Chapter 10

Question 1

Earthquake

Answer 1

The vibration/shaking of the earth caused by a sudden release of energy.

Question 2

Elastic rebound

Answer 2

Rock is strained around the fault and stores elastic energy for thousands of years. When the stress is greater than the frictional fault strength, kinetic energy is released as an earthquake and the rock springs back to the original shape.

Question 3

Causes of earthquakes (3)

Answer 3

Fault movements related to tectonic activity, movement of magma below volcanoes, human activity.

Question 4

Hypocenter:

Answer 4

Location where the fault initially breaks or explosion occurs. Energy spreads out from the focus like ripples on a pond.

Question 5

Epicenter

Answer 5

Point on the earth’s surface directly above the hypocenter

Question 6

Seismology

Answer 6

Study of earthquakes

Question 7

Seismograph

Answer 7

Instrument that measures ground movement as earthquake occurs

Question 8

Seismogram

Answer 8

Record of an earthquake made on a seismograph

Question 9

Seismologist

Answer 9

Person who studies seismology

Question 10

Seismic Waves

Answer 10

Generated by an earthquake and travel away from the hypocentre. Separated into body waves and surface waves.

Question 11

Body waves

Answer 11

Waves that travel through the Earth (parallel and shear)

Question 12

P-waves

Answer 12

Compressional and longitudinal body waves that are faster than S-waves and travel parallel to the direction of travel. Divided into reflection and refraction

Question 13

S-waves

Answer 13

Shear and transverse body waves that travel normal to the direction of travel and can’t go through liquids.

Question 14

Surface waves

Answer 14

Waves that travel along or just below the surface with an amplitude that decreases with depth. (Rayleigh and Love waves)

Question 15

Rayleigh waves

Answer 15

Waves that travel in a retrograde elliptical particle motion

Question 16

Love waves

Answer 16

Waves that travel with horizontal (back and forth) motion

Question 17

P-wave velocity through sandstone

Answer 17

2.0-2.5 km/s

Question 18

P-wave velocity through quartzite

Answer 18

5.5-6.0 km/s

Question 19

P-wave velocity through limestone

Answer 19

5.0-5.5 km/s

Question 20

P-wave velocity through granite

Answer 20

5.5-6.0 km/s

Question 21

P-wave velocity through gabbro

Answer 21

6.5-7.0 km/s

Question 22

P-wave velocity through ultramafic rocks

Answer 22

7.5-8.5 km/s

Question 23

P-wave velocity through air

Answer 23

0.3 km/s

Question 24

P-wave velocity through water

Answer 24

1.4-1.5 km/s

Question 25

P-wave velocity through petroleum

Answer 25

1.3-1.4 km/s

Question 26

How to locate the source of an earthquake (5 steps)

Answer 26

1. Measure the arrival times of P-waves and S-waves waves and find the difference in time between them. 2. Compare this to the calculated travel times and look for the distance between lines where the difference in arrival times is the same. 3. Calculate The Distance To The Earthquake 4. Repeat steps 1-3 at at least three seismic stations. 5. Draw a circle at each station. The intersection of these circles is the epicenter.

Question 27

Results of locating the source of an earthquake (3)

Answer 27

1. Direction of the waves 2. Time at which the earthquake occurred 3. Depth of the hypocenter

Question 28

Earthquake distribution

Answer 28

80% of all earthquakes occur in the circum-Pacific belt. 15% within the Mediterranean Asiatic belt. 5% occur along oceanic spreading ridges or within plate interiors.

Question 29

Annual earthquake numbers

Answer 29

900,000+ earthquakes occur per year with 31,000+ of them strong enough to be felt.

Question 30

Wadati-Benioff zones.

Answer 30

Dipping seismic zones in a subduction zone that defines plate geometry.

Question 31

Magnitude

Answer 31

Quantitative measure of the energy released by an earthquake

Question 32

Richter scale scale

Answer 32

Increase of 1 in magnitude is a 10-fold increase in amplitude and a 30-fold increase in energy.

Question 33

How to use the Richter scale

Answer 33

1. Measure A = maximum amplitude of oscillation with period of 0.8 s in mm 2. Determine the distance to epicenter (Δ) in kilometers from time between P-wave and S-wave arrivals. 3. Use M = log(A) + 2.76log(Δ) - 2.48

Question 34

Seismic-moment magnitude scale

Answer 34

Uses the area of the fault that slips and offset (D) to compute the magnitude.

Question 35

Seismic wave velocity ranking

Answer 35

1. P waves (fastest) 2. S-waves 3. Surface waves.

Question 36

Seismic wave propagation

Answer 36

As pressure increases, P-wave velocity increases and causes P-wave paths to bend. Where the composition changes, we have a discontinuity

Question 37

Repeat time of Canadian earthquakes

Answer 37

450 years

Question 38

Direct earthquake destruction

Answer 38

Multi-story concrete buildings are prone to collapse with horizontal ground motion (S-waves). Steel Frame Buildings Do Much better as they flex.

Question 39

Factors determining earthquake intensity (7)

Answer 39

1. Earthquake magnitude 2. Distance from the epicenter 3. Focal depth of the earthquake 4. Population density 5. Building construction 6. Duration of ground shaking 7. Near surface geology (rock type, amplitude of wave increases in softer material)

Question 40

Indirect earthquake destruction (4)

Answer 40

Liquefaction (soil loses its cohesive strength during ground shaking and acts like dry sand), fires, tsunamis, landslides

Question 41

Earthquake induction

Answer 41

Earthquakes can be induced in the earth by the injection of water, and by filling reservoirs. However, it might be possible to release small amounts of the energy stored in rock sand thus avoiding a large earthquake. One possible means of earthquake control is fluid injections along locked segments of an active fault.

Question 42

Crust

Answer 42

Felsic rocks

Question 43

Mantle

Answer 43

Mafic rocks

Question 44

Mohorovicic discontinuity

Answer 44

30-40 km thick separation between the crust and mantle.

Question 45

P-Wave velocity rule

Answer 45

Gets faster the deeper in the earth, the more magic the rock