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Earth's background free oscillations

Suda¹, Nawa, Fukao

¹N. Suda and K. Nawa, Department of Earth and Planetary Sciences, Nagoya University, Nagoya, Japan. Y. Fukao, Earthquake Research Institute, University of Tokyo, Tokyo, Japan.

Science (New York, N.Y.)

|April 8, 1998

Summary

Earth is constantly undergoing free oscillations, even when there are no major earthquakes. These continuous seismic oscillations suggest an unknown internal Earth process is driving them.

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Area of Science:

Geophysics
Seismology
Earth Dynamics

Background:

Earth's free oscillations were traditionally viewed as temporary events following significant seismic activity.
Previous understanding limited the observation of these oscillations to periods after large earthquakes.

Purpose of the Study:

To investigate the presence and nature of Earth's free oscillations during seismically quiet periods.
To determine the source of continuous, observable free oscillations in the Earth.

Main Methods:

Analysis of data from the International Deployment of Accelerometers (IDA) gravimeter network.
Observation and frequency analysis of Earth's free oscillations.
Numerical modeling to test potential excitation sources.

Main Results:

Earth exhibits observable free oscillations even in the absence of large earthquakes.
The dominant oscillations are fundamental spheroidal modes within the 2-7 millihertz frequency range.
The cumulative effect of numerous small earthquakes does not account for the observed incessant oscillations.

Conclusions:

Earth's background free oscillations are a persistent phenomenon.
The source of these continuous oscillations is an unidentified dynamic process within the Earth.
Further research is required to understand the mechanisms driving these incessant seismic oscillations.

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