Microseisms and Atmospheric Oscillations

Abstract

THE surface of the earth is in constant movement with amplitudes of a few thousandths of a millimetre, and this movement is picked up and registered by instruments set up to record the passage of waves caused by earthquakes. An earthquake starts from a definite focus, but a microseism is any ground movement which has not been started by an earthquake. Bertelli, who first used the name ‘microseism’ in 1878, probably intended the name to cover only those waves of 5 ± 2 sec. period which were somewhat regular in character and which, beginning with small amplitudes, grew in intensity and then died out in a length of time up to a few days.