Earthquakes & Volcanoes — Drills · Grade 9 Science

Chapter: Earth’s Interior & Plate Tectonics

What these drills covers

By the end of Earthquakes & Volcanoes you should be able to:

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

Vocabulary used: focus (hypocenter), epicenter, seismic wave, hot spot.

Problem 1

The point underground where an earthquake originates is the
  1. epicentre
  2. focus
  3. fault line
  4. shadow zone
Answer and explanation

focus

The focus is the origin at depth; the epicentre is the point on the surface directly above it.

Problem 2

Which wave type arrives first at a seismic station?
  1. P-waves
  2. S-waves
  3. Surface waves
  4. They arrive together
Answer and explanation

P-waves

P-waves are fastest, which is why they are called primary.

Problem 3

How many seismic stations are needed at minimum to locate an epicentre by triangulation?
Answer and explanation

3

Each station gives a distance circle; three circles intersect at one point.

Problem 4

A larger gap between P-wave and S-wave arrival times means the station is
  1. closer to the epicentre
  2. further from the epicentre
  3. at the epicentre
  4. on a different plate
Answer and explanation

further from the epicentre

The faster P-wave pulls further ahead over a longer path.

Problem 5

Explosive volcanoes are most associated with
  1. mid-ocean ridges
  2. subduction zones
  3. transform faults
  4. stable interiors
Answer and explanation

subduction zones

Water carried down with the subducting plate produces sticky, gas-rich magma that erupts violently.

Problem 6

Magnitude scales are logarithmic, so a magnitude 6 releases roughly how much more energy than a magnitude 5?
  1. Twice
  2. Ten times
  3. About thirty times
  4. The same
Answer and explanation

About thirty times

Each whole step is about a thirtyfold increase in energy released, though amplitude increases tenfold.

Problem 7

Explain how the difference in arrival times between P- and S-waves gives the distance to an earthquake.
Answer and explanation

P-waves travel faster than S-waves, so the gap between their arrivals grows with distance travelled. A station measures that gap and reads the corresponding distance from a travel-time graph built from many past earthquakes. The result is a distance, not a direction, which is why readings from at least three stations are combined to fix the epicentre.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Two earthquakes of the same magnitude cause very different damage. Give two reasons.
Answer and explanation

Depth matters: a shallow focus delivers more energy to the surface than a deep one of the same magnitude. So does what is above — population density, building construction and ground conditions, since loose or saturated sediment amplifies shaking while solid bedrock does not. Magnitude measures the energy released, not the harm done.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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