Steve Malone of the seismographic network said they were still not sure Saturday whether the Mount Hood earthquake was directly related to volcanic activity or related to the movement of the earth's plates and stresses and strains that caused the May earthquakes and the larger Scotts Mills quake in Oregon's Willamette Valley in 1993.

Those quakes, he said "are run of the mill quakes that occur throughout the Pacific Northwest."

"The Mount Hood quake had some characteristics that make it somewhat different from those but not clearly volcano-related," he said.

"It had some characteristics of both types of events."

• Mt Hood Uplift