By: Ramesh P. Singh, Ph.D., School of Life and Environmental Sciences, Chapman University
Efficient energy transfer from the epicenter of Sunday’s magnitude-3.8 quake northeast of New Delhi, along with quieting of urban noise due to the COVID-19 lockdown, made the quake noticeable by many in India’s capital region.
Citation: Singh, R. P., 2020, Pandemic lockdown sensitizes New Delhi to earthquake risk, Temblor, http://doi.org/10.32858/temblor.087
A small-magnitude earthquake occurred near the National Capital Region (NCR) of India at 5:15 p.m. local time on Sunday. According to the U.S. Geological Survey (USGS), the magnitude-3.8 quake originated at approximately 6 miles (10 kilometers) depth. Generally, such a small-magnitude quake is nondamaging, and on a normal day, most people wouldn’t even notice it. The USGS reports that in this case, the quake was widely felt.
Earthquake intensity varies
The severity of an earthquake — its intensity — is a function of a number of factors, including rock type, background noise, and distance from quake epicenter. This is not to be confused with earthquake magnitude, which is a single value that describes essentially how large an earthquake is. Intensity, however, can vary, even within a relatively small area.
Sunday’s earthquake occurred northeast of New Delhi and about 5 miles (8 kilometers) from Khakhra, in the NCR. The region lies in the eastern part of the Indo-Gangetic river plain. The bulk of the plain is underlain by a thick pile of accumulated sediment deposited by the Indus River over millions of years. New Delhi and the neighboring Delhi-Haridwar Ridge, however, sit atop mainly igneous and metamorphic basement. Unlike sediments, these hard rock types efficiently transmit seismic energy from the epicenter of an earthquake.
The NCR is not unfamiliar with earthquakes. Those in the region have felt past quakes that occurred as far away as the northern Himalaya. It is likely that the hard basement rocks in the Delhi-Haridwar Ridge play a key role in transmitting earthquake energy through the NCR.
A quiet capital
A number of recent reports show that while major metropolitan areas are under lockdown due to COVID-19, significant decreases in human activity are clearing the seismic airways across the planet. Seismometers are detecting less seismic “noise” — the everyday hum caused by our movements — than normal. This background noise usually masks shaking from small quakes.
India, like many other countries, is under a lockdown order. Because the quake struck while most people were sheltering in their homes and everyday background noise was limited, such a small-magnitude quake was noticeable. The USGS “Did you feel it?” map for Sunday’s earthquake registered 242 responses. Last year, a magnitude-4.0 earthquake, 1.6 times larger than the magnitude-3.7 from Sunday, struck close to the site of this most recent quake. That quake registered only 32 “Did you feel it?” responses. It appears that the pandemic lockdown is heightening people’s sensitivity to earthquakes.
A reminder to prepare
One question that emerges from this observation is whether heightened sensitivity to earthquake shaking due to the lockdown will serve to remind people that earthquakes are a real threat, or if the pandemic itself will continue to overshadow this hazard.
This quake should serve to remind local and national governments to consider earthquake preparation a priority in the Indo-Gangetic basin, home to 900 million people. A large-magnitude earthquake is expected in the Himalaya. When and where it will hit, however, is impossible to predict, as is its effect on the NCR. The government could try to deploy a dense network of GPS stations in order to monitor and study the earthquake potential throughout the region.
It is reasonable for governments to take this opportunity to review building designs and infrastructure such as bridges, schools and hospitals. Strict enforcement of building codes and efforts to retrofit existing buildings could save lives and minimize economic damage should a major earthquake hit the region.
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Godin, L., & Harris, L. B. (2014). Tracking basement cross-strike discontinuities in the Indian crust beneath the Himalayan orogen using gravity data–relationship to upper crustal faults. Geophysical Journal International, 198(1), 198-215.