A strong earthquake hit off the south of Puerto Rico early Tuesday morning, the US Geological Survey said. The shallow 6.5 magnitude quake struck 13.6 kilometers (8.5 miles) south of the city of Ponce, USGS said, revising down its initial reading of 6.6. It was not expected to generate a tsunami, the Tsunami Warning Center said. A 5.8-magnitude earthquake shook the island on Monday, toppling houses and causing power outages, but there were no reports of casualties. bur-rbu/mtp