14 quakes in 2 months may not lead to a big one in NCR
Still, monitoring them is key to being prepared , they add. Scientists at the National Centre for Seismology (NCS) underlined that earthquakes cannot be forecast and the only thing to do is to be aware of the activities in vulnerable pockets such as the Delhi region.Updated: Jun 05, 2020 04:17 IST
Wednesday night’s minor tremor in Noida was the fourteenth (14th) to hit Delhi and the National Capital Region (NCR) over the past two months, but the increased frequency may not necessarily indicate a major one is coming, say seismologists.
Still, monitoring them is key to being prepared , they add. Scientists at the National Centre for Seismology (NCS) underlined that earthquakes cannot be forecast and the only thing to do is to be aware of the activities in vulnerable pockets such as the Delhi region.
Only two of the 14 tremors have been above magnitude 3.5, according to NCS data.
“While these [minor earthquakes] may be because of activity in the local faults, we have to remember that north Delhi is close to the Himalayan belt where the Indian plate is subducting under the Eurasian plate. That region is seismically very active. We need to monitor even these small earthquakes critically because we do not know how much energy is there and how much has been released through these small events,” said Kalachand Sain, who heads the Wadia Institute of Himalayan Geology. Subducting is the process by which one tectonic plate moves under another.
“We really need to understand the subsurface scenario now. Occasionally great earthquakes can happen and so we need to build infrastructure and buildings accordingly.”
Any major earthquake in the Himalayan belt can also impact Delhi and NCR.
A P Pandey, an NCS seismologist, said there have been numerous small earthquakes in Delhi and Haryana over the past three years and that a few have been above magnitude 4. “There are many faults and fissures in this region which could be active. In the past three years, there have been numerous small earthquakes in this region. Luckily, we did not see a much bigger earthquake …we are close to the Himalayas. The Himalayan plate is moving in the north-northeast direction and subducting beneath the Eurasian plate. So, there is a lot of energy along weak zones which are sometimes released through fissures and lineaments.”
A fissure is a crack or a fracture ; a lineament is a linear feature corresponding to a fault -- such as a valley or a mountain range.
He added the small earthquakes since April have been along lineaments. “Only the one with 4.5 magnitude was along the juncture of the Mahendergarh and Delhi-Sargoda faults. It is good that energy or stress is being released through these lineaments. Otherwise, there can be a big release which can cause widespread damage.”
The Himalayas are vulnerable to major earthquakes of over magnitude 8.
“Nobody can say when or where this energy will be released. So, it is best to be prepared. We have, however, identified vulnerable pockets,” Pandey said.
NCS head (operations) J L Gautam said it is not abnormal to record so many earthquakes within a couple of months in the Delhi-NCR region “There are a number of small faults in this region. The earthquake last [Wednesday] night was in Uttar Pradesh in Gautam Buddha Nagar. There is the Mathura fault, Moradabad fault, Delhi-Haridwar ridge, Delhi-Sargoda fault, Mahendergarh and Dehradun fault. So, small earthquakes happen in this area. It is not abnormal. That does not mean we cannot expect a big earthquake.”
According to Indian Institute of Science’s seismic hazard mapping in 2004, the terrain of Delhi is flat in general except for the NNE-SSW trending ridge. “This is one of the prominent features of Delhi. This is considered as an extension of the Aravalli hill, which is buried under the Yamuna alluvium in the northern parts of Delhi. River Yamuna, which is another prominent feature of Delhi, enters the city from the north and flows southward with an eastern bend near Okhla. This path forms a tri-junction with the Lahore-Delhi ridge and the Delhi-Haridwar ridge. This region is seismically active and shows sporadic activity aligned in NNE-SSW direction, nearly perpendicular to the Himalayan arc. Proximity of Himalayan region makes Delhi susceptible to the earthquakes from Himalayan seismic sources also."