Effects of Earthquakes

Understanding Earthquake Effects

When an earthquake strikes, it creates a chain of effects. Some happen right away. Others develop hours, days, or even months later. Scientists group these effects into three categories: primary, secondary, and tertiary.

The same size earthquake can have very different effects in different places. A magnitude 7.0 earthquake in Japan might kill 100 people, while the same size quake in Haiti killed 160,000. The difference depends on how people prepare, how they build, and how quickly help arrives.

Understanding these effects helps countries prepare better. Nigeria has low earthquake risk compared to Japan or California. However, Nigerian students must learn about earthquake effects for WAEC and NECO exams. This knowledge also helps understand global disasters.

Primary Effects of Earthquakes

Primary effects occur immediately when the earthquake happens. They result directly from ground shaking and crustal movement. These are the most obvious and immediate impacts.

Ground Shaking

Ground shaking is the most noticeable primary effect. The ground moves violently in all directions. Strong shaking can last from a few seconds to several minutes. During the 2011 Japan earthquake, shaking lasted nearly six minutes.

Shaking intensity depends on several factors. Earthquakes closer to the surface shake more violently. Soft ground like clay or sand shakes more than solid rock. Mexico City sits on an ancient lake bed. This soft ground makes earthquakes feel much stronger there.

Building Collapse and Destruction

Violent shaking causes buildings to collapse. This is the main cause of death in earthquakes. Poorly built structures fall quickly. Buildings without earthquake-resistant design crumble when foundations shift.

The 2010 Haiti earthquake killed so many people because buildings were weak. Many used poor concrete and had no steel reinforcement. Even government buildings and hospitals collapsed. In contrast, Japan’s strict building codes save thousands of lives during earthquakes.

Infrastructure also suffers. Bridges collapse. Roads crack and buckle. Railway tracks bend. Ports and airports become unusable. After the 1995 Kobe earthquake in Japan, major highways collapsed, blocking rescue efforts.

Loss of Life and Injuries

Earthquakes kill people in several ways. Collapsing buildings trap and crush victims. Falling debris strikes people trying to escape. Broken glass cuts fleeing residents. The 1923 Kanto earthquake in Japan killed over 140,000 people, mostly from collapsing buildings and fires.

Injuries range from minor cuts to severe trauma. Broken bones, head injuries, and crush injuries are common. Hospitals become overwhelmed. Many injured people cannot get treatment because medical facilities are also damaged.

Crustal Fracturing and Ground Rupture

The Earth’s surface can visibly split during earthquakes. Deep cracks called fissures appear in the ground. In the 1906 San Francisco earthquake, the ground split along the San Andreas Fault. Some fissures were several meters wide.

Ground rupture destroys everything crossing the fault line. Buildings sitting on the fracture split in half. Roads become impassable. Pipelines for water, gas, and oil break. These breaks cause secondary problems like fires and water shortages.

Displacement of Land

Earthquakes can move land vertically or horizontally. Coastal areas may rise or sink. The 1964 Alaska earthquake raised some coastal areas by 11 meters. Other areas sank below sea level. This changes coastlines permanently.

Horizontal movement shifts land sideways. The 2011 Japan earthquake moved the main island of Honshu 2.4 meters to the east. This movement was so large that it affected Earth’s rotation and shortened the day by 1.8 microseconds.

Secondary Effects of Earthquakes

Secondary effects happen because of the earthquake but are not direct results of ground shaking. These effects can occur from minutes to days after the main shock. Often, secondary effects cause more deaths than primary effects.

Tsunamis

Tsunamis are giant ocean waves created when underwater earthquakes displace water. Not all earthquakes cause tsunamis. Only earthquakes under the ocean or near coasts can create them. The earthquake must also move the sea floor vertically.

The 2004 Indian Ocean tsunami was the deadliest in history. The earthquake lifted the sea floor several meters. This displaced billions of tons of water. Waves traveled across the Indian Ocean at 800 km per hour, the speed of a jet plane.

Tsunami waves grow taller as they reach shallow water. In deep ocean, they might be only one meter high. Near shore, they can reach 30 meters or more. The waves rush inland, destroying everything in their path. The 2011 Japan tsunami waves reached 40 meters in some areas.

Tsunamis can strike minutes or hours after the earthquake. People near the coast must move to high ground immediately after feeling strong shaking. Warning systems give distant coasts several hours to evacuate.

Fires

Fires are a major secondary hazard, especially in cities. Earthquakes break gas lines and electrical wires. Sparks ignite leaking gas. Overturned stoves and lamps start fires. The 1906 San Francisco earthquake started over 50 fires.

These fires spread quickly for several reasons. Water mains break, leaving fire hydrants dry. Firefighters cannot reach blazes because roads are blocked. The 1906 San Francisco fire burned for three days. It destroyed more of the city than the earthquake itself.

The 1923 Kanto earthquake in Japan struck at lunchtime. Many families were cooking over open flames. Thousands of fires started simultaneously. Fire tornadoes formed, killing tens of thousands who had survived the shaking.

Landslides and Avalanches

Earthquakes trigger landslides, especially in mountainous areas. Shaking loosens rock and soil on steep slopes. Entire hillsides collapse. Landslides bury villages and block roads. They dam rivers, creating dangerous lakes that can later flood downstream areas.

The 2008 Sichuan earthquake in China triggered over 15,000 landslides. Some were enormous. One landslide buried the town of Beichuan, killing thousands. Landslides accounted for about 30% of deaths in this earthquake.

The 2005 Kashmir earthquake triggered massive landslides in the Himalayan mountains. The steep terrain and loose rock made conditions ideal. Landslides blocked roads for weeks, preventing rescue teams from reaching remote villages.

In snowy mountains, earthquakes trigger avalanches. The 2015 Nepal earthquake caused a massive avalanche on Mount Everest. It killed 19 climbers at base camp, making it the deadliest day in Everest’s history.

Liquefaction

Liquefaction happens when waterlogged soil loses strength during shaking. The process turns solid ground into something like quicksand. Buildings sink. Underground tanks float to the surface. Roads buckle and crack.

Liquefaction occurs in areas with loose, sandy soil and shallow groundwater. River deltas, coastal areas, and reclaimed land are most vulnerable. The ground shakes, water pressure builds, and soil particles separate.

The 1964 Niigata earthquake in Japan showed dramatic liquefaction effects. Apartment buildings tilted and fell over, yet remained mostly intact. They simply sank into liquefied ground. Residents walked out of windows that were now at ground level.

Port facilities suffer severely from liquefaction. The 1995 Kobe earthquake liquefied soil under port cranes and warehouses. Kobe’s port, one of the world’s busiest, was unusable for years. Japan lost billions in trade.

Aftershocks

Aftershocks are smaller earthquakes that follow the main shock. They can continue for months or even years. Aftershocks happen as the Earth’s crust adjusts to new stresses. Some are nearly as strong as the main quake.

The 2023 Turkey earthquake produced a magnitude 7.5 aftershock just nine hours after the 7.8 main shock. This second quake collapsed buildings already weakened by the first. Rescue workers had to flee as structures crumbled around them.

Aftershocks terrorize survivors. People are afraid to go inside buildings. They sleep outdoors even in cold weather. The psychological stress is enormous. Every aftershock triggers panic.

Tertiary Effects of Earthquakes

Tertiary effects are long-term consequences that develop in the weeks, months, or years following an earthquake. These effects result from the cascade of primary and secondary impacts.

Disease Outbreaks

Earthquakes create conditions for disease outbreaks. Water treatment plants stop working. Sewage systems break. Clean water becomes scarce. People drink contaminated water and become sick.

Cholera and typhoid are common after earthquakes. Both spread through polluted water. The 2010 Haiti earthquake caused a cholera outbreak that killed over 10,000 people. This was separate from earthquake deaths.

Crowded emergency shelters help diseases spread. Thousands of people live in small spaces with poor sanitation. Respiratory infections spread quickly. Inadequate food and stress weaken immune systems.

Bodies buried under rubble pose health risks if not removed quickly. In hot climates, decomposition happens rapidly. Disease can spread from corpses to water supplies.

Economic Losses

Earthquake damage costs billions. The 2011 Japan earthquake caused about $235 billion in damage, making it the costliest natural disaster in history. Rebuilding takes years or decades.

Businesses close permanently. Workers lose jobs. Tourism stops. The economy can take years to recover. Some cities never fully recover. Port-au-Prince, Haiti still shows earthquake damage over a decade later.

Insurance companies pay massive claims. Sometimes they go bankrupt. Governments must borrow money to rebuild. This creates debt for future generations.

Homelessness and Displacement

Millions lose homes in major earthquakes. The 2008 Sichuan earthquake left 5 million homeless. People live in tents or temporary shelters for years. Children grow up in refugee camps.

Some areas become permanently uninhabitable. The Fukushima nuclear disaster, triggered by the 2011 earthquake and tsunami, created an exclusion zone. Over 150,000 people cannot return home due to radiation.

Displaced people face many hardships. Children miss school. Families separate. Traditional communities break apart. The social fabric tears.

Psychological Trauma

Survivors suffer lasting psychological effects. Post-traumatic stress disorder (PTSD) is common. People have nightmares and flashbacks. They cannot concentrate or sleep. Fear of aftershocks causes constant anxiety.

Children are especially vulnerable. Those who lose parents or witness deaths may struggle for life. The trauma affects their education, relationships, and mental health.

Entire communities suffer collective trauma. The 1923 Kanto earthquake changed Japanese society. People became more focused on disaster preparedness. The trauma shaped national identity.

Food Shortages

Earthquakes disrupt food production and distribution. Farmland cracks and becomes useless. Irrigation systems break. Roads needed to transport food are destroyed.

Stored food is lost when warehouses collapse. Markets cannot operate. Even when food is available, prices skyrocket. Poor people cannot afford to eat.

The 2015 Nepal earthquake struck before harvest season. Farmers could not plant crops because they were rebuilding homes. Landslides covered terraced fields. Food shortages lasted months.

Factors That Affect Earthquake Impact

The same magnitude earthquake can have vastly different effects. Several factors determine the severity of impacts.

Building Quality and Codes

Strict building codes save lives. Countries like Japan, Chile, and New Zealand have tough earthquake regulations. Buildings must withstand strong shaking. Even in major earthquakes, modern buildings usually survive.

Poor countries often lack building codes. Even when codes exist, corruption allows builders to ignore them. The 2008 Sichuan earthquake collapsed many schools. Investigators found builders had used cheap materials and cut corners.

Population Density

Earthquakes in crowded cities kill more people. More people means more potential victims. High-rise buildings house hundreds. If one collapses, deaths are massive.

Rural earthquakes affect fewer people. The 2008 Sichuan earthquake hit mountainous areas. If the same quake struck Shanghai, deaths could have been millions instead of thousands.

Time of Day

When an earthquake strikes matters enormously. Nighttime quakes catch people sleeping. They cannot escape collapsing buildings. The 1960 Agadir earthquake struck at night, killing one-third of the population.

Daytime quakes during work hours trap people in offices and factories. School earthquakes can be catastrophic. The 2008 Sichuan quake struck at 2:28 PM when schools were full.

Depth of Earthquake

Shallow earthquakes cause more damage than deep ones. Shallow quakes occur less than 70 km underground. Their energy reaches the surface with little loss. Deep earthquakes waste energy traveling through rock.

The 2010 Haiti earthquake was only 13 km deep. This shallow depth concentrated its energy near Port-au-Prince. A deeper earthquake of the same magnitude would have caused less damage.

Distance from Epicenter

Areas closest to the epicenter suffer most. Shaking intensity decreases with distance. However, local geology can create exceptions. Soft soil amplifies shaking even far from the epicenter.

Comparison of Earthquake Effects

Nigeria’s Earthquake Risk

Nigeria has very low earthquake risk. The country sits in the middle of the African Plate, far from plate boundaries. Most Nigerian earthquakes are too small to feel. The strongest recorded Nigerian earthquake was magnitude 4.5 in 1939.

However, Nigerians should understand earthquakes for several reasons. WAEC and NECO exams test this knowledge. Nigerians travel and work in earthquake zones. Understanding disasters helps in emergency management careers.

West Africa’s geological stability is why cities like Lagos can have tall buildings without expensive earthquake protection. This is an advantage Nigeria has over countries like Japan or Indonesia.

Common Exam Mistakes

WAEC examiners report these frequent mistakes when students write about earthquake effects:

• Confusing effect categories: Students call tsunamis a primary effect. Tsunamis are secondary because they result from the earthquake, not from direct shaking.
• Only listing effects: When asked to “explain,” students write “loss of life, destruction of property.” This is listing, not explaining. You must say HOW and WHY these occur.
• Mixing up terms: Students confuse landslides with liquefaction. Landslides are earth sliding down slopes. Liquefaction is soil turning liquid.
• Forgetting tertiary effects: Most students only mention primary and secondary effects. Questions asking for “all effects” require tertiary impacts too.
• No examples: Generic answers like “buildings collapse” score low. Specific examples like “the 2010 Haiti earthquake collapsed the presidential palace” score higher.
• Poor organization: Jumping between different types of effects randomly. Use clear paragraphs: one for primary, one for secondary, one for tertiary.
• Missing the cascade: Not explaining how one effect causes another. For example, earthquake breaks water pipes (primary), leading to fire hydrants without water (secondary), allowing fires to spread (secondary), causing disease from poor sanitation (tertiary).

Practice Questions

Multiple Choice Questions

1. Which of the following is a primary effect of earthquakes?
a) Tsunami waves
b) Disease outbreaks
c) Ground shaking ✓
d) Fire spreading

2. Liquefaction occurs when:
a) Mountains collapse into valleys
b) Waterlogged soil loses strength during shaking ✓
c) Ocean water floods coastal areas
d) Underground water dries up

3. The 1906 San Francisco earthquake caused most damage through:
a) Primary ground shaking only
b) Secondary fires that burned for days ✓
c) Tertiary disease outbreaks
d) Liquefaction of soil

4. Which factor does NOT affect earthquake impact severity?
a) Building quality and codes
b) Population density
c) Time of day
d) Name of the city ✓

5. Aftershocks are classified as:
a) Primary effects
b) Secondary effects ✓
c) Tertiary effects
d) Not actual earthquake effects

Essay Questions

1. Distinguish between primary and secondary effects of earthquakes, giving THREE examples of each. (12 marks)

Examiner’s Tip: “Distinguish” means show clear differences. Define each category first, then give examples with explanations. Don’t just list.

Sample Answer Structure:

• Definition: Primary effects occur immediately from ground shaking; secondary effects happen later as consequences (2 marks)
• Primary example 1: Building collapse happens instantly when foundations fail during shaking, killing trapped occupants (2 marks)
• Primary example 2: Ground rupture splits earth along fault lines, destroying roads and pipelines crossing the fracture (2 marks)
• Primary example 3: Land displacement raises or lowers coastal areas, like Alaska rising 11 meters in 1964 (2 marks)
• Secondary example 1: Tsunamis form when underwater quakes displace water, like 2004 Indian Ocean waves killing 227,000 (2 marks)
• Secondary example 2: Fires start from broken gas lines, spreading when water mains fail, as in 1906 San Francisco (1 mark)
• Secondary example 3: Landslides occur when shaking loosens slopes, burying villages like in 2008 Sichuan (1 mark)

2. Explain FIVE factors that determine the severity of earthquake effects. (10 marks)

Examiner’s Tip: Each factor needs an explanation and example. Don’t just name factors.

Sample Answer Points:

• Building quality: Earthquake-resistant buildings save lives; Japan’s strict codes mean magnitude 7 quakes kill dozens, while Haiti’s poor construction caused 160,000 deaths from a similar quake (2 marks)
• Population density: Crowded cities suffer more casualties; if 2008 Sichuan earthquake hit Shanghai instead of mountains, millions might have died instead of thousands (2 marks)
• Earthquake depth: Shallow quakes concentrate energy near surface; Haiti’s 13 km deep quake was more destructive than deeper quakes of same magnitude (2 marks)
• Time of occurrence: Nighttime earthquakes trap sleeping people; Agadir’s night quake killed one-third of population because residents couldn’t escape bedrooms (2 marks)
• Secondary hazards: Tsunamis and fires often kill more than shaking; 2004 Indian Ocean tsunami killed people thousands of kilometers from earthquake (2 marks)

3. Describe the tertiary effects of earthquakes and explain why they can be as deadly as primary effects. (8 marks)

Examiner’s Tip: First describe what tertiary effects are, then give examples, then explain their deadliness.

Sample Answer Structure:

• Definition: Tertiary effects are long-term consequences occurring weeks to years after the earthquake (1 mark)
• Disease outbreaks: Broken water systems and sewage cause cholera and typhoid; Haiti’s 2010 cholera outbreak killed 10,000 people separately from earthquake deaths (2 marks)
• Economic collapse: Businesses close, jobs disappear, poverty increases; 2011 Japan earthquake cost $235 billion, causing long-term economic hardship (2 marks)
• Food shortages: Damaged farmland and broken distribution systems create starvation; Nepal’s 2015 quake prevented planting, causing months of hunger (1 mark)
• Explanation of deadliness: Tertiary effects kill slowly over time, accumulating deaths; poor medical care, malnutrition, and disease can eventually kill as many as the initial collapse (2 marks)

4. With reference to specific earthquakes, explain how the same magnitude earthquake can have different impacts in different countries. (12 marks)

Examiner’s Tip: Compare two earthquakes of similar magnitude but different impacts. Use specific examples and numbers.

Sample Answer Structure:

• Introduction: Compare 2010 Haiti earthquake (magnitude 7.0, 160,000 deaths) with similar magnitude Japanese earthquakes (often under 100 deaths) (2 marks)
• Building standards: Haiti had no enforced building codes, using weak concrete; Japan requires earthquake-resistant design with flexible foundations and reinforced structures (3 marks)
• Preparedness: Japan has tsunami warning systems, earthquake drills, and emergency supplies; Haiti lacked warning systems and disaster plans (2 marks)
• Economic factors: Japan’s wealth allows expensive safety measures; Haiti’s poverty meant even government buildings were unsafe (2 marks)
• Population density: Haiti’s crowded slums with poorly built homes increased casualties; Japan’s modern housing codes despite high density reduced deaths (2 marks)
• Conclusion: Preparedness, building quality, and economic resources matter more than earthquake magnitude in determining impact (1 mark)

Memory Aids

Primary vs Secondary vs Tertiary

Mnemonic: “I See Late” (Immediate, Secondary, Late-term)

• I (Immediate) = Primary: Ground shaking, Building collapse, Crustal fracturing
• S (Secondary) = Minutes to days: Tsunamis, Fires, Landslides, Liquefaction
• L (Late-term) = Tertiary: Disease, Economic loss, Trauma, Homelessness

Secondary Effects Acronym: “TFLLA”

Remember the five main secondary effects:

• T = Tsunamis
• F = Fires
• L = Landslides
• L = Liquefaction
• A = Aftershocks

Factors Affecting Impact: “BPTDD”

Five key factors that determine severity:

• B = Building quality
• P = Population density
• T = Time of day
• D = Depth of earthquake
• D = Distance from epicenter

Cascading Effects Chain

Remember how effects cascade (one causes another):

Earthquake → Broken pipes (primary) → No water for fire hydrants (secondary) → Fires spread (secondary) → Homelessness (tertiary) → Disease from poor sanitation (tertiary)

Related Topics

• Major Earthquakes of the World – Learn about specific historical earthquakes and their impacts
• Causes of Earthquakes – Understand why earthquakes happen and plate tectonics
• Earthquake Measurement – Study how scientists measure earthquake magnitude and intensity
• Tsunami Formation and Effects – Deep dive into how earthquake-generated waves affect coastlines
• Disaster Preparedness and Management – How countries reduce earthquake damage through planning