Earthquakes

Definition:
Seismic waves are waves of energy that travel through Earth's layers, and are a result of
earthquakes, volcanic eruptions, magma movement, large landslides and large man-made
explosions that give out low- frequency acoustic energy
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of
the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates
seismic waves.
Plate Tectonic Theory:
1. About: The plate tectonic theory is widely accepted to explain earthquakes.
According to this theory, the Earth's crust is comprised of solid, mobile plates,
including continental, oceanic, or both types of crust. These plates float on the
semi-fluid asthenosphere and move due to thermal convective currents within the
Earth.
2. Plate Composition: The Earth's crust is divided into 6 major plates (Eurasian,
American, African, Indian, Pacific, and Antarctic) and 20 minor plates. These plates
constantly move relative to each other, leading to tectonic events along their
margins.
3. Constructive Plate Boundaries: These boundaries are characterised by continuous
addition of geomaterials. Molten materials from the Earth's mantle upwell along
mid-oceanic ridges, leading to the formation of new crust as they cool and solidify.
Divergent plates move away from mid-oceanic ridges, and new crust is added to their
trailing ends.
4. Destructive Plate Boundaries: At these boundaries, two convergent plates collide.
The heavier plate is subducted below the lighter plate, resulting in the loss of crustal
materials. This process leads to the formation of deep oceanic trenches and volcanic
arcs.
5. Conservative Plate Boundaries: These boundaries involve plates passing each other
without collision. This movement neither creates nor destroys crust, resulting in
lateral sliding along fault lines.
6. Impact: The movement of tectonic plates is responsible for various geological
phenomena such as earthquakes, volcanic eruptions, and the formation of mountain
ranges. Understanding plate tectonics helps in assessing earthquake hazards,
planning for disaster mitigation, and interpreting Earth's geological history.
Pacific Ring of Fire

Earth's major earthquakes happen in zones along the edges of tectonic plates.
This is evident from historical records and modern seismic data. The most
significant zone is the Circum-Pacific Belt, impacting coastal regions around the
Pacific Ocean. It's responsible for 80% of earthquake-released energy and due to
frequent volcanic activity, it's nicknamed the "Pacific Ring of Fire."
EARTHQUAKE DISASTER REDUCTION AND MANAGEMENT
The effective measures of earthquake disaster reduction and management must be based
on standard methodology of disaster emergency management as follows:

Pre-disaster Stage/Phase (PMP)

preparedness (P) mitigation (M) prevention (P)

Post-disaster Stage/Phase (3R Phase)

rescue and relief (R) disaster recovery (R) rehabilitation (R)

I. Pre-Disaster Stage:
1. Preparedness:
1. Surveying and mapping seismic hazard zones, conducting earthquake hazards analysis,
and assessing earthquake risk.
2. Implementing precautionary and protective measures, including provision of
infrastructure such as temporary shelters, water supply, and communication systems.
3. Predicting earthquake occurrences through advanced techniques and public awareness
campaigns.
4. Identifying factors contributing to seismic risks and vulnerability, such as weak building
structures and high-density settlements.
5. Assessing and reducing structural vulnerability by following appropriate building codes,
retrofitting old buildings, and strengthening infrastructure.
2. Prevention:
1. Division of regions into earthquake risk zones based on vulnerability assessments, such as
India's five earthquake risk zones.
2. Avoiding human settlements in high-risk earthquake zones.
3. Implementing earthquake-resistant architectural designs and using high-quality building
materials.
4. Restricting construction of high-rise buildings and large dams in earthquake-prone areas.
5. Mitigating environmental factors that contribute to seismic activity, such as groundwater
mining, deforestation, and quarrying in high seismic zones.
3. Mitigation:
1. Educating residents in earthquake-prone areas about safety measures to follow during
earthquakes.
2. Restricting urban growth in hilly areas with high earthquake vulnerability.
3. Implementing measures to prevent reservoir-induced seismicity (RIS) by avoiding the
construction of large dams in high seismic zones.

India is divided into five earthquake risk zones based on the level of
potential damage:

 Zone I (Least Risk): Parts of Punjab, Haryana, Uttar Pradesh, Bihar,

West Bengal, Maharashtra, Kerala, Rajasthan (excluding Kutch).
 Zone II (Low Risk): Southern Punjab, Haryana, Uttar Pradesh,
Rajasthan, coastal Orissa and Tamil Nadu.
 Zone III (Moderate Risk): Southern and southeastern Rajasthan,
Madhya Pradesh, Maharashtra, Karnataka, southern Bihar, northern
Orissa.
 Zone IV (High Risk): Jammu & Kashmir, Himachal Pradesh,
northern Punjab & Haryana, Delhi, western Uttar Pradesh,
Uttarakhand foothills, Bihar, Sikkim.
 Zone V (Very High Risk): Parts of Jammu & Kashmir, Himachal
Pradesh, Uttarakhand, extreme north Bihar, entire Northeast India,
Kutch region of Gujarat.

This zoning system helps authorities prioritize earthquake preparedness

and mitigation efforts in areas facing higher risks.

II. Post-Disaster Stage: Three R Phase of Earthquake Disaster Management

1. Rescue and Relief (R):
- Rescue Operation: Immediate efforts are focused on search and rescue operations to
locate and extricate individuals trapped in rubble.
- Provision of Relief: Emergency relief measures include providing temporary shelters, such
as tents or public buildings, supplying clothing, food, safe drinking water, and medicines, and
deploying medical teams and ambulances.
- Restoration of Essential Services: Restoration of electricity supply, transportation, and
communication systems is prioritized to facilitate relief efforts and communication.
2. Rehabilitation (R):
- Rehabilitation Activities: This phase involves restoring basic services damaged or made
non-functional by the earthquake, repairing damaged structures, and revitalizing the
economy.
- Physical and Mental Recovery: Efforts are made to support the physical and mental
recovery of disaster victims and survivors, including restoring social and cultural life.
3. Reconstruction and Recovery (R):
- Reconstruction Efforts: Activities initiated for the complete restoration of affected services,
infrastructure, and buildings, including repair and replacement of houses and buildings,
revival of economy, and resumption of normal public life.
- Comprehensive Restoration: Reconstruction encompasses repair and replacement of
damaged structures, revival of economic activities, and restoration of social and cultural life
to bring affected communities back to normalcy.
These phases are interdependent and aim to address the immediate needs of affected
populations, restore essential services, and facilitate the long-term recovery and
rehabilitation of earthquake-affected areas.

Initiatives taken by the Indian government to mitigate earthquake risks:

1. Centralized Body (NCG):

 Established a National Core Group (NCG) with earthquake engineering
experts and administrators.
 Responsibilities include:
o Developing strategies to reduce earthquake impact.
o Advising state governments on mitigation strategies.
o Creating earthquake-resistant building plans and manuals.
o Encouraging states to adopt national building codes.
 o Training professionals (architects, engineers, masons) on
earthquake-safe construction.
2. Building Code Enforcement:
 Emphasizes reviewing and updating state building bylaws to prioritize
structural safety during earthquakes.
3. Standardisation Committee (AC):
 Formed an Apex Committee (AC) to revise Bureau of Indian Standards (BIS)
codes for multi-hazard resistant constructions.
4. State Level Body (HSC):
 Established Hazard Safety Cells (HSC) in each state led by the Chief
Engineer (PWD).
 Responsibilities include:
o Implementing building codes in government constructions.
o Reviewing designs of government buildings for safety.
o Advising the state government on overall building safety.
- Additional Measures:
 National program to train engineers and architects in earthquake risk
mitigation.
 Training programs for rural masons.