BUENOS AIRES (Reuters) - The strongest earthquake to hit north-central Argentina in six years shook the area on Sunday but, because of its depth, caused no reported damage, earthquake monitoring centers said.

The U.S. Geological Survey in Washington said the tremor had a magnitude of 6.9 and originated 380 miles below ground. It set the epicenter 90 miles southeast of Santiago del Estero and 510 miles north-northwest of Buenos Aires.

"We expect no damage from this earthquake because of the depth,'' U.S. Geological Survey spokeswoman Trudy Harlow said.

"This is the largest earthquake in the general area since May 10, 1994, which was an earthquake of the same size and depth. That earthquake caused no damage,'' she said.

But Harlow said the deeper the quake the wider the area in which tremors are felt.

Police in Santiago del Estero said they had not felt the quake, but civil defense officials in nearby La Rioja Province said they had felt a slight tremor.

"We felt it here, but it was very light,'' said Nicolas Luna of the city of La Rioja's civil defense office. "No damage has been reported.''

"I don't think there was any damage with these characteristics,'' Millan said, referring to the quake's depth. ''The earth tends to lessen the power of seismic waves.''