An earthquake measuring 4.7 on the Richter scale, centred 63km southwest of the millennium city of Gurugram in Haryana, shook the national capital region (NCR) on Friday even as the residents had begun to put behind a series of tremors experienced till June 8 last month.
The latest tremor is likely to trigger fresh curiosity over earthquakes in the region and raise questions over safety of residents from seismic activities. There is no proven technology in the world to predict earthquakes with certainty in terms of location, time and magnitude, therefore information and awareness are considered key tools for better understanding of the phenomenon.
Here are 10 important points that will help in understanding the recent earthquakes.
1. A series of 16 earthquakes or so were recorded in the NCR from April this year till June 8 with the last one in the series being a mild one centred near Delhi with an intensity of 2.1 magnitude. The epicenter of the tremor was recorded south east of Rohtak in Haryana at latitude 28.85 and longitude 76.76. Most of the earthquakes registered in the series were mild barring a couple above 3.5 magnitude including a 4.5 magnitude earthquake that had hi Rohtak on May 30.
2. The National Centre of Seismology has said that the tremors were being monitored and studied by a team at the national centre. It had also termed the occurrence of mild tremors in this region as a normal phenomenon. J L Gautam, head of operations at the NCS had said that it was not abnormal to record several earthquakes within a couple of months in the NCR.
3. Delhi and NCR is also vulnerable to quakes because of its proximity to Himalayas. There are many faults, ridges and lineaments transverse to the Himalayan arc. A major earthquake in the Himalayan seismic belt may be a threat to Delhi-NCR. However, the experts also described these events as “non-linear” to suggest they shouldn’t be seen as events connected on a timeline. NCS said the several mild earthquakes in a very short period could be attributed to “minor adjustments” of the tectonic plates.
4. Delhi-NCR is in the second highest seismic hazard zone which comes under Zone IV. The tremors in the NCR could be a result of shifting in any of the several fault lines in the region incuding the Mathura fault; Moradabad fault; Delhi Haridwar ridge; Delhi Sargoda fault; Mahendergarh and Dehradun fault. The vulnerability of a region can be understood from past seismicity, calculation of strain and mapping of active faults.
5. The NCS has also said that the occurrence of a series of small earthquakes can neither be extrapolated to predict a big earthquake in the region nor can it be used to rule it out. In other words, the agency has made it clear that earthquakes cannot be forecast. The Wadia Institute of Himalayan Geology also made a similar point and said that small magnitude tremors in Delhi-NCR do not necessarily indicate that a bigger one was around the corner.
6. According to experts, sometimes a vulnerable zone remains quiet or experiences small magnitude earthquakes that do not indicate any bigger earthquake, or can receive a sudden jolt by a big earthquake without any warning. All the quakes recorded in Delhi-NCR are due to the release of energy, which have accumulated as a result of northward movement of the Indian plate and its collision with the Eurasian plate, through the fault or weak zones.
7. The experts at NCS have maintained that while there is no need to panic, it was important to be prepared and take precautionary measures to mitigate the risks associated with a big earthquake.
8. A petition was moved in Delhi High Court last month seeking directions to Delhi government and the civic authority to prepare an action plan to safeguard structures in the national capital against a big earthquake. The court had asked the AAP government, Delhi Development Authority (DDA) and the three municipal corporations (MCD) to respond to questions on preparedness to deal with a major tremor. The court also directed the authorities to make the public aware about the action plan in place.
9. The National Disaster Management Authority (NDMA) had requested the state government in the region to take steps to ensure compliance of building bye laws for the safety of upcoming constructions. They bylaws specify requirements to make buildings earthquake resilient.
10. The NDMA had also suggested that the states identify the vulnerable structures including lifeline buildings and retrofit them to reduce their vulnerability to moderate to severe earthquakes. It also called for the retrofitting of private buildings in a phased manner. It also suggested that regular mock exercises were conducted and governments released SoPs for immediate response after an earthquake.