Seismic Hazards

Question 1

How Earthquakes are caused

Answer 1

1)Earthquakes are caused by the tension that builds up at all three types of plate margin.
2)When the plates jerk past each other it sends out shockwaves (vibrations). These vibrations are the earthquake.
3) The shockwaves spread out from the focus. The focus doesn’t have to be a single point-for example, it could be along a fault line. Near the focus the waves are stronger and cause more damage.
4) The epicentre is the point on the Earth’s surface where the earthquake is felt first. It’s straight above the focus.
5) Earthquakes cause the ground to shake, and sometimes to rupture (split apart) along the fault.

Question 2

The Richter scale

Answer 2

The Richter scale measures the magnitude of an earthquake (how powerful the shaking is). It doesn’t have an upper limit, and it’s logarithmic. Major earthquakes are above 7.

Question 3

The Moment Magnitude Scale

Answer 3

Is based on the total amount of energy released by an earthquake. Like the Richter scale, it is logarithmic and has no upper limit. It is more accurate than the Richter scale, especially for large earthquakes, so it’s more widely used.

Question 4

The Mercalli scale

Answer 4

Measures the impacts of an earthquake using observations of the event (eg. reports and photos). The scale is between 1 and 12, with 1 being an earthquake that’s only detected by instruments, and 12 being an earthquake that causes total destruction.

Question 5

The Mercalli scale

Answer 5

Measures the impacts of an earthquake using observations of the event (eg. reports and photos). The scale is between 1 and 12, with 1 being an earthquake that’s only detected by instruments, and 12 being an earthquake that causes total destruction.

Question 6

Tsunamis

Answer 6

Are large waves caused by the displacement of large volumes of water
Triggered by underwater earthquakes. The earthquakes cause the seabed to move, which displaces water.

Question 7

Landslides and Avalanches

Answer 7

Shaking of the ground can dislodge rock, soil or snow, causing landslides or avalanches that move downslope quickly.
Shaking can also loosen ground material, making it easier for water to infiltrate. The weight of the extra water may trigger a landslide even after ground shaking has stopped.

Question 8

Soil liquefaction

Answer 8

When soil is saturated with water, the vibrations of an earthquake can cause it to act like a liquid.
This makes the soil weaker and easier to deform, so it’s more likely to subside, especially where it has a heavy weight on top of it(e.g. a building)