By K.S. Jayaraman
Oct 16 (IANS): Continuous monitoring of water levels in the foothills of the Himalayas can warn about an impending earthquake in the region, which is due for a major temblor.
This recommendation to the Ministry of Earth Sciences has come from Ramesh Singh, professor of environmental sciences at California's Chapman University, who is also president of the Natural Hazards Group of the American Geological Union.
Singh says the utility of monitoring the water levels of underground aquifers for predicting earthquakes in quake-prone regions has been confirmed from analysis of water level data in a bore hole collected during the earthquake that rocked Nepal's Gorkha district on April 25, 2015.
The findings of the study carried out by Singh and three seismologists from China have recently been published in the journal Techtonophysics.
The Gorkha quake, one of the deadliest in Nepal, killed about 5,000 people mainly in Nepal, a few in bordering India, two in Bangladesh and one in China, and injured about 9,200 people.
Whenever earthquakes occur, widespread cracks and deformations on the earth's surface are common, resulting in changes in groundwater levels, Singh told this correspondent in an email.
In China, many parameters are being monitored in water wells, including water level, water temperature, and water radon concentrations to detect any signal prior to an impending earthquake.
According to the scientists, due to seismic wave propagation, the volume of an aquifer expands and contracts, forming fractures that change the water flow in a bore well sunk into the aquifer.
In the case of the Gorkha quake, the scientists considered the water level in a bore well -- called "Jingle" well -- atop an aquifer in China's Shanxi province, 2,769 kilometres from the temblor's epicenter. The data was analysed soon after the Nepal earthquake.
A "spectrum analysis" of the co-seismic response of the bore hole water level showed large amplitude oscillations with a maximum peak-to-peak value of about 1.75 metres associated with ground vibrations generated by the earthquake, says their report.
In addition, the analysis revealed the arrival of a possible precursor wave at the "Jingle" well about 6.5 hours prior to the actual occurrence.
"The study of co-seismic changes in groundwater has emerged as an important research area which can provide an improved understanding of earthquake processes and corresponding changes in surface and subsurface parameters," Singh said.
Water level data in close proximity to the epicenter may be of great importance in getting early warning signals of an impending earthquake, he said. China and the United States routinely monitor aquifer water levels at 15-minute intervals.
In the light of the finding, Singh said that "India's Ministry of Earth Sciences may consider deploying water level sensors in the Himalayan foothills areas, which may provide valuable information about an impending earthquake in the Himalayan region, which is due for a major earthquake."
Such data, he added, "is also useful in understanding the dynamic nature of the Indian plate".
However Arun Bapat, former head of Earthquake Engineering Research at the Central Water and Power Research Station in Pune, says he has some reservations about the study's conclusion that water level changes observed in the bore hole were the warning signal for the Gorkha earthquake.
"Various effects associated with a large earthquake (Magnitude 7.5 or more) such as electrical, magnetic, geological, tectonic, hydraulic, radioactivity, etc., have been observed within about 600 to 800 km from the epicenter (but not beyond)," Bapat told IANS.
Bapat said the magnitude of the Gorkha quake was about 6.5 to 6.75 which is considered as moderate. "The effect of this quake on water level changes at a distance of 2,769 kilometres from its epicenter is almost not possible."