The fault lines beneath us: Lessons from Myanmar's earthquake for Bangladesh

The major earthquake that struck Myanmar on 28 March at about 12:50 PM local time, with its epicentre located 15 km from the second-largest city, Mandalay, caused massive destruction in Myanmar and resulted in significant damage in the neighbouring countries. Myanmar and Thailand declared disasters in affected areas and are struggling with rescue operations. 

According to the United States Geological Survey (USGS), the earthquake's magnitude was 7.7 and originated at a depth of only 10 km. At least 11 aftershocks were recorded with magnitudes exceeding 4.5 Mw, and one aftershock, measured at 6.7 Mw, struck just 10 minutes after the main shock. Such a high-magnitude and very shallow-depth earthquake understandably causes intense ground shaking, leading to catastrophic destruction and the loss of thousands of human lives in surrounding densely populated areas. Bangkok, the capital city of Thailand, situated 1,000 km south of the earthquake epicentre, was also affected by this earthquake and reported significant casualties. 

While the epicentral distance from major Bangladeshi cities is much shorter (Dhaka—600 km; Sylhet—520 km; Chittagong—427 km; Cox's Bazar—400 km), its effect was very insignificant in Bangladesh compared to the distant cities of Bangkok or southern China. To understand this apparently perplexing phenomenon, we have to understand the geological perspective of the earthquake.

Earth's surface is divided into several tectonic plates, and earthquakes generally occur at convergent plate boundaries, where two or more tectonic plates collide. These tectonic plates are constantly moving at certain velocities. 

The Indian Plate is one such tectonic plate, which hosts Bangladesh in its northeastern part, moving in a northeast direction at a rate of about 4-5 cm/year and colliding with the Eurasian Plate to the north and Burmese Plate to the east. This collision resulted in major mountain belts to the north (Himalayan Mountain Belt) and the east (Indo-Burman Ranges). 

The constant plate movement also generates major active faults at or near the plate boundaries. These faults accommodate the stresses associated with plate movement. When the accumulated stress exceeds the elastic limit of rocks, it releases energy in the form of earthquakes. A number of active faults exist on the northeastern margin of the Indian Plate. From north to south, the Main Frontal Thrust (2,500 km), Oldham Fault (110 km), and Dauki Fault (300 km) are the major active faults in the north, aligned approximately east-west. 

From east to west, the Sagaing Fault (1,200 km), Kabaw Fault (500 km), Churachandpur-Mao Fault (300 km), Kaladan Fault (270 km), and Chittagong Coastal Fault (300 km) are the major active faults in the east, aligned approximately north-south. All these faults are capable of producing moderate (5.0 to 5.9 Mw) to major earthquakes (7.0 to 7.9 Mw) and a few of them are even capable of producing great earthquakes (>8.0 Mw). The Sagaing Fault, which separates the Burmese Plate from the Sunda Plate, is one such major active fault, responsible for the latest 7.7 Mw earthquake.

Historically, all these active faults have produced major to strong earthquakes that have devastated the region. Some of the major earthquakes that have occurred in this region include the 1762 Chittagong-Arakan earthquake (8.8 Mw), the 1842 Pabna earthquake (7.3 Mw), the 1868 Sylhet earthquake (7.5 Mw), the 1869 Cachar earthquake (7.5 Mw), the 1885 Manikganj (Bengal) earthquake (6.9 Mw), the 1897 Assam earthquake (8.7 Mw), the 1918 Srimangol earthquake (7.6 Mw), the 1923 Mymensingh earthquake (7.1 Mw), the 1930 Dhubri earthquake (7.1 Mw), and the 1961 Assam-Manipur earthquake (7.6 Mw). 

The 1762 Chittagong-Arakan earthquake also triggered a tsunami, which devastated the entire coastal belt of Bangladesh and Myanmar. If all these earthquakes are plotted on a tectonic map, their positions align with the major active faults mentioned earlier.

In Myanmar, the north-south oriented dextral Sagaing Fault is the most active plate boundary fault, accommodating about 2.0-2.3 cm/year of plate movement and having generated several major seismic events (9 earthquakes) over the last century. 

The capital city, Naypyidaw, approximately 250 km south of Mandalay, along the same Sagaing Fault, was also severely damaged due to the southward propagation of the earthquake rupture along this fault. Since the southern tip of the Sagaing Fault is connected to another network of strike-slip faults extending toward Bangkok (Thailand), seismic energy from this earthquake was transferred through these faults, reaching Bangkok's soft sediments and causing intense ground shaking. 

Conversely, the impact of this earthquake was much lower in the east-west direction, which is perpendicular to the Sagaing Fault alignment.

While all major Bangladeshi cities are much closer to the epicentre than Bangkok, they are situated a few hundred kilometres west of the Sagaing Fault. Since seismic energy from this earthquake mainly propagated in a north-south direction, Bangladesh's western position reduced its impact. 

However, three major active faults—the Dauki Fault, the Chittagong Coastal Fault (CCF), and the Madhupur Fault (150 km long)—are situated in northern, eastern, and central Bangladesh, respectively. Their proximity to major cities (CCF: 230 km from Sylhet, 150 km from Dhaka; Dauki Fault: 30 km from Sylhet, 160 km from Dhaka; Madhupur Fault: 50 km from Dhaka) makes Bangladesh highly vulnerable to earthquake hazards. All these faults produced major earthquakes in the past and are capable of producing 7+ Mw earthquakes in the near future. 

Bangladesh is in an earthquake risk zone due to these three active faults, together with other regional active faults mentioned earlier. There is a clear seismogenic gap in the eastern part of the Dauki Fault and the northern part of the CCF, which specifically makes the north and east parts of the country highly vulnerable to earthquake hazards.

Earthquake hazards depend on three main factors: magnitude, depth, and population density. This recent earthquake in Myanmar combined all three, causing devastating damage to the country, which is already ravaged by civil war. For Bangladesh, any major or great earthquake within the country or its close proximity raises additional concerns that can further amplify the damage. Bangladesh is entirely situated on thick layers of soft sediments, which may amplify the shaking and cause further damage. 

Such loose, unconsolidated, water-bearing sediments can also trigger large-scale liquefaction due to seismic waves' interaction with these loose sediments. Additionally, major earthquakes could trigger mud volcanoes, as evidenced in the Chittagong Hill region, possibly linked to the 1762 Chittagong-Arakan earthquake. 

Altogether, high population density, poor infrastructure, a soft sedimentary basin, poorly enforced building codes, the possibility of extreme fire hazards, and road blockages make Bangladesh extremely vulnerable to earthquakes.

Therefore, understanding earthquake hazards and improving earthquake monitoring and preparedness is urgent and imperative for Bangladesh. 

While Bangladesh has a National Earthquake Monitoring and Research Centre under the Bangladesh Meteorological Department, it lacks resources and capabilities beyond basic earthquake reporting. This centre should be integrated into the Geological Survey of Bangladesh (GSB) or restructured under the Ministry of Science and Technology with proper logistics and human resources. 

Collaboration with international agencies such as the United States Geological Survey (USGS), German Research Centre for Geosciences (GFZ), India's National Centre for Seismology, and Nepal's National Earthquake Monitoring and Research Centre is essential to fully assess Bangladesh's seismic hazard. We must recognise that an earthquake of similar magnitude within or near Bangladesh would be far more devastating than in Myanmar due to our extreme population density in poorly planned urban development.

Dr Md Sakawat Hossain is a professor at the Department of Geological Sciences, Jahangirnagar University, and currently a visiting scholar at the Department of Geological Sciences, University of Missouri-Columbia, USA. 

Zakia Sultana is a research associate at the Department of Geological Sciences, Jahangirnagar University.

Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the opinions and views of The Business Standard.