Quakes outside seismic zones worry experts

Two earthquakes within 24 hours struck the Khulna region, triggering panic in an area not typically known for seismic activity.

According to the Met office, yesterday’s 5.4-magnitude quake had its epicentre in Assasuni of Satkhira, 188km southwest of Dhaka. It struck at 1:52pm.

The tremor was felt in several districts, including the capital, and in Kolkata, where people rushed out of homes, offices and schools as buildings shook across the city.

On Thursday, a 3.2-magnitude tremor originated in Kaliganj of Jhenaidah, a neighbouring district of Satkhira.

A total of nine earthquakes struck Bangladesh in the past 27 days, raising concerns among experts and residents.

Nabidul Islam, a resident of Kaliganj upazila in Satkhira, said he was sitting on his sofa when the quake struck.

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“At first, I thought my head was spinning. Then I realised the sofa itself was shaking violently. I jumped up, called my wife, and ran outside,” he said.

The man in his mid-60s said he had never experienced anything like it. “We’ve felt tremors before, but never a jolt like this in my life. It was terrifying. Many of my neighbours were screaming in panic.”

What alarmed him most, he added, was learning that the epicentre was in his own district, near his upazila.

Earlier, three earthquakes that rattled Narsingdi within 32 hours in November last year caused panic among Dhaka residents and became a widely discussed issue nationwide.

Of the nine earthquakes recorded this month, four occurred in Satkhira and Sylhet -- two in each district -- while the rest were reported in Gazipur, Sunamganj, Mymensingh, Chapainawabganj and Jhenaidah.

The unusual frequency of seismic activity within such a short span has sparked fresh anxiety among people.

All the quakes ranged from 3.0 to 5.4 on the Richter scale and were categorised by the Bangladesh Meteorological Department (BMD) as minor to moderate.

According to the BMD, over the past 14 months, 38 tremors occurred within Bangladesh or along its borders in 15 districts, including Dhaka, Narsingdi, Gazipur, Mymensingh, Sunamganj, Sylhet, Moulvibazar, Habiganj, Satkhira, Jhenaidah, Jashore, Rangpur, Kurigram, Bandarban, and Thakurgaon.

These measured between 2.9 and 5.7 on the Richter scale.

Prof Syed Humayun Akhter, former chairman of the Department of Geology at Dhaka University, told The Daily Star that the epicentre was at a shallow depth of less than 10km, which caused the strong shaking.

Akhter said he does not expect an earthquake stronger than a moderate one in Satkhira, as the district does not fall within a seismically active zone.

“Still, people need to be careful while constructing houses,” he said, pointing to cracks formed in many homes by yesterday’s tremor.

Bodruddoza Mia, chairman of Dhaka University’s geology department, said Bangladesh is in a tectonically active zone.

“Earthquakes of magnitude four to five are expected and will continue to occur,” he said.

He said the country lacks updated data on active fault lines within its borders. While the Dauki and Madhupur faults are well known, many others remain unmapped.

He said the government should conduct a fresh seismic survey, as the last one was carried out several decades ago.

“With modern technology, we will be able to update our seismological map to pinpoint earthquake risks more precisely,” he said.

Bazlar Rashid, deputy director of the Geological Survey of Bangladesh, said the last seismic mapping was conducted in 1979.

He said the country’s internal fault lines are unlikely to trigger a “mega-earthquake”, as geological mapping has yet to identify any “mega-thrust” fault line within Bangladesh.

However, experts have previously warned that 7.0-magnitude earthquakes occur in this region roughly every 150 years, and magnitude-8 events every 250-300 years.

The last major earthquake in this region was an 8.1 in 1897, which originated in Assam. In 1918, a 7.6 magnitude earthquake struck the Srimangal area, causing extensive damage.

According to the experts, Bangladesh sits at the junction of the Indian, Myanmar and Eurasian tectonic plates.

The Dauki Fault in Sylhet, the Chattogram-Arakan Fault along the Chattogram-Teknaf belt, and the Sagaing Fault in Myanmar together place the country at extremely high seismic risk.