Frequent earthquakes around Delhi linked to groundwater pumping
doi:10.1038/nindia.2021.72 Published online 17 May 2021
Earthquakes along the Aravalli-Delhi Fold Belt (ADFB) – spanning north of Delhi to Udaipur in India’s northwest – appear to be more frequent around the national capital, a region that extracts maximum groundwater for agricultural and domestic use. A team of geophysicists now suggest a link between the increased seismic activity and the ‘alarming’ increase in groundwater pumping in the Delhi region1.
Simulating data around space-based gravity change, earthquake frequency, GPS, rainfall and well-level groundwater, the scientists, led by Bhaskar Kundu of the National Institute of Technology (NIT), Rourkela, suggest that the pressure on groundwater aquifers may be the trigger for increased seismic activity in the region.
“Groundwater pumping leads to reduction in water load in the aquifers causing subsurface faults to unclamp, thereby promoting failure,” Vineet Gahalaut, chief scientist at the National Geophysical Research Institute (NGRI) in Hyderabad, and a co-author of the study told Nature India. This means that earthquakes in this region are either triggered or their frequency is modulated by the groundwater withdrawal patterns, he said. The combined effect of aquifer contraction and basement rock expansion modulate the effective stress regime and seismicity on the faults of the region, he added.
The ‘low magnitude but moderate seismicity rate’ of Delhi region correlates with groundwater pumping for extensive irrigation, urban activities, and seasonal loading of freshwater aquifers. To understand how much groundwater was being extracted in northwest India and the region surrounding Delhi, the researchers explored 156 months of NASA’s Gravity Recovery and Earth Climate Experiment (GRACE) data and Global Land Data Assimilation System (GLDAS), from January 2003 to December 2015.
They estimated that groundwater storage in the region was changing at an ‘alarming’ rate of around 1.6 cm per year. Although the entire Aravalli-Delhi Fold Belt experiences earthquakes, the Delhi region appears to be more active seismically, having witnessed several moderate and strong historical earthquakes in 1720, 1831, 1956 and 1960. Most of these earthquakes occurred in the upper 25 km of the Earth’s crust. The study suggests that recent earthquakes in the region have good correlation with the timing of the seasonal hydrological loading cycle. “During the water loading period – June to September monsoon time – seismicity is the lowest, whereas it is relatively high during the unloading period.”
“Such hydrological processes may trigger earthquakes, but what causes them in the intraplate region (away from the plate boundary regions like the Himalayan arc) still needs to be explored,” Gahalaut said. It is also a good prompt for future explorations into the seismogenic potential of the region and to determine the maximum magnitude of an earthquake which may occur here, he said. With hydrological modeling, in-situ and satellite-based observations, the researchers also indicate alarming groundwater extraction rates across the Indo-Gangetic Basin in north-western India.
‘Induced seismicity’ is of concern to scientists observing a direct link between water withdrawal rates and earthquakes. They suggest that this may be a promising tool to mitigate the occurrence of induced earthquakes. Delhi could represent other mountain valley regions in the world that experience similar overexploitation of aquifers and suffer from ground subsidence and seismicity, the authors suggest. “The two-way coupling between fluid flow and mechanical deformation processes also holds promise for uncovering hidden basement faults and effective forecasting of human-induced earthquakes,” Gahalaut pointed out.
Earlier, another study led by Kundu found links between the heavy extraction of groundwater in the Indo-Gangetic basin for over five decades to the devastating magnitude 7.8 earthquake in Nepal in April 20152.
Similar studies are underway in other regions of India. In Maharashtra, scientists are trying to understand the phenomenon of induced earthquakes in a reservoir of the Koyna Dam. “There too, water loading seems to be the primary driver,” said Madhavan Rajeevan Nair, secretary in India’s Ministry of Earth Sciences.
Globally, earthquakes have been associated with extraction of water, oil and gas3. Ramesh Singh, a geophysicist at Chapman University in California said the Indian government must think of rotation of crops to minimise use of groundwater in agriculture. “Dedicated water wells that can be monitored will provide good information about the changes in stress possibly leading to earthquakes,” he told Nature India.
In the past few decades identifying human-induced earthquakes and understanding their geodynamics have become a focal point in terms of both socio-political and scientific discussion, Kundu said. More than 700 events have been documented in the human-induced earthquake database called HiQuake. "We have strengthened this database by adding another compelling scenario of groundwater extraction-induced seismicity around the Delhi region," he said.
The study adds to the growing body of evidence on how modest stress changes from non-tectonic loads can influence the activity of small earthquakes. “They are still tectonic earthquakes, but apparently influenced by changing amounts of water at the Earth's surface and in the ground,” said Roland Burgmann, Professor in the Department of Earth and Planetary Science at the University of California, Berkeley.
With improved seismicity records and continuous studies, it should be possible to solidify these linkages, he said.
(Correction on 18 May 2021: The name of the lead scientist, his affiliating institute and quote have been updated.)