Lesson 12-What is seismicity and how do we monitor seismic activity?

Question 1

Epicentre

Answer 1

• Point on the surface of the Earth directly above crust, where seismic waves are first felt

Question 2

Focus

Answer 2

• Point within the earth crust where the earthquake originates

Question 3

Seismic waves

Answer 3

• Waves of energy which travel through the crust casued by released by the release of pressure from an earthquake

Question 4

Primary (P) waves

Answer 4

• Compressional (longitudinal) waves are where particles vibrate paralell to the direction of movement
• 6-7km/s
• Travel through solids, liquids and gases

Question 5

Secondary (S) waves

Answer 5

• Transverse (similar to light and sea waves), particles), particles vibrate at right angles to the directiomn of the movement
• slower than 2.5 - 4km km/s, travel through solids

Question 6

Suface (Love and Rayleigh)

Answer 6

• Travel at speeds similar to S waves
• arrive after the S waves have passed
• Rayleigh waves similar to ocean waves
• Circular motion

Question 7

Can we warn people about earthquakes?

Answer 7

• Waves that move the fastest (P waves) dont shake the ground but they are recorded on seismometres
• This can tell us an earthquake is about to happen- named the P-wave warning system

Question 8

Can we predict earthquakes?

Answer 8

• We can predict earthquakes based on history of the plate boundary
• Can measure vibrations in earths crust (seismometer)
• Emissions of radon gas

Question 9

How can seismic waves be recorded?

Answer 9

• Can be measured by seismography
• These graphs can record the amplitude of seismic waves by recording P and S waves
• Can then be translated to numerical scale of Richter scale

Question 10

How are seismic waves recorded in Japan?

Answer 10

• When there is a P-wave detection from any of the 4,235 seismometers in Japan
• JMA predict location of epicentre
• Can then warn people in that area through TV and radio

Question 11

What are shadow zones?

Answer 11

• Parts of the earth which do not tetect earthquakes because certain waves cant travel through the outer core

Question 12

P-wave shadow zone

Answer 12

• The area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any seismic waves, therefore cannot be recorded there
• P waves get refracted so create smaller shadow zones

Question 13

S-wave Shadow zone

Answer 13

• Bigger and exists as S waves (earthquakes waves) cannot travel through the liqued outer core so they create a big shadow zone

Question 14

Exam question-Outline the features of seismic waves and account for the shadow zone (4 Marks)

Answer 14

• P waves are the first waves are the P-waves. These travel around 6-7km/s through solids, liquids and gases. Longitudinal that can be detected up to a minute before the ground begins to move.
• Next, the other type of waves are the S-waves. These can only travel through solids at a speed of 2.5km - 4km/s and are also reffered to as transverse waves

Question 15

How do we measure the magnitude of earthquakes ?

Answer 15

• Richter scale-logrythmic and measures the energy released
• Macarli scale-depends on many factors other than energy like rock type
• Moment Magnitude Scale-the total amount of energy released by an earthquake, better at measuring larger earthquakes

Question 16

Evaluations of Modified Mercalli scale

Answer 16

+There is a set of criteria that diffrentiates earthquake
+Qualitative scale
-No use within isolated, rural areas where damage is limited
-Based on observations/opinions

Question 17

Evaluations of Richter Scale

Answer 17

+Logarithmic scale
+Can compare with other earthquakes globally
+Objective definition of power of an earthquake as no opinion is involved
-Quantative measurement
-Open ended as theres no upper limit