mode theory of the Earth's free oscillations excited by random atmospheric loading is developed. The displacement field is expressed in the frequency domain in general terms of the cross-spectral density of air pressure disturbance. For spatially homogeneous and isotropic disturbance the cross-spectral density is approximated by the power spectral density and the coefficient of coherence with a coherence length much shorter than the wavelengths of normal modes. With this approximation the spectrum of ground acceleration is represented as the product of the pressure force term and the Earth response term. The final expression of the acceleration spectrum includes the effect of the gravity attraction of a disturbed air mass. A synthetic spectrum is calculated, using a power law decaying air pressure spectrum consistent with observations, assuming a frequency-dependent coherence length of air pressure fluctuation, taking into account the effect of the gravity attraction of a disturbed air mass. This synthetic spectrum exhibits distinct peaks of fundamental modes and complex troughs consisting of overtone modes, in quantitative agreement with the peaks and troughs of the observed spectrum.

Received 3 May 2000; revised 9 December 2001; accepted 14 December 2001; published 28 September 2002.

Now lets take the shock waves from a large quake and add them to the “free earth oscillations.” We know these shock waves travel around the world because seismographs around the world can and do detect them. What kind of an affect would they have on this oscillation and how long does this affect last? Take Care…Don in creepy town