Plate movement, awareness may have cut Indonesian toll: expert

"Most probably the quakes were caused by horizontal shifts in the continental plates," said Subardjo, a seismology expert with the Indonesian meteorological agency.

"So although similar amounts of energy were released, it had a different effect than when the quakes are caused by vertical shifts of the plates."

It was a vertical shift that caused the massive quake that unleashed the 2004 Indian Ocean tsunami, which killed 168,000 people in Aceh province at the tip of Sumatra and more than 50,000 others in the region.

"It appears that this didn't happen in the recent string of quakes in Bengkulu," Subardjo told AFP.

Authorities here automatically issue tsunami warnings for shallow underwater quakes at magnitudes higher than 6.3.

Land damage on the other hand may have been limited by the geology specific to the areas near the epicentre, including Bengkulu, a city of about 300,000 people, he said.