A powerful earthquake shook Indonesia on Wednesday, killing 10 people, injuring scores and triggering a small tsunami that hit one city on the island of Sumatra, authorities said.The 8.4-magnitude quake off Sumatra damaged homes, mosques and shopping malls along the coast and could be felt in at least four countries, with tall buildings swaying as far as 1,200 miles away. It was followed by a series of aftershocks, the strongest of which registered at a magnitude of 6.6 and triggered a second tsunami alert for Indonesia, which was lifted about an hour later, said Suhardjono, an official with Indonesia's meteorological agency, who goes by only one name.