(MODULE 7.1) GEOLOGICAL HAZARDS - EARTHQUAKES

Question 1

waves of energy produced by an earthquake

Answer 1

seismic waves

Question 2

what are the causes of earthquakes?
1.
2.
3.

Answer 2

1. release of energy in faults
2. volcanic eruptions
3. mineral transformations

Question 3

the classic explanation of why earthquakes take place.

Answer 3

elastic rebound theory

Question 4

explain the elastic rebound theory
1.
2.
3.
4.

Answer 4

1. tectonic forces act upon a fault over many years
2. buildup of energy causes the rock to bend
3. built up energy is released, causing the rock to break
4. the rocks rebound to a permanently displaced shape

Question 5

the longer the energy of tectonic forces is stored up, ___.

Answer 5

the more likely that a strong earthquake will occur.

Question 6

the point within the earth where seismic waves first originate

Answer 6

focus or hypocenter

Question 7

the point on the earth’s surface directly above the focus

Answer 7

epicenter

Question 8

types of seismic waves
1.
2.

Answer 8

1. body waves
2. surface waves

Question 9

seismic waves that travel through the earth’s interior, spreading outward from the focus in all directions

Answer 9

body waves

Question 10

seismic waves that travel on earth’s surface away from the epicenter

Answer 10

surface waves

Question 11

types of body waves
1.
2.

Answer 11

1. p wave
2. s wave

Question 12

a compressional or longitudinal wave in which rock vibrates back and forth parallel to the direction of wave propagation

Answer 12

p wave

Question 13

characteristics of a p wave
1.
2.
3.

Answer 13

1. rock vibrates parallel to wave of propagation
2. very fast, 4km/s to 7km/s
3. first to arrive at a recording station

Question 14

transverse wave propagated through a shearing motion perpendicular to the direction of wave propagation

Answer 14

s wave

Question 15

characteristics of an s wave
1.
2.
3.

Answer 15

1. travels near the surface and vibrates perpendicular to wave propagation
2. slower than p wave, 2km/s to 5km/s
3. second to arrive at a recording station

Question 16

types of surface waves
1.
2.

Answer 16

1. love waves
2. rayleigh waves

Question 17

the ground moves side to side in a horizontal plane perpendicular to the direction of wave propagation

Answer 17

love waves

Question 18

this type of surface wave causes the ground to move in an elliptical path opposite to the direction the wave passes

Answer 18

rayleigh waves

Question 19

the instrument used to measure seismic waves

Answer 19

seismometer

Question 20

a recording device that produces a permanent record of earth motion detected by a seismometer

Answer 20

seismograph

Question 21

a recording device that produces a permanent record of earth motion detected by a seismometer

Answer 21

seismograph

Question 22

the paper record of earth vibration

Answer 22

seismogram

Question 23

how is the location of an earthquake determined?
1.
2.

Answer 23

1. seismographs record seismic waves. from the seismogram, P and S wave arrival is measured, from which the P-S time interval is determined. the larger the P-S time interval, the farther the earthquake is from the recording station.
2. this activity is repeated for at least 3 stations to triangulate the epicenter of the earthquake.

Question 24

80% of all earthquakes occur in the ___.
15% occur in the ___.
5% occur in the ___.
more than ___ quakes strong enough to be felt are recorded each year.

Answer 24

1. circum-pacific belt
2. mediterranean-asiatic belt
3. 150,000

Question 25

a measure of an earthquake’s effect on people and buildings

Answer 25

intensity

Question 26

intensities are expressed as roman numerals ranging from I to XII on the ___.

Answer 26

modified Mercalli scale

Question 27

this method of measuring the size of an earthquake is done through calculating the amount of energy released by the quake using the ___.

Answer 27

Richter scale

Question 28

After measuring a specific wave on a seismogram and correcting for the type of seismograph and for the distance from the quake, scientists can assign a number called the ___.

Answer 28

magnitude

Question 29

the higher the magnitude of an earthquake is, the less frequent it occurs. that is due to the ___.

Answer 29

elastic rebound theory

Question 30

the trembling and shaking of the land that can cause buildings to vibrate

Answer 30

ground motion

Question 31

the frequency of shaking differs for different seismic waves.

high body frequency waves shake ___ more, whereas low frequency surface waves shake ___ more.

Answer 31

1. low buildings
2. high buildings

Question 32

intensity of shaking also depends on type of subsurface material. ___ amplify shaking more than rocks do.

Answer 32

unconsolidated materials

Question 33

intensity of shaking also depends on type of subsurface material. ___ amplify shaking more than rocks do.

Answer 33

unconsolidated materials

Question 34

what are unconsolidated materials?

Answer 34

unconsolidated materials are materials that have not undergone compression to the point of having its moisture squeezed out (aka consolidation)

Question 35

buildings on soft sediment are __ than buildings on hard rock.

Answer 35

damaged more

Question 36

a particularly serious problem just after an earthquake because of broken gas and water mains and fallen electrical wires.

Answer 36

fires

Question 37

can be triggered by the shaking of the ground

Answer 37

landslides

Question 38

how is a tsunami formed?

Answer 38

when a section of sea floor rises/falls during an earthquake, the water over the moving area is lifted or dropped, forming a fast wave which slows down and builds in height as it approaches a shoreline.

the water will rise for 5 to 10 minutes due to its long wavelength.

Question 39

this type of ground failure occurs when water-saturated soil/sediment turns from a solid to a liquid due to earthquake shaking.

Answer 39

liquefaction

Question 40

how does liquefaction work?

Answer 40

the vibration or shaking of loosely packed grains of soil will result to the destabilization of soil, increasing the space between grains.

Question 41

how can the effects of earthquakes be controlled?
1.
2.
3.

Answer 41

1. create earthquake-resistant structures
2. pumping fluids into seismic gaps in order to cause smaller earthquakes and prevent large ones
3. develop an early warning system