Lecture 5 - Assessing earthquake hazards using geomorphology

Question 1

What is the difference between earthquake hazard and risk?

Answer 1

• Hazard: anticipated ground motion at a site

- Risk: possible damage of losses to society

Question 2

What is ground motion measured by?

Answer 2

Peak Ground Acceleration (PGA)

- units of g

Question 3

Why are earthquakes not predictable?

Answer 3

• We don’t know how much energy is accumulated because we don’t know how much energy is released
• Stress does not accumulate linearly in crust
• No definitive precursors of large earthquakes

Question 4

What is Probabilistic Seismic Hazard Analysis (PHSA)?

Answer 4

• A mathematical approach to calculate seismic hazard using models for the location and size of potential and future earthquakes.
• Based on worse case scenario

Question 5

How do we calculate PHSA?

Answer 5

Rate of exceeding ground motions

1. Source model: m, magnitude; L, location; r, rate at which earthquakes of different m are expected to occur
2. Attenuation relations: PGA, ground motion; D, distance

Question 6

What are the five steps to PHSA?

Answer 6

Step 1: Identify the earthquake source
Step 2: Identify the distribution of earthquakes magnitude
Step 3: Characterized the distribution of source-to-size distances for each source
Step 4: Predict PGA
Step 5: Combine information to produce a hazard curve

Question 7

How can tectonic geomorphology help predict earthquakes?

Answer 7

• We can map faults
• We can reconstruct the distribution of earthquakes in the past
• We can reconstruct the effects of fossil earthquakes away from faults
• In summary we can provide the data for the model covering the past