Scientists give verdict on popular theory that massive Himalayan earthquake is ‘overdue’

Large earthquakes are unpredictable and do not arrive at regular intervals, according to a new study that challenges the myth of an “overdue” massive earthquake in the Himalayas.

The research overturns a common assumption that major earthquakes of around magnitude 7 or higher follow predictable cycles, with regions such as Northern India and the US western coast “overdue” for the next big one.

Though some of these regions are prone to large quakes, long intervals without a major event do not guarantee that a big one is imminent, scientists say.

In the study, researchers analysed 6,000 years of earthquake records preserved in the sediments of Rara Lake in western Nepal – the longest such record ever assembled for the Himalayas.

Here, each time a strong shaking occurs, underwater slopes are disturbed, leaving distinctive layers in the lakebed sediment.

Scientists identified about 50 such layers spanning 6,000 years.

This is the first time earthquake timing has been verified statistically by combining geological records with modern instrumental earthquake data.

The findings were then compared with other long-term earthquake records from Indonesia, New Zealand, Chile and the Pacific Northwest of the US.

Everywhere, scientists found that earthquake patterns are unpredictable.

Active seismic periods were followed by long quiet spells, and no region showed a regular, cyclical pattern.

This indicates that accurate predictions for an “overdue” big one cannot be made.

“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,” said seismologist Zakaria Ghazoui-Schaus from the British Antarctic Survey (BAS).

“Six thousand years of data show us that major earthquakes can happen at any time,” said Dr Ghazoui-Schaus, an author of the study published in the journal Science Advances.

Until now, several previous research has previously predicted the hazard risk of regions based on “periodic” and “quasi-periodic” quake recurrence models.

These models assumed earthquakes follow relatively regular cycles, which has now been debunked, researchers say.

This carries significant implications for earthquake preparedness across the Himalayan zone from Afghanistan through India, Nepal, China and Myanmar, widely referred to as the world’s Third Pole after the Arctic and the Antarctic.

Despite Nepal’s devastating 2015 earthquake, which killed approximately 9,000 people, the new research suggests seismic risk to the area has not diminished.

They urge regional authorities to prioritise the enforcement of building codes for all new construction, and to retrofit 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,” Dr Ghazoui-Schaus said.

“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,” he explained.