Geology 120 Test 3

Front 1

P Waves

Back 1

Slinky "push"
Fastest
Compressional

Front 2

S Waves

Back 2

Slinky "waved"
Slower
Side-to-side, Up and down
More damage than P waves

Front 3

Fault ruptures occurr how deep?

Back 3

Fault ruptures occurr 5 -100 km deep

Front 4

Point of rupture?

Back 4

Hypocenter (focus)

Front 5

Surface above rupture?

Back 5

Epicenter

Front 6

Measure earthquake effects in ____

Back 6

Measure earthquake effects in G (gravity)

Front 7

Recognizing fault in the field—5 Ways

Back 7

1. Offset of strata
2. Offset of streams
3. Topography
4. Offset of manmade features
5. Surface water

Front 8

Strike-slip movement occurs which way (primarily)?

Back 8

side-to-side, not up-down

Front 9

1 g is equal to ________

Back 9

Free-fall acceleration at 32ft/sec^2

Front 10

humans can sense ~_____ g?

Back 10

~0.001g

Front 11

Non resistant building crumble at ~___?

Back 11

~.1g

Front 12

What soil resists earthquakes best?

Back 12

bedrock

Front 13

What soil resists earthquakes least?

Back 13

landfill

Front 14

What soil amplifies shaking?

Back 14

Wet, unconsolidated soil

Front 15

What is a fault?

Back 15

Any crack offsetting rock

Front 16

What is a joint?

Back 16

A crack without offset

Front 17

A large offset is measured in ______

Back 17

Km

Front 18

A small offset is measured in ______

Back 18

mm

Front 19

3 types of faults

Back 19

1. Strike-slip
2. Normal
3. Reverse

Front 20

Reverse fault hanging wall moves up or down?

Back 20

hanging wall moves up

Front 21

Are thrust faults obvious?

Back 21

No, they hide themselves

Front 22

What are thrust faults?

Back 22

Very low angle reverse fault

Front 23

How to identify offset strata?

Back 23

Different rock types, weird juxtapositions

Front 24

How to topographically identify fault?

Back 24

scarp: cliff formed on fault plane

Front 25

en echelon shears

Back 25

tiny parallel cracks
shears “step”to left or right

Front 26

\\\\\\\\\\\\

Back 26

scarp =L SS = left-stepping EE shears

Front 27

////////////

Back 27

LL SS = right-stepping EE shears

Front 28

How to recognize fault via surface water/springs (2 ways)

Back 28

1. fault “grinding”produces clay
-> clay blocks water (aquitard)
2. Sag ponds –torn apart by fault mvt

Front 29

How to locate earthquake?

Back 29

P-S wave difference = distance from quake

Front 30

2 ways to measure earthquake size

Back 30

Modified Mercalli
Richter

Front 31

Modified Mercalli: What is it good for?

Back 31

Measuring old earthquakes through journals, etc., because it is subjective (windows breaking, trees shaking)

Front 32

Modified Mercalli uses what symbol to measure?

Back 32

Roman numeral

Front 33

Richter uses what scale (not richter scale)

Back 33

Logarithmic scale
(M4 ten times larger than M3
M5 one hundred times larger than M3 )

Front 34

How to measure using Richter Magnitude?

Back 34

1. Start with seismographic record
2. Measure time btwn P & S wave arrivals
3. Measure height at highest mark

Front 35

Problems with Richter Scale (3)

Back 35

1. Amplitude varies by material
2. Richter Scale doesn’t consider damage
3. Moment Magnitude Scale (Mw)

Front 36

Explain "Amplitude varies by material"

Back 36

weak mud = higher amplitude= bigger M
bedrock = lower amplitude= smaller M

Front 37

How to calculate using Moment Magnitude

Back 37

Considers length of fault rupture x distance moved

Front 38

Advantages of Moment Magnitude Scale (2)

Back 38

More consistent #’s
Better for bigger quakes
(Richter inconsistent >7.5)

Front 39

Disadvantages of Moment Magnitude Scale (2)

Back 39

Not every quake ruptures ground or
displaces big subduction quakes
Takes much longer to calculate