18- Earthquake Engineerign

Question 1

Empirical strategies

Answer 1

Uses probability analysis- likelyhood of earthquake at given intensity happening in location, based on frequency, magnitude and spatial distribution of historical earthquakes
Establishing construction standards based on susceptibility and risk
Evaluating risk for insurance purposes(higher rates in high-risk areas)
Risk based site selection (eg for nuclear plants)

Question 2

Recurrence rates

Answer 2

Prediction of an earthquake hazard level based on the probability that an earthquake of a given magnitude will happen at some location over a given period of time

Assume a uniform distribution of earthquakes over time along same plate boundary, however in some areas earthquakes are clustered in time, in these areas plates may be sliding past each other or may be stuck and storing strain to be released as larger magnitude quake

Question 3

Seismic gaps

Answer 3

Section of a fault that has produced earthquakes in the past but is now quiet. Strain is now building in each seismic gap, raising the probability a large quake will soon occur

Question 4

Early warnings of earthquake

Answer 4

-foreshocks
-change in land shape near fault
-fluctuations in groundwater levels
-fluctuations in magnetic field and electrical resistance of ground
-radon gas

Question 5

Earthquake hazard

Answer 5

Involves:
Likelihood and frequency of earthquakes
Capacity to cause damage

Question 6

Earthquake risk

Answer 6

Includes:
Consideration of the consequences of the hazard
=hazard x consquences

Question 7

Ground amplification

Answer 7

Unconsolidated rock and soil sediments have a tendency to increase the amplitude and spduration of seismic waves, increasing the potential for damage

Question 8

Structural damage

Answer 8

Buildings have fundamental frequencies depending on height, design and construction materials
- high frequency has greater affect on shorter buildings, and vice versa

Question 9

Liquefaction

Answer 9

Conversion of stable, cohesional soil to fluid mass, causing damage to structures

In areas where loose soil is saturated with water, causes water pressure to increase, leading to reduction in strength and stiffness of soil

Question 10

Liquefaction mitigation/prevention

Answer 10

Mostly focus on “densifying” the soil
Dynamic compaction : heavy weight dropped on soil to compact loose sediments.
Compaction grouting: inject water/sand/cement mix into ground to cause compaction of loose soil
Vibroflotation: inserting a vibrating probe into ground to cause compaction of sediment