Seismicity

Question 1

Focus

Answer 1

The point at which this pressure release occurs within the crust

Question 2

Epicentre

Answer 2

The point immediately above the focus on the Earth’s surface

Question 3

What are the three broad categories of earthquakes

Answer 3

• shallow focus
• intermediate focus
• deep focus

Question 4

Shallow focus

Answer 4

0-70km deep
Greatest damage
75% of all the earthquake energy released

Question 5

Intermediate focus

Answer 5

70-300km deep

Question 6

Deep focus

Answer 6

300-700km deep

Question 7

Where do seismic waves radiate from

Answer 7

The focus, rather like the ripples in water when a rock is thrown into a pond

Question 8

What are the three main types of seismic waves

Answer 8

• primary (P) waves
• secondary (S) waves
• surface (L) waves

Question 9

Primary (P) waves

Answer 9

Travel fastest
Compressional
Vibrating in the direction in which they are travelling

Question 10

Secondary (S) waves

Answer 10

Travel at half the speed of P waves

Vibrating at right angles to the direction of travel

Question 11

Surface (L) waves

Answer 11

Slowest
Near to the ground surface
Some shake at right angles
Some have a rolling motion (vertical ground movement)

Question 12

Where do P and S waves travel

Answer 12

Through the interior of the earth and are recorded on a seismograph