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Tectonics pt4 (earthquakes) - Coggle Diagram
Tectonics pt4 (earthquakes)
Antonomy of earthquakes
Focus
-- the place where the earthquake starts within the crust/mantle.
Epicentre
-- this is the area above the focus, on the surface where the earthquake is strongest.
Siesmic waves
-- this is the energy created by the earthquake.
Fault line
-- this is an extended break in the rock formation.
Earthquake
-- this is the suddern movement of the ground.
Fault scar
-- this is a cliff that has formed by the movement of the ground into new positions.
Hazard
-- this is when a tectonic event poses a threat to humans either socially (killing people), economically or enviromentally.
Causes of earthquakes
Mid ocean ridges where the plates are pulling apart.
Transform boudaries where plates are moving side by side.
Ocean trenches where the plates are subducting.
Collision zones where two plates meet.
Hotspots
Human actions
Fracking
Mining
Nuclear testing
Old plate boundaries.
Isostatic inbalnce caused by changes in land level (mainly due to melting ice).
Types of faults
Normal faults
-- this is where the hanging wall has moved down relative to the footwall. These occur when two blocks of rock are moving apart.
Reverse fault
-- this is where the hanging wall has been pushed up along the foot wall. These occur when two blocks of rock are moving together.
Strike slip faults
-- this is where the rock is moving parrel to each other. These occur on transform plate boundaries.
Types of siesmic waves
Surface waves (L)
Slow travelling.
Low frequency
Waves can move the ground side to side, perpindicualr to the direction the wave is traveling. They can also move the ground up and down in a motion similar to waves in a sea.
Waves can only move through the outer crust.
Primary waves (P)
Fast traveling.
Low frequency.
Cause the ground to compress and expand (move back and forth) in the direction of travel.
Can move through solids and liquids.
Secondary waves (S)
Half the speed of P waves.
High frequency.
Causes the ground to move up and down (at right angles to the direction of travel)
Can only move through solids (crust and mantle).
Focuses
Shallow focus
Located at a depth of no more than 70km.
These occur in the cold and brittle rock which fracture due to high stress in the crust.
These are more frequent, but low strength earthquakes.
They can still be high strength, but it is uncommon.
Deep focus
These are located at depths of 70-700km, this depth has meant they are poorly researched and not much is known about them.
Infrequent, but higher strength.
Occur in the subducation zone of plate boundaries (the bienoff zone) where rocks are no longer brittle.
Measuring earthquakes
Richter scale
Measures the magnitude and amplitude of an earthquake on a logorithmic scale.
Not very effective measuring earthquakes over a size of 6.5.
Very useful for measuring smaller earthquakes and measuring earthquakes over a long period of time.
Modified Mercalli scale
Measures the damage done by and earthquake on an arbitary scale of 1 to 12.
It is not very useful for measuring earthquakes where people don't live as all it measures is the impact an earthquake has on people.
It is very useful for comparing the impact of earthquakes on different countries.
Moment Magnitude scale
Measures the magnitude of an earthquake on a logorithmic scale.
It is unable to acuretaly measure the size of an earthquake that is smaller then 3.5.
Provides the most acurate measurement of large earthquakes as it uses the amount of physical movement cause by an earthquake.
Earthquake hazards
How are earthquakes generated
1st
-- The crust is cold and brittle compared with the hot rock neaby and the crust is full of small and large cracks called faults.
2nd
-- These faults are hundreds of miles long, but when can't see them as they are deep in the crust and compressed together.
3rd
-- The powerfull forces that causes these crustal peices to compress are also causing them to move very slowly.
4th
-- When two peices that are next to each other they can get stuck in the faults, until the forces moving them prove to powerful and the rocks are forced to move.
5th
-- This sudden movement of rock causes the rocks around to shake and causes the release of siesmic waves.
Impacts earthquakes have on the Earth
Creation of mountian chains and fault scarps
The Himilayers are fold mountians created by earthquakes.
The Tibitean Plateau shows evidence of major tectonic faults due to the number of fault scarps.
Fault scarps
Rift valleys and ocean ridges
Rift valleys
-- As the plates move apart from each other through a process of earthquakes they leave a valley behind. An example of one of these is the East African Rift Valley.
Ocean ridges
-- As plates move appart from each other they create an underwater valley flanked on either side by under water mountians. An example of this is the mid-Atlantic ridge.
Hazards of earthquakes
Disease
Earthquakes can destroy santitation facilities which can enable waterborne diseases to enter the water supply. It is very common for Cholera to break out in areas where there has been an earthquake.
Tsunamis
Underwater earthquakes cause the ground to rise and this leads to the mass displacement of water; this creates a large and powerful wave.
Ground shaking/displacement
Factors infleucing the impact of ground shaking
Types of waves.
Length of time the ground shakes.
Depth of focus.
Rock type (how easily energy can move through the rock).
Earthquake magnitude.
Distence from epicentre.
Ground shaking can lead to:
Building collapse (more likely when ground is moving horzontally).
Pipeline/sewer disruption.
Destruction of infaustruture.
Damage to water supply.
This can lead to the spread of disease.
Building collapse
Landslides and avalanches
These can be caused by ground shaking and/or liquefaction making the ground unstable.
They are made worse by soft geology, deforestation (weakening the soil) and heavy rain.
Impacts
Can create natural dams which block water flow and can lead to later on down stream.
Can block roads to make search and rescue difficult.
Can destroy dams, leading to flooding.
Flooding
Fires
Liquefaction
Liquefaction
-- this is where the ground looses its physical strength and cohesion and begins to act more like a liquid.
Occurs in:
Areas with high soil saturation.
Areas with fine grained sand.
Changes in hazard risk over time
Types of hazards
Climatealogical
-- these are hazards caused by the climate.
Meteological
-- these are hazards caused by the weather.
Hydrological
(these have seen the greatest in increase since 1900) -- these are hazards caused by water (e.g flooding).
Geophysical
(the most stable in frequency of occurence) -- these are hazards created by tectonics (e.g earthquakes).
Biological
-- these are diseases.
Park disaster responce curve
This is a model that shows the stages of impact and recovery from a tectonic event. Although each curve is different there can be broad similarities.
The shape of the curve is dependent on:
Wealth of a country.
Strength of the event.
Number of people impacted/denisty of the area impacted.
Stages
Stage 1
-- life is normal, nothing has happed, quality of life is normal.
Stage 2
-- disaster hits, quality of life drops.
Stage 3
-- short term responce occurs, social impacts are reduced, quality if life stops decling.
Stage 4
-- long term responce/recovery, quality of life begins to improve.
Stage 5
-- Long term recovery complete, quality of life has improved and in some ACs is higher then it was before the disaster.