At nearly midnight on August 31, an earthquake struck Afghanistan. It flattened hundreds of remote mountain villages, has till now claimed 2200 lives and caused 3640 to be injured. Authorities fear the death count may increase once contact is established with every affected village.
The reason casualties were high is because the earthquake struck at night, catching people unawares. The buildings, made of mud and timber or bricks and concrete, collapsed, trapping inhabitants in the rubble. The earthquake that struck Morocco on September 8, 2023, claiming 2,600 lives had also struck late at night. The earthquake that struck Myanmar in March this year struck at noon but still claimed more than 5,000 lives in that country. In all these cases, if people had been aware of an impending earthquake, the casualties may have been less, but we do not as yet have the science to predict earthquakes.
“Seismologists cannot predict when and where a large earthquake will occur,” says Jnana Ranjan Kayal, former deputy director general of the Geological Society of India (GSI). “They can, however, map the zones vulnerable to seismic upheavals.”
An earthquake occurs when a tectonic plate moves along the edge of another plate. As the plates grind together, pressure builds up and eventually breaks loose, releasing energy equivalent to several nuclear blasts. The young Himalayan mountains mark the place where the Indian plate meets the Eurasian plate, making the whole region prone to earthquakes. The last severe earthquake in the Himalayan region struck Nepal in 2015. Seismologists fear that a Great Himalayan Earthquake with a magnitude of 8.2 is on the way. The Myanmar earthquake was but a warning sign.
The uppermost layer of Earth’s atmosphere is called the ionosphere. This layer has an abundance of electrons as the gas molecules here are ionised by ultraviolet rays from the sun. It is also known to react to thunderstorms and solar flares. Changes are also observed in the ionosphere ahead of earthquakes as the density and flow of electrons in the ionosphere changes due to shifts in Earth’s tectonic plates. For the past decades, the total electron content (TEC) in the atmosphere has been investigated as a potential earthquake precursor.
Studies have shown that TEC values fluctuate before earthquakes. These fluctuations (mostly rise) could be used to indicate impending quakes.
“TEC has emerged as a potential tool for monitoring ionospheric anomalies preceding seismic events, enhancing early warning systems,” says Gopal Sharma, a geologist at North Eastern Space Applications Centre (NESAC) at Umiam, Meghalaya. He was a key member of the team that published a study of the Moroccan quake in Geosciences. Experienced in tectonics and earthquake studies, and trained at the Indian Space Research Organisation’s Indian Institute of Remote Sensing in Dehradun, Sharma’s current research focus is on ionospheric earthquake precursor detection.
TEC monitoring utilises signals from the Global Navigational Satellite System or GNSS, which is a constellation of artificial satellites that provide positioning, navigation and timing services on a global or regional basis. While global positioning satellite (GPS) is the most prevalent GNSS, other nations too have their own systems, such as the Indian Regional Navigation Satellite System (IRNSS) operated by the Government of India. The GPS station located in Rabat in Morocco, 355 kilometres north of the epicentre of the Morocco quake, helped Sharma and fellow researchers monitor the electronic disturbances before and after the earthquake.
Our analysis illustrated TEC fluctuations within the 30-day window preceding the earthquake. Between August 17 and 19, on August 22, as well as from September 2 to 3, a series of conspicuous positive anomalies were identified. Moreover, a significant positive anomaly was detected on the precise day of the earthquake,” says Sharma.
In earlier research published in Quaternary Journal, Sharma and his colleagues reported that TEC values increased before the 2015 Nepal earthquake. “TEC variations (mostly high TEC) had been observed during a period of eight days prior to four earthquakes: April 1, 2015 at Pipalkoti (Uttarakhand); and three subsequent quakes in Nepal on April 25 and 26, 2015 and May 12, 2015.”
These findings hold immense promise for an eventual early warning system.
“Continuous TEC monitoring in active regions like the Himalayas may provide a possible avenue for detecting potential earthquake-related ionospheric anomalies, deriving an early anomaly detection system,” Sharma tells The Telegraph.
Earthquake forecasters also monitor very low frequency (VLF) radio transmissions in the ionosphere. Tamal Basak, a physicist at Ionospheric & Earthquake Research Centre and Optical Observatory at Sitapur, West Bengal, has been tracking VLF signals. According to him, both VLF radio waves and TEC ionospheric measurements can provide useful information for earthquake prediction, but their strengths and weaknesses differ.
He says, “VLF emissions have the advantage of potentially providing information on earthquake magnitude, epicentre and time of occurrence, even allowing for the distinction between foreshocks and mainshocks. TEC, on the other hand, can be used to detect anomalies in the ionosphere that may precede earthquakes, although research is ongoing to determine the most accurate methods for using these anomalies.”
Kayal of the GSI is not convinced. “Predicting earthquakes, even if it is possible, is of no practical use. If an earthquake is predicted to occur within 10 to 15 days in Calcutta, can we vacate the city for that period? Instead, we should learn to live with nature, creating an earthquake-resilient society like that of Japan.”
