In the wake of the recent series of tremors in Delhi-NCR, Wadia Institute of Himalayan Geology has said that such tremors are not unusual in the Delhi-NCR region, but indicate that strain energy is built-up in the region.
The autonomous institute under the Department of Science and Technology said that since the seismic network is quite good, present micro to minor earthquakes in and around Delhi-NCR could be recorded.
The Delhi-NCR has been identified as the second highest seismic hazard zone (Zone IV).
Sometimes, a vulnerable zone remains quiet, experiences small magnitude earthquakes that do not indicate any bigger earthquake, or receives a sudden jolt by a big earthquake without any call.
Out of 14 small magnitude earthquakes in the Delhi-NCR, the May 29 Rohtak earthquake had the magnitude of 4.6.
"Though it cannot be predicted, a stronger earthquake posing a threat to people and properties cannot be ruled out. Since an earthquake cannot be predicted by any mechanism, the tremors cannot be described as the signal of a big event," Dr. Kalachand Sain, Director Wadia Institute of Himalayan Geology said.
The historical earthquake catalog shows that there were strong earthquakes of 6.5 magnitude at Delhi in 1720; 6.8 at Mathura in 1803; 5.5 near Mathura in 1842; 6.7 near Bulandshahar in 1956; 6.0 near Faridabad in 1960; 5.8 near Moradabad in 1966 in the Delhi-NCR.
All the earthquakes in Delhi-NCR are due to the release of strain energy, which have been accumulated as a result of northward movement of Indian plate and its collision with the Eurasian plate, through the fault or weak zones.
There are so many weak zones and faults in the Delhi-NCR: Delhi-Haridwar ridge, Mahendragarh-Dehradun subsurface fault, Moradabad fault, Sohna fault, Great boundary fault, Delhi-Sargodha ridge, Yamuna river lineament, Ganga river lineament etc.
These energy can be released through the weak zones and faults in the form of earthquakes ranging from micro (8.0) earthquake, defined as per the amount of energy released.
The small magnitude earthquakes are frequent, but large magnitude earthquakes are rare to very rare. It is the large earthquakes that cause severe damages both to structures and properties.
The rupture areas due to large earthquakes show gaps along the Himalayan arc, which have not experienced great earthquakes for a long time, and are identified as the future potential zones for great earthquakes.
The subsurface structures, geometry, and disposition of faults and ridges are to be investigated thoroughly using Geo-scientific studies in and around Delhi and NCR.
Since the soft soils do not support the structures' foundations, structures anchored to bedrock or stiff soils in earthquake-prone areas suffer less damage.
Thus, soil liquefaction studies are to be carried out to know the thickness of soft soils. Active faults are to be delineated, and lifeline structures or other infrastructures are to be avoided from nearby active faults, and to be constructed as per the guiding principles of the Bureau of Indian Standard (BIS). The outcome of recent micro zonation studies for Delhi-NCR by IMD should be considered for important construction.
Earthquakes are not predictable but there lies a probability of a large to great earthquake with magnitude 6 and more in the highest seismic potential zone V and IV, which fall in the entire Himalaya and Delhi-NCR.
The only solution to minimise the loss of lives and properties is the effective preparedness against the earthquake.
