The common assumption that major earthquakes follow predictable cycles – and that regions can be ‘overdue’ for the next big one – has been debunked by a study analysing 6,000 years of data.
British Antarctic Survey (BAS) researchers examined records preserved in the sediments of Rara Lake in western Nepal, assembling the longest record of its kind for the Himalaya.
They concluded that large earthquakes arrive in unpredictable bursts and lulls, not at regular intervals.
“The ‘overdue’ myth is just that – a myth,” said Dr Zakaria Ghazoui-Schaus, a Paleo-seismologist from BAS who led the study. “Our research shows that major earthquakes are just as random and unpredictable as smaller ones. The science is blunt: major quakes don’t run to a timetable.”
Rara Lake is a high-mountain lake in western Nepal and acts as a natural archive of seismic history as each time strong shaking occurs, underwater slopes are disturbed, leaving distinctive layers in the lakebed sediment. The researchers identified about 50 such layers spanning 6,000 years.
For the first time in the Himalaya, they combined this geological record with modern instrumental earthquake data to test earthquake timing statistically.
They compared the findings with long-term earthquake records from Indonesia, New Zealand, Chile and the Pacific Northwest of the United States and found the same pattern emerged everywhere.
Earthquakes cluster unpredictably, they concluded, with active periods followed by long quiet spells and no region showed the regular, cyclical pattern that many hazard models assume.
“6,000 years of data shows us that major earthquakes can happen at any time,” said Dr Ghazoui-Schaus. “This substantially increases seismic hazard estimates – the risk models which shape government policies in earthquake regions, and the prioritisation of public investment and aid.”
The findings have major implications for the Himalayan arc, from Afghanistan through India, Nepal, China and Myanmar.
Nepal’s 2015 earthquake killed about 9,000 people – and more than a decade on, the study is a reminder that seismic risk has not diminished.
Vulnerable communities continue to be at risk from uneven enforcement of building regulations, rapid urban growth and stretched humanitarian budgets.
The researchers stress the importance of enforcing building codes for all new construction and retrofitting existing high-importance buildings like schools and hospitals as a matter of urgency.
“We recommend that the public, politicians and policymakers should treat earthquake hazards as a constant, uneven threat. Response plans need to be ready for bursts as well as lulls in earthquakes of all sizes – because the next event, big or small, could happen at any time,” said Dr Ghazoui-Schaus.
Read more on Cambridge Independent
