Changes in the Earth's rotational energy induced by earthquakes

Abstract

The kinetic energy of the Earth's rotation can be separated into two parts: the spin energy and the polar‐motion energy. Here we derive rigorous formulae for their changes, where the polar‐motion energy change is related to the polar‐motion excitation function via a treatment of reference frames. The formulae are then used to compute co‐seismic energy changes induced by the static displacement field produced in an idealized earth model by a total of 11015 major earthquakes that occurred during the period 1977 to 1993. An extremely strong statistic is found for the earthquakes' tendency to increase the Earth's spin energy; the rate during 1977 to 1993 was +6.7 GW, about the same as the total seismic‐wave energy release. The corresponding polar‐motion energy changes are 10−6 times smaller and had no detectable statistical tendency in their signs. Copyright © 1995, Wiley Blackwell. All rights reserved