The Wadia Institute of Himalayan Geology (WIHG) recently commented on the series of tremors experienced in the National Capital Region-Delhi (Delhi-NCR), saying they are consistent with the anticipated strain energy build-up in the region. As an autonomous entity of the Department of Science and Technology, WIHG’s remarks offer crucial insights into seismic activities in the area.
Understanding Earthquake Predictions
In science, predicting earthquakes remains a complex task. Tremors do not necessarily serve as warnings of a bigger earthquake; nevertheless, the possibility of a stronger, life-threatening earthquake should never be dismissed. Understanding a region’s vulnerability involves reviewing past seismicity, calculating strain budgets, and mapping active faults. At times, a vulnerable zone may remain calm with occasional small magnitude earthquakes, or sometimes, it could experience a large, sudden earthquake with no warning.
Delhi-NCR is considered the second highest seismic hazard zone, known as Zone IV. Yet, recent events in Delhi-NCR cannot be defined as foreshocks unless a significant earthquake follows. Foreshocks consist of all minor tremors before a major earthquake in a particular region.
Why Earthquakes Occur in Delhi-NCR
Two factors contribute to earthquakes: the release of strain energy and plate tectonics. Strain energy builds up after the northward movement of the Indian plate and its collision with the Eurasian plate, and is later released through weak zones or faults. The Himalayan seismic belt, where these plates collide, plays a vital role.
Delhi-NCR’s proximity to the Himalayas, which is within two seismic potential zones, V and IV, means it’s susceptible to major earthquakes. These zones have historically experienced significant seismic activity.
India’s Seismic Zones
India has four seismic zones (II, III, IV, and V) based on seismicity, past earthquakes, and regional tectonic setup. Previously, earthquake zones were divided into five categories by severity. However, the Bureau of Indian Standards (BIS), the seismic hazard map and codes official publishing agency, grouped the country into four zones by combining the first two.
Each seismic zone corresponds to different degrees of potential earthquake damage, ranging from minor (zone II) to the most active region (zone V). Seismic Zone V is the most vulnerable to earthquakes, having experienced shocks in excess of 7.0 magnitude and with intensities higher than IX on the MM scale (Modified Mercalli Intensity).
Seismic Waves, Richter Scale, and Mercalli Scale
Seismic waves are vibrations from earthquakes that travel through the Earth and are recorded on seismographs. These instruments present a zigzag trace that shows the varying amplitude of ground oscillations beneath it.
Earthquake events can be measured through two scales: the Richter scale which reflects the energy release during an earthquake and the Mercalli scale which accounts for the visible damage caused by the event.
The Path Ahead
Although earthquakes cannot be predicted, there is a likelihood of a large earthquake (magnitude 6 or more) occurring in seismic potential zones V and IV, encompassing the entire Himalaya and Delhi-NCR. The only solution to mitigate the loss of lives and property is effective preparedness against earthquakes. Countries like Japan have proven this effectively with their preparedness efforts.
While earthquakes are unpredictable phenomenons, with public participation, cooperation, and adequate understanding, we can better prepare ourselves and minimize potential damage and loss.
