Geography Tectonics

Frequency

How often a tectonic hazard occurs over a period of time

Magnitude

Measure of the energy released by an earthquake

Focus

Point inside the Earth where the earthquake starts and energy is released from this point

Epicentre

Point on the Earth’s surface directly above the focus

P waves

• Primary waves

• Fastest seismic waves

• Travel through solids and liquids

• Cause compression movemen

S waves

• Secondary waves

• Slower than P waves

• Travel through solids only

• Cause side to side movement

L Waves

• Surface waves, also called Love waves

• Travel along the Earth’s surface

• Usually cause the most damage to buildings

Liquefaction

• When saturated ground loses strength during shaking

• Buildings can sink or collapse

Pyroclastic flow

• Fast moving cloud of hot gas, ash, and rock from a volcano

• Extremely dangerous and destructive

Lahar

• Volcanic mudflow made of ash and water

• Flows rapidly down slopes and valleys