Earthquakes Flashcards
What is an earthquake
Vibrations or shaking in the earths crust caused by movements at plate boundaries or at fault lines (cracks in the earths surface)
Most common boundaries earthquakes occur
Transform
Convergent
What is energy released by an earthquake in the form of
Seismic waves that give a series of shocks called tremors
Small earthquakes before big earthquake
Foreshock
Small earthquakes after big earthquake
After shocks
Define focus/ hypocentre
Origin of the earthquake deep within the crust, point where seismic waves radiate outwards from
Define epicentre
Point on the earths surface directly above the focus where the most damage occurs
Define fault
A break in the rocks that make the earths crust along which rocks on either side move
Define Fault scarp
A feature on the surface of the earths that looks like a step caused by a slip in the fault
Causes of earthquakes
Slipping plates
Sinking plates
Ice age
Ancient faults
Types of earthquakes
Shallow focus
Intermediate focus
Deep focus
Where do shallow focus earthquakes occur
All types of plate boundaries
Less than 80km below the surface
Most destructive as closer to surface
Where do intermediate focus earthquakes occur?
At oceanic and continental subduction zones
Up to 300km below surface
Where do deep focus earthquakes occur
At oceanic and oceanic subduction zones
More than 300km below the surface
Don’t do too much damage to surface as they occur so deep
What’s a Wadati-Benioff zone?
Dipping, roughly flat zones of increased earthquake activity as an oceanic plate sinks beneath another plate. (Subduction zones)
Deep focus earthquakes occur here
Way of predicting earthquakes
Measuring rock stress Measuring randon gas emissions Observing unusual animal behaviour Identifying seismic gaps Early warning systems
How can rock stress be measured
Strainmeters (measure build up of stress along fault lines)
Tiltmeters (changes in slope and bulging)
Seismographs (minor movements in earths crust (foreshocks and aftershocks)
Examples of unusual animal behaviour before earthquakes
Snakes come out of hibernation
Animals refuse to enter buildings
Restless pets
What are seismic gaps
An area on a fault where little to no seismic activity has occurred for a long period eg Guerro Gap Mexico
% of earthquakes at Pacific ring of fire
80%
Speak about Earthquakes at convergent plate boundaries
Most common
Most intense
Japan 2011- tsunami under ocean (where Pacific and Eurasian collide)
China and India (indo Australian and Eurasian plate collide) recieve Kanu earthquakes
Discuss earthquakes at transform plate boundaries
SAN Andreas fault 1300km long
Pacific and North American plate
1906 8.3 earthquake san franc
Two scales used to measure earthquakes
Mercalli scale
Richter scale
What does the Richter scale measure
Intensity of an earthquake by energy released from the earthquake
How is the Richter scale measurements taken
Seismometers
One to record primary waves (horizontal shaking)
Another to record secondary waves (vertical shaking)
How can the epicentre of an earthquake be found by a seismologist
At least three readings are needed from different seismic locations
By measuring the time between each recording at the seismic station, seismologists can estimate how far the waves have travelled.
They then draw circles representing distance from the station the wave travelled and where their circles intersect is the epicentre
Explain the increasing measurements on the Richter scale
Each unit is 10 times more energy than the previous
What is the mercalli scale measured with
No instruments
Based on human observation and experience of the effects to people, the natural world and man made structures
Measurements on the mercalli scale
Ranges from 1-12
1 being a weak earthquake not felt by humans
5 being a moderate earthquake, a noticeable shake in the ground and
12 being almost complete destruction
Factors effecting earthquake damage
Economic development of country - less developed have poor buildings and infrastructure more likely to collapse
Population density - urban v rural
Time of day - people aren’t on roads at night
Rock type - igneous withstand tremors better than sedimentary
Depth of focus - shallow v deep focus
Energy and duration
Ways of reducing the effects of earthquakes
Earthquake drills
Efficient urban planning
Early warning system
Earthquake proof infrastructure
What is cross bracing
When frames of buildings are reinforced with steel which joins the building together allowing it to moves as a single unit and not splitting apart
Ways of earthquake proofing infrastructure
Cross bracing
Deep foundations into solid rock
Weights on roof counterbalance shakings
Several emergency staircases and exits
Shock absorbers in foundations
Roof covering area immediately outside building to prevent pedestrian being showered with broken glass
Base isolation - bottom section absorbs seismic waves
Foundations with flexible springs as shock absorber
When was observing animal behaviour used for earthquake prediction
Tianj, China
When was japan earthquake/tsunami we study
Richter scale
How many dead
Mention an effect
2011
9
25,000
Fukushima power plant, loss of jobs and slowdown in production , towns shifted
When was Nepal earthquake we study
Richter scale (magnitude)
How many made homeless
Mention an effect
2015 7.8 3 million homeless Avalanche - transport systems damaged (providing aid was therefore difficult) Disease in camps
When was Haiti earthquake we study
Richter scale
How many dead
Mention an effect
2010
7
300,000 dead under rubble
€6 billion in aid
Japan disaster prevention day
Sept 1
Earthquake at transform plate example
1906
SAN Francisco
Big earthquake for San Andreas fault predicted when
2032
Example of an earthquake at divergent
Mozambique 2006
Example of poor urban planning
2008
Sichuan, China
9000 schoolchildren died whilst buildings around remained intact
Example of a building which is earthquake proof
Burj khalifa (worlds tallest building)
Example of economic slowdown post earthquake
2004
Christmas tsunami Thailand
Fear to travel
