Lecture. 8 - Locating and Measuring Earthquakes

Question 1

P - Waves
S - Waves

Answer 1

P are compressional
S waves are shear

Question 2

Two types of surface waves

Answer 2

Love waves
Rayleigh waves

Question 3

What controls P waves and S waves

Answer 3

Composition and temperature
S waves cannot travel through a liquid
P waves can travel through a liquid

Question 4

Use of P waves to analyse Earths internals

Answer 4

Shadow zone caused by shear waves not being able to travel through the outer core.
Refraction of P waves by a slower outer liquid core also causes P wave shadow.

Question 5

What do seismometers do?

Answer 5

• detect the passage of seismic waves
• Use a system of masses and springs to sense ground movement

Question 6

What do seismograms do?

Answer 6

• Record rotates continuously and a pen gradually moves across the recording drum

Question 7

What three components of ground motion do they measure?

Answer 7

• vertical
• north-south
• east-west

Question 8

How are earthquakes located?

Answer 8

P - waves travel faster than S - waves so the time difference increases with increasing distance.
P to S time difference can be used to determine epicentral distance from a recording station.
Knowledge of epicentral distance from a few stations can be used to locate the epicenter.

Question 9

General form of magnitude scales

Answer 9

M = log(A/T) + f(d,h) + Ceq + Crec,
A is amplitude of displacement
T is period
F is correction for epicentral distance
h is focal depth
Ceq is source region correction
Crec is a station correction

Question 10

Richter scale (local magnitude)

Answer 10

Based on amplitudes of seismic waves
A logarithmic scale
Scale is invalid of earthquakes larger than 8

Question 11

Surface wave magnitude

Question 11

Surface wave magnitude

Question 12

Moment Magnitude

Answer 12

Mw = (log M0)/1.5 - 6.0
Preferred scale to use because it is more accurate at higher magnitudes.