Earthquakes 4

Question 1

list 5 hazards related to earthquakes

Answer 1

1. Ground shaking
   -> structural damage to buildings
2. Liquefaction
3. Fires
4. Tsunami
5. Landslides / subsidence

Question 2

which direction of shaking damages buildings the most?

Answer 2

horizontal shaking
-> buildings are designed to take vertical load

Question 3

Why are ground conditions important?

Answer 3

the ground filters our the frequencies of EQ

• affects duration of shaking
• influences stability of structures

Question 4

What ground material is more problematic?

Answer 4

soft and wet ground

Question 5

intensity of ground motion in bedrock

Answer 5

less intense

Question 6

intensity of ground motion in well-compacted sediment

Answer 6

less intense

Question 7

intensity of ground motion in water saturated sediment

Answer 7

more intense!

Question 8

What kinds of buildings leads to more shaking?

Answer 8

• tall
• poorly designed
• less cohesive or flexible material

Question 9

What are some good material for building design and why?

Answer 9

wood
steel
reinforced concrete

-> flexible, strong

Question 10

What are some bad material for building design and why?

Answer 10

brick
stone
concrete (without steel)

-> brittle failure, poor shear strength

Question 11

What is an example of retrofitting?

Answer 11

bad material can sometimes be retrofit

ex/ putting in a steel frame

Question 12

soft first storey

Answer 12

weight on weak supports
shear failure = collapse

Question 13

What is resonance?

Answer 13

• all objects vibrate at characteristic frequencies
• controlled by size, composition, structure

Question 14

a key design factor to control

Answer 14

avoid critical resonance at earthquake frequencies

Question 15

Resonance disasters happen when

Answer 15

the forcing vibrations are tuned to one of the primary resonance frequencies of the structure

Question 16

Short buildings (stiff) tend to resonate at ____

Answer 16

high frequencies
- fast vibrations with low amplitudes

Question 17

Tall buildings (flexible) tend to resonate at ____

Answer 17

low frequencies
- slow vibrations with big amplitudes

Question 18

Some examples of tuning buildings to avoid resonance

Answer 18

• mass dampers
  (pendulum in building that counters sway)
• seismic base isolation system
  (decouple building from its base)

Question 19

What is liquefaction?

Answer 19

unconsolidated materials liquefy in soft wet sediments

• loses cohesion and flows
• dense objects can sink
• sand volcanoes form

Question 20

Sand volcanoes

Answer 20

cones of sediment brought to surface with water as it flows

Question 21

What happens to friction force and water pressure before and after liquefaction?

Answer 21

Before: strong sediment
- high friction force
- low water pressure in pore space

After: grains vibrate
- friction forces decrease
- increase water pressure in pore space push grains apart

Question 22

Liquefaction: why do objects like cars get stuck in the ground when shaking stops?

Answer 22

1. water pressure drops
2. grains stop vibrating
   = ground becomes firm again

Question 23

Liquefaction most hazardous in

Answer 23

Richmond, Delta

«refer to map on slides»

Question 24

Describe our secondary system of fire hydrants

Answer 24

connected to seawater and generators

Question 25

How do fires occur as a result of EQ?

Answer 25

buildings collapse and burn
water, electric, gas lines break
roads inaccessible

Question 26

EQ generated tsunami often occur at

Answer 26

convergent margins

-> not usually part of divergent or transform unless caused by landslide

Question 27

Landslides happen when

Answer 27

unstable ground fail when shook