Effect of earthquakes on the Chandler wobble and the secular polar shift

Abstract

The representation of the displacement fields due to the faults associated with major earthquakes by the elasticity theory of dislocations shows that these fields are very extensive, both laterally and vertically. The changes in the products of inertia of the earth are computed, using dislocation theory, for several large faults that have been analyzed in the literature. From the changes in the products of inertia, the contribution to the excitation of the Chandler wobble and the resulting polar shift are calculated. To estimate cumulative effects these results are averaged over latitude, longitude, and fault azimuth, and their dependence on magnitude is examined. The relation between fault length and magnitude is used to provide additional information on the dependence of the contribution to the wobble and the polar shift on magnitude. Earthquake statistics are considered and a random-walk theory is applied to arrive at expressions for the cumulative effects on the Chandler wobble excitation and the secular polar shift. It is shown that, although only a very few earthquake faults have been analyzed and a half-space theory is applied, the results are compatible with the hypothesis that earthquakes excite the Chandler wobble. The secular polar shift, assuming that earthquakes do excite the wobble, is shown to be comparable with the astronomically observed value.