The Impact of Earthquakes (Leaving Cert Geography): Revision Notes

The Impact of Earthquakes

Earthquakes can strike suddenly and violently without warning, causing devastating effects on human communities and the environment. Understanding what makes earthquakes destructive and how we can reduce their impact is crucial for protecting lives and property.

Factors that determine earthquake destructiveness

Several key factors influence how much damage an earthquake will cause when it strikes:

Physical factors

Intensity refers to the amount of energy an earthquake releases. Higher intensity earthquakes tend to be more destructive, with the most devastating earthquakes typically occurring at subduction zones where tectonic plates collide.

• Depth plays a crucial role in determining damage levels.
  • Shallow focus earthquakes prove more destructive than deep focus earthquakes when all other factors remain equal, as the seismic energy has less distance to travel before reaching the surface.
• Location significantly affects the scale of destruction.
  • Urban areas face greater risks due to their dense populations and tall buildings, putting more people in harm's way compared to rural regions.
• Time of day influences casualty numbers.
  • Earthquakes striking at night often trap more people in their homes, leading to higher death tolls as people cannot evacuate quickly.
• Local geology determines how seismic waves travel through the ground.
  • Areas with unconsolidated surface materials (loose, sandy, or soggy soils) experience greater damage because these materials can liquefy during the earthquake.

Secondary effects

Earthquakes can trigger additional hazards that often cause more damage than the original tremor:

• Landslides and avalanches: The 2015 Nepal earthquake (magnitude 7.8) triggered major landslides that blocked rivers and caused flooding. An avalanche on Mount Everest killed 19 people.
• Tsunamis: The 2004 Indian Ocean earthquake (magnitude 9.3) off Sumatra didn't directly cause widespread damage, but the resulting tsunami devastated coastal communities across multiple countries.

Human factors

Architecture and building standards greatly influence survival rates. Developed countries like the USA typically have higher quality construction materials and stricter building regulations compared to developing countries like Nepal. This means buildings are less likely to collapse during earthquakes in wealthier nations.

Technological advancement affects response capabilities. Developed countries maintain sophisticated emergency services, rescue equipment, and communication systems. They also stockpile emergency supplies and run public education programmes teaching earthquake response procedures.

Effects of earthquakes

Damage to infrastructure

Earthquake vibrations cause buildings, bridges, and other structures to sway and crumble. Falling debris becomes extremely dangerous and accounts for many earthquake deaths. Rescue workers must carefully search through rubble to find survivors trapped underneath collapsed structures.

The 2010 Christchurch, New Zealand earthquake severely damaged the city centre, toppling two bell towers on the Catholic Cathedral and destroying many historic buildings.

Tsunami

When underwater earthquakes occur, they can displace massive amounts of water, creating devastating tsunami waves. As tectonic plates move suddenly, they can force the overlying plate upwards, creating an excess hump of water on the ocean surface. This water then radiates outwards in all directions at speeds reaching 800 km/h.

Most tsunamis result from uplifts of less than one metre, but powerful earthquakes can create much larger waves. For boats in deep ocean waters, tsunamis remain barely noticeable. However, as waves approach coastlines, the shallow seabed causes them to slow down and increase in height, often quadrupling in size before hitting the shore.

Liquefaction

During intense ground shaking, soil can become saturated with groundwater and lose its ability to support structures, behaving like quicksand. This process causes buildings to collapse as their foundations sink into the liquified ground.

Liquefaction caused extensive damage in Christchurch, New Zealand (2010) and contributed significantly to the destruction in Kobe, Japan (1995). In Kobe, entire apartment blocks collapsed as their foundations sank, while broken gas and sewage pipes led to fires across the city, contributing to 5,000 deaths.

Reducing earthquake effects

While earthquakes cannot be prevented, proper planning and preparation can dramatically reduce casualties and damage.

Early warning systems

Modern seismograph networks can detect earthquake primary waves and alert communities before the more destructive secondary and surface waves arrive. The warning time depends on distance from the epicentre - sometimes only seconds, but occasionally up to a minute of advance notice.

Even brief warnings allow people to take protective action, trains to slow down, and factory assembly lines to stop safely.

Earthquake-proof infrastructure

In earthquake-prone regions like California and Japan, strict building regulations have significantly reduced structural damage. Key earthquake-resistant features include:

• Flexible design: Buildings are constructed to be slightly elastic rather than rigid, allowing them to sway with seismic waves without breaking apart
• Strong foundations: Structures are built on solid rock rather than soil to avoid liquefaction damage
• Mechanical dampers: These act as shock absorbers, reducing vibration energy
• Steel reinforcement: Building frames are reinforced with steel to prevent collapse
• Cross-bracing: This minimises the effect of shearing forces during earthquakes

Bridges receive similar treatment, being designed to sway gently without breaking during seismic events.

Efficient urban planning

Smart city planning can prevent the "domino effect" where one collapsed building causes others to fall. Buildings are spaced appropriately to avoid this chain reaction.

Essential services like hospitals, schools, and fire stations are located in areas least likely to experience severe tremors, ensuring emergency services remain operational and children stay safe.

Emergency preparedness

Effective earthquake preparedness includes:

• Installing earthquake drills to familiarise people with emergency procedures
• Placing utility pipelines (water, gas, electricity) deep underground with automatic shut-off valves
• Constructing power stations away from fault lines
• Retrofitting older buildings with steel-reinforced concrete frames
• Maintaining emergency supplies and communication systems

Case studies

Haiti earthquake (2010)

Background: Haiti, located on the Caribbean island of Hispaniola, ranked as one of the world's poorest countries in 2010. Over 70% of its 10 million people lived below the poverty line, and it ranked 149th out of 182 countries on the UN Human Development Index. The country sits on a transform plate boundary where Caribbean and North American plates slide past each other, but had very few building regulations to protect against earthquakes.

Short-term effects:

• Over 3.5 million people affected, with 230,000 deaths and 300,000 injuries
• Approximately 1.5 million people (20% of the population) became homeless, living in temporary camps
• 250,000 homes destroyed or severely damaged
• Water shortages due to contaminated river supplies
• Rescue efforts hampered by damaged airports, seaports, and communication networks
• Hospital overcrowding as medical facilities were damaged
• Prison inmates escaped, leading to increased crime and violence

Long-term effects:

• Contaminated drinking water caused a cholera outbreak killing nearly 6,000 people
• Many injured children and disabled people were left without adequate care
• Unemployment rose to 20% as 30,000 commercial buildings were damaged, devastating industries like textiles
• 60% of government buildings were damaged, severely affecting public administration
• Tourism industry collapsed due to damaged hotels and transport infrastructure
• Important landmarks including the Presidential Palace and Port-au-Prince Cathedral were destroyed or severely damaged

Japanese earthquake and tsunami (2011)

Background: Japan consists of a chain of volcanic islands in the Pacific Ocean and ranked as the world's 12th most developed country in 2011 according to the UN Human Development Index. Due to its location on the Pacific Ring of Fire, Japan has extensive experience with earthquakes and tsunamis, with its most devastating previous earthquake occurring in 1923, killing 140,000 people.

Short-term effects:

• Approximately 16,000 deaths, with over 90% from drowning
• 25,000 people injured, many caught by surprise despite believing they were on safe high ground
• Contaminated water supplies affected 1.5 million people
• Nearly 4.4 million households lost electrical power

Long-term effects:

• 2,500 people remain missing
• Over 125,000 buildings completely collapsed, leaving 250,000 people homeless
• Transport and communication networks were destroyed but rebuilt rapidly
• The tsunami triggered explosions at three reactors in the Fukushima Daiichi Nuclear Power Plant Complex when cooling systems failed due to power loss
• Residents within 20 km of the nuclear plant were evacuated due to massive radiation release
• Many areas remain uninhabitable, and agricultural products from the region face ongoing consumer rejection
• The World Bank estimated economic costs at US$235 billion, making it the costliest natural disaster in history