Scientific Frontline: "At a Glance" Summary
- Main Discovery: A comprehensive 6,000-year study overturns the assumption that major earthquakes follow predictable cycles, demonstrating instead that they occur in random clusters and lulls.
- Methodology: Scientists analyzed sediment layers in Rara Lake, Nepal, to track historical shaking and statistically compared this 6,000-year timeline against modern instrumental data and records from Chile, New Zealand, and the US.
- Key Data: The research identified approximately 50 distinct seismic events over the 6,000-year period, constituting the longest earthquake record ever assembled for the Himalayan region.
- Significance: The findings invalidate "periodic" hazard models that predict "overdue" events, suggesting that current risk assessments may underestimate the threat during quiet periods.
- Future Application: Policymakers are advised to shift focus from prediction-based planning to constant preparedness, specifically through the strict enforcement of building codes and the retrofitting of critical infrastructure.
- Branch of Science: Paleoseismology and Geophysics
- Additional Detail: The study results align with the stochastic nature of smaller earthquakes, indicating that large-scale seismic events are equally random and lack a definable timetable.
New findings challenge ‘overdue earthquake’ myth and urge Himalayan policymakers to treat seismic risk as constant.
A new study published in Science Advances has overturned a common assumption about earthquake prediction: that major earthquakes follow predictable cycles, and that regions can be ‘overdue’ for the next big one.
Researchers from British Antarctic Survey (BAS) analyzed 6,000 years of earthquake records preserved in the sediments of Rara Lake in western Nepal – the longest such record ever assembled for the Himalaya. Their findings show 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 Paleoseismologist 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.”
Reading the deep past
Rara Lake, a high-mountain lake in western Nepal, acts as a natural archive of seismic history. Each time strong shaking occurs, underwater slopes are disturbed, leaving distinctive layers in the lakebed sediment. The research team identified approximately 50 such layers spanning 6,000 years.
For the first time in the Himalaya, researchers combined this geological record with modern instrumental earthquake data to test earthquake timing statistically. They then compared their findings with long-term earthquake records from Indonesia, New Zealand, Chile and the Pacific Northwest of the United States.
The same pattern emerged everywhere: earthquakes cluster unpredictably, with active periods followed by long quiet spells. No region showed the regular, cyclical pattern that many hazard models assume.
Challenging outdated models
Seismic hazards are commonly assessed using ‘periodic’ and ‘quasi-periodic’ recurrence models, which represent and predict the probability of major seismic activity. These computer models, often based on limited observations, assume earthquakes follow relatively regular cycles – an assumption the new research shows to be unfounded.
The research represents the first statistical comparison of lake sediment earthquake records with instrumental data for Nepal and the wider Himalaya, bridging deep geological time with modern seismology.
“Six thousand years of data shows us that major earthquakes can happen at any time,” said Ghazoui-Schaus. “This substantially increases seismic hazard estimates – the risk models which shape government policies in earthquake regions, and the prioritization of public investment and aid.”
The vast mountain landscape of the Himalaya includes glaciers and lakes – flowing downstream to deliver water to 1.9 billion people.
What this means for policy
The findings carry significant implications for earthquake preparedness across the Himalayan arc, from Afghanistan through India, Nepal, China and Myanmar.
“We recommend that the public, politicians and policymakers should treat earthquake hazards as a constant, uneven threat,” continued Ghazoui-Schaus. “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.”
Ten years after Nepal’s devastating 2015 earthquake, which killed approximately 9,000 people, the study serves as a reminder that seismic risk has not diminished. Uneven enforcement of building regulations, rapid urban growth, and stretched humanitarian budgets continue to increase risk for vulnerable communities.
The researchers highlight the need for holistic governance of major earthquake risks. They stress the importance of authorities prioritizing enforcement of building codes for all new construction and retrofitting existing high-importance buildings like schools and hospitals as a matter of urgency. They also suggest governments develop investment and response plans that recognize the equal probability of clusters of earthquakes and long quiet periods.
Additional information: This research contributes to the UKRI/NERC-Funded Highlight Topic project ‘The Big Thaw’, which is improving predictions of snowfall and other hazards in high altitude mountain regions and building collaborative partnerships with researchers around the world, including Nepal.
Published in journal: Science Advances
Title: Occurrence of major earthquakes is as stochastic as smaller ones
Authors: Zakaria Ghazoui, Jean-Robert Grasso, Arnaud Watlet, Corentin Caudron, Abror Karimov, and Yusuke Yokoyama
Source/Credit: British Antarctic Survey
Reference Number: es021226_01
