Earthquakes: Causes, Effects, and Preparedness

Few natural events strike with as little warning as an earthquake. The ground we treat as the very definition of stability can shift in seconds, bringing down buildings, roads, and lives. A large part of the subcontinent sits on geologically active terrain, which makes understanding earthquakes less of an academic exercise and more of a practical necessity. This post breaks down why earthquakes happen, how their strength is measured, how seismic risk is mapped across the country, and what genuine preparedness looks like.

What causes an earthquake 🔗

An earthquake is simply the shaking of the Earth’s surface caused by a sudden release of energy stored in the crust. That energy travels outward as seismic waves, which is what we feel as tremors. The point inside the Earth where the rupture begins is the focus (or hypocentre), and the point directly above it on the surface is the epicentre, where shaking is usually strongest.

The role of tectonic plates 🔗

The outer shell of the Earth is broken into large slabs called tectonic plates that are in constant, slow motion. Most earthquakes happen along the boundaries where these plates meet, grind, and lock against one another. Stress builds up over years or centuries, and when the rocks finally slip, the stored energy is released all at once. The subcontinent sits on the Indian Plate, which is pushing northward into the Eurasian Plate at roughly five centimetres a year. This ongoing collision built the Himalayas and continues to make the Himalayan belt and the Northeast among the most seismically active regions in the world.

Other triggers beyond plate movement 🔗

While tectonic activity is the dominant cause, it is not the only one. Volcanic eruptions can produce tremors as magma forces its way through the crust. Large water reservoirs behind big dams can also induce seismicity: the sheer weight of impounded water and changes in underground pressure can stress nearby faults, a phenomenon documented at sites like the Koyna Dam in Maharashtra. Finally, large underground nuclear explosions generate artificial seismic waves strong enough to register on seismographs, which is precisely how nuclear tests are detected internationally.

How earthquakes are measured 🔗

There are two very different things we might want to know about an earthquake: how much energy it released, and how strongly it shook a particular place. These are measured separately, and confusing the two is a common mistake.

Magnitude: the Richter and moment magnitude scales 🔗

Magnitude measures the total energy released at the source, so a single earthquake has only one magnitude value. The Richter scale, developed by Charles Richter in 1935, was the first widely used measure. It is logarithmic, meaning each whole-number step represents about ten times greater ground motion and roughly 31 times more energy released. The trouble is that the Richter scale becomes unreliable for very large earthquakes, where it tends to saturate above magnitude 7. For this reason, scientists now prefer the moment magnitude scale (Mw), which calculates energy from the area of the fault that ruptured and how far the ground slipped. It works accurately across all earthquake sizes and has effectively replaced the Richter scale for moderate-to-large events, though news reports often still loosely call any magnitude figure a “Richter” reading.

Intensity: the Mercalli scale 🔗

Intensity, by contrast, measures the effects of shaking at a specific location, so a single earthquake produces a range of intensity values that are highest near the epicentre and fade with distance. The Modified Mercalli Intensity scale runs from I to XII using Roman numerals and is based entirely on observed effects: what people felt, how objects moved, and how much structures were damaged. A reading of I means the quake was detected only by instruments, while XII means near-total destruction. Because it depends on damage and eyewitness accounts, the Mercalli scale is most useful in inhabited areas and is the better tool for comparing how badly different places suffered.

Seismic zones in India 🔗

Because different regions face very different levels of risk, the country is divided into seismic zones. The first detailed zoning map in 1970 split the land into five zones numbered I to V, where Zone I carried the lowest risk and Zone V the highest. Over time, scientists realised that Zone I and Zone II faced broadly similar low hazard, so Zone I was eventually merged into Zone II. Under the standard that is currently in force, IS 1893 (Part 1): 2016 prepared by the Bureau of Indian Standards (BIS), the country is divided into four zones: Zone II (low risk), Zone III (moderate), Zone IV (high), and Zone V (very high). Zone V, which covers the Himalayan states, the Northeast, and the Kutch region of Gujarat, makes up roughly 11 percent of the land area and is associated with the most severe shaking, corresponding to intensity IX and above.

The proposed Zone VI and its withdrawal 🔗

Seismic maps are revised as our scientific understanding improves, and a recent episode shows how complicated that process can be. In late 2025, the BIS notified a revised code, IS 1893:2025, that introduced an entirely new highest-risk category called Zone VI and reclassified the whole Himalayan arc into it, using modern probabilistic hazard modelling rather than relying mainly on past earthquake locations. However, the revision was withdrawn in early 2026 after the Ministry of Housing and Urban Affairs raised concerns about steep construction cost increases and inadequate consultation with stakeholders. As a result, the 2016 standard with its four zones remains the applicable code. The episode is a useful reminder that disaster policy must balance scientific ambition with economic and practical feasibility.

The effects of earthquakes 🔗

The damage an earthquake causes is usually divided into primary and secondary effects. Primary effects are the direct result of ground shaking: collapsing buildings, cracked roads, fallen bridges, and ruptured pipelines. The most lethal of these is structural collapse, because most earthquake deaths are caused not by the shaking itself but by falling buildings.

Secondary effects follow as a consequence and can sometimes be worse than the initial quake. These include landslides in hilly areas, liquefaction where water-saturated soil temporarily behaves like a liquid and swallows foundations, fires from broken gas and electrical lines, and tsunamis when an earthquake displaces the seabed. Beyond the physical destruction lies a long economic and social tail: disrupted water and power, homelessness, ruined crops, and the slow, expensive work of reconstruction that can stretch on for years.

The 2001 Bhuj earthquake: a turning point 🔗

No event illustrates these dangers better than the Bhuj earthquake of 26 January 2001. It struck at 8:46 AM on Republic Day, with a moment magnitude of 7.7 and an epicentre near Chobari village in the Kutch district, around 20 kilometres from the town of Bhuj. The shaking lasted only a couple of minutes, but the destruction was staggering. Estimates of the death toll range from about 13,800 to over 20,000, with roughly 167,000 people injured and well over a million buildings damaged or destroyed.

According to the Bhuj Area Development Authority, much of the heavy casualty count was traced to the collapse of multi-storey buildings due to poor design, along with narrow, congested lanes that left people little room to escape. Investigations afterwards found that a large share of the destruction came not from the magnitude alone but from buildings that were never designed to resist seismic forces. The disaster exposed how dangerous unregulated construction can be in a high-risk zone, and it became the catalyst for serious reform. In its aftermath, the Gujarat State Disaster Management Authority was created, and at the national level the experience fed directly into the Disaster Management Act of 2005 and the formation of the National Disaster Management Authority.

Preparedness and mitigation 🔗

Earthquakes cannot be prevented or reliably predicted, so the entire strategy rests on reducing the harm they cause. The encouraging truth is that earthquakes do not kill people; poorly built structures do. That single insight shapes almost everything in modern disaster planning.

Earthquake-resistant construction and building codes 🔗

The most effective protection is building structures that can flex and absorb seismic energy without collapsing. The BIS publishes a family of codes for this purpose, including IS 1893 for general design criteria and IS 4326 and IS 13920 for the detailed practice of earthquake-resistant construction. These specify features such as ductile reinforcement, strong beam-column joints, and continuous load paths that hold a building together during shaking. The hard part is not writing the codes but enforcing them. As studies of the Bhuj disaster by institutions like the National Information Centre of Earthquake Engineering have shown, codes only save lives when local authorities actually inspect construction and certify compliance. Retrofitting older buildings, especially schools, hospitals, and other public structures built before modern codes, is an equally important part of the picture.

Community awareness and institutional readiness 🔗

Engineering alone is not enough. Public training in how to respond during shaking, such as the “drop, cover, and hold on” practice, can dramatically cut injuries. Securing heavy furniture, keeping an emergency kit with water and first aid, and knowing safe spots in each room are simple steps that make a real difference. At the institutional level, the National Disaster Management Authority issues guidelines, coordinates mock drills, and supports early-warning research and rapid-response systems. Preparedness, in other words, is a chain that runs from the engineer’s drawing board to the household’s emergency bag, and the chain is only as strong as its weakest link.

What do you think? If the 2001 Bhuj earthquake proved that enforcement of building codes matters more than the codes themselves, what would it take for your own city or town to take that lesson seriously? And was the withdrawal of the stricter 2025 seismic code a sensible response to economic reality, or a missed opportunity to make high-risk regions genuinely safer?

References

1. https://www.usgs.gov/programs/earthquake-hazards/moment-magnitude-mw
2. https://www.usgs.gov/programs/earthquake-hazards/modified-mercalli-intensity-scale
3. https://en.wikipedia.org/wiki/Earthquake_zones_of_India
4. https://www.drishtiias.com/daily-updates/daily-news-analysis/rollback-of-seismic-code-of-2025
5. https://www.britannica.com/event/Bhuj-earthquake-of-2001
6. https://bhujada.com/earthquake-2001/
7. https://www.nicee.org/Bhuj.php
8. https://ndma.gov.in/Natural-Hazards/Earthquakes