Our planet’s tectonic plates have been grinding against and diving below one another since time immemorial. However, the earthquakes that result from all the geological jostling have been actively monitored for less than 2 millennia. Researchers have now proposed how liquefaction features known as sand dikes can be used to both pinpoint and precisely date ancient earthquakes. The team published their findings in Earth and Planetary Science Letters.
The Calling Card of Liquefaction
One of the relatively little known dangers of earthquakes is liquefaction, in which strong shaking causes water-rich sediments to lose their structural integrity and behave almost like a liquid. When the ground is no longer solid, the results can be catastrophic—buildings can tilt substantially or even sink, and buried infrastructure like pipes can rise to the surface.
Liquefaction is therefore one fingerprint of a strong earthquake. And fortunately for researchers hoping to better understand past earthquakes, liquefaction leaves behind a calling card: sand dikes. These subsurface intrusions of fine-grained sediments resemble upward-pointing icicles. Sand dikes form in a matter of seconds when mixtures of sand and water are squeezed into cracks opened by ground shaking and the water later drains away. “They give undisputed evidence that an earthquake has occurred,” said Devender Kumar, a scientist at the National Geophysical Research Institute, a research laboratory of the Council of Scientific and Industrial Research, in Hyderabad, India.
Determining when a sand dike formed would therefore reveal when its parent earthquake occurred. And understanding such timing has long been a research goal, said Kumar. “That’s the most important question we need to answer in paleoseismology.”
“This is the million-dollar question.”
To get a handle on the timing of ancient earthquakes, previous studies turned to radiocarbon dating of organic matter found near sand dikes. But that technique comes with its own uncertainties, said Ashok Kumar Singhvi, a geoscientist at the Physical Research Laboratory in Navrangpura, India, and Shantou University in Shantou, China. It’s impossible to know whether the organic material was laid down contemporaneously with the sand dike and therefore the earthquake, said Singhvi. “This is the million-dollar question.”
Younger, but Why?
Another technique, known as optically stimulated luminescence, can be used to date sand dike sediments directly. This method relies on measuring the energy stored up over time in quartz grains from the natural radioactive decay of elements like thorium, uranium, and potassium. Earlier investigations using optically stimulated luminescence showed that sand dike sediments tend to be younger than their host rocks, a tantalizing clue that the luminescence signals in sand dike sediments could be reset, or zeroed out, by an earthquake. But no one had ever conclusively demonstrated this zeroing out effect.
Anil Tyagi, a physicist also at the Physical Research Laboratory, and his colleagues, including Kumar and Singhvi, set out to do just that. Heat, light, and pressure can all reset a material’s luminescence signal, the team knew. But sand dikes form underground, meaning light couldn’t be the culprit, and in sediments that are too soft to generate sufficient pressure, Tyagi and his collaborators concluded. That left heat.
Using a theoretical model developed in the 1970s, the researchers calculated the increase in temperature associated with the formation of a sand dike. Heating occurs simply because of friction, said Kumar: Sediment grains run into each other as they pour upward into a crack in excess of several tens of meters per second. The team estimated that temperatures of up to 450°C were attainable, particularly in the centers of dikes, where sediment grains would be inflowing the fastest.
Tyagi and his colleagues experimentally verified that temperature estimate by analyzing sediment samples taken from five sand dikes in northeastern India. The team calculated that most of the samples had experienced heating to at least 350°C. Such temperatures are sufficient to reset the luminescence signal of quartz grains, earlier work has shown.
“We have a direct method to date sand dikes, and hence past earthquakes.”
These findings demonstrate that quartz grains do indeed zero out their ages when sand dikes form. That fact makes sand dikes valuable and accurate tracers of past ground shaking, said Singhvi. “We have a direct method to date sand dikes, and hence past earthquakes.”
These results are convincing and pave the way for paleoseismological investigations, said Naomi Porat, a luminescence dating scientist who recently retired from the Geological Survey of Israel and who was not involved in the research. In 2007, Porat and her colleagues published a paper that suggested that sand dikes’ luminescence signals were being reset, but the team didn’t posit a mechanism. “We left it as an open question,” said Porat. “It’s so nice to see this paper,” she added. “I waited for 20 years.”
—Katherine Kornei (@KatherineKornei), Science Writer
Citation: Kornei, K. (2025), Spiky sand features can reveal the timing of ancient earthquakes, Eos, 106, https://doi.org/10.1029/2025EO250364. Published on 30 September 2025.
Text © 2025. The authors. CC BY-NC-ND 3.0
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