Tsunami Records Of The Last 8000 Years In The Andaman Island, India, From Mega And Large Earthquakes
This research was published in Nature: Scientific Report in 2019. IIT Kanpur research team has done this pioneering and one-of-its-kind of research under the
leadership of Professor Javed N Malik, from the Department of Earth Sciences. On 26th December 2004, a mega-earthquake with magnitude 9.3occurred in the Sumatra-Andaman region, resulting in a large coseismic rupture and a giant tsunami that took more than 250,000 lives.
A natural catastrophe of this scale led to the Ministry of Earth Sciences (MoES) and the Indian National Centre of Ocean Information Services (INCOIS) realizing the significance of understanding the recurrence pattern of such giant tsunamis and their effects along the Indian coastline. They realized that knowledge of these patterns can help us plan our strategies towards better mitigation plans, in urban planning along the coastline, in preparing inundation maps or tsunami hazard maps considering different earthquakes (i.e., mega and large earthquakes and associated tsunamis) and their effects along the Andaman & Nicobar coastlines as well as the east coast of Indian mainland.
Prof. Javed Malik from IIT Kanpur had experience in identifying the signature of ancient tsunamis preserved in coastal sediments. During initial research studying published historical chronicles (mentioning events those took place in 1679, 1762, 1847, 1881 and 1941), they found a few earthquakes and tsunamis from sediment records which probably occurred in and around the Andaman region during the historic period.
Prof. Javed took this task to hunt down tsunamis. Prof. Javed and his team started hunting for signatures of ancient tsunamis from the Andaman Islands (from 2005 onwards). He, along with his team, published a few research papers demonstrating such events. His recent research findings from the Badabalu Beach located along the Southeast coast of the Andaman Island revealed evidence of at least seven tsunamis in the last 8000 years that have affected the coastlines adjoining the Indian Ocean. The researchers found evidence that these tsunamis were triggered by mega and large magnitude earthquakes occurring along the Sumatra-Andaman region. Based on the depositional structures, grain size, contacts between different sediment units, micro-fossil content observed in sediment cores and shallow pits, 19 sediment units were identified.
Micro-fossil and geochemical analysis revealed characteristic signatures similar to that observed in other global tsunami deposits. Optical and carbon ages of these units (22 ages) were obtained from the cores (geoslices) and trenches (pits) from Badabalu. Based on the signatures of tsunami events preserved in sediment cores, micro-fossil, and geochemical studies (carried out under the supervision of Prof. Paul) and ages, seven tsunamis from the last 8000 years have been identified. These tsunamis correspond to historical tsunamis that occurred in 1881, 1762, and 1679 CE, and provide evidence for prehistoric tsunamis in 1300-1400 CE, 2000-3000 BCE and 3020-1780 BCE, and before 5600- 5300 BCE.
The researchers found an unexplained hiatus of two or three millennia ending around 1400 CE, which could be attributed to accelerated erosion due to Relative Sea-Level (RSL) fall at ~3500 BP. The tsunamis in 660-880 CE and 1300-1400 CE were giant comparable to the one in 2004 triggered by mega earthquakes. The tsunamis assigned to 1679, 1762, and 1881 (associated with large earthquakes), by contrast, were nearly confined to the northeast Indian Ocean. Sources have not been determined for the three earliest of the inferred tsunamis. They suggested a recurrence of 420-750 years for mega-earthquakes having different source, and a shorter interval of 80-120 years for large magnitude earthquakes.
Lack of comprehensible historical data poses a big challenge for a proper tsunami hazard evaluation for the Andaman Nicobar islands as well as the east coast of mainland India. A poor understanding of such catastrophic events implies a huge risk associated with the failure of existing and upcoming nuclear power plants and lifeline infrastructure near the densely populated coastal areas of India. This IIT Kanpur research, data gathered, new insights in tsunami will help Indiasafeguard and lessen the impact of future tsunami.