*Seismic Hazards 2

Where do most seismic hazards occur?

Around destructive and conservative plate margins, but the can also occur around constructive margins.

What 3 factors affect the nature of an earthquake and its magnitude?

• Margin type

• Rate of Movement

• Depth of Focus

Where do the biggest earthquakes occur?

At destructive plate margins, where one plate is forced beneath another at the subduction zone.

What does the subduction of a plate cause?

Causes massive pressure to build up, causing a huge earthquake when it is released.

What do earthquakes at constructive margins tend to be like?

Lower magnitude than at destructive or conservative margins.

How much do tectonic plates move?

They move in relation to each other at different rates, between about 1 and 15cm per year.

What is there no clear relationship of regarding rate of movement of tectonic plates?

There’s no clear relationship between rate of movement and earthquake magnitude.

What can an earthquake’s focus be?

It can be close to the Earth’s surface or deep below it.

What do earthquakes tend to be like when there is a deep focus?

Tend to be higher magnitude than shallow focus earthquakes.

But, why do deep focus earthquakes tend to create less damage?

Because shock waves generated deeper in the Earth have to travel further to reach the surface, which reduces their power.

How frequently do earthquakes occur globally?

Hundreds of low magnitude earthquakes happen around the world every day.

High magnitude earthquakes occur much less often.

What can be said about the number of earthquakes that occur flobally?

It varies from year to year.

What can be said about the randomness v. regularity of earthquakes?

Earthquakes and other seismic hazards don’t seem to follow a clear pattern or trend - their occurrence is largely random.

What is the predictability of earthquakes like?

Scientists can monitor movement of tectonic plates to predict which areas are at risk from seismic hazards.

But what is the issue with predicting seismic hazards?

It’s currently impossible to tell when an earthquake will strike a particular place, and what magnitude it’s likely to be.

What does the severity of a seismic hazard also depend on?

Where it occurs e.g. a mid ocean earthquake may have fewer impacts than one on land.