Scientists have found that the Himalayas played a role in the generation of the magnitude-9.2 Sumatran earthquake on 26 December 2004, which, together with the massive tsunami that followed, killed more than 250,000 people, making it one of the deadliest natural disasters in history.
An international team of scientists, including from the National Centre for Antarctic and Ocean Research in Goa, who wanted to find out what caused such a large earthquake and tsunami have found that the Himalayas, several hundred kilometres away from Sumatra, was an accomplice.
Results of their research, conducted as part of the International Ocean Discovery Programme, have been published in the 26 May issue of the journal Science.
Scientists had thought that sediments piling up at plate boundaries, also known as subduction zones, would put the brakes on a rupture, making it less likely to start a huge tsunami. But an examination of core samples drilled from the sediments feeding into the plate boundary between Indonesia and the Indian Ocean showed something different.
From an oceanographic ship, the research team drilled down 1.5 km below the seabed and sampled the sediment and rocks from the tectonic plate that feeds the Sumatra subduction zone. The researchers found that, over time, the sheer volume of Himalayan grist was compressing the thick sediments to generate warm temperatures and strengthen the sediment prior to subduction.
This resulted in a very large fault area and increase in the severity of the earthquake "and helped ensure that the full force of the rupturing fault reached the sea floor, amplifying the tsunami". Based on the research, India's foremost expert in tsunami geology at the Jawaharlal Nehru Centre for Advanced Scientific Research in Bengaluru, had this to say:
The authors’ suggestion that the strengthened sediments within the subduction zone off Sumatra may have played a role in facilitating the deadly tsunami is very interesting. But this could be only one of the factors. [...] There are geometrical considerations. Proximity to the trench and therefore the depth of water are other factors that decide if the earthquake would actually lead to a tsunami.CP Rajendran in an email to IANS correspondent
Rajendran said the insight from this study will indeed help in reevaluating the tsunami hazards off the Makran Coast and Cascadia off the north-western coast of the US, which are repositories of huge accumulation of sediments like off Sumatra.
(Published in an arrangement with IANS, this article has been edited for length.)
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