2020 has been marked in almost all the usual natural disasters that mankind knows about. Forest fires, floods, earthquakes, you name it. Speaking of earthquakes, India is a hotspot for the earthquake occurrence due to the dynamic interaction between the Indian and the Asian plate. So, how prone is India to earthquakes? Or should I state, which areas in India are more prone to earthquakes? Let’s see…
Earthquakes can be described as the movement of the land surfaces due to release of seismic waves from within the Earth’s lithosphere. Earthquakes all by itself can be pretty destructive. Higher magnitude earthquakes can cause violent shaking of the ground, thus destroying structures, and sometimes disturbing the local topographic scene too. The triggered effects in Nature due to earthquake include tsunami (in case of offshore source of origin), landslide, and in some rare cases, volcanic activity.
The term earthquake, in the general scientific respect, is associated with seismic activity. The source of the seismic activity though, can be either natural, or manmade. Some of the common causes of occurence are: faulting, mine blasts, landslide, nuclear testing or volcanic activity. The original point of disturbance within the lithosphere is known as the hypocentre, and the extrapolation of the point on the ground level is known as the epicentre.
The magnitude, or the strength of an earthquake, can be measured in various scales. But the most commonly known is the Richter magnitude scale. Nowadays, moment magnitude scales have a preference within the seismological authorities, but it is still reported as the Richter scale. The Richter scale is based on the logarithm values detected from the amplitude of seismic waves. It gives the measure of the energy given out by the earthquake. The Richter scale starts off from 1.0 and theoretically has no upper limit. But on the basis of historic records, the limit has been set for 8.9 as of now. Another scale, the Mercalli Damage Risk scale, measures the earthquake on the basis of its effect on the surface. Measured from the minimum of ‘not felt’, the scale goes up to the higher end category ‘extreme’. In terms of sumericals, the scale goes from 1-12. An important point to note is that the energy and effect of the earthquake are always not in relation, as for they depend on various factors.
Trends Within India
With India being a very large country in terms of territorial area, the areas are divided into various zones in accordance to the past seismological activity and the natural factors of the area. At present, the map produced by Bureau of Indian Standards dividends the whole country into four zones (Zones 2, 3, 4, 5). Zone 5 experiences highest Damage Risk of seismic activity and Zone 2 the lowest.
- Zone 5 (Very Severe Damage Risk Zone) are the areas most susceptible to the risk of earthquakes of Damage Risk 9 or more. This zone includes the entire North Eastern region, Andaman Nicobar island groups, some parts of Jammu & Kashmir and Uttarakhand, Ladakh, Himachal Pradesh, northern regions of West Bengal, Rann of Kutch, North and Central Bihar and Uttarakhand.
- Zone 4 (Severe Damage Risk Zone) are areas which are prone to experience the earthquakes of Damage Risk 8. Regions like North Punjab, Chandigarh, Western Uttar Pradesh, Sunderbans, Terai, the NCR, Sikkim, and the remaining parts of Jammu & Kashmir and Uttarakhand. The Patan area in Maharashtra also comes under this zone.
- Zone 3 (Moderate Damage Risk Zone) usually has the probability to have earthquakes of Damage Risk 7. Goa, Lakshadweep Islands, Rajasthan, Jharkhand, Madhya Pradesh, Chattisgarh, Kerala, Tamil Nadu, Andhra Pradesh, Karnataka, Maharashtra, and the remaining parts of Bihar, West Bengal and Uttar Pradesh,
- Zone 2 (Low Damage Risk Zone) accounts for regions that tend to experience earthquakes of intensity 6 and less. All the remaining areas of India fall under this category.
The Bureau of Indian Standards has provided some guidelines for construction of buildings, with certain parameters being assigned on the basis of the seismic zones. With a large part of the country, and by virtue of that, a large part of the population being susceptible to strong earthquakes, construction of legal and anti earthquake structures are a necessity of the present time.