Download File - singhscience

Before you look in more detail about
earthquakes you first need to understand
the structure of the earth
Key PointOuter core is
liquid!
The Earth is almost a sphere. These are its main layers, starting
with the outermost:
•
•
•
•
crust - relatively thin and rocky
mantle - has the properties of a solid, but can flow very slowly
outer core - made from liquid nickel and iron
inner core - made from solid nickel and iron
Tectonic Plates?
• The outermost layer of the Earth is
made up of tectonic plates.
• These plates
are slowly
moved by
convection
currents.
Convection currents cause the
plates to move....
Convection currents can lead to
earthquakes...
• Radioactive decay takes place in the
mantle, this produces a lot of heat, which
causes the mantle to flow in convection
currents. The hot rock rises then cools,
causing the plates to move. As the plates
move they slide past each other. There is
friction between the plates. Sometimes
they get stuck, the pressure and energy
builds up. Eventually they slip releasing
the energy as an earthquake.
Seismic Waves?
• These are waves that travel through
the earth when an earthquake occurs.
You need to learn the properties of the
two types of waves.
Key Point- Seismic
waves like any other
waves will refract!
Key Points
• S waves cannot pass through the liquid
outer core, but P waves can. When P
waves pass from solid to liquid, then
from liquid to solid, there are sudden
changes in direction – they are
reflected and refracted. Seismic waves
are also reflected and refracted as
they pass into different rock types.
Seismometers
are machines
that can
detect
seismic waves
Detecting earthquakes
• Earthquakes are detected using
a seismometer – a piece of equipment that picks
up the vibrations in the earth. A scientist can
work out the location of an earthquake by
calculating the time difference between the
arrival of the S and P waves. Information from
three different seismometers is compared to
work out the exact location of the earthquake –
the epicentre. This is called triangulation.