Updated 2026-08-23intermediate

TOEFL Reading Practice #018 — Two Waves, One Earthquake

Free TOEFL Reading practice: Two Waves, One Earthquake. 11 questions with a full passage and answer key.

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How to use this practice: Read the passage once without a dictionary, then answer the questions on your own. Tap “Answer” under each question to reveal just the correct letter — no explanations, so you can keep testing yourself.
1

Passage

Read the full passage. Bracketed letters like [A] mark the four positions for the insert-text question.

Two Waves, One Earthquake

¶1 An earthquake releases a burst of energy, and that energy does not travel through the Earth as a single, uniform vibration. Seismologists sort the resulting vibrations into two main types, called primary waves and secondary waves. The two types differ in how fast they move and, more importantly, in what kind of material they can pass through. That second difference might sound small. In fact, it became the key that let scientists learn what lies thousands of kilometers beneath their feet, without ever digging down to see it.

¶2 Primary waves, often called compressional waves, are the first to arrive at any measuring station after an earthquake begins. They move by squeezing and stretching the material they pass through. They push particles forward and then pull them back in the same direction the wave itself is traveling. This push-pull motion lets P-waves travel faster than any other seismic wave, often more than twice as fast as the second type. It also lets them pass through almost anything. Solid rock, liquid rock, water, and even air can all carry a P-wave. This is because the wave only needs to compress and expand the material, not bend it sideways.

¶3 Secondary waves, or S-waves, arrive at a station only after the primary waves have already passed. [A] Rather than pushing particles forward, an S-wave shakes them from side to side, at a right angle to the direction the wave is traveling. [B] That side-to-side motion makes S-waves slower than P-waves, and it also makes them far more selective about which materials they can pass through. [C] Solid rock resists being pushed sideways and springs back into its original shape, and that resistance is exactly what allows an S-wave to keep moving forward. [D] A liquid offers no such resistance. It simply flows out of the way instead of springing back, so an S-wave disappears completely once it reaches a liquid layer.

¶4 This contrast became the key to studying a place no one could ever visit. In 1906, the seismologist Richard Oldham noticed something strange. S-waves from large earthquakes never reached measuring stations on the far side of the planet, even though P-waves from the same earthquakes did. He reasoned that a wide band deep inside the Earth was blocking S-waves while still letting P-waves through, a region now called the shadow zone. Only a liquid can stop an S-wave completely. Oldham concluded that the outer core, the layer beneath Earth's rocky mantle, had to be liquid rather than solid rock. No one had dug a single meter to reach that conclusion.

  • seismologist: a scientist who studies earthquakes and the seismic waves they produce
  • shadow zone: an area on Earth's surface where a specific type of seismic wave cannot be detected
2

Questions

11 questions — every TOEFL Reading question type, in test order.

Q1 · Vocabulary
The word squeezing in paragraph 2 ("squeezing and stretching the material they pass through") is closest in meaning to
  1. A. compressing
  2. B. breaking
  3. C. freezing
  4. D. lifting
Answer
Correct: A
Q2 · Reference
The word It in paragraph 2 ("It also lets them pass through almost anything.") refers to
  1. A. the second type
  2. B. a measuring station
  3. C. an earthquake
  4. D. this push-pull motion
Answer
Correct: D
Q3 · Essential Term
Based on the information in the passage, the term compressional wave (as used in "often called compressional waves") can best be explained as
  1. A. a general term used for any vibration caused by a natural disaster
  2. B. another name for a primary wave, which pushes and pulls material in the same direction it is traveling
  3. C. the result of a primary wave passing through solid rock instead of liquid
  4. D. another name for a secondary wave, which moves material from side to side
Answer
Correct: B
Q4 · Factual Information
According to paragraph 2, why can P-waves travel through both solid and liquid material?
  1. A. because the wave only needs to compress and expand the material it passes through, not bend it sideways
  2. B. because liquids resist being pushed sideways more strongly than solid rock does
  3. C. because P-waves travel more slowly than S-waves through solid rock
  4. D. because P-waves were discovered before S-waves were identified
Answer
Correct: A
Q5 · Negative Fact
According to paragraph 3, all of the following are true of S-waves EXCEPT
  1. A. They arrive at a measuring station only after P-waves have already passed.
  2. B. They move particles side to side, at a right angle to the direction they are traveling.
  3. C. They can pass through liquid material without losing any speed.
  4. D. They travel more slowly than P-waves do.
Answer
Correct: C
Q6 · Sentence Simplification
Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 4? Incorrect choices change the meaning in important ways or leave out essential information.

Highlighted: "He reasoned that a wide band deep inside the Earth was blocking S-waves while still letting P-waves through, a region now called the shadow zone."
  1. A. He discovered that a region deep inside the Earth blocked seismic waves, without specifying which type could still pass through.
  2. B. He concluded that a region deep inside the Earth blocked S-waves but allowed P-waves to pass through, and he named that region the shadow zone.
  3. C. He concluded that the region blocked P-waves while allowing S-waves to pass through freely.
  4. D. He argued that a shadow zone forms only after the very largest earthquakes on record.
Answer
Correct: B
Q7 · Inference
Based on the information in paragraphs 2 and 3, what can be inferred about why P-waves are always the first waves detected after an earthquake, no matter what lies between the earthquake and the measuring station?
  1. A. Because P-waves travel more slowly through liquid than through solid rock, they take longer to reach distant measuring stations.
  2. B. Because S-waves are detected first only in areas where the ground is especially soft.
  3. C. Because P-waves and S-waves travel at exactly the same speed once they enter solid rock.
  4. D. Because P-waves can travel through any material and move faster than S-waves, they will always reach a measuring station before S-waves do, no matter what lies in their path.
Answer
Correct: D
Q8 · Rhetorical Purpose
The author mentions that "Solid rock, liquid rock, water, and even air can all carry a P-wave" in order to
  1. A. list the different layers that make up the interior of the Earth
  2. B. explain why S-waves disappear once they reach a liquid layer
  3. C. illustrate how many different kinds of material a P-wave's push-pull motion allows it to travel through
  4. D. compare the speed of P-waves to the speed of sound traveling through open air
Answer
Correct: C
Q9 · Paragraph Relation
How does paragraph 4 relate to paragraphs 2 and 3?
  1. A. It contradicts the description of P-waves given in paragraph 2.
  2. B. It shows how the distinction between P-waves and S-waves described in paragraphs 2 and 3 made it possible to determine what material exists deep inside the Earth.
  3. C. It introduces a third type of seismic wave that paragraphs 2 and 3 do not mention.
  4. D. It argues that the difference between P-waves and S-waves described earlier turned out not to matter.
Answer
Correct: B
Q10 · Insert Text
Look at the four squares [■] in paragraph 3 that indicate where the following sentence could be added.

However, that selectivity depends entirely on one property of the material the wave is passing through.

Where would the sentence best fit?
  1. A. Square A
  2. B. Square B
  3. C. Square C
  4. D. Square D
Answer
Correct: C
Q11 · Schematic Table 3 pts
Directions: Complete the table by matching the phrases below to the category they belong to. Two of the answer choices will NOT be used. This question is worth 3 points.

P-waves S-waves

  1. A. Push and pull particles in the same direction the wave is traveling
  2. B. Travel faster than the other type and are always the first waves to arrive at a measuring station
  3. C. Can travel through solids, liquids, and gases
  4. D. Shake particles from side to side, at a right angle to the wave's direction of travel
  5. E. Cannot travel through liquid, because liquid offers no resistance to being pushed sideways
  6. F. Slow down and disappear once they reach Earth's solid inner core
  7. G. Were first detected using equipment placed on the ocean floor in 1906
Answer
Correct: P-waves: A, B, C · S-waves: D, E