Chapter 8: Earthquakes

Question 1

fault

Answer 1

a fracture plane on which sliding takes place

Question 2

Earthquake

Answer 2

an episode of ground shaking

Question 3

seismologist

Answer 3

geoscientists who study earthquakes

Question 4

seismicity

Answer 4

earthquake activity

Question 5

seismic waves

Answer 5

the energy released by vibrating rocks caused by an earthquake which travels away from the source in the form of waves

Question 6

fault displacment

Answer 6

the distance between two ends of the offset marker (at a fault)

Question 7

fault line/trace

Answer 7

the ground surface exposure of a fault (whether it appears due to erosion of

Question 8

stress

Answer 8

a push, pull, or shear

Question 9

elastic behavior

Answer 9

rock bends slightly but doesn’t break

Question 10

elastic rebound theory

Answer 10

when slip takes place, the once-bent rocks adjacent to the fault rebound and vibrate back and forth until they regain their relaxed shape, thereby relieving the elastic strain.

Question 11

stick-slip behavior

Answer 11

alternation between stress buildup and earthquake-generating slip events on existing faults

Question 12

mainshock

Answer 12

the major earthquake

Question 13

foreshocks

Answer 13

smaller earthquakes that precede the main shock (earthquake)

Question 14

aftershocks

Answer 14

endured by a region affected by an earthquake in the days to months following, tend to be 10 times smaller than the main shock

Question 15

focus

Answer 15

the location where seismic waves first begin to be generated, also known as the hypocenter

Question 16

shallow focus earthquakes

Answer 16

occur in the top 60km of the Earth

Question 17

intermediate-focus earthquakes

Answer 17

takes place between 60 and 300 km

Question 18

deep focus earth quakes

Answer 18

occur down to a depth of about 660km

Question 19

epicenter

Answer 19

the point on the surface of the Earth that lies directly above the focus

Question 20

categories of seismic waves

Answer 20

• body waves

- surface waves

Question 21

body waves

Answer 21

pass through the interior of the Earth

- cause material to vibrate in two different ways; compressional and shear

Question 22

surface waves-

Answer 22

travel along the Earth’s surface; vibrate in two different waves

• up and down, rolling undulations
• side to side, back and forth

Question 23

compressional waves

Answer 23

body waves that cause particles of material to move back and forth parallel to the direction in which the wave itself moves (squeeze together, then expand)

Question 24

shear waves

Answer 24

body waves that cause particles of material to move back and forth perpendicular to the direction in which the wave itself moves (up and down)

Question 25

types of waves all together

Answer 25

P-waves: fastest
S-waves: next fastest (60% of the speed of p-waves)
L-waves: Slow
R-waves: Slow

Question 26

P-waves

Answer 26

Primary Waves: compressional body waves

Question 27

S-waves

Answer 27

Secondary Waves: shear body waves

Question 28

L-waves

Answer 28

Love Waves: surface waves that cause the ground to shimmy back and forth

Question 29

R-waves

Answer 29

Rayleigh Way: surface waves that cause the ground to undulate up and down

Question 30

seismometer (also known as seismograph)

Answer 30

measures the ground motion produced by an Earthquake and can be configured in two ways

• vertical motion
• horizontal motion

Question 31

seismogram

Answer 31

an earthquake record produced by a seismometer

Question 32

travel time curve

Answer 32

the time delay between P-waves and S-waves, depicted on a graph whose horizontal axis indicates distance from the epicenter and whose vertical axis indicates time.

Question 33

earthquake intensity

Answer 33

refers to the degree of ground shaking

Question 34

Modified Mercalli Intensity (MMI) scale

Answer 34

represent intensity at a location by a Roman numeral, intensity greater closer to the epicenter and decreases further away

Question 35

Earthquake magnitude

Answer 35

represents the amount of energy released from the seismic source, as indicated by the amplitude of ground shaking recorded by a seismometer

Question 36

richter scale

Answer 36

a logarithmic scale for defining earthquake magnitude

Question 37

moment magnitude

Answer 37

the most widely used scale to describe Earthquake magnitude; scientist measure the amplitudes of several different seismic waves, determine the dimension of the slipped area on the fault, and estimate the displacement that occurred, also a logarithmic scale

Question 38

seismic belts/zones

Answer 38

most correspond to plate boundaries, earthquakes here are called plate-boundary earthquakes

Question 39

intraplate earthquakes

Answer 39

earthquakes that occur away from plate boundaries