SEATTLE (AP) _ A mild earthquake rattled north-central Washington early Tuesday, but there were no reports of damage or injuries.

The quake at 2:57 a.m. registered about 3.3 on the Richter scale, said Chris Jonientz-Trisler of the University of Washington's geophysics center.

Preliminary analysis indicated the epicenter was in the relatively sparsely populated Stayman Flats area, she said.

The Richter scale is a measure of ground motion in which every increase of one number means a tenfold increase in magnitude. An earthquake of 3.5 can cause slight damage in a local area.

The 1964 Alaska quake which killed 131 people measured 8.4 on the Richter scale, while the San Francisco earthquake of 1906 is estimated to have registered 8.3 on the scale.