Tectonic Processes & Hazards - EQ1 - 1.3A - Earthquakes Flashcards
What is the Benioff zone
- At a convergent plate boundary
- the subduction process involves the descent into the mantle of a slab of cold hydrated oceanic lithorsphere, about 100 km thick,
- that carries a relatively thin cap of oceanic sediments
- The Benioff zone is an area of seismicity corresponding with the slab being thust downwards in the subduction zone
- The different ……..&………. of rock at this point produce numerous earthquakes.
- It is the site of …………../…….. earthquakes.
- This theory is an important factor in determining …………. ……….., since it determines the ………..&………….
- The different speeds and movements of rock at this point produce numerous earthquakes.
- It is the site of intermediate/ deep-focused earthquakes.
- This theory is an important factor in determining earthquake magnitude, since it determines the position and depth of the focus
This theory is an important factor in determining….
earthquake magnitude, since it determines the position and depth of the focus
Define epicentre
point on the earth’s surface vertically above the focus
Define fault
- a fracture or zone of fractures between 2 blocks of rock
Define focus
- place inside the earth’s crust where the earthquake originates and a pulse of energy radiates out in all directions
What is a fault scarp
- A steep slope or cliff formed by movement along a fault line, which results in the displacement of Earth’s surface
Sequence of an Earthquake
How does an earthquake start? (1)
- There is gradual build-up of tectonic strain which stores elastic energy in crustal rocks
Sequence of an Earthquake
(2) When the ……………………. exceeds the …………….., the rock ………..
When the build up of pressure exceeds the strength of the fault, the rock fractures
Sequence of the Earthquake
(3) What happens when the rock fractures
- This produces a sudden release of energy, creating Seismic waves that radiate away from the point of fracture (focus).
Sequence of the Earthquake
(4) This produces a sudden release of energy, creating Seismic waves that radiate away from the point of fracture (focus)……….
- The brittle crust then rebands either side of the fracture, which is the ground shaking, that is, the earthquake felt on the surface
An earthquake’s energy is released as ………… These waves radiate out from the ……….
- An earthquake’s energy is released as seismic waves. These waves radiate out from the focus
Primary & Secondary waves are called ……waves, because…
Primary & Secondary waves are called body waves, because they travel through the Earth’s body
Love waves & Rayleigh waves are …….. waves, because….
Love waves & Rayleigh waves are surface waves, because they travel along the Earth’s surface.
The overall severity of an earthquake is linked to the ………….&………. of these wave types
- amplitude and frequency
Primary Waves (P) - body or surface?
body
Primary Waves (P) - speed?
- Fastest (rate of about 8 km/sec)
- Reach the surface first
Primary Waves (P) - travel through?
- Travel through liquids and solids
Primary Waves (P) - motion?
- Cause backwards and forwards shaking - pushes & pulls ( these are vibrations caused by compression) in the direction of travel
Primary Waves (P) - damage?
least damaging
Secondary Waves (S) - body or surface?
body
Secondary Waves (S) - speed?
- Slower than P waves (about 4 km / sec)
Secondary Waves (S) - travel through?
- Only travel through solids
Secondary Waves (S) - motion?
- up and down movement