Earthquake Evidence & Hazard Risk — Practice · Grade 9 Science

Chapter: Earth’s Interior & Plate Tectonics

What this practice covers

By the end of Earthquake Evidence & Hazard Risk you should be able to:

8 questions, multiple choice and written answer, each with a worked explanation.

Vocabulary used: epicenter, intensity, vulnerability.

Problem 1

A larger S–P arrival gap usually indicates a station is…
  1. closer to the source
  2. farther from the source
  3. directly above every source
  4. measuring only sound
Answer and explanation

farther from the source

P and S arrivals separate more as their paths lengthen.

Problem 2

Why can one station’s distance estimate not give a unique epicenter?
Answer and explanation

Many locations can lie at the same distance from one station.

Problem 3

Name a way to reduce earthquake risk without preventing earthquakes.
Answer and explanation

Strengthen buildings or infrastructure and improve preparedness; these reduce vulnerability.

Problem 4

Two towns have similar hazard; one has weak crowded buildings and the other reinforced sparse buildings. Compare risk. Explain the reasoning in your own words.
Answer and explanation

The first town plausibly has higher risk; a numerical estimate needs more detailed evidence.

Hazard is comparable, but exposure and vulnerability differ.

The crowded weak buildings increase the potential consequences.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 5

How could a town reduce earthquake risk without changing plate motion? Show the reasoning, not just the conclusion.
Hints

Separate event likelihood from likely consequences.

Answer and explanation

Improve building resilience, emergency planning and infrastructure vulnerability; these reduce consequences.

Problem 6

Three stations give distances to a quake. Why intersect distance circles?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Each distance constrains possible locations; their intersection estimates a common epicenter under the model.

Problem 7

A probability forecast differs from warning about an event already detectedA probability forecast differs from warning about an event already detectedDefined event • region • time interval • uncertaintyA 30-year probability is not a date on a calendar.A detected event can trigger warning before stronger shaking arrives.Rupture detectedLater shaking arrival
Original conceptual distinction between defined-interval probabilities and detected-event warning. The diagram supplies no actual hazard probability, geographic warning range or guaranteed seconds of lead time. Use official local information for operational safety decisions.
Interpret the supplied visual model. Why does early warning not demonstrate an ability to name the exact earthquake date before rupture?
Answer and explanation

Warning follows detection of an event already underway. Exact-date prediction before rupture is a different and unsupported claim in this model.

Read the chronological arrows as detection followed by later shaking at a selected distant place. This is not a guaranteed advance prediction.

Warning follows detection of an event already underway. Exact-date prediction before rupture is a different and unsupported claim in this model.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 8

One station gives a modeled epicenter distance of 120 km. A proposed building retrofit lowers susceptibility to shaking. Explain what the distance constrains and which risk component the retrofit changes.
Answer and explanation

The distance defines an approximate set of possible source locations around the station, not a unique direction. The retrofit changes vulnerability, while local physical hazard is not necessarily changed. Additional stations and verified building-performance evidence are needed.

The distance defines an approximate set of possible source locations around the station, not a unique direction. The retrofit changes vulnerability, while local physical hazard is not necessarily changed. Additional stations and verified building-performance evidence are needed.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Browse all courses