EARTHQUAKES Flashcards
Explain briefly a fault line
The fault line is the fracture in rock caused when plates move. Almost all earthquakes originate along a fault line.
Explain briefly a focus
The focus is the point on the fault line where the earthquake begins. The depth of the focus has a direct impact on the amount of damage it causes.
Shallow focus -
They occur close to the Earths surface. They are very dangerous earthquakes as the energy released only has to travel a short distance to the surface.
Intermediate focus -
Occur 71 - 300km below the surface and are usually located within the Earth’s solid upper mantle.
Deep focus
Occur 300 - 700km below the surface. Deep-focus earthquakes typically occur along subduction zones.
What are seismic waves?
They are vibrations caused by the earthquake sent out from the focus. Also known as tremors and shockwaves.
Explain briefly an epicentre
The epicentre is the point on the surface directly above the focus and where seismic waves are the strongest. The further from the epicentre that seismic waves travel, the less energy they will have.
Earthquakes occur at what plate boundaries.
Convergent boundaries
Divergent boundaries
Transform boundaries.
What plate boundary do the most powerful earthquakes occur along?
Convergent boundaries.
Most powerful earthquakes occur along _____ ______
Subduction zones.
Oceanic oceanic plate collision:
The oceanic plate sinks under the overlying plate. The two plates lock together building pressure and stress. After several years the rock breaks and the oceanic plate subducts further in a sudden movement. This triggers a violent earthquake. These are referred to as megathrust earthquakes.
Continental - Oceanic Plate Collision:
Japanese Earthquake 2011:
- sudden movement of the Pacific plate underneath the Eurasian plate.
- Sudden movement pushed the Eurasian plate upwards.
- This created a tsunami that destroyed Japan’s coastline.
Continental - Continental Plate Collision.
- Pressure from the converging plates creates friction as layers of rock in the crust buckle upwards.
- This causes the plates to lock together
- Pressure builds and the rock breaks allowing the plates to move suddenly.
- Have shallow focus making them highly destructive.
- 2015 Nepal earthquake :
- Collison of Indo-Australian and Eurasian plates (7.8 magnitude)
Divergent boundaries
Magma rises as the crust rips apart causing vibrations.
Tears along rift valleys rocks are broken leading to strong earthquakes as a result of elastic rebound.
Transform boundaries
Friction causes them to lock together.
Pressure and stress build up between the rocks.
They eventually break.
The plate jolts forward and triggers an earthquake.
San Andreas Fault. The Big One 2032.
Who measures earthquakes?
Seismologist
What instrument do seismologists use?
Seismograph
What are the three types of seismic waves?
P - Waves
S - Waves
Surface Waves
What are P - Waves
Primary waves.
First waves to arrive during an earthquake
Fastest
They don’t have a lot of energy
Don’t cause a lot of damage
What are S - Waves?
Secondary waves
Cause crust to move up and down
More energy than p - waves
Ground shakes more noticeably
What are surface waves?
Last waves to arrive
Travel slowly along the surface
Responsible for almost all of the damage
Move crust up and down and side to side
Sway violently and collapse (infrastructure)
What are the three types of scales used to measure earthquake activity?
Richter Scale
Mercalli Scale
Moment magnitude scale
Richter Scale:
It is a logarithmic scale - each step on the scale represents a tenfold increases in the magnitude of the earthquake.
Moment magnitude scale:
Combines seismograph readings with the amount of rock movement at the fault.
Logarithmic scale
Mercalli Scale:
Based on observations of those who experienced the earthquake and the impact it had on the environment around it. There are 12 grades and scale uses roman numerals.
List three negative effects of an Earthquake and briefly explain two of them.
Damage to Infrastructure:
- Seismic waves are sent out from the focus causing buildings and bridges to sway and collapse.
- Falling debris can lead to a loss of life as it can crush or suffocate people.
Tsunami:
- When earthquakes occur beneath the sea causing huge waves (tsunamis)
- When a plate subducts the pressure can cause the overlying plate to jolt upwards which creates an excess hump of water.
Liquefaction
Briefly explain two factors that affect the damage caused by earthquakes.
Depth:
- A shallow-focus earthquake with the same magnitude as a deep-focus earthquake is likely to cause more damage.
Developing vs Developed countries:
- There are more deaths due to earthquakes in developing countries as they have lower-quality buildings. This means they are more likely to collapse while developed countries have earthquake-resistant buildings that withstand seismic waves better.
Briefly explain two ways of reducing the effects of an Earthquake.
Earthquake - Resistant Buildings:
- Earthquake-prone zones (Japan and California) have buildings that can withstand seismic waves better.
- For example, foundations of buildings are built on stone rather than on soil preventing the building from being damaged by liquefaction.
Early Warning Systems:
- They alert people of seismic activity before it arrives.
- The systems receive messages from seismographs that detect P - Waves.
