Challenging the earth shattering implications
A research study was recently shared across print and electronic media, which predicted that a 9.0 magnitude mega earthquake will hit the central eastern part of Bangladesh, especially in and around Dhaka city. This prediction not only puts the 140 million residents of the capital city at risk, but also raises grave concerns about the fate of costly public and private civil structures, industries, flyovers and other necessary public amenities.
In fact, the prediction is even more ominous because most of the recent infrastructure were designed and built to withstand about 7-magnitude earthquakes that may hit this region. Understandably, the prediction of a 9.0 magnitude earthquake is frightening news for the government, since most of the infrastructure projects, such as power stations, multi-storied garments manufacturing factories, airports, sea ports, mega-bridges, dams, satellite towns, economic zones, etc. in Bangladesh was undertaken to withstand earthquakes lesser than or equal to 7.0 magnitude, not 9.0! This could be a grave concern for investors in both the public and private sectors.
The outcome of the research and several interviews of the authors shared across the social media have become viral, causing quite a bit of anxiety among the residents. One of the authors even suggested complete abandonment of the city! Thus, in this pretext, it is necessary to examine the outcome of the scientific study, which was published recently in the reputed journal Nature Geoscience.
The research paper postulated the existence of a plate boundary in and around Bangladesh. This is somewhat of a strange finding, since other maps created by scientists from a number of reputed institutions and organisations across the world (GSB, USGS, GSI, DU, RU, etc.) do not show any kind of plate boundaries (birth places of all earthquakes) or deformation zones in and around Bangladesh! As a matter of fact, the aforementioned maps, known as the Geological and Tectonic maps of Bangladesh, were prepared by many renowned local and foreign geo-scientists in the past separately and jointly on the basis of geophysical, bore hole and outcrop data.
What is more baffling is that the researchers took the liberty of shifting the meeting place of plate boundaries several hundred kilometres west of the actual place known to the scientists of the world. They did it on the basis of ground movement which was estimated by several GPSs. Shifting of the subduction zone is also up for debate, as it is an established fact that the plate in the location of interest is moving side by side and not subducting (the downward movement of the edge of a plate beneath another plate). If the plates are not subducting, then there is an extremely low probability of earthquake, which contradicts the said published research. Additionally, the westward movement of the plates was ascertained using only the GPS data interpretation. But predicting earthquake of any intensity not only requires long-term GPS data observation, but also requires detailed geophysical survey (beyond basement), bore hole (for 3-D basin modeling) and outcrop data interpretation along with historical records of earthquake occurrences in that region.
Thus, to bring everything into context, the published research in Nature Geoscience clashes with the existing knowledge regarding the Geological and Tectonic maps of Bangladesh, such as: a) the existence of subduction or deformation zone which was never mentioned or determined before (therefore, not yet established); b) whether that locked up deformation zone can produce an earthquake of that magnitude; c) will the mega-earthquake have the intensity to shake Dhaka along with the Bengal Basin as predicted; and d) whether the casualties of life and properties will be as much as predicted or later opined by authors.
Government agencies dealing with earth science, especially geology (as earthquake is a geological phenomenon) needs to address this issue by undertaking projects to conduct detailed studies on an urgent basis. Detailed deep geophysical surveys of several tens of sq. kms, followed by drill holes that were done for oil and gas in the past, will help immensely in finding subsurface plate boundaries or deformation zones. A 3-D model of the Bengal Basin needs to be prepared from different deep drill-hole data of the country to fully understand the severity of earthquake in different parts of the basin. If data is gathered in this manner, then only will the people of the country, especially the residents of Dhaka city, come to know about the total scenario. This study will also help the public and private investors upgrade their project status.
It is advisable not to panic after reading the published research outcome at this moment, and there is no need to change the existing earthquake probability (seismic hazard zoning map), as long as further studies - like geophysical surveys especially seismic, bore-hole data interpretation and basin modelling - are conducted, as this will provide a complete scenario of the earthquake situation in the context of Bangladesh.
The writer is Director General (Retd), Geological Survey of Bangladesh, and Professor of the Department of Oceanography, University of Dhaka.
E-mail: [email protected].
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