Spatial variations in the tectonic hazard risk EQ1

Causes -  Sudden movement within the Earths crust, usually along a pre-existing fault. The movement is due to a gradual build up of pressure between the plates and then they suddenly move.

Global Distribution - Mainly along plate boundaries and in the Ring of Fire - Pacific Ocean. Can occur in the middle of plates. This is when they are called intraplate earthquakes.

The sudden movement of the plates creates vibrations of 3 different kinds

- P waves (fast)

- S waves (slower)

- L waves (surface)

The hypocentre of the earthquake is where the pressure of the earthquake is released. The epicentre is the point directly above this on the earths surface. This is where the shock waves are strongest.

The overall severity of the earthquake is determined on the frequency and amplitude of the waves. S and L waves = More destructive than P waves. They cause fracturing, ground shaking and three secondary hazards:

Secondary Hazards

- Liquefaction - this is where seismic waves trigger the ground to lose its shape and structure by turning squidgy, this can cause buildings to settle into the ground and can collapse.

- Landslides - these occur where slopes are weakened by seismic waves and slide due to gravity

- Tsunamis -  A long, high sea wave caused by a earthquake. Can become a hazard in itself and can cause more secondary damage than the earthquake itself. Out at sea they aren't a hazard due to their low waves however as they aproach the coastline, they gain in height and the sea becomes shallower.

Causes - Magma rises through cracks and weaknesses of the earth's crust. When this pressure is released, eg through the movement of plates, magma explodes to the surface causing an explosion.

Global Distribution - Mainly in the Ring of Fire, most are near plate boundaries (Destructive, Convergent and Constructive, Divergent). Can occur on hotspots -   places in the middle of plates.

Primary Hazards:

- Pyroclastic flows. The frothing of magma at the vent produces bubbles that burst explosively to eject hot, poisenous gases as well as hot ash. Clouds form these gases and materials are most lethal when they roll down the sice of a volcano

- Tephra (ash falls). These are rock fragments that are ejected into the earths atmosphere and vary in sizes. The accumilation of Tephra on roofs can cause fires and can cause buildings to collapse.

- Lava Flows. Flows of molten rock, often fast moving and lethal.

- Volcanic Gases. These are mixed gases that are emitted during explosive eruptions. The carbon dioxide is particularly dangerous.

Secondary Hazards:

- Lahars. These are mudflows created by the combinatio of heavy rain on slopes covered with a fine layer of volcanic material.

- Jokulhaups. Flooding caused by volcanic eruptions beneath glaciers. Causing them to melt.