Dhaka, Aug 12 - The latest threat of earthquake-triggered tsunami has abated, but disaster-prone Bangladesh faces a high risk of moderate to strong quakes, experts have warned.

Bangladesh also faces the risk of tsunami as four active sources of earthquake in the Bay of Bengal can generate tremors with a magnitude of over 7 on the Richter scale, affecting the country seriously.

The observatory at Bangladesh University of Engineering and Technology (BUET) recorded 86 tremors of over four magnitude during January 2006-May 2009. Another four earthquakes took place with magnitude of over five during the period.

The meteorological department detected at least 90 earthquakes taking place in the country between May 2007 and July 2008, nine of them above five on the Richter scale and epicentres of 95 percent being within a 600 km radius of Dhaka city.

Experts say it is these minor tremors that indicate the possibility of much more powerful earthquakes hitting the country.

According to a seismic zoning map prepared by BUET, 43 percent areas in Bangladesh are rated high risk, 41 percent moderate and 16 percent low, Mehdi Ahmed Ansary told The Daily Star.

The map, which is being drawn up under the supervision of Ansary with funding provided by the science and information and communications technology ministry, divides the country into three earthquake vulnerability zones.

The current zoning map has, however, not been included in the Bangladesh National Building Code (BNBC) that needs to be urgently updated, pointed out Ansary who is also vice-president of the Bangladesh Earthquake Society.

In the zoning map of 1993, 26 percent of the country was high risk, 38 percent moderate and 36 percent low in terms of earthquake vulnerability.

A.S.M. Maksud Kamal, an expert on earthquake and tsunami preparedness, said four sources of earthquake in the Bay of Bengal are active and can generate tsunami.

He said one of the sources generated an earthquake of 7.8 magnitude in 1762 which generated waves in rivers and other closed water bodies, and around 100 people were killed in boat capsizes at that time in the Buriganga.

Kamal said all the four sources in the Bay called F1, F2, F3 and F4 have a capability of generating earthquakes of over seven magnitude creating tsunami which will affect Bangladesh.

In that case the sea level will rise by 4-5 metres at Nijhum Dwip.