EARTHQUAKE FOCAL MECHANISMS AND CONTINENTAL DRIFT

Abstract

By studying the first motions of earthquakes recorded at seismograph stations throughout the world it is possible to determine the type of faulting which takes place at the focus of an earthquake. Three main types of faulting are observed:

thrust faulting, which is common in island arc provinces;

normal faulting, which is common along mid-ocean ridges; and

strike-slip faulting, which occurs along fracture zones.

In the New Guinea-Solomon Islands region all three types of faulting have been observed: thrust faulting along the mainland of New Guinea and in the island arc provinces at the northern margins of the Solomon Sea; normal faulting on the "seaward" side of the deep ocean trenches; and strike-slip faulting in the zone of seismicity under the Bismarck Sea.

An analysis of the focal mechanism solutions indicates that the New Guinea region is divided into at least three small rigid plates, all moving separately.