Is the city ready for a bigger one?

There is a similarity between two earthquakes that occurred this year and two others occurred 211 years ago.

In 1812, two consecutive earthquakes hit the vicinity of Dhaka in April and May.

Although their magnitude could not be verified, it was learned that the two quakes caused massive damage in two areas of Dhaka.

Moderate to strong quakes take place in places with earth fissures every 200 to 250 years. Experts have warned of a growing risk of earthquakes in Dhaka and adjacent areas that may cause a large-scale damage.

The capital city experienced a mild quake at 5:57am on Friday.

According to the US Geological Survey (USGS), it was a quake of magnitude 4.3 with its epicenter at Dohar near Dhaka. Its source was 10 kilometers below the surface. No damage or casualties have been reported from the earthquake, but it triggered panic among the people, and some left their residences in the early hours fearing a catastrophe.

Earlier, a magnitude 4 earthquake took place in Rupganj of Narayanganj on 25 April. The people could not feel it properly as its source was 17 km below the surface. The deeper the epicenter of an earthquake, the less the tremor is felt.

According to the earthquake monitoring center of Dhaka University’s geology department, a total of 52 mild, moderate, and severe earthquakes occurred within Bangladesh and 200 km areas of its neighborhood in the last 485 years.

Of them, around eight quakes took place in Dhaka and its adjacent areas in the last 12 years, with epicenters at Narayanganj, Mymensingh, Narsingdi, and Dohar. Most of the previous quakes had originated from different areas in Sylhet and Chattogram.

Syed Humayun Akhter, vice-chancellor of Bangladesh Open University and former professor of Dhaka University’s geology department, said the number of earthquakes around Dhaka has been increasing throughout the last 12 years. Six quakes occurred in Cumilla and Chandpur districts from 2008 to 2012. The epicenters of the subsequent quakes were mainly in Sylhet, Chattogram, and Cox’s Bazar areas.

The seismologist further noted that the earthquake epicenters are frequently found around Dhaka in recent years. The Indian plate is subducting under the inland Burma plate passing through Bangladesh, and a good amount of energy is accumulating there. This energy may emit at any time and cause strong vibrations.

"So, we have to resume stuck programmes immediately to deal with the earthquakes," he added.

According to the Indian meteorological department, including two in Bangladesh, a total of 14 mild to moderate earthquakes have taken place in South Asian countries in the last month.

There are 2.1 million buildings in Dhaka, as estimated by the civil engineering department of Bangladesh University of Engineering and Technology (BUET). Of them, 600,000 buildings are six stories or above.

During an earthquake, around 90 per cent of deaths are caused by building collapse. After the quake in Nepal in 2015, the BUET proposed to mark the buildings likely to be exposed to an earthquake in Dhaka.

In the process, the highly risky buildings were supposed to be marked with red color and that of moderate risk with green color. But the proposal did not gain momentum despite several phases of discussions.

After the devastating earthquake in Turkey, the Rajdhani Unnayan Kartripakkha (Rajuk) held a meeting on 22 March to identify vulnerable buildings. A final report was supposed to be submitted within the next month, but it did not happen.

Rajuk chairman Anisur Rahman Miah said, "We held a meeting on the earthquake last Thursday. We had earlier identified 3,500 buildings at risk of an earthquake in Dhaka under a project. However, it is not possible for us alone to survey all the buildings in Dhaka city. Therefore, we will conduct the survey through a third party and take necessary measures in this regard."

According to the disaster management department, 13 areas across the country are now at risk of earthquakes, with three hill districts and Jaintapur of Sylhet being at severe risk.

All possible earthquake zones are at least 100 km away from Dhaka. Seismologists have said that if an earthquake of magnitude 7 or 8 occurs within a stretch of 100 to 200 kilometers, Dhaka may experience strong tremors and see its weak buildings collapse.

The soil in the expanded or new residential areas of Dhaka is soft and weak. If a multi-storied building is constructed here without following the proper rules, there is a risk of collapse even with a moderate level of vibration.

Mehedi Hasan Ansari, a BUET professor and seismologist, said, "As the number of earthquakes increased around Bangladesh in the last year and the first few months of the current year, it can be said for sure that there is a risk of major earthquakes around Dhaka. So, we need to be careful before a big disaster. We should not delay in making the city earthquake-resistant."