Which type of seismic wave is recorded first on a seismograph?
- A.Secondary waves
- B.Primary waves
- C.Surface waves
- D.Love waves
Correct answer
Explanation
The correct answer is B, Primary waves. P waves are longitudinal, moving the particles of the medium back and forth along the direction of travel by compression and rarefaction. They are the fastest of all seismic waves and therefore always reach a station first and appear first on the seismogram, which is exactly why they are named primary.
Option A, secondary or S waves, are transverse and travel more slowly, so they arrive after the P waves; the time gap between the two arrivals is used to calculate the distance to the epicentre. Options C and D, surface waves, which include Love and Rayleigh waves, are generated when body waves reach the surface; they are the slowest of all and arrive last, yet they cause the heaviest damage because of their long rolling motion along the ground. The order of arrival to remember is P, then S, then surface waves.
Read the full article: Earthquakes and Volcanoes: Waves, Belts and Types
Practice Questions
View allWhich of the following seismic waves cannot travel through liquids?
- A.P waves
- B.S waves
- C.Love waves
- D.Rayleigh waves
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Secondary or S waves are transverse, so the particles of the medium move at right angles to the direction of travel.
Read the full explanation →The point inside the earth where an earthquake originates is known as the
- A.Epicentre
- B.Fault line
- C.Focus
- D.Shadow zone
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The focus, also called the hypocentre, is the point below the surface at which the strained rock ruptures and releases its stored elastic energy as seismic waves.
Read the full explanation →The Richter scale is used to measure which of the following?
- A.Intensity of damage caused by an earthquake
- B.Magnitude of energy released by an earthquake
- C.Depth of the focus of an earthquake
- D.Height of tsunami waves
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The Richter scale, devised by Charles F. Richter in 1935, expresses the energy released at the source of the shock.
Read the full explanation →Barren Island, the only active volcano in India, is located in which of the following?
- A.Lakshadweep
- B.Gulf of Kutch
- C.Andaman and Nicobar Islands
- D.Sundarbans delta
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Barren Island lies in the Andaman Sea, to the east of the main Andaman group, and is the only active volcano in India and in South Asia.
Read the full explanation →The instrument used to record the waves produced by an earthquake is called a
- A.Seismograph
- B.Barograph
- C.Hygrometer
- D.Altimeter
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A seismograph carries a mass that stays nearly still while the ground and the frame move under it, and the relative motion is traced as a wavy line.
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