Download Extreme Natural Events

Extreme
Natural Events
Earthquake processes.
Stage 1.
 Magma
rises to the crust within the
mantle. This creates friction and causes
the plates to move.

What are the 3 main ways plates move
 1.
 2.
 3.
Stage 2
 Pressure
builds between plates and
sometimes small earthquakes are felt.
 Sudden rupture of the plates along a fault
line happens, and the earth shakes for 1540 seconds.
 The centre point of the rupture inside the
earth is called the focus. Seismic waves
radiate in all directions from the focus. The
centre point on the earths surface above
the focus is called the epicentre.
Stage 2: waves
P
waves (primary): first felt, does little
damage.
 S waves (secondary): arrives shortly after P
wave. I makes the ground shake vertically
(up & down) and horizontally (side to side)
like jelly. These can be very damaging.
 L waves (long wave): arrives last, like water
rippling, it moves the ground sideways and
can be very damaging.
Recap
 An
earthquake focus is where
earthquakes start. Energy is release when
rocks suddenly snap
 The epicentre is on the surface, directly
above the focus.
 A seismograph is an instrument that
detects earthquake waves and records
them on a graph called a seismograph.
Stage 3
 The
earthquake can damage land and
buildings, phone lines can be down and
mobile networks overloaded.
 First response, save as many people as
possible.
Stage 4: aftershocks
 Can
be felt days, weeks, months
afterwards, they can be large and
destructive.
Recovery
 State
of emergency may be declared by
Civil Defence. Immediate concerns are
the injured, food, shelter for survivors.
 Unsafe areas are evacuated, schools,
halls and maraes are used as shelter
centres.
Stage 6: rehabilitation
 The
rebuilding of buildings, roads, services
and economic facilities may take months
and is very costly.
Sequence of events
1.
2.
3.
4.
5.
6.
7.
Stress in tectonic plates
Foreshocks shocks may happen before
the big one
Earthquake happens
Shaking is felt once waves surface
Shaking lasts few seconds or several min.
Aftershocks occur
Process starts again
Earthquake processes

Create a flow chart in your books, using these
phrases put them in their correct order.







Stress causes rupture at the plate boundaries
Seismic waves radiate out from the earthquakes
focus.
Ongoing global plate movement
The earthquake is felt by people as the seismic
waves surfaces.
Stress builds up in rocks at plate boundaries
Movement along a fault line or the creation of a
new fault line *(4)
The point on the earths surface reached first by the
seismic waves is the epicentre. *(6)