The risk of Indian Ocean earthquakes and tsunamis similar to the 2004 Sumatra disaster is greater than previously thought, researchers say.

British and Canadian scientists said the risk in the western Indian Ocean of an earthquake-caused tsunami that could threaten the coastal areas of Pakistan, Iran, Oman, India and other countries has been underestimated.

Writing in the journal Geophysical Researcher Letters, the researchers say earthquakes similar in magnitude to the 2004 Sumatra earthquake could occur in an area beneath the Arabian Sea known as the Makran subduction zone.

Subduction zones are where two of the Earth's tectonic plates collide and one is pushed beneath the other, and earthquakes in those zones can cause significant movement of the seabed that displaces large volumes of water and can result in a tsunami.

The 2004 Sumatran earthquake triggered devastating tsunamis along the coasts of landmasses bordering the Indian Ocean, killing over 230,000 people in flooded coastal communities.

While the Makran subduction zone has shown little earthquake activity since the late 1940s, it is a large zone that could initiate large-magnitude earthquakes, the researchers said.

Modeling suggests "the potential earthquake rupture zone extends a long way northward, to a width of up to 350 kilometers (215 miles) which is unusually wide relative to most other subduction zones," Gemma Smith of the University of Southampton School of Ocean and Earth Science said.

That and thicker than normal seabed sediments means "the Makran subduction zone is potentially capable of producing major earthquakes, up to magnitude 8.7-9.2," she said. "Past assumptions may have significantly underestimated the earthquake and tsunami hazard in this region."