Earthquakes

Key Words:

Term	Definition
Earthquake	Shaking or vibration of the Earth's crust
Seismologist	People who study earthquakes
Seismograph	Machines that measure the magnitude/strength of an earthquake
Focus	Place within the crust where an earthquake occurs
Epicentre	Area on the surface directly above the focus where tremors and shock waves reach the surface first

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Geography

Earthquakes

Term	Definition
LDC	Shaking or vibration of the Earth's crust
Terrain	People who study earthquakes
Geology	Machines that measure the magnitude/strength of an earthquake
Emergency Aid	Place within the crust where an earthquake occurs
Development Aid	Area on the surface directly above the focus where tremors and shock waves reach the surface first
Tsunami	Series of large waves caused by the displacement of large volumes of water

What's covered:

• What earthquakes are
• How they occur
• Where they occur
• How they are measured and predicted
• The impact of earthquakes, with named examples

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Earthquakes

Common topics in the exam:

• Links to plate boundaries – eg. distribution of earthquakes.
• Diagram of an Earthquake
• Earthquake-proof buildings
• Case Study: Nepal

Earthquakes:

Figure 1: Be able to label this

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Earthquakes

Geography

• Created by the sudden release of energy along a fault line due to the movement of tectonic plates.

• Seismic waves/tremors that radiate out are called shock waves.

• Shock waves spread out from the focus deep within the Earth's crust.

• Directly above this is the epicentre where most of the destruction will take place.

• Waves that occur after the main earthquake are called aftershocks.

Location:

• Occur at convergent, divergent and transform plate boundaries.

• The most dangerous earthquakes are associated with subduction zones.

• The subduction zone off the coast of Japan is the most deadly in the world as the Pacific plate is brought under the Eurasian plate.

• This area is part of the Pacific Ring of Fire – where the world's most active volcanoes and earthquakes are.

• Earthquakes can also occur at transform plate boundaries eg the San Andreas fault.

• They also occur at divergent plate boundaries eg. Mid Atlantic Ridge but they are not frequent or dangerous.

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Earthquakes

Figure 2: Pacific Ring of Fire

Categories of Earthquakes:

1 Shallow focus:

• Focus is found close to the surface – less than 80km from it.

• They are the most common and dangerous type of earthquake causing great destruction and loss of life.

• Occur at plate boundaries as a result of plates sinking and becoming stuck and then released which releases large amounts of energy.

2 Deep Focus:

• These are found at a much deeper level – greater than 300km.

• Located at subduction zones as one plate moves beneath the other.

• Occur so deep under the surface that they rarely cause damage as the shock waves have farther to travel and lose their energy.

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Earthquakes

Measuring Earthquakes

1️⃣ Seismograph:

• A machine that is sensitive to movement and detects, measures and records seismic waves.

• Primary waves/P-waves are the fastest waves that travel through molten material.

• Secondary waves/S-waves are slower as they travel through rock.

• Surface waves are the slowest and travel along the surface.

2️⃣ Richter Scale:

• Used to measure ground movement caused by an earthquake and its magnitude/strength.

• For every point on the scale the damage is increased 10 times.

• Example: a level 4 earthquake is 10 times stronger than a level 3 but 100 times stronger than a level 2.

• The most powerful earthquake ever recorded was 9.5 in Chile in 1960.

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Earthquakes

Mercalli Scale:

• Measures the damage caused by earthquakes.
• Scale ranges from I to XII (1-12 in Roman Numerals)
• Example: III/3 would be objects hanging from the ceiling swaying back and forth.
• It only uses observations so is not as accurate or reliable as the other two.

Figure 3: Richter Scale

Predicting Earthquakes

Important to do so, in order to prevent loss of life. However, it is not an exact science, instead predictions are made by seismologists who make reasonably accurate predictions based on a number of factors:

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Geography

Earthquakes

• Seismic activity is studied to see if any long-term patterns emerge in plate movement such as the length of time between earthquakes and the severity of these. These earthquakes are plotted along the fault line with areas not previously hit by earthquakes marked as vulnerable

• Tiltmeters measure bulging of the surface of the land

• Radon gas levels are constantly monitored

• Lasers measure rock/ground movement

• Level of water in wells will rise when stress is placed on the Earth's crust so this is also monitored

• Animal behaviour can also be an indication – before the 2004 South-East Asia tsunami, elephants fled to high ground before the earthquake struck

Figure 4: Plotting previous seismic activity

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Geography

Earthquakes

• Time of day: night time = people asleep, no time to evacuate, everyone inside buildings

• Magnitude: stronger = more damage

• Depth of focus: shallow or deep?

• Distance from epicentre: Where are the shockwaves the strongest? How long do they last for?

• Population density: lots of people = higher chance of loss of life

• Preventative measures: Are there earthquake-proof buildings or other measures to reduce the effect of earthquakes? 1st world vs 3rd world?

  • Economic wealth – LDCs (Less Developed Countries) will not be prepared as they have less money for things such as earthquake-proof buildings

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Earthquakes

Effects of Earthquakes

Short Term:

• Loss of life
• Destruction of buildings
• Landslides/Avalanches
  • Can happen for days after, e.g. Nepal, 2015
• Tsunamis
  • Can occur if the earthquake happens under an ocean
  • E.g. South-East Asia 2004 – killing almost 250,000 people
• Disruption and damage to services
  • Water supply/sewage/gas
• Liquefaction
  • Sand/Gravel mixes with water, turned into liquid mud which cannot support structures – leads to buildings collapsing

Long Term:

• Outward Migration
  • People leave the area, in turn leading to homelessness
  • 24,000 people left Nepal in 2015 and lived in makeshift camps as their homes were destroyed

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Earthquakes

Geography

• Disease

  • Exposed corpses, damaged sewage pipes all lead to the quick spread of disease as these can also affect the water supply

• Economic Slowdown

  • Shops/industry damaged, people lose their jobs, economy diverted as money is spent on rescue operations and repairing damage, tourism will decline due to safety fears

Limiting Earthquake Damage:

Strict planning laws are the best way to limit damage as earthquakes don't kill people – the side effects do e.g. falling buildings. Japan has strict planning laws – can't build in areas susceptible to liquefaction or on fault zones – and high standard of earthquake proof buildings with the following:

• Flexible columns to allow for swaying
• Rollers for side to side movement
• Fire-proofing of old buildings – when gas pipes break, this can cause fires
• Deeper foundations for stability and cross beams to make them stronger

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Earthquakes

However, LDC's do not have the same budget as Japan to enforce these changes and update buildings. They have more basic measures in place such as:

• Hollow, light blocks
• Low-rise structures
• Reinforced concrete pillars in the corner of buildings (equivalent to deeper foundations/cross beams)
• Items secured to walls – e.g. presses with cups/plates in them will have bars across the front to stop them falling out during an Earthquake

Case Study: Nepal Earthquake, 25th April 2015

Where/Why?

• 7.8 magnitude earthquake hit 77km north of Nepal's capital city, Kathmandu
• This region lies along an active fault line over 1,000km long and this earthquake was a dangerous shallow earthquake as the focus was only approx. 15km below the surface of the Earth
• It directly/indirectly affected 8 million people

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Earthquakes

Geography

• Indian plate and overriding Eurasian plate collided – they are converging at a rate of 5cm per year and this collision is why the Himalayan mountain range is getting higher (Mt. Everest is still growing)

• Original earthquake was followed by strong aftershocks and another earthquake triggered by the stress of this seismic activity

• The last major earthquake to hit the region was in 1934 when 17,000 people were killed. The pattern of earthquakes in this region have been recorded since the 13th century with seismic gaps of 75 -80 years

• The biggest aftershock came on the 12th of May – 17 days after the original earthquake hit and it registered 7.3 on the Richter Scale. The epicentre was 76km away from the Mt. Everest base camp. It affected Northern India, Tibet and Bangladesh, killing 48 people and injuring up to 1,000 people. 6 more aftershocks were also felt in the region with none of these recording a strength of more than 5 on the Richter Scale

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Earthquakes

Effects

• 8,000 killed, 10,000 injured

• Rescue teams used sniffer dogs and heat-seeking equipment to search for survivors for the days after but this was not possible in remote areas, so local people had to search through the rubble

• Many villages were destroyed or buried by avalanches and landslides (earthquakes and aftershocks caused 3,000 of these) such as those in Langtang Valley 435 people lived here but now only one house still exists as the rest slid 700 metres downhill

• 130,000 buildings destroyed, including 60m high Dharahara Tower built in 1832 for queen of Nepal

• 24,000 were homeless having fled the region

• Immediate cremation of deceased was ordered to prevent the spread of disease

• Tourism was majorly affected and is a big long-term effect, causing economic downturn

  • Over 100,000 visitors trekked Mount Everest and the surrounding region in 2013, providing a major source of income for locals
  • Due to safety fears these numbers have massively declined

• Difficult terrain meant that delivering aid (food, shelter, clean water) was slow

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Earthquakes

• Nepal govt. estimated that they needed €1.7 billion in aid to rebuild and repair infrastructure such as roads and hospitals
  • Govt. has been criticised for being corrupt in the past so this aid is slow in coming with UN giving €3 million in aid and Ireland delivering 63 tonnes of life-saving supplies
  • But future growth and redevelopment will be very difficult and slow

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Earthquakes

Tsunamis

Warning Systems

• Tsunami is a large wave created by an earthquake under the ocean

• Can have devastating effects in minutes so an early warning system is essential

• 28 countries in the Pacific have these systems including Japan

  • Tsunami sensors collect data on the ocean floor as do tide gauges
  • This information is then transmitted via a satellite to tsunami warning centres to be interpreted
  • Regular updates are then provided on local television and radio stations
  • Local authorities are responsible for evacuation plans

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Earthquakes

Case Study: Japanese Earthquake, 11 March 2011

Where/Why?

• 8.9 magnitude Earthquake lasting 2 and a half minutes, 130km off the coast of Japan also causing a Tsunami

• Japan is located on a convergent plate boundary at a subduction zone, marked by the deep-sea Japan trench – part of the Pacific Ring of Fire

  • Here, the Pacific Plate is sinking underneath the Eurasian Plate

• Tension built up between the two plates and eventually the edge of the Eurasian Plate jumped backwards 5-8 metres over a 180km stretch of land

• A shallow focus earthquake occurred as a result which displaced a large volume of water, creating a tsunami

• The waves remained quite small in the ocean but built up to approx. 10 metres high once they hit shallow water

• The huge wave flew inland for several kilometres leaving a path of destruction in its wake

• Tsunami warnings were only received 10 minutes before the wave hit so locals did not have time to react

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Geography

Earthquakes

Effects

• Coast was transformed into a muddy swamp of material thrown up by the tsunami

• Towns and villages were completely destroyed including a town of 10,000 people

• 27,000 people were killed with 90% of them drowning as a result of the tsunami

• Fukushima nuclear power plant was damaged sparking fears of a radioactive leak - a state of emergency was declared as a result with a 20km radius cleared around the plant as radioactive material leaked out

• 500,000 left homeless but the earthquake itself did little structural damage due to Japans strict building regulation

Figure 7: Location of Earthquake