Tectonic Hazards

Plate Boundary

Where two plates make contact as a result of converging, diverging or sliding past each other.

Hotspot Volcanoes

It is where the crust above a plume is weak, the magma breaks through and volcanic activity occurs, as in the Hawaiian islands.

They occur at locations on the Earth’s surface where there are rising currents of magma (plumes).

They are not associated with plate boundaries.

Mid-Atlantic Ridge

It marks a divergent or constructive plate boundary running the length of the Atlantic. It is in effect a submerged mountain range made up largely of extruded basaltic rocks.

In places, the volcanic mountains rise above the oceans surface as islands. So the hazards are volcanic eruptions and occasional earthquakes.

Oceanic Crust

• It’s an underlying ocean basins.

• Thin.

• Composed mainly of basalt.

Continental Crust

• Underlying the contents

• Thicker

• Composed of mainly granite

Paleo-magnetism

It results from cooling magna locking in the Earth’s magnetic polarity. From this locked in magnetic alignment, scientists can work out:

• When there were periods of large-scale tectonic activity in geological history

• The directions and speeds of present and past plate movements

Locked fault

It is a fault that is not slipping.

It is stuck because the friction along it is greater than the shear stress across it.

The strain in the fault builds up.

Eventually the frictional resistance is overcome and the strain is suddenly released.

Such a release usually results in a large magnitude earthquake with devastating consequences.

For example the 2004 Indian Ocean tsunami was due to a huge locked fault.

Benioff Zone

It is the boundary between an oceanic plate which is undergoing subduction beneath an overriding continental plate.

The sinking oceanic plate is colder than the crust into which it is sinking.

This causes sudden stresses that may trigger earthquakes.

Seismic waves - p waves

Primary (p-waves) - vibrations caused by compression, they spread very quickly

Seismic waves - s waves

Secondary (s-waves) - they vibrate at right angles to the direction of travel, they move more slowly than primary waves

Seismic waves - L waves

Long (L-waves) - they are surface waves with high amplitude