Seismic monitoring around Mount St. Helens, Washington, for 28 days during the summer of 1970 showed that the frequency of local earthquakes was from 3 to 13 per day and very similar to the activity previously observed near Mount Rainier, Washington. The epicenters of the well-recorded earthquakes form a roughly linear pattern trending northeast from the summit area. This is the only obvious trend in the epicenter distribution. Recent geological investigations have not revealed faults or other major geological discontinuities along this trend. This pattern of epicenters seems to be approximately aligned with the remnants of five ancestral St. Helens plug domes that trend southwest from the summit region.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.