Earthquakes are…: VIDEO
* Note in the video they say “Hypocenter”. In the book, it
is called the “Focus”. On the exam, FOCUS will be used.
…ground movements. They happen when blocks of rock
(tectonic plates) move suddenly and release energy.
The energy released is known as SEISMIC WAVES.
There are 2 main types of seismic waves. VIDEO here.
P waves: Primary Waves
They are the first waves felt during an earthquake
They are faster than S waves
They move objects left to right
S waves: Secondary waves
They are stronger than P waves
They move slower so are felt later
The particles on the Earth move at right angles to the
direction the wave is moving.
In the earth, along a fault, where the earthquake begins.
Above the focus on the Earth’s surface is the epicenter.
Seismic waves flow out from the focus in all directions
They occur near tectonic plate boundaries
As the plates move, pressure builds up near the edges.
If there is too much pressure, the plates move
suddenly. This is an earthquake.
The plate movements cause FAULTS. Faults are breaks
in the Earth’s crust. The plates move along these
faults. Convection Currents in the Mantle, move the
Most happen near tectonic plate boundaries.
This is where there is the most stress from plate movement.
Normal Fault Click for video
Normal Faults happen at DIVERGENT boundaries
All of the Red lines show a
divergent boundary (Mid ocean ridge)
Reverse Fault Click for video
Reverse Faults happen at CONVERGENT boundaries
Ex: Mariana Trench.
The Mariana plate and Pacific plate
are converging. The Pacific plate
subducts the Mariana Plate.
Strike Slip Fault Click for video
Strike Slip Faults happen at TRANSFORM boundaries
Ex: San Andreas
North American plate colliding with
the Pacific plate.
Which Seismic wave moves the fastest?
P or primary waves
What is the point where an earthquake happens in the
It is called the focus.
3. What is the term given the process which moves tectonic
The process which moves tectonic plates is called Convection.
Which type of plate boundary can be found at strike slip
A Transform boundary
At convergent boundaries, name the faults that occur.
Reverse Faults occur at convergent boundaries.
If you have questions about this topic:
See me before exams (at lunch, break time, after
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Re-watch the videos and read the power points