Earthquakes: Causes, Effects & Responses

Earthquakes are one of the most destructive natural hazards on Earth. This lesson covers how and why earthquakes happen, the effects they have on people and the environment, and how communities respond. You will study contrasting case studies from a higher-income country (HIC) and a lower-income country (LIC) — a key requirement of the AQA specification.

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How Earthquakes Occur

An earthquake is a sudden and violent shaking of the ground caused by the release of energy stored in rocks along a fault line or plate boundary.

The Process

1. Tectonic plates are constantly moving, but friction at plate boundaries causes them to lock together.
2. Stress (pressure) builds up over time as the plates continue to be pushed by convection currents.
3. When the stress exceeds the strength of the rocks, they fracture and the plates suddenly move.
4. Energy is released as seismic waves that radiate outward from the point of fracture.

Key Terms

Term	Definition
Focus	The point within the Earth's crust where the earthquake originates
Epicentre	The point on the Earth's surface directly above the focus
Seismic waves	Waves of energy released during an earthquake
Aftershock	A smaller earthquake that follows the main shock, often causing additional damage
Fault	A fracture in the Earth's crust where movement has occurred

Measuring Earthquakes

Scale	What It Measures	Notes
Richter Scale	Magnitude (energy released)	Logarithmic: each whole number is 10x more powerful
Moment Magnitude Scale (MMS)	Magnitude (more accurate)	Used by scientists today; replaced Richter for large quakes
Mercalli Scale	Intensity (felt effects)	Ranges from I (not felt) to XII (total destruction)

Exam Tip: The Richter and Moment Magnitude scales measure energy released (magnitude), while the Mercalli scale measures the effects felt by people (intensity). Make sure you know the difference.

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Earthquake Effects

Earthquake effects are divided into primary effects (caused directly by the shaking) and secondary effects (caused as a result of primary effects).

Primary Effects

• Building collapse — poorly constructed buildings are most vulnerable.
• Road and bridge destruction — cutting off transport and rescue routes.
• Deaths and injuries — from falling debris and structural collapse.
• Damage to infrastructure — gas pipes, water mains, and electricity lines broken.

Secondary Effects

• Fires — ruptured gas mains ignite, especially dangerous when water supplies are damaged.
• Tsunamis — undersea earthquakes can displace water, generating devastating waves.
• Landslides and avalanches — triggered by ground shaking on steep terrain.
• Disease — contaminated water supplies and lack of sanitation.
• Economic losses — loss of business, cost of rebuilding, reduced tourism.
• Homelessness — displacement of thousands or millions of people.

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Case Study: Nepal Earthquake 2015 (LIC)

Background

Detail	Information
Date	25 April 2015
Magnitude	7.8 Mw
Focus depth	15 km (shallow)
Location	Gorkha district, ~80 km northwest of Kathmandu
Plate boundary	Collision (Indian and Eurasian plates)
Country type	LIC (GDP per capita ~$730 at the time)

Primary Effects

• 8,800+ people killed and over 22,000 injured.
• Over 600,000 homes destroyed and 288,000 damaged.
• Historic temples and monuments in Kathmandu Valley destroyed (UNESCO World Heritage Sites).
• Roads blocked by rubble, especially in mountainous areas.

Secondary Effects

• Avalanches on Mount Everest killed 19 climbers — the deadliest day in Everest's history.
• Landslides blocked rivers and roads, isolating remote villages for weeks.
• Over 2.8 million people displaced from their homes.
• Psychological trauma — widespread PTSD, especially among children.
• Economic damage estimated at $7 billion (approximately half of Nepal's GDP).

Responses

Immediate responses:

• The Nepalese army and police began search and rescue within hours.
• International aid arrived: India, China, the UK, and the US sent rescue teams.
• The UN launched a $415 million appeal for humanitarian aid.
• Temporary shelters (tarpaulins and tents) were distributed to displaced people.
• Field hospitals were set up by organisations such as the Red Cross.

Long-term responses:

• The government launched the National Reconstruction Authority to coordinate rebuilding.
• Stricter building codes were introduced requiring earthquake-resistant construction.
• Schools and hospitals were rebuilt to improved standards with international funding.
• Training programmes taught local communities how to build earthquake-resistant homes.
• However, reconstruction was slow — two years later, many families were still in temporary shelters.

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Case Study: L'Aquila Earthquake 2009 (HIC)

Background

Detail	Information
Date	6 April 2009
Magnitude	6.3 Mw
Focus depth	9.5 km (shallow)
Location	L'Aquila, central Italy
Plate boundary	Destructive (African and Eurasian plates)
Country type	HIC (Italy — one of the G7 nations)

Primary Effects

• 309 people killed and over 1,500 injured.
• 67,000 people made homeless.
• Over 10,000 buildings damaged or destroyed, including historic churches and the university.
• A student dormitory collapsed, killing several university students.

Secondary Effects

• Aftershocks continued for months, causing further structural damage and psychological distress.
• $16 billion in estimated damage.
• Tourism and local businesses suffered significant losses.
• Ongoing legal controversy: six scientists were initially convicted (later overturned) of manslaughter for failing to adequately warn of the earthquake risk.

Responses

Immediate responses:

• Italian emergency services (Civil Protection Department) responded within an hour.
• Temporary tent camps and hotels housed displaced residents.
• The Italian government declared a state of emergency and allocated emergency funds.
• Search and rescue teams used sniffer dogs and thermal imaging equipment.

Long-term responses:

• A "new town" was built on the outskirts of L'Aquila to rehouse residents.
• Tax breaks and financial support were offered to businesses and residents.
• Historic buildings were carefully restored (ongoing — some still unfinished more than a decade later).
• Improved monitoring systems were installed in the region.

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Comparing the Two Case Studies

Factor	Nepal 2015 (LIC)	L'Aquila 2009 (HIC)
Magnitude	7.8	6.3
Deaths	8,800+	309
Homes destroyed	600,000+	~10,000 buildings damaged
Emergency response time	Slow in remote areas	Within one hour
Building quality	Many poorly built structures	Some modern, some old and vulnerable
Recovery speed	Very slow; years of reconstruction	Faster but still ongoing after a decade