Comparing earthquakes
Pick two earthquakes by their magnitude, from a small 3 to a great 8, and see how many times more the ground shakes and how many times more energy the bigger one lets out. Find why the 7.8 Gorkha earthquake of 2015 was so much worse than a 5.
Core concept
Magnitude is a logarithmic scale: each step of 1 means 10 times the shaking on a seismograph and about 32 times (10^1.5) the energy
Topic: Our planet and sky
Nepal sits where the Indian plate pushes under the Eurasian plate, so earthquakes are common. A seismograph draws the shaking of the ground as a wavy line, and the magnitude comes from how tall the waves are. The scale is logarithmic: each step of 1 means the waves are 10 times taller, so a magnitude 7 shakes 10 × 10 = 100 times more than a 5. The energy: What is needed to make things move, heat up, light up or grow. All key words grows even faster: about 10^1.5 ≈ 32 times for each step. That is why a magnitude 8 lets out about 32 times the energy of a 7, and about a thousand times that of a 6. Using powers of 10 lets one short scale cover quakes from the tiny to the huge.
What you will learn
- Explain why the magnitude scale is logarithmic.
- Find how many times more shaking and energy one earthquake has than another.
- Link the size of an earthquake to the damage it can do and to staying safe.
Before you start
- Know powers of 10 (10², 10³) and the laws of indices.
Materials
- A news report on the 2015 Gorkha earthquake
Equipment
- None
Procedure
- Record a magnitude 7 against a magnitude 5.
- Compare a 6 with a 5, then an 8 with a 7, and record each.
- Swap them round: a 5 against a 7, and record.
How this simulation is simplified
- Moment magnitude: the shaking (wave height) grows 10 times and the energy 10^1.5 ≈ 31.6 times for each step of 1.