Earthquake risks and structural vulnerabilities in Bangladesh

Part - 1

Bangladesh, a densely populated country is situated on seismically dynamic Bengal Basin. The area is shaped by sedimentary deposits of numerous rivers drainage systems and active tectonic processes. Numerous plate tectonics convergences in this area and makes it vulnerable to shattering earthquakes. The combination of sedimentation loads and the continuous stresses due to movement of tectonic plates?in subsurface rocks implies seismic risk, which warrants great challenge to infrastructure and preparedness for disasters. A powerful earthquake can strike without notice and can trigger unmanageable rescue effort, catastrophic loss of life and widespread destruction particularly in major urban cities like Dhaka, Chattogram and Sylhet.

Bangladesh has a long history of noteworthy seismic activity dating back centuries. The first documented earthquake occurred in 1548 where present Chattogram and Sylhet districts were shaken violently. The earth cracked open in various places and ejected up water and mud of sulphureous smell. Earthquake in 1642 and 1663 were also significant. The quake of 1762, with magnitude 8.5-8.8, produced uplift, subsidence and a tsunami along the coast from Chittagong to Arakan.

In 1885, the earthquake of around magnitude 7.0 struck the Manikganj area, causing substantial damage across the region. The grate Bengal Earth quake in 1897, with an estimated magnitude of 8.0, caused widespread destruction across the Bengal region, demonstrating the catastrophic potential of seismic events in the area. However, powerful earthquakes have been rare in Bangladesh in recent decades, raising concern among scientists as the strain is building beneath the surface.

In recent decades, the preferences in high-rise residential and commercial developments have accelerated sharply, driven by land scarcity in urban areas. Many of these structures are allegedly built without adherence to National Building Code particularly seismic design standards due to regulatory limitations. Seismic design requires more reinforcement which increases construction cost. Under-reinforcement increases concerns regarding the structural resilience. The poor construction practices and inadequate regulatory oversight put millions at risk of a large-scale disaster that scientists caution is already overdue.

Thousands of modern buildings collapsed in the recent 2023 earthquake in Turkey's Gaziantep and Kahramanmara? cities. This disaster exposed serious defects in building safety and emergency systems as modern structures were collapsed regardless of the potential risks. Many collapsed buildings were poorly built, lack in material standards and proper safety standards. Earthquakes also cut off power, water, communication and transport systems in addition of physical damage.

This earthquake has uncovered how poorly constructed buildings, especially those built without compliance to building codes are most prone to collapse. Similar risks exist in cities like Tokyo, Los Angeles and Mexico City where earthquakes regularly threaten crowded urban areas. To reduce risks, it demands designing quakeproof building design, retrofitting old structures, enforcing stricter construction compliance and developing advanced early warning systems. Training programs teach communities how to respond during disasters, like evacuation drills and first aid to save more lives. Community awareness programs have also become crucial to save lives during disasters. Recent earthquakes have served as strong reminders that even technologically advanced cities must continuously improve their disaster management strategies to minimize loss of life and structural damages.

Earthquake Risks in Bangladesh: The geographical formation of Bangladesh makes it dissimilar from any other place on Earth. The world's highest and prominent mountain range the Himalayas is at the north. Three major rivers the Ganges, Brahmaputra and Meghna originate and flow from the Himalayas and other nearby mountain ranges eventually converge inside Bangladesh forming one of the world's largest river systems. These rivers transport huge amounts of mud and sand from the mountain range and deposit inside the country. These deposits created the world's largest delta. Bangladesh stands among one of the rainiest places of the Earth. Bangladesh is not formed just by sediments of rivers and flooding but also by the happening of the sub-surface activities, where tectonic plates are moving. Bangladesh is located at the junction of dynamic Indian and the Eurasian tectonic plates. The Indian plate is shifting at the rate of 6 centimeters northeast each year and sub ducting beneath the Eurasian plate at the rate of 45 millimeter per year.

This collision of tectonic plates formed the Himalayas which is still actively rising. Additionally, the Burmese micro plate pressing from the east and subducting beneath Eurasian plate at 35 millimeter per year. All these active pressure forces create significant stresses beneath the soil in and around Bangladesh. Three major fault lines namely Dauki fault, Madhupur fault and Eastern Plate boundary are exist within the country.The 150 km long Madhupur fault spreading north-south located between Madhupur region and Jamuna flood plain.The Dauki fault, extended about 300 km east-west and positioned along the southern edge of the Shillong Plateau (Meghalaya- Bangladesh border). Finally, the Assam-Sylhet fault, stretches about 300 km long from northeast to southwest is situated in the southern Surma basin. Seven major earthquakes strikethe area of Bangladesh over the past 150 years. (To be continued)

Concluding Part

Two had the epicenter (Srimongal Earthquake of 1918 and Bengal Earthquake of 1885)inside the country. Analysis and study of past earthquake epicenters show, Dhaka has crossed over 130 years, Chittagong over 250 years and Sylhet about 100 years, which increased the potential of strong earthquake in the area. Extended silence of potential earthquake (seismic gap) along the region has increased the likelihood of occurring strong earthquake. According to a seismic zoning map prepared by the BUET, 43% areas in Bangladesh is classified as high risk, 41% as moderate and 16% low. The area of Bangladesh has been divided into three seismic Zones for seismic design considerations of structures.Zone-1, Mymensingh-Sylhet is with the likely magnitude of 7 on Richter Scale. Zone-2,Dhaka-Comilla-Chattogram and Tangail are with the likely magnitude of 6 on Richter Scale. Zone-3,remaining areas of the country is with magnitude of Richter scale 6.This complex geological setting makes Bangladesh one of the most seismically active and vulnerable regions in South Asia.

The risk is further amplified by rapid and unplanned urbanization. Cities like Dhaka, Chittagong and Sylhet are booming in high rise construction of residential and commercial buildings often without proper engineering standards or earthquake silent designs. Infrastructures of Bangladesh faces critical seismic susceptibility due to poor construction practices and workmanship, deficient construction material standards and often nonconformity of structural design with the Bangladesh National Building Code (BNBC 2020). Nonconformity structural design includes, inadequate or no shear walls and insufficient moment resisting frames which render buildings prone to failure during high magnitude events.

Dhaka's population density (47,400/km²) deepens this risk, where even a magnitude 6.0 Richter Scale earthquake could trigger catastrophic casualties. Bengal Basin's alluvial sediments increase potential of high liquefaction and amplify seismic wave factors. Readiness and awareness among government concern agencies and the public remain usually inadequate. Efforts to enforce building codes and train rescue teams are often limited. Numerous old buildings, schools and hospitals are still not retrofitted to withstand earthquakes. The lacking in suitable land use planning and emergency response systems further worsens the hazard. Earthquake preparedness need to be prioritized as a national emergency issue.

Earthquake Preparedness: A National Priority: Earthquakes cannot be prevented. The growing potential of a high magnitude quake mandate urgent national attention. It is critical to enhance efforts for earthquake risk reduction. Experts emphasized on the significance of organizing efforts according to their specific roles in each phase of disaster management to ensure effective and synchronized response. In pre-earthquake phase preparedness, mitigation and prevention should be the prime focus confirming communities, buildings and infrastructure are better prepared to withstand seismic wave. Ensuing a disaster, the immediate rescue and relief operations to become the priority including the delivery of provisional shelters for affected people for up to three months. A continuing inclusive recovery strategy of minimum three years must fit in for infrastructure rebuilding with community restoration programs to restore critical services and to establish seismically resilient urban frameworks.

Civil Military collaboration can enhance effective disaster response by integrating logistical expertise, discipline and rapid mobilization capabilities of armed forces with civil authorities' understanding of local knowledge, community network and infrastructure. Critical success factors include inter-operable communication, training drills simulation in multi risk scenarios, cohesion and a hybrid command hierarchy that integrates military operational precision with civilian governance frameworks. The synergy by pre-established protocols for resource sharing, rescue operations and medical support are essential. Public awareness campaigns should comprise both civil and military institutions for better community engagement. It necessitates joint planning, preparedness, post-disaster recovery efforts and civil-military cooperation to minimize the loss of life, property and to ensure efficient relief distribution.

Earthquake risk reduction requires strict enforcement of building codes, regular safety drills by concern authorities, updated early warning and efficient communication systems. Potential damage can be significantly minimized by enhancing public awareness on earthquake safety and ensuring strict regulation of construction practices. Bangladesh will remain highly vulnerable to severe human casualties and widespread economic loss to potential earthquake without prompt and coordinated efforts.

Though, Bangladesh is positioned in a high-risk seismic zone, she has great potential to strengthen her resilience by coordinated preparedness and practical planning. Bangladesh can certainly minimize the risks associated with earthquakes by increasing awareness among citizens and joint efforts from all concern authorities. Harmonization and synergy among the ministries of finance, health, food and disaster management, housing and NGOs can greatly enhance the preparedness of the nation. Bangladesh can ensure a faster and more effective response to emergencies by strengthening facilities such as modern fire and civil defense services, well-equipped hospitals, efficient ambulance networks and rescue equipment. Public awareness through television, radio, newspapers and social media can increase response of citizens with knowledge, safety measures and emergency response. Bangladesh can transform its vulnerability into strength with proper application of the national building code, regulatory oversight, community engagement and capacity building. Joint efforts from the government organs, armed forces, professionals and citizens will prepare the nation to face future challenges with confidence.