The S Wave Project for Focal Mechanism Studies. The Alaska Earthquake Sequence of 1964

摘要

The polarity of the P wave first motion in the main shock yields a single well determined nodal plane with strike N66 degrees E, dip 85 degrees to the southeast. The focal mechanism of the earthquakes related to the main shock bear a remarkable similarity to one another and to the main shock. In all but three cases there is a single steeply dipping nodal plane of P. For earthquakes in the Kodiak Island region this plane has the same orientation as that of the main shock. For earthquakes to the east of Prince William Sound the near vertical nodal plane P shows a systematic change in orientation corresponding to the change in trend of the tectonic features. For all of these shocks excellent S wave data permit the determination of the second nodal plane, indeterminant from the P wave data. It is found to have a dip of about 10 degrees to the northwest or north. By inference, the second nodal plane of the main shock has the same orientation. (Author)