08:02 PM MST on Wednesday, March 24, 2004

By TERESA BELL and BRUCE SUSSMAN, kgw.com Staff

SISTERS, Ore. -- Numerous minor earthquakes have shaken the area outside the small Central Oregon town of Sisters in the past two days, raising new questions about a bulge in the nearby Three Sisters Wilderness Area.

Experts are studying a bulge in the Three Sisters Wilderness Area that they believe is linked to the earthquake swarm. (KGW Photo)

Seismologists with the USGS office at the Cascades Volcano Observatory in Vancouver, Wash., recorded a swarm of 48 small quakes in the area on Tuesday alone. In some cases, the quakes were mere minutes apart.

Experts said the quakes were too small to cause any damage and it’s unlikely residents even felt them.

But they weren’t too small to record on seismographic equipment. The micro-quakes measured up to 1.5 in magnitude.

Experts said the minor quakes continued on Wednesday with the total number exceeding 100 for the two-day period.

Scientists said the earthquakes were centered three miles west of the South Sister volcano.

Seismologists said a bulgenear the volcano seems to be growing and one theory is that it somehow caused the swarm of earthquakes. They first started detecting the bulge in 1997.

The Cascades Volcano Observatory indicated the quakes started at 10 a.m. Tuesday and hit their peak later that day. As of Wednesday evening, they said the quakes were dying down gradually.

(The Associated Press contributed to this report.)