The Dehradun-based Wadia Institute of Himalayan Geology (WIHG) has sought to allay fears about the numerous earthquakes that have shaken up the Delhi National Capital Region in the past weeks. These tremors are not unusual in the region and indicate build-up of strain energy. In fact, most of these quakes are being talked about largely because seismic recording technology is so good that it is able to pick up micro and minor quakes in the region.
Of the 14 quakes recorded in the region in the past few weeks, only the quake of May 29, which was had its epicentre in Rohtak, measured 4.6 on the Richter scale. The others were all much less in magnitude.
The institute said that while humans still do not have enough understanding to predict when, where and of what magnitude an earthquake could occur, past seismicity data helps give an understanding of the vulnerability of an area. This, along with the mapping of active faults and the calculation of strain budget helps identify areas into seismic hazard zones. Delhi NCR is in Zone IV, the second highest hazard zone.
Given the current limitations in predicting quakes, the recent events cannot be termed foreshocks scientifically, and therefore, cannot be termed as the signal of a big event. Only after a big quake has occurred do events in the run up to it get classified as foreshocks. The WIHG, however, emphasised that given the vulnerability of the region as a Zone IV, the possibility of a big quake with a magnitude of 6 or more, that can pose a threat to people and property, can never be ruled out. To deal with that eventuality, however, rustling up panic is not the situation.
Good earthquake drills and construction that is compatible with earthquake resistant rules can help mitigate damage from big quakes in crowded areas; something that Japan, which sits atop a high seismic zone, has proved.
All the earthquakes in Delhi NCR are due to the release of strain energy that gets accumulated as a result of the northward movement of the Indian plate and its collision with the Eurasian plate, through fault or weak zones. There are many such faultlines nearby -- the Delhi Jaridwar ridge, Mahendragarh Dehradun subsurface fault, Moradabad fault, Sohna fault, Great Boundary Fault, Delhi-Sargodha ridge, the Yamuna and Ganga river lineaments.
The energy gets built up because of relative movement of the tectonic plates. The energy is released in the form of earthquakes, ranging from micro (less than 3 on the Richter scale), minor (3-3.9), light (4 - 4.9), moderate (5 - 5.9), strong (6 - 6.9), major (7-7.9) or great (more than 8).
There are also many faults, ridges and lineaments transverse to the Himalayan arc, which is only 200km from the Delhi NCR. Thus, a major earthquake in the Himalayan seismic belt can also be a big threat to the capital region. Most of the Himalayan and sub Himalayan regions are in Zone V and IV, thus vulnerable always.
Delhi's last big shake-up happened in 1966, when a 5.8 quake was epicentred near Moradabad. In 1960, a 6 point quake epicentred near Faridabad occurred.