Impending Major Earthquakes: A Guide to Nepal and Northern India’s Seismic Risks

While some experts argue that northern India and western Nepal are overdue for significant earthquakes, recent studies indicate this notion may be a myth. Historical data reveals small earthquakes have occurred randomly in the region for thousands of years.

Frequently, officials and media label densely populated fault-adjacent areas, such as Istanbul, Seattle, and Tokyo, as being “overdue” for a major earthquake. The last significant earthquake on the central Himalayan fault segment in India and Nepal was recorded in 1505. Some researchers suggest that earthquakes in the area occur approximately every 500 years, indicating that a major quake could be on the horizon, as highlighted in a study.

However, new findings reveal at least 50 earthquakes of magnitude 6.5 or higher have transpired in this region over the past 6,000 years, including 8 since 1505, according to this research. Notably, these earthquakes did not exhibit regular patterns, occurring randomly instead.

“It is essential to shift our focus from debating the periodicity of earthquakes in the Himalayas to acknowledging that they occur randomly, and assess the risks accordingly,” emphasizes Zakaria Ghazoui-Schaus of the British Antarctic Survey, who participated in the research.

The relentless collision of the Indian and Eurasian tectonic plates forming the Himalayas contributes to one of Earth’s largest seismic zones. This extensive 2,400-kilometer fault has generated powerful earthquakes, including the catastrophic 7.8 magnitude earthquake in 2015 that tragically claimed nearly 9,000 lives in and around Kathmandu.

Despite this, limited evidence of seismic activity has been found in the central fault section just west of Kathmandu, sparking concerns that pressure in this “seismic gap” could lead to a devastating magnitude 8 or 9 earthquake.

Ghazoui-Schaus suggests that this perception stems from a “knowledge gap” rather than tectonic inactivity. Traditional methods for locating earthquake evidence in the Himalayas often involve digging trenches to find surface cracks, which might detect major quakes but overlook smaller “shadow earthquakes” that did not cause surface damage.

Former British Geological Survey seismologist Roger Masson states, “Traditional paleoseismology only yields sparse records of the largest earthquakes, while historical catalogs generally suffice for earthquakes up to magnitude 4.” This bias leads to inflated estimates of long “occurrence intervals,” or “recurrence periods,” which represent the average time between earthquakes of a certain magnitude in an area.

To enhance the seismic record of the central Himalayas, Ghazoui-Schaus and his team visited Rara Lake in western Nepal in 2013, collecting a 4-meter sediment core using a rubber boat.

The researchers analyzed sediment cores containing turbidites—layers that finely layer sediment on coarser sediments deposited on the lake bed by underwater landslides caused by earthquakes. Their analysis identified 50 earthquakes of magnitude 6.5 or greater over the past 6,000 years, each dated according to its core depth, likely releasing energy that alleviated fault tension, says Ghazoui-Schaus.

Statistical evaluations indicated that while earthquakes often occur in swarms, these swarms are random. This finding aligns with seismologists’ expectations based on contemporary records, marking one of the first confirmations through paleoseismological evidence.

If I were constructing a house in western Nepal, I would certainly prioritize building it more robustly,” notes Ghazoui-Schaus. Masson adds that despite the random occurrence of earthquakes, calculating the average interval between them remains valuable for anticipating seismic activity that could threaten vulnerable structures like bridges and dams.

“When planning for the next century, it’s crucial to estimate how many earthquakes of specific magnitudes may occur. Being prepared ensures we can withstand quakes whenever they strike, regardless of whether it’s next year or a decade from now,” he states succinctly.