EARTHS CONTINUOUS OSCILLATIONS OBSERVED ON SEISMICALLY QUIET DAYS

Analysis of IDA gravimeter data between 1983 and 1994 and GEOSCOPE dat a between 1988 and 1094 show that fundamental modes of the Earth, for frequencies between 2 and 7 mHz, are excited even on seismically quiet days. Amplitudes of acceleration are slightly less than one ngal(10(- 9) gal). Examination of a sequence of shorter time interval records su ggests that the Earth is oscillating continuously. Currently, both atm ospheric excitation and tectonic motions are possible cause(s) of thes e oscillations.