Moderate earthquake risk on the rise

An earthquake of 5.6 magnitude jolted the country on Saturday morning, shaking the capital and elsewhere.

Seismologists said this was the strongest earthquake that struck Bangladesh in the past 25 years since a 5.8 magnitude earthquake was felt in Barlekha of Sylhet in 1998.

Bangladesh witnesses a sudden rise in moderate earthquakes.

Data from Bangladesh Meteorological Department (BND) shows magnitude 5 or more on Richter scale or moderate earthquakes hit the country six times in 2023, and three times in 2002.

Moderate earthquakes struck the country once every two to four years from 1972 to 2017.

Such earthquakes have increased suddenly in recent years.

Seismologists said earthquakes occur from sudden movement of Earth's crust. It occurs along fault lines, cracks in Earth's crust where tectonic plates meet.

Though soil in Bangladesh is built up with alluvium, there is stone or hard soil 8-30 kilometres deep from ground soil. When two crusts collide, shakes are felt on the upper ground.

Experts think one such earthquake happened on Saturday.

A 5.6 magnitude earthquake is not that strong compared to other strong earthquakes that have happened elsewhere in the world. Since the epicentre of Saturday's tremor was surrounded by rivers and alluvium soil, no big damage was reported. However, cracks in buildings and damages and injury caused by panic were reported from various places of the country including Dhaka and Cumilla.

When the tremor struck on Saturday, students at several residential halls of Dhaka University started panicking. Plaster fell off from the wall and glass panels of doors were shattered at Haji Mohammad Mohsin Hall. In panicked, Minhajur Rahman, a student of Islamic history and culture, jumped out of a window from the 1st floor of Room 233 at Masterda Surja Sen Hall. He was later taken to Dhaka Medical College.

More than 100 workers were injured at Amir Shirt Factory in Chupuya area of Chauddagram, Cumilla after the panicked workers tried to leave the factory in a hurry during the earthquake. Three of the injured were sent to Cumilla Medical College Hospital.

Bangladesh Open University vice chancellor and seismologist Syed Humayun Akhter thinks huge force remains accumulated underground in the area where the Lakshmipur earthquake happened. Earthquakes may occur anywhere from Sylhet to Cox’s Bazar anytime. Earthquakes happened in Ramganj yesterday, Saturday, and in Rupganj, Narayanganj five months ago, and these incidents are the warning sign of a big earthquake, he added.

According to the Bangladesh Metrological Department and the United States Geological Survey, a 5.4 magnitude earthquake hit the country in October and the epicenter was Sherpur. Prior to this, a 5 magnitude earthquake shook the country on 11 September, a 5.3 magnitude earthquake on 14 August, a 5 magnitude earthquake on 16 June and a 5.1 magnitude earthquake on 23 June, and the epicenter of all of these four earthquakes were Sylhet.

Three earthquakes with 5 magnitude or more on Richter scale jolted the country in 2022. A 5.2 magnitude hit the country on 23 January and a 5.1 magnitude earthquake on 15 August. A total of 17 earthquakes, mostly between 4 and 5 magnitude, were felt in the country that year while epicenter of 10 of those tremors were Chattogram and Sylhet.

Seismologists said it is very unlikely that strong earthquake like that of Japan, Nepal and Afghanistan will hit Bangladesh, and earthquakes with 6 to 7 magnitude rarely occur in Bangladesh. They, however, think moderate earthquakes may cause damage in the country’s big cities including Dhaka.

Two teachers of the University of Chittagong -- Md Abdullah Al Zaman and Nusrath Jahan Monira – have researched the patterns of earthquakes that occurred in Bangladesh from 1976 to 2016. Researchers found tremors felt in Bangladesh were between 4 and 5 magnitude on Richter scale. A total of 282 earthquakes, occurred in these 40 years, and 77 per cent of the tremors were between 4 and 5 magnitude while 12 percent were between 5 and 6 magnitude.

Dhaka University vice chancellor and seismologist ASM Maksud Kamal told Prothom Alo, “The Lakshimpur earthquake is a warning on the rise in moderate earthquakes, and before that, we have learned about earthquake along with faults. But, recent earthquakes including the Lakshimpur have been happening at the earth crusts in our areas. Strong earthquakes may not occur in these earth crusts, but moderate tremors may cause huge gender for us. As a result, epicenters of such moderate epicenters will have to be found across the country, and once epicentres can be detected, earthquake resilient buildings can be built, as well as volunteers and rescue equipment can be kept ready.”

This report appeared in the print and online editions of Prothom Alo and has been rewritten in English by Hasanul Banna