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Lessons / Restless Earth

Restless Earth · 5 min · 4 steps

Why Taiwan has earthquakes

Plays here

Goal. Explain why earthquakes follow plate boundaries, using this month's real earthquakes.

Steps

  1. Predict

    Before you look: are earthquakes spread evenly over the Earth?

    • Yes, they can happen anywhere equally
    • No, most of them follow narrow lines
    • Most happen in the middle of the oceans
    Show the answer

    No, most of them follow narrow lines. Most of them follow narrow lines.

    Each earthquake dot is magnitude 4.5 or more from the past week. The plate edges glow brighter where there were more earthquakes in the last 30 days. Most earthquakes sit on these narrow lines.

  2. Taiwan sits where the Philippine Sea Plate pushes into Asia at about 8 cm a year, and the whole island is being squeezed. Tap the boundary line across western Taiwan to open its card.

  3. Most of Taiwan's strong earthquakes happen near the east coast and offshore, around Hualien, where the Philippine Sea Plate is pushed against the island. Faults in the west break too: the Chi-Chi earthquake of 1999 killed about 2,400 people.

  4. The same collision squeezes Taiwan upwards. The Central Mountain Range is still rising, and Yushan, the highest peak, reaches 3,952 m.

The common mistake

Myth

Plates float on a sea of lava.

Fact. The mantle under the plates is solid rock. It is hot enough to creep very slowly, a few centimetres a year, like extremely stiff putty. Molten rock exists only in small pockets, such as under volcanoes.

Check yourself

Question 1

Where do most of Taiwan's large earthquakes happen?

  • Along the west coast
  • Near and off the east coast
  • Evenly over the island
Show the answer

Near and off the east coast. Most strong earthquakes happen near and off the east coast, where the Philippine Sea Plate meets Taiwan. The western faults have fewer earthquakes, but some have been very damaging.

Question 2

About how fast does the Philippine Sea Plate move towards Taiwan?

  • About 8 mm a year
  • About 8 cm a year
  • About 8 m a year
Show the answer

About 8 cm a year. About 8 cm a year, roughly twice as fast as fingernails grow. Over a million years that adds up to 80 km.

Question 3

Why do the boundary lines change brightness from week to week?

  • The plates change shape every week
  • They are coloured by the number of recent earthquakes nearby
  • They show the depth of the sea
Show the answer

They are coloured by the number of recent earthquakes nearby. Each segment is coloured by the earthquakes of magnitude 4.5 or more within 150 km in the chosen period. The plates themselves barely change in a human lifetime.

Words in this lesson

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Curriculum

Taiwan 12-year curriculum (108 課綱), natural science
Ia-Ⅳ-2 · Ia-Ⅳ-3 · Ia-Ⅳ-4 · EIa-Vc-4 · EMd-Vc-4
US Next Generation Science Standards
MS-ESS2-3 · MS-ESS3-2
England national curriculum
KS3 Geography: geological timescales and plate tectonics