That fits in with historical reports of tsunamis in the area, some of which have the potential to be very large, the three scientists reported in the journal Eos.

"I marked out faults and what appear to be landslide deposits," Grindlay said in a telephone interview.

"We also identified these large cracks on the sea floor that appear to have potential for future landslides. They are about 35 to 40 kilometers (20 to 25 miles) long and they are right off the north coast of Puerto Rico."

They range in depth from 1,000 metres (3,200 feet) to 3,000 metres (10,000 feet), she said, and some are similar to the fault that caused the Dec. 26 quake off the coast of Indonesia that generated the tsunami that left 300,000 people dead or missing in the Indian Ocean area.

As with all quakes, it was impossible to predict when one would occur and what sort of tsunami it might generate, if it caused one at all, Grindlay said.

Movement of the sea floor or a landslide could cause such a wave. It could affect Haiti, the Dominican Republic, Puerto Rico, Jamaica, the Bahamas and the Virgin Islands, she said.

"There is the potential for the tsunami to travel across the ocean but by the time it reaches the (US) Atlantic coast it will probably be a small wave," she said.

At least 10 significant tsunamis have been documented in the northern Caribbean since 1492.

All 10 were triggered by movement along this plate boundary, which runs 2,000 miles (3,200 km) from the north coast of the island of Hispaniola, home to Haiti and the Dominican Republic, to the Lesser Antilles, the researchers said.

One destroyed Port Royal, Jamaica in 1692, and another killed at least 10 Jamaicans in 1780.

In 1946, a magnitude 8.1 earthquake in the Dominican Republic caused a wave that killed 1,800 people.

More could die if another tsunami hits because 35.5 million people now live along vulnerable coasts, the three geologists said.

Other experts have noted there are several active Caribbean volcanoes that could set off an inundating wave.

In January, US officials said they would spend $37.5 million over two years for new deep-sea warning systems aimed at giving near-total coverage for the US coastline.