An uptick in mild quakes. Are we on the precipice?

Over the last two decades, earthquake specialists have been warning that a massive and devastating earthquake could strike Bangladesh at any time. They point out that Bangladesh has not experienced a massive earthquake for more than 150 years; and the country falls among regions that are susceptible to massive earthquakes every 150 years or thereabouts.  

The discussion about the risk of earthquakes in Bangladesh took centre stage in the aftermath of the devastating earthquake in Nepal in 2015, which killed at least 8,964 and injured around 22,000 people. Now, the conversation on earthquakes has resurfaced, stemming from the unmistakable uptick in the frequency of earthquakes over the last two months. 

Earthquake researchers find this pattern unusual and say that it indicates the possibility of a massive earthquake hitting Bangladesh in the near future. 

Why has the frequency of earthquakes increased? 

A 4.9 magnitude earthquake hit merely kilometres away from Dhaka in May 2023. A mild earthquake of 5.2 magnitude on the Richter Scale jolted Dhaka and other parts of the country on 5 December 2022. 

A 5.3 magnitude earthquake jolted Dhaka on 2 October. The epicentre of the earthquake was 3 km from Resubelpara in India's Meghalaya.

"In the last four to five years, the number of earthquakes has not crossed more than 30 per year. But over the last two months, around 34 earthquakes have been recorded," said earthquake expert Professor Mehedi Ahmed Ansary at the Department of Civil Engineering, Buet. 

"If you count up this year, the number of earthquakes will be around 100 recorded earthquakes."

Bangladesh, or specifically this historical region, has a history of massive earthquakes, including two 7-magnitude earthquakes and one 8-magnitude earthquake some 150 years ago. Our region suffered five massive earthquakes from 1869 to 1930. 

The earthquakes include the 7.5 magnitude Cachar earthquake in 1869, the 7.3 magnitude Bengal earthquake in 1885, the 8.7 magnitude Great Indian earthquake in 1897, the 7.6 magnitude Srimangal earthquake in 1918 and the 7.1 magnitude Dhubri earthquake in 1930. 

Professor Ansary said, "We [specialists who study earthquakes] say that 7-magnitude earthquakes come after a 150-year cycle. The 8-magnitude earthquake comes after a 250-year cycle. 

"Our prediction is the earthquake can happen at any moment because it has fallen into the 150-year cycle. It can also happen 10 years later. But the earthquake will happen in the bracket of 140 to 160 years," said Professor Ansary. 

"[Now Bangladesh] has crossed the 150-year mark. It has been 154 or 155 years [since the last major earthquake]." 

Professor ASM Maksud Kamal at the Department of Disaster Science and Climate Resilience of Dhaka University, agrees that the possibility of a massive earthquake is substantial, because there hasn't been one in the region for more than 100 years. 

"What we are witnessing is activity [mild earthquakes] as a result of the energy accumulated on the small fault lines. That energy is coming out," said the earthquake expert. 

He said that the plates and fault lines are building up strain inside the earth because the Indian plate is moving in the northeastern direction. At the same time, the Burmese plate is moving in the western direction. The Tibet plate is moving in the southern direction. 

"Due to the movements of the plates, the plate boundaries are building up the strain. On the other hand, the fault lines are active and are colliding, building up more strain. We are seeing this energy being released through mild earthquakes," explained Professor Kamal. 

Professor Kamal is concerned because there are large fault lines like the Dauki fault bordering Bangladesh and the Eastern Boundary fault going through Bangladesh. The Dauki fault consists of three segments and the Eastern Boundary fault also consists of three faults. 

Kamal pointed out that one of the segments of the Eastern Boundary fault stretches from Arakan to Cumilla, another segment stretches from Cumilla to Sylhet, and the other is from Shylet to Assam – and all three segments are active. A major earthquake event can happen at any time from any segment of the Eastern Boundary fault.

"The eastern segment of the Dauki fault has not released any kind of energy in our known history. There is a geological activity ongoing, which can trigger a massive earthquake," said Kamal.  

What do mild earthquakes mean?

The small earthquakes have a meaning. Before the strong earthquake in Turkey, a couple of thousand mild earthquakes were felt in Turkey – foretelling a major earthquake that could strike at any moment. 

Professor Ansary said that it is seen around the world that after a series of mild earthquakes, a strong earthquake happens.

Definitely, activity in the fault has increased. The proof is that a 5-magnitude earthquake does not happen in our region in general. But now, two five-magnitude earthquakes happened one after another – one was inside Bangladesh and the other was outside Bangladesh, according to Professor Ansary. 

He said that the difference between Bangladesh and Turkey is that a strong earthquake happens every 40 years in Turkey. In our case, it's one in every 150 years. 

"Another difference is that the population in Turkey is low. Our population density is far higher. If the casualty in Turkey is 50,000 [in February this year, a strong earthquake killed more than 50,000 people], several lakh people will die in our country," said Professor Ansary. 

Professor Kamal said Bangladesh has around 13 geological fault lines which can cause earthquakes of 6-7 magnitudes. In our known history, earthquakes happened from two fault lines. No earthquake has happened from the other 11 fault lines. 

But the recurrence period of some of the fault lines is 350 years, some 300 years and some 500 years. These fault lines have the characteristic of creating an earthquake of a magnitude of 5.5 to 7 on the Richter scale. 

The fault lines that are related to Silchar (Assam, India) can not hold the energy for long inside the earth. The reason is the length of these fault lines is short in size. These small geological fault lines release their energy in the form of earthquakes between 5 and 5.5 magnitudes of earthquakes.

However, it is difficult to say when the earthquake will strike because we could not conduct an in-depth study on the recurrence period in our country. We can provide a primary insight on the basis of our empirical study. But these require further studies, and then it will be possible to provide an informative result, according to Professor Kamal. 

What to do now?

The effective technology to predict earthquakes has not yet been developed in the world. At different times, the US and Japan have spent millions of dollars. The prediction is limited to 10 seconds, which cannot save lives. It is not easy to come out of a building within 10 seconds. 

The only way to save life is to strengthen the buildings in Dhaka. Experts have long been asking the authorities to be cautious, ever since the Nepal earthquake happened. Now the time to raise awareness has run out. 

Professor Ansary said that now we have to take initiative to assess the building and strengthen the buildings. There are 21 lakh buildings in the 1,500 square kilometres under Rajuk. Of them, the number of five-story and above buildings is around six lakh. Around 30% of the six lakh buildings are vulnerable.  

We will have to prepare. In the past, preparation would mean creating awareness. Now we will have to assess whether the city buildings have the capacity for earthquake resistance. 

"Rajuk should now issue letters to the building owners for assessment and submission of certificates. To do this, the process to appoint a third-party engineering firm has been continuing endlessly," said Ansary.  

A committee was formed in 2016 to appoint five firms in each of the eight zones of Dhaka to check new, as well as old buildings, and submit the certificate to Rajuk. But, the initiative has not made much progress.