Tsunami experts could not understand why Monday's forceful earthquake off Indonesia (search) failed to produce massive waves similar to those generated by the Dec. 26 quake that killed at least 175,000 people in the same region.

A magnitude 8.7 quake shook Indonesia's west coast, killing hundreds of people and spreading panic that another devastating tsunami was on the way.

There was no tsunami, but a small wave was detected by a tide gauge on Cocos Island (search) near Australia, about 1,500 miles south of the epicenter, according to the Pacific Tsunami Warning Center on Oahu.

"I'm baffled an earthquake this size didn't trigger a tsunami near the epicenter," said Robert Cessaro, a geophysicist at the center, which is operated by the National Oceanic and Atmospheric Administration (search).

Center Director Charles McCreery said earthquakes of at least 8.0 magnitude usually generate major tsunamis.

"We expected some destructive tsunami with some distant destructive effects. It was surprising," he said.

The latest event also demonstrated "there's a whole world of uncertainty about trying to judge a tsunami based on the earthquake data," he said.

The warning center initially estimated the Dec. 26 earthquake to have a magnitude of 8.0, but it turned out to be larger, with a magnitude of 9.0.

Monday's preliminary estimate was magnitude 8.5 but had no destructive tsunami.

"The one we initially thought was bigger turns out to have no effect," McCreery said. "The one we initially thought was smaller had a huge effect. This is the challenge of tsunami warning."

The warning center, established in 1949, came under heavy criticism following the December tsunami for not being more aggressive about warning Asian nations and possibly saving thousands of lives.

Earlier this month, a group of 58 European tsunami survivors and relatives of victims sued NOAA and other agencies, alleging the center did not do enough to warn people about the disaster.

"Although we certainly wish that somehow the event unfolded in a way that we could've done more for the region, we really did all we could under the circumstances," McCreery said.

Since then, several Indian Ocean nations have established communications with the center and are now on its alert list. On Monday, the facility was able to alert those nations.

The Indian Ocean has no warning center similar to the one in Hawaii.