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Physical Geography: Earthquakes - Coggle Diagram
Physical Geography: Earthquakes
Earthquakes
Occur due to the movement of tectonic plates
Shaking or vibration of the Earth’s crust
Sudden release of energy along a fault line
Seismic waves/tremors are known as shocks
Location
Subduction zones, e.g. Pacific Ring of Fire
Transform plate boundaries, e.g. San Andreas Fault
Divergent plate boundaries, e.g. Mid-Atlantic Ridge
Terms
Focus
Epicentre
Fault line
Shock waves
Aftershocks
Categories
Shallow focus
Deep focus
Seismic waves
There are three types of waves that shake the Earth’s crust:
Primary or P-waves
Fastest waves and the first to be recorded
Travel through molten material
Secondary or S-waves
Slower-moving waves that travel through rock
The second to arrive
Surface waves
Slowest of all three waves and the last to arrive
Travel along the surface
Cause things to move up, down and side to side
The Richter scale
Used to measure the magnitude of an earthquake
Open-ended scale
Each point on the Richter scale is a 10-fold increase in power
The Mercalli scale
Measures earthquake damage
Developed by Giuseppe Mercalli in 1902
Scale of 12 points, I–XII
1 means no damage
12 means complete devastation
Earthquake prediction
Seismologists study the history of earthquake activity
Plot patterns of earthquake activity along a fault line
Greater the time since the last earthquake striking, the more imminent is the next
Seismic gaps
The time gap between earthquakes
Period of inactivity
Tiltmeters record changes that occur to levels of land
Tell-tale signs, e.g. animal behaviour
Lasers monitoring ground movement
Level of water can rise just prior to an earthquake
Radon gas levels measured
Factors that determine the damage caused by an earthquake
Depends on a number of factors:
Time of day
Magnitude of the earthquake
Depth of the focus
Distance from the epicentre
Duration of shaking
The effects of earthquakes
Short-term effects
Loss of life
Destruction of buildings and communication links
Landslides and avalanches
Tsunamis
Long-term effects
Outward migration
Disease
Economic slowdown
Ways to limit earthquake damage
Linked to level of development
Developed economies more earthquake-proof
Less developed or developing economies are most affected
Earthquake-proof buildings: flexible columns, rollers, fire-proofing, deeper foundations, cross beams
LDCs’ basic building regulations: lighter blocks, low-rise structures, reinforced concrete, all items secured to the walls
Nepal earthquake, 2015
7.8 magnitude earthquake
11.56 on 25 April 2015
77 km north of Kathmandu, dangerous shallow focus earthquake, depth of 15 km
Converging Indian and Eurasian plates. Fault line ruptured for 150 km eastwards
Biggest aftershock 12 May, 7.3
6 more aftershocks
Killed approximately 8,000, injured over 10,000
Multiple rescue teams
Ruined many villages, e.g. Langtang Valley
130,000 homes destroyed
24,000 people left living in makeshift camps
Immediate cremations
Tourism affected as earthquake triggered avalanches on Mount Everest
3,000 landslides
Difficult terrain
£273 million spent on emergency aid
63 tonnes of life-saving humanitarian supplies
€1.78 billion needed in developmental aid
Government corrupt
Tsunami warning systems
Tsunami: a large wave created by an earthquake under the ocean
Early warning system needed to prevent loss of life
Tsunami sensors
Tide gauges
Satellites
Tsunami warning centres
Information bulletins
Evacuation plan
Japanese earthquake, 2011
8.9 magnitude earthquake which also caused a tsunami
Located at a subduction zone on a convergent plate boundary between Pacific and Eurasian plates
130 km off the east coast of Japan
11 March 2011
Tension as plates stuck together
Eurasian plate moved upwards 5–8 m
Shallow focus earthquake
Created a tsunami with waves of up to 10 m in height
Waves caused destruction several kilometres inland
Tsunami warnings issued only 10 minutes before waves struck
Coast was transformed into a muddy swamp
Town of 10,000 people destroyed
More than 27,000 people killed
A state of emergency was declared
Half a million people were left homeless
Little structural damage due to Japan's strict building regulations