'In terms of seismic risk, most of Bangladesh including Dhaka is moderately safe'

A continuous warning bell has been ringing across Bangladesh on earthquake risks after the recent devastating earthquakes in the Turkey-Syria region, followed by the latest earthquake that struck Afghanistan on Tuesday.  

Several geologists and experts have been raising the alarm that Bangladesh awaits a similar fate. However, in contrast, a former director of the Geological Survey of Bangladesh and a Massachusetts-based engineering geologist Mir Fazlul Karim says otherwise. 

North-eastern Bangladesh, including Sylhet city and parts of Chittagong and Chittagong Hill Tracts, are proven to be earthquake-prone, whereas the other two-thirds of the country is relatively stable. 

Recently, The Business Standard spoke to Karim to discuss at length the ground realities of Bangladesh in the event of an earthquake.  

Give us an idea about the tectonic geology of Bangladesh. 

The tectonic configuration and geological formation of Bangladesh are very much complex. Though this is a tiny country, the Bengal Basin is a living model of an active and complex geological entity consisting of a dynamic deltaic depositional complex, and heterogenous and multidimensional tectonic deformational settings from three tectonic plates. 

There could be about 50 types of ground conditions in this small country. Every ground unit has unique properties and characteristics in terms of the response to the earthquake forces, including liquefaction potentiality. 

When we explain the ground scientifically, we see the earth's surface is divided into many tectonic plates. Each plate has individual characteristics. For example, we live on the Indian plate, neighbouring several other plates like the Eurasian plate. Bangladesh lies at a junction of more than one tectonic plate, making the country an earthquake-prone country of mostly medium magnitude earthquakes. 

Although, the earthquake history of Bangladesh and the surrounding regions indicate that the country is seismically active. Bangladesh's landmass or the Bengal Basin is the world's youngest active delta, significantly influenced by regional or distal tectonic forces and earthquake events. 

In the Bengal basin, three types of earthquake source areas are identified: intra-plate, transitional and inter-plate. The seismic behaviour of these source areas is deeply related to the tectonic structure and basement or crustal configuration of the Bengal basin. The good news is these source areas are buried under more than 30 km of sedimentary deposits making the earthquake-generating system passive. 

Our study identifies that the Bengal basin is severely segmented due to both vertical and lateral differential stress conditions from aforesaid three tectonic plates. It is speculated that the crustal segmentation has weakened the earthquake source structures and we have not found any capable structures in Bangladesh that would cause earthquakes larger than magnitude 7.5 Mw. 

But Bangladesh has threats of strong earthquake sources outside of its territory. If a stronger earthquake shakes North-east India, Myanmar and even long-distance Sumatra, it will cause minor destruction and panic in Bangladesh.

After the disastrous earthquakes in Turkey and Syria, many experts warned that Bangladesh would face a similar blow and possibly severe damage at any time. How do you compare the two countries' vulnerabilities to earthquakes? 

The occurrences of extraordinary earthquakes are common in the Turkey-Syrian region due to the tectonically active plates conjunction of the Anatolia, Arabia and African plates. The North Anatolian Fault is like the San Andreas fault of California and the African plate is like the Indian plate and subducts under the Arabian plate in the northeast like the India-Burma plates. 

This makes the region suffer such types of devastating earthquakes and aftermath. 

Interestingly, in terms of global earthquake preparedness, earthquake monitoring concerns the Turkish early warning system is not smarter than the European nations. Despite their technological advancement and earthquake risk management, the country, along with Syria, experienced unmanageable devastation. This was not only because of the earthquake forecasting or preparedness glitch. I believe the incident is a unique example of engineering failures, including the selection of building materials, ground development, design and age of the infrastructures.  

The devastation indicates that constructions were not sustainable due to inappropriate design. It might have been intentional or unintentional and requires investigation. Such destruction could happen in Bangladesh too if we do not consider the state of ground condition and engineering geology of the sites under development. 

Commonly, Bangladeshi engineers apply concrete reinforcement, columns and frame structures to make the buildings stronger. On the other hand, there were not many frame structures among the collapsed buildings in Turkey and Syria as presently practised in Bangladesh.  A serious violation of the Building Code by the builders and administrators was asserted by global experts. 

The geometrical configuration of the Turkey-Syria tectonic plate segments and juncture is totally different from the Bangladesh setting. Geologically Bangladesh ground is formed of very newly deposited sediments out of the Ganges-Brahmaputra delta building system. While Turkey-Syria ground is formed of very ancient (Precambrian) and very dense igneous and metamorphic rocks. Earthquake wave energy travels very fast under these conditions. That's why the earthquake shook the surface there quickly and caused severe destruction of the buildings and infrastructures that resembled collapsing forts of sand. 

Geologically, Bangladesh is a safer place compared to the Turkey-Syria region. 

What is your take on many Bangladeshi experts predicting monumental damage from earthquakes in the country? 

Many scientists have estimated that there is a great possibility of the occurrence of earthquakes of 8.2 to 9.0 Mw in the country. I believe this prediction is overrated because geologically Bangladesh does not have any extraordinary geological structures that would accumulate so much energy to generate such great earthquakes in a single event. 

In fact, the earthquake risk of Bangladesh is not fully understood because we have not studied the earthquake risk according to a scientific method. The model-based findings are not well supported by the appropriate field geology of Bangladesh and the three-dimensional geometrical presentation of earthquake source structures – while the models are also not verified. 

I believe that the estimated uncertain and unverified prediction is going to be a serious concern and a burden for the people of Bangladesh, especially regarding earthquake disaster management concerns. Also, it is going to hinder the ongoing development process of the country.  

The existing geological maps, records and our historical geological experience indicate that the earthquake risk in Bangladesh is truly moderate. The majority of Bangladesh occupies a lower seismic hazard zone according to the global seismic response maps, including the city of Dhaka. 

In terms of seismic risk, Dhaka city can be considered one of the safest cities in the world.

Though most of the country occupies a light to moderate seismic risk zone, the folded hills in the northeast and east of Bangladesh are prone to moderate to strong earthquakes. The last strong earthquake with a 7.5 Mw Richter scale (known as Srimangal Earthquake) occurred in Bangladesh in 1918. Many Mughal and ancient structures including Lalbagh Fort survived the shock from the Srimangal Earthquake due to the very good ground condition of Dhaka city. 

The present-day's practice of building engineering is far more advanced than that of Lalbagh Fort and I believe that the infrastructures are considerably well engineered to sustain a shake like the Srimangal earthquake provided the Bangladesh Building Code is followed by the builders and verified by the owners or urban administrators. 

Earthquakes are a global phenomena. Historically, Bangladesh is a moderate earthquake-prone country. But geologically, Bangladesh is devoid of any massive earthquakes-generating fault lines or other structures that caused the tragic Turkey-Syria earthquakes of early February. 

Bangladesh should continue the ongoing development process, including underground tunnels.