In DepthGeophysics

How the Himalayas primed the Indonesian tsunami

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Science  26 May 2017:
Vol. 356, Issue 6340, pp. 794
DOI: 10.1126/science.356.6340.794

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The magnitude-9.2 earthquake that struck off the coast of Sumatra in Indonesia on 26 December 2004, causing a tsunami that killed more than 250,000 people, had an unexpected accomplice: the Himalayas. New work shows that rock eroding from the peaks and piling up as sediment on the Indian Ocean floor helped ensure that the full force of the rupturing fault reached the sea floor, amplifying the tsunami. Scientists had once expected that such sediment would serve as a shock absorber, preventing the earthquake’s slip from reaching too high. But an examination of cores drilled from the sediments feeding into the plate boundary between Indonesia and the Indian Ocean found that the sheer volume of Himalayan grist was compressing and heating these sediments into proper rock faster than expected. The finding could raise risk assessments for similar faults, including the Cascadia subduction zone off the Pacific Northwest coast.