Earthquake

Earthquake Overview and Its Impacts in Bangladesh

What is an Earthquake?

An earthquake is a natural phenomenon that occurs when there is a sudden release of energy from within the Earth’s crust, resulting in seismic waves. These waves can cause significant damage to structures, landscapes, and the individuals residing in the affected areas.

Causes of Earthquakes in Bangladesh

Tectonic Plate Movements

Bangladesh is situated at the convergence of the Indian and Eurasian tectonic plates. The Indian Plate is gradually moving northward, resulting in pressure against the Eurasian Plate. This collision creates stress that leads to seismic activity, often resulting in earthquakes.

Himalayan Uplift

The collision between the Indian and Eurasian Plates has caused the uplift of the Himalayas, contributing further to seismic activity in the region. The pressure generated from this tectonic movement can trigger earthquakes.

Fault Lines

  • Shillong Plateau Fault: To the east of Bangladesh, this fault zone has the potential to generate earthquakes. It is part of the larger tectonic activity associated with the collision of the Indian and Eurasian plates.

  • Human Activities: Non-natural activities such as mining and the construction of large reservoirs (like dams) can also induce earthquakes. The weight of water behind dams can lead to minor tremors, although these are generally less powerful than tectonic earthquakes.

Earthquake Zones in Bangladesh

Risk Classification

  1. High Risk Zone (Zone 1): Includes areas such as Mymensingh, Sylhet, Rangpur, and Lalmonirhat.

  2. Moderate Risk Zone (Zone 2): Includes Bogura, Dinajpur, Dhaka, Comilla, Panchagarh, etc.

  3. Low Risk Zone (Zone 3): Includes Khulna, Jessor, Barisal, and Patuakhali.

Basic Seismic Coefficient

  • Zone 1: $0.08g

  • Zone 2: $0.05g

  • Zone 3: $0.04g

Historical Earthquakes in Bangladesh

Significant Events

  • 1762 Arakan Earthquake: Occurred on April 2 and had a magnitude between 8.5 and 8.8. This earthquake triggered a local tsunami and caused at least 200 fatalities. It also changed the Brahmaputra River's course and uplifted St. Martin's Island by 2-2.5 meters (6 to 8 feet 2 inches).

  • 1897 Earthquake: Recorded a magnitude of 8.7 primarily along the Dauki Fault. At that time, there were only 100 pucca buildings in Dhaka, with significant damage occurring to 10, including the historical Ahsan Manjil.

  • 1918 Mymensingh or Srimangal Earthquake: This earthquake reached a magnitude of 7.4.

Effects of Earthquakes in Bangladesh

Imagining an earthquake of magnitude 6.5 or more in Dhaka, the probable scenarios include:

  • Panic among residents due to lack of preparedness and knowledge on how to respond during an earthquake.

  • Building collapse, particularly those with shallow foundations due to a phenomenon known as liquefaction.

  • Potential damage to flood protection embankments during monsoons, which could lead to sudden submergence of large areas.

  • Fires initiated from gas lines in residential buildings.

  • Complete failure of water supply due to power outages affecting deep tube wells.

Specific Consequences

  • Damage to roads and blocked traffic due to debris.

  • Collapse of hospitals, endangering lives of patients.

  • Possible casualties from school building collapses.

  • Aftershocks causing further structural failures.

  • Inadequate rescue operations hindered by road blockages and damaged equipment.

Earthquake Risk Mitigation in Bangladesh

To reduce the impact of potential earthquakes, several strategies are recommended:

  • Inventory of vulnerable buildings and those at risk due to their location on steep hillsides.

  • Creation of an earthquake vulnerability atlas for major cities.

  • Strict enforcement of building codes for new constructions, especially high-rises.

  • Awareness programs conducted by government and NGOs to inform the public about earthquake preparedness, emphasizing what to do before, during, and after an earthquake.

Priority Measures for Disaster Mitigation

  • Increase public awareness through various means including education, training, and media.

  • Refined assessment of ground motion and identification of local soil effects.

  • Regular updates of building codes and laws to enforce the construction of earthquake-resistant structures.

  • Implementation of automatic safety systems for utilities during major quakes.

  • Post-earthquake recovery facilities and urban planning adjustments designed to mitigate earthquake impacts.