A new analysis of sediment cores from a Nepali lake reveals that major earthquakes in the central Himalayas occur randomly rather than at regular intervals, challenging fears of an imminent massive quake. Researchers identified at least 50 events of magnitude 6.5 or larger over the past 6,000 years, including eight since 1505. This finding suggests the region has experienced more seismic activity than previously thought.
The central segment of the Himalayan fault, spanning northern India and western Nepal, has long been considered a potential site for a devastating earthquake due to a major event in 1505 and limited subsequent records. Some studies proposed a recurrence interval of about 500 years, fueling concerns of an approaching magnitude 8 or 9 quake in what was termed a 'seismic gap' west of Kathmandu.
However, a team led by Zakaria Ghazoui-Schaus at the British Antarctic Survey analyzed a four-meter sediment core extracted from Lake Rara in western Nepal in 2013. Using evidence of turbidites—layers formed by earthquake-triggered underwater landslides—they documented 50 earthquakes of magnitude 6.5 or greater spanning 6,000 years. Notably, eight of these occurred after 1505, indicating ongoing random activity that has likely released built-up energy.
'We have to stop discussing and having long debates over the periodicity of earthquakes in the Himalayas and come to an agreement that it’s a random process … and consider the risk within that framework,' Ghazoui-Schaus stated. The study, published in Science Advances (DOI: 10.1126/sciadv.adx7747), found earthquakes clustering randomly, aligning with modern seismic observations.
Traditional paleoseismology, which relies on surface ruptures from trenches, often misses smaller 'shadow earthquakes' that do not breach the ground, leading to incomplete records skewed toward large events. Roger Musson, a retired seismologist from the British Geological Survey, noted: 'You are only going to have a very sparse record of the largest earthquakes' with these methods.
The Himalayan fault results from the ongoing collision of the Indian and Eurasian plates, creating one of the world's most active seismic zones. The 2015 magnitude 7.8 earthquake near Kathmandu, which killed nearly 9,000 people, underscores the region's hazards. Despite the random nature of quakes, Ghazoui-Schaus emphasized caution in construction: 'If I have to build a house in western Nepal, I would definitely be more cautious in the way that I would build.' Musson added that average intervals remain useful for planning infrastructure like dams over the next century, ensuring resilience regardless of timing.
