What is an Earthquake?
An earthquake is a natural geological phenomenon characterized by a sudden release of energy in the Earth’s crust, resulting in seismic waves that propagate through the Earth’s surface. It occurs when there is a sudden slip or movement along a fault, a fracture in the Earth’s crust where two blocks of rock have moved past each other. The point within the Earth where the earthquake originates is called the focus, and the point directly above it on the Earth’s surface is called the epicenter.
Earthquakes can cause significant damage to structures, landscapes, and communities, making them one of the most destructive natural disasters. The study of earthquakes and their effects is known as seismology.
Types of Earthquakes:
- Tectonic Earthquakes: These are the most common type of earthquakes and occur due to the movement of tectonic plates, which are large pieces of the Earth’s lithosphere that float on the semi-fluid asthenosphere beneath them. Tectonic earthquakes are further classified into three types:
- Normal Fault Earthquakes: These earthquakes occur when the hanging wall (the block of rock above the fault) moves downward relative to the footwall (the block of rock below the fault).
- Reverse Fault Earthquakes: In reverse fault earthquakes, the hanging wall moves upward relative to the footwall.
- Strike-Slip Earthquakes: In these earthquakes, the blocks of rock slide past each other horizontally along the fault plane.
- Volcanic Earthquakes: Volcanic earthquakes are associated with volcanic activity and occur as magma moves beneath the Earth’s surface. These earthquakes can indicate an impending volcanic eruption.
- Induced or Human-Induced Earthquakes: These earthquakes are triggered by human activities, such as reservoir-induced seismicity from the filling of large dams, hydraulic fracturing (fracking), and geothermal energy extraction.
- Collapse Earthquakes: These earthquakes are caused by the collapse of underground caverns, mines, or other large voids.
- Explosion Earthquakes: These earthquakes are triggered by the detonation of nuclear or chemical explosives.
The severity of an earthquake is measured on the Richter scale or moment magnitude scale (Mw). The Richter scale measures the amplitude of seismic waves, while the moment magnitude scale considers the energy released by an earthquake.
Earthquake Zones in India
India is a seismically active country due to its location on the boundary of the Indian Plate, which is colliding with the Eurasian Plate. As a result, several earthquake zones are distributed across the country. The seismic zones in India are classified based on the level of seismicity, with Zone V being the most seismically active and Zone II being the least active. These zones are used in building codes and construction practices to ensure that structures are designed to withstand potential earthquake forces.
Zone V (Severe Intensity Zone):
- This zone covers the most seismically active regions, including parts of the Himalayan region, the Kutch region in Gujarat, and the North-Eastern states.
- It is considered to have the highest level of seismicity and is prone to experiencing the most severe earthquakes in the country.
Zone IV (High-Intensity Zone):
- This zone includes areas around Zone V and covers certain regions in Jammu and Kashmir, Himachal Pradesh, Uttarakhand, North-Eastern states, and parts of Gujarat and Rajasthan.
- It is a high seismicity zone, and earthquakes in this region can cause significant damage to structures and infrastructure.
Zone III (Moderate Intensity Zone):
- Zone III includes regions around Zone IV and covers areas in parts of Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Orissa, Andhra Pradesh, and parts of Tamil Nadu and Maharashtra.
- While the seismicity is lower than in Zones IV and V, earthquakes in this zone can still cause damage to poorly constructed buildings.
Zone II (Low-Intensity Zone):
- This zone covers the remaining parts of the country, including most of the plains and peninsular regions of India.
- It is the least seismically active zone, but even in this zone, earthquakes of higher magnitudes can have an impact on poorly designed structures.
Some major earthquakes in India
- 1905 Kangra Earthquake:
- Date: April 4, 1905
- Magnitude: 7.8
- Epicenter: Kangra, Himachal Pradesh
- The Kangra earthquake is one of the most severe earthquakes recorded in the Himalayan region. It caused widespread destruction in Kangra and surrounding areas, resulting in the death of about 20,000 people.
- 1934 Bihar-Nepal Earthquake:
- Date: January 15, 1934
- Magnitude: 8.3
- Epicenter: Nepal-Bihar border
- This earthquake is one of the most devastating in Indian history, causing severe damage in Bihar and Nepal. It resulted in the loss of approximately 10,600 lives.
- 1950 Assam-Tibet Earthquake:
- Date: August 15, 1950
- Magnitude: 8.6
- Epicenter: Assam-Tibet border
- This earthquake affected Assam and the neighboring regions in Tibet, China. It caused significant damage to buildings and infrastructure, and the death toll reached around 1,500.
- 1993 Latur Earthquake:
- Date: September 30, 1993
- Magnitude: 6.4
- Epicenter: Latur, Maharashtra
- The Latur earthquake struck the Maharashtra region and caused severe damage to Latur and nearby towns. The death toll was approximately 10,000, and many more were injured.
- 2001 Gujarat Earthquake:
- Date: January 26, 2001
- Magnitude: 7.7
- Epicenter: Bhuj, Gujarat
- This earthquake struck the western state of Gujarat and caused extensive damage to buildings, infrastructure, and human lives. It is estimated that over 20,000 people lost their lives, and thousands were injured.
- 2015 Nepal Earthquake:
- Date: April 25, 2015
- Magnitude: 7.8
- Epicenter: Nepal (close to the India-Nepal border)
- Although the epicenter was in Nepal, this earthquake had a significant impact on several states in India, particularly Bihar and Uttar Pradesh. The death toll in India was around 2,000, and thousands were injured.
List of all major earthquakes in India
- 2015 India/Nepal Earthquake
- 2011 Sikkim Earthquake
- 2005 Kashmir Earthquake
- 2004 Indian Ocean Earthquake
- 2001 Bhuj Earthquake
- 1999 Chamoli Earthquake
- 1997 Jabalpur Earthquake
- 1993 Latur Earthquake
- 1991 Uttarkashi Earthquake
- 1941 Andaman Islands Earthquake
- 1975 Kinnaur Earthquake
- 1967 Koynanagar Earthquake
- 1956 Anjar Earthquake
- 1934 Bihar/Nepal Earthquake
- 1905 Kangra Earthquake
Impacts of earthquakes
An earthquake can have multiple impacts on the affected region and its inhabitants. These impacts can be devastating and wide-ranging, affecting various aspects of life and the environment. Some of the multiple impacts of an earthquake include:
- Human Casualties and Injuries: The most immediate and significant impact of an earthquake is the loss of human lives and injuries. Buildings and infrastructure may collapse, trapping people inside and causing fatalities or severe injuries.
- Destruction of Infrastructure: Earthquakes can cause widespread damage to buildings, roads, bridges, and other essential infrastructure. This can disrupt transportation, communication, and access to vital services like healthcare and clean water.
- Displacement of People: Earthquakes can force people to leave their homes due to damage or fear of aftershocks. This displacement can lead to temporary or long-term homelessness, creating humanitarian challenges.
- Economic Losses: The destruction of property, infrastructure, and businesses can result in substantial economic losses for individuals, communities, and the country as a whole.
- Aftershocks: Aftershocks are smaller earthquakes that follow the main earthquake. They can continue for days, weeks, or even months, causing additional damage and hampering recovery efforts.
- Tsunamis: In coastal areas, large earthquakes beneath the ocean can trigger tsunamis, which are massive sea waves capable of inundating coastal regions and causing further devastation.
- Landslides: The shaking during an earthquake can destabilize slopes and trigger landslides, especially in hilly and mountainous regions, leading to more destruction and potential loss of life.
- Fires: Earthquakes can rupture gas lines, electrical wires, and other flammable sources, leading to fires that can quickly spread and cause further damage.
- Environmental Impact: Earthquakes may impact the environment, such as changes in groundwater levels, ground subsidence, and alterations to natural landscapes.
- Psychological Trauma: Survivors and witnesses of earthquakes often experience psychological trauma and post-traumatic stress disorder (PTSD) due to the fear, loss, and uncertainty associated with the event.
- Public Health Challenges: Earthquakes can overwhelm healthcare facilities and disrupt access to medical services, leading to health crises and disease outbreaks in the aftermath.
- Impact on Livelihoods: Disruptions to businesses and agriculture can affect livelihoods and lead to economic hardships for individuals and communities.
- Community and Social Disruptions: Earthquakes can strain social cohesion and community structures, as people may have to rely on support systems for their survival and recovery.
Steps taken by India to mitigate earthquakes
- Mitigation measures for earthquakes in India are coordinated by the National Center for Seismology, a department under the Ministry of Earth Sciences. This center receives earthquake monitoring and hazard reports and operates in three divisions: Geophysical Observation System, Earthquake Hazard and Risk Assessment, and Earthquake Monitoring & Services.
- The National Earthquake Risk Mitigation Project (NERMP) plays a significant role in enhancing earthquake mitigation programs, both in non-structural and structural components. By focusing on high-risk areas, the NERMP aims to reduce vulnerability. The National Disaster Management Authority (NDMA) oversees the project and has prepared a detailed project report (DPR) for its implementation.
- India has a comprehensive National Building Code (NBC), which is a national regulation controlling building construction across the country. First published in 1970 and later updated in 1983, the NBC received significant amendments in 1987 and 1997. The latest version, the National Building Code of India 2005 (NBC 2005), incorporates current international best practices and addresses challenges posed by natural disasters.
- The Building Materials & Technology Promotion Council (BMTPC) is actively involved in lifeline structural retrofitting projects to raise awareness among the public and various governmental organizations. By assisting in reducing vulnerability in existing public and private structures, BMTPC aims to support policymakers and the general population in earthquake risk reduction efforts.
To mitigate the impacts of earthquakes, preparedness measures such as building codes, early warning systems, emergency response plans, and public awareness campaigns are crucial. Proper urban planning and earthquake-resistant construction can also help minimize the damage and protect lives and property during seismic events.