Plate Tectonics & Earthquakes Cheat Sheet

A printable reference covering plate boundaries, seismic waves, earthquake magnitude, epicenters, and earthquake safety for grades 7-9.

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Plate tectonics explains how Earth’s lithosphere is broken into moving plates that shape continents, oceans, mountains, volcanoes, and earthquake zones. This cheat sheet helps students connect plate motion to the landforms and hazards they see on maps. It is useful for reviewing boundary types, earthquake measurements, and how scientists locate an epicenter. Students in grades 7-9 need these ideas to interpret diagrams, data tables, and seismic maps clearly. The most important concepts are that plates move because of forces in Earth’s interior and interact at convergent, divergent, and transform boundaries. Earthquakes happen when stress builds along faults and is suddenly released as seismic waves. Key formulas include speed = distance / time, distance = speed x time, and S-P time = S-wave arrival time - P-wave arrival time. Earthquake magnitude is logarithmic, so each increase of 1 magnitude means 10 times greater wave amplitude and about 32 times more energy released.

Key Facts

The lithosphere is divided into tectonic plates that move slowly over the softer asthenosphere at rates of a few centimeters per year.
Plate speed can be calculated with speed = distance / time, using units such as cm/year or km/million years.
At divergent boundaries, plates move apart, magma rises, and new crust forms at mid-ocean ridges or rift valleys.
At convergent boundaries, plates move toward each other, and the denser plate may subduct beneath the less dense plate.
At transform boundaries, plates slide past each other horizontally, often producing shallow earthquakes along faults.
S-P time = S-wave arrival time - P-wave arrival time, and a larger S-P time means the earthquake epicenter is farther from the seismograph.
Seismic wave distance can be estimated with distance = wave speed x travel time when the wave speed and travel time are known.
A magnitude increase of 1 means 10 times greater seismic wave amplitude and about 32 times more energy released.

Vocabulary

Tectonic plate: A large, rigid piece of Earth’s lithosphere that moves slowly over the asthenosphere.
Fault: A break in Earth’s crust where rocks move past each other because of stress.
Epicenter: The point on Earth’s surface directly above the focus of an earthquake.
Focus: The underground point where an earthquake begins and energy is first released.
Seismic wave: A wave of energy that travels through Earth after an earthquake or explosion.
Subduction: The process in which one tectonic plate sinks beneath another plate at a convergent boundary.

Common Mistakes to Avoid

Confusing the focus with the epicenter is wrong because the focus is underground while the epicenter is on the surface directly above it.
Thinking all plate boundaries create the same features is wrong because divergent, convergent, and transform boundaries produce different landforms and earthquake patterns.
Using only one seismic station to locate an epicenter is wrong because scientists need data from at least three stations for triangulation.
Treating earthquake magnitude as a normal counting scale is wrong because the magnitude scale is logarithmic, so each whole number increase is much larger.
Assuming P-waves and S-waves travel at the same speed is wrong because P-waves travel faster and arrive at seismographs first.

Practice Questions

1 A tectonic plate moves 50 cm in 10 years. What is its average speed in cm/year?
2 A P-wave arrives at 10:04:20 and an S-wave arrives at 10:06:50. What is the S-P time in minutes and seconds?
3 An earthquake has magnitude 6 and another has magnitude 4. How many times greater is the wave amplitude of the magnitude 6 earthquake?
4 Explain why deep earthquakes are common near subduction zones but not at mid-ocean ridges.