An earthquake is the shaking and vibration of the Earth’s crust due to movement of the Earth’s plates.
Earthquakes are found at constructive, desctructive and conservative plate boundaries. This means they are found in zones around the world.
Latest earthquakes in the world – past 7 days.
Earthquakes occur at plate boundaries because of the build up of friction that occurs are plates try to move past each other and get stuck.
Plate boundary Friction builds up when… destructive margins one plate tries to sink below the other collision zones
plates are pushing together
constructive margins both plates try to move over the mantle conservative margins plates moving alongside each other get stuck
Features of an earthquake:
Focus: the point inside the crust where the pressure is released
Epicentre: the point on the Earth’s surface directly above the focus
Seismic waves: the energy released by the earthquake travels in waves
Earthquakes can have a deep focus (300-700km) where the earthquake happens far down in the crust or a shallow focus (0-70km deep) where the happens nearer the surface of the crust. When earthquakes have a shallow focus they tend to do more damage as the shaking is greater.
The power of an earthquake is measured using a seismometer. This detects the vibrations caused by an earthquake and plots them on a seismograph. The strength or magnitude of an earthquake is measured using the Richter scale which is a logarithmic scale which means that a magnitude 6 earthquake is ten times stronger than a magnitude 5 earthquake, and 100 x stronger than a magnitude 4. This scale allows you to directly compare the magnitude (strength) of an earthquake however, strength of earthquake doesn’t allow correlate with damage. To overcome this the Mercalli scale measures the effects. It has twelve points of the scale (but uses Roman numerals I – XII), to view the different intensities click here.
Composite volcanoes are usually found at destructive plate boundaries. When the oceanic crust sinks into the mantle and melts it forms magma. As it then mixes with sea water it is less dense so it rises through the continental crust to form a volcano.
- Composite volcanoes usually have steep sides and are made up of alternate layers of ash and lava.
- Lava is acidic and is sticky. It will not flow far.
- Eruptions are usually violent with the volcanoes erupting ash, steam, lava and rock.
- They don’t happen very often.
Shield volcanoes are found at constructive plate boundaries. As the two plates move apart magma rises up from the mantle. It then rises up through a vent forming a volcano.
- Shield volcanoes have a wide base and gently sloping sides.
- Lava is basic, runny and flows a long way.
- Frequent eruptions but not particularly violent.