Seismograph is used to measure:

The correct answer is Earthquakes.Key Points

• Plate Tectonics:
  • Seismographs can provide indirect evidence supporting the theory of plate tectonics.
  • By recording earthquake patterns and magnitudes around the world, they help illustrate the world’s tectonic plate boundaries where earthquakes are common.
• Epicenter and Focus of Earthquakes:
  • Seismographs play a crucial role in locating the epicenter (geographical location directly above the focus on the surface) and the focus (actual location within the earth where the earthquake originates) of an earthquake.
  • Data collected from minimum three seismograph stations is used to triangulate the epicenter of an earthquake.
• Seismic Wave Speed Variations:
  • P-waves (primary waves) and S-waves (secondary waves) recorded by seismographs travel at different speeds and through different parts of the Earth's interior.
  • Based on their arrival times at seismograph stations, we can infer properties of the Earth's interior, such as the presence of a molten outer core (which S-waves cannot travel through).
• Seismicities:
  • Analysis of seismographs can help identify areas known as seismicities - geographical zones with a high frequency of earthquakes.
  • Historical data from seismographs can therefore be used to predict regions where future earthquakes may occur.
• Earth's Interior Structure:
  • Seismograph readings help scientists understand the Earth's interior structure better.
  • For instance, changes in seismic wave velocity indicate interfaces between different layers of the Earth's interior, such as the crust, mantle, and core.
• Human-Induced Seismic Activity:
  • Seismographs not only capture natural seismic activity, but also man-made seismic events such as those resulting from mining, reservoir-induced seismicity, nuclear tests, and construction work.

Additional InformationEarthquake Waves:

• Earthquake waves are vibrations in the Earth's crust caused by seismic events like earthquakes or volcanic activity.
• Two main types: body waves and surface waves.

Body Waves:

• Generated at the earthquake's focus and travel in all directions through the Earth's interior.
• Interact with surface rocks, generating surface waves.
• Changes in velocity and direction due to material density differences.
• Two types: P-waves (primary waves) and S-waves (secondary waves).

P-Waves (Primary Waves): 

• Fastest seismic waves, reaching the surface first.
• Similar to sound waves, they travel through gaseous, liquid, and solid materials.
• Provide important information about the Earth's interior structure.

S-Waves (Secondary Waves):

• Arrive at the surface after P-waves.
• Can only travel through solid materials, not liquids or gases.
• Vital for understanding the Earth's interior composition and structure.

Surface Waves:

• ​Generated by interaction between body waves and surface rocks.
• Slowest seismic waves, causing significant damage.
• Displace rocks and contribute to structural collapses.