Morris, Minn. (A.P.) -- Midwesterners hardened to the threat of tornadoes and floods were surprised by another of nature's tricks Wednesday when an earthquake shook portions of four states.

The quake, which registered 5.0 on the Richter Scale, caused no injuries or major damage. Affected by the 10 a.m. trembling was a 60,000-square-mile area of western Minnesota, southeastern North Dakota, eastern South Dakota and northwestern Iowa.

The quake was only the seventh recorded in Minnesota during the last 130 years and the first since 1950, according to the Minnesota Geological Survey.

It rattled dishes and windows, shook buildings and startled residents of the area, many of whom have been battling floods and tornadoes since April.

Waverly Person of the Earthquake Information Center in Denver described the quake as moderate, but added that "it could have caused much damage in a heavily-populated area."

He said the center of the quake was about 10 miles west of Morris, a west-central Minnesota community of 5,336 persons.

People in Morris first attributed the tremors to a train derailment, falling trees and furnace explosions, the Stevens County sheriff's office said.

Dennis Myers, 23, of Morris, studies earthquakes as his hobby and has built a seismograph from a coffee can and an electric clock motor.

"I just woke up when the tremors began," Myers said. The tremors lasted about two minutes, and then came the big thud. The earthquake lasted about three or four seconds.

Earthquakes are so rare in the Upper Midwest, said Robert Provost of the Minnesota Insurance Information Center, that "hardly anyone" in the state has insurance which covers earthquake damage to property.

The tremors were felt as far north as Fargo, N.D., and adjacent Moorhead, Minn., a population center of about 100,000 persons 100 miles north of Morris.

Other large cities which felt the tremors were Sioux Falls, S.D., population 75,000, about 160 miles to the south, and Sioux City, Iowa, with about 90,000 residents, 250 miles south of Morris.

The National Weather Service said persons in a 12-story building in Sioux City reported that the building swayed. The NWS said tremors also were felt on the upper floors of St. Paul Ramsey Hospital.

Person said that, by comparison, the earthquake that struck California's San Fernando Valley in 1971, killing 54 persons and causing millions of dollars in property damage, measured 6.5 on the Richter Scale. The California quake was 15 times stronger than the one which hit the Midwest since every increase of one number on the Richter Scale means a tenfold increase in magnitude.