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Delhi earthquake: What is ‘in-situ material heterogeneity’?
The tremor that struck Delhi early on Monday was due to natural variations in the region's geological features and was not caused by plate tectonics.
After parts of Delhi NCR experienced "strong" tremors from a 4.0-magnitude earthquake on Monday morning, National Center for Seismology (NCS) attributed it to “in-situ material heterogeneity”. This factor, rather than plate tectonics, makes the national capital highly vulnerable to seismic activity.
Speaking to PTI, a senior scientist explained that the tremor that struck Delhi early on Monday was due to natural variations in the region's geological features.
What is ‘in-situ material heterogeneity’?
“In-situ material heterogeneity” refers to variations in the geological features of the region. Although a 4.0-magnitude quake is considered moderate, its impact was amplified by its shallow depth of 5 km and proximity to densely populated areas.
National Center for Seismology (NCS) Director OP Mishra explained to PTI that it was a shallow-depth earthquake, which is why the tremors were felt strongly. He also noted that the quake was not linked to plate tectonics but rather to local geological conditions. "People panicking was natural," he added.
Mishra also mentioned that aftershocks between 1.0 to 1.2 magnitude could occur. Experts highlight that shallow earthquakes – those occurring at depths of less than 10 km – tend to feel stronger as seismic waves don't have to travel far to reach the surface. Additionally, the epicenter's location within the city meant the effects were heightened, particularly in high-rise buildings, which are designed to sway during seismic activity.
The earthquake, with its epicentre near Jheel Park in Dhaula Kuan, caused residents in nearby areas to hear loud noises as the earth shifted this morning.
Hours after the earthquake struck Delhi, tremors were also felt in Bihar at approximately 8:02 am on Monday. This tremor originated just 10 km below the Earth's surface, but no casualties or damage have been reported so far.
However, Mishra clarified that the earthquakes in Delhi and Bihar are unrelated, explaining that such events "depend on the rock shearing strength, which differs between the two states."
Delhi region experiences frequent tremors
The Delhi region, situated in northern India, regularly experiences tremors from both far-field and near-field earthquakes originating from the Himalayas and local sources, respectively.
In 2007, Dhaula Kuan experienced a 4.6 magnitude earthquake, but its impact was not as severe as Monday’s tremor because it occurred at a depth of 10 km, according to National Centre for Seismology Director OP Mishra.
Delhi is classified in seismic zone IV on India's seismic zoning map, the second-highest category for seismic risk.
The national capital faces moderate to high seismic activity risks due to historical earthquakes from the Himalayas, such as the 7.5 magnitude Garhwal Himalaya quake in 1803, the 6.8 magnitude Uttarkashi earthquake in 1991, the 6.6 magnitude Chamoli earthquake in 1999, the 7.8 magnitude Gorkha earthquake in 2015, and several moderate quakes from the Hindukush region.
Local earthquakes recorded in the region include the 6.5 magnitude Delhi earthquake in 1720, the 5 magnitude Mathura earthquake in 1842, the 6.7 magnitude Bulandshahar earthquake in 1956, and the 5.8 magnitude Moradabad earthquake in 1966.
Seismologically, the region has a history of earthquakes. Mishra explained that while a 4.6 magnitude earthquake occurred within a 6 km radius earlier, the deeper depth of 10 km made it less impactful. He clarified that Monday's quake was not caused by plate tectonics but by "in-situ material heterogeneity," referring to local geological conditions.
(With PTI inputs)
