Locating and measuring earthquakes

Question 1

Explain the stick-slip process for earthquake generation on fault planes

Answer 1

Stress and strain builds up over hundred and thousands of years
Strain released in seconds or minutes
Presumes pure elastic deformation
Plates slip back to original position, rebound
Energy release

Question 2

What is another name for a P wave?

Answer 2

Compression waves

Question 3

What is another name for an S wave?

Answer 3

Shear waves

Question 4

What is the definition of a P wave?

Answer 4

Waves where the particle motion is in the same direction as travel <——->

Question 5

What is the definition of an S wave?

Answer 5

Waves where the particle notion is in another direction to the direction of travel </\/\/\/\/>

Question 6

What is a rayleigh/surface wave?

Answer 6

Waves that move over the earth’s surface rather than within it

Question 7

What determines the speed of P and S waves?

Answer 7

The composition and temperature of internal earth liquid

Question 8

What waves cannot travel through liquids?

Answer 8

S waves- creates a shadow zone

Question 9

How does a seismometer work?

Answer 9

Suspended pendulum embedded in the earth’s surface measures how much it moves up and down and side to side from its original postition
Can detect each kind of wave

Question 10

How does a seismometer work out the amplitude of waves?

Answer 10

Transforms waves received into an electrical signal

Question 11

How is wave information used to locate earthquakes?

Answer 11

P and S waves produced at same time but travel at different speeds so they arrive at global stations at different times
Use delay times to work out distance, using known speeds of waves
Triangulate the position
Where circles cross= epicentre

Question 12

What are the two assumptions that earthquake magnitude scales work on?

Answer 12

-For the receiver, the larger earthquakes will generate larger amplitude arrivals
-Amplitude of arrivals will behave in a predictable/linear manner

Question 13

What scale is used in the Richter scale?

Answer 13

Logarithmic scale based on the ampltiude of seismic waves

Question 14

What waves are measured for the Richter scale?

Answer 14

P and S waves

Question 15

Name two reasons why the Richter scale is invalid

Answer 15

-May not be appropriate for other locations as it was designed purely for Southern Californian earthquakes
-Does not work for earthquakes larger than 8

Question 16

What does the surface wave magnitude scale measure?

Answer 16

The 20 second period surface wave

Question 17

Why is the surface wave magnitude scale useful?

Answer 17

It correlates well with the damage caused on the surface

Question 18

What waves are measured for the body wave magnitude scale?

Answer 18

P waves

Question 19

What does the seismic moment and moment magnitude measure?

Answer 19

The elastic energy released by an earthquake and the deformation occuring

Question 20

Why do seismologists prefer the seismic moment and moment magnitude scale?

Answer 20

It is based on the earthquake mechanism itself, not just the waves it generates
It is more accurate at higher magnitudes