Lecture #7 - Earthquakes

Question 1

What are quakes the result of?

Answer 1

Rupture of rocks along a fault line

Question 2

How is the energy of a quake released as?

Answer 2

Seismic waves

Question 3

What is the difference between the Epicentre and the Focus?

Answer 3

Epicentre is where the earthquake actually happens below ground
Focus is the place on the surface directly above the epicentre

Question 4

How do we measure earthquakes?

Answer 4

Moment Magnitude Scale

Question 5

What is the Moment magnitude scale determined by?

Answer 5

• area ruptured
• amount of movement along a fault
• The elasticity of the crust

Question 6

What is the Modified Mercalli Intensity Scale?

Answer 6

• Qualitative scale based on the damage to structures and the affect on people.

Question 7

What causes the sudden movement along the fault ?

Answer 7

• Stress builds up, causing inconsistent movement in the fault.
• When stress is greater, it causes the fault to jump forward, causing and earthquake

Question 8

Where to seismic wave originate?

Answer 8

At the focus

Question 9

What are Blind faults?

Answer 9

Faults located below the surface

-aka can’t see em

Question 10

What are the 2 types of faults based on the directions of the displacement of rock or sediment?

Answer 10

1. Strike -Slip fault

2. Dip Slip Fault

Question 11

What are the 3 types of dip slip faults?

Answer 11

1. Reverse
2. Thrust
3. Normal

Question 12

What are the 3 categories that faults can fall into?

Answer 12

1. active
2. Potentially active
3. Inactive

Question 13

What is a Tectonic Creep?

Answer 13

The slow movement of rock or sediment along fracture caused by stress

Question 14

In what places to seismic waves travel?

Answer 14

Through the body of the earth and along the surface

Question 15

What are body waves?

Answer 15

Include P and S waves

Question 16

What are P waves?

Answer 16

Primary waves

• move fast
• push pull motion
• Can travel through solid and liquids

Question 17

What are S waves?

Answer 17

Secondary waves

• move slowly
• Up and down motion
• Can only travel through solids

Question 18

What are surface waves?

Answer 18

Seismic waves that form when P and S waves reach earths surface and then move along it
-move slower than body waves

Question 19

What are some factors that determine what shaking people feel from ta quake?

Answer 19

• Magnitude
• Distance to epicentre
• Focal depth
• Direction of the rupture
• Soil and rock type

Question 20

What happens to shaking as you increase distance form the epicentre?

Answer 20

-Shaking decreases

Question 21

How do you calculate where the epicentre is?

Answer 21

Triangulation

• measured n 3 different seismographs
• where they all intercept is where it is

Question 22

What happens to the waves as they spread outwards?

Answer 22

They become less intense

Question 23

What is the relationship between focal depth and shaking?

Answer 23

As focal depth increases, the shaking decreases

Question 24

what is directivity?

Answer 24

Quake energy is focused in the direction f the rupture

Question 25

relationship between ground motion and hetero/homogeneous soils?

Answer 25

Homogenouse can transmit energy more quickly Heterogenous slows down the energy -mountians can also slow down the structure

Question 26

What is Amplification?

Answer 26

An increase in ground motion during an earthquake

Question 27

Can 2 quakes at the same magnitude have the same impact?

Answer 27

Depending on where they are they can have very different impacts

Question 28

What is the Earthquake cycle?

Answer 28

Hypothesis that explains successive earthquakes on a fault | -Strain drops abruptly after an earthquake and then slowly builds back up

Question 29

What are the 3 stages in a typical cycle?

Answer 29

- inactive period - Strain produces minor - foreshock prior to the big shock

Question 30

What is a fore shock?

Answer 30

a small to moderate quake that occurs before and in the same general area as the main shock

Question 31

What are plate boundary earthquakes?

Answer 31

Quakes that occur o faults separating lithospheric plates | - can have strike slip, thrust and normal

Question 32

What is a strike slip quakes?

Answer 32

occur along transform faults where plates slide horizontally past each other

Question 33

What is a thrust quake?

Answer 33

Occur on faults that separate converging plates

Question 34

What is normal fault quake?

Answer 34

occur on faults associated with divergent plate boundaries

Question 35

What are interpolate quakes?

Answer 35

A quake on a fault in the interior of a continent. | -far from a plate boundary

Question 36

What are the 2 active interpolate zones?

Answer 36

Mississippi River valley | St Lawrence River valley

Question 37

What are the 2 regions in the US that could have a high M value?

Answer 37

- St. Louis | - Memphis

Question 38

What are some Primary effects of quakes?

Answer 38

- Ground shaking | - Surface Rupture

Question 39

What are some Secondary effects?

Answer 39

- Liquefaction - Land level change - Landslides - Fires - Tsunamis

Question 40

What is a ground rupture

Answer 40

displacement along faults causes cracks in the surface

Question 41

What is a Fault Scarp?

Answer 41

A linear escarpment at earth surface formed by movement along a fault during a quake

Question 42

What is Liquefaction?

Answer 42

The transformation of water saturated sediment from solid to liquid

Question 43

What are landslides?

Answer 43

Ground motion produced by a quake can cause rock and sediment to move downslope

Question 44

How can quakes cause fires?

Answer 44

the sock can sever power lines and gas lines which can catch on fire

Question 45

What are the natural service functions of quakes?

Answer 45

- Provide pathways for the downward flow of surface water - Can channel water to surface discharge points - new material resources can be exposed

Question 46

How can humans produce quakes?

Answer 46

- Weight of damns can create new faults - Injecting liquid waste into the earth - Testing nuclear weapons

Question 47

How do we estimate seismic risk?

Answer 47

By using hazard maps

Question 48

What are the 4 precursors to quakes?

Answer 48

1. The pattern and frequency of earthquakes (based on foreshocks and micro earthquake) 2. Land level changes 3. Seismic Gaps 4. Physical and chemical changes

Question 49

How much times does the current earthquake warning systems give us?

Answer 49

15-30 seconds | - all forecasts have to be scientifically received before they are forecasted