Seismograph
Also called: Seismometer · Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"
Meaning
A seismograph is an instrument that records seismic waves when they reach the surface. Its record shows three parts in order. P-waves arrive first, S-waves arrive after a short delay, and surface waves arrive last. The gap between the P-wave and S-wave arrival times tells how far away the earthquake was. With records from three stations, the epicentre can be pinpointed. This is called triangulation. Seismograph records from around the world also show how waves behave deep inside the earth.
Example
India's National Center for Seismology, under the Ministry of Earth Sciences, uses records from its network of seismographs to report the magnitude and location of earthquakes, including Himalayan tremors.
Don't confuse with
- Richter scale / Mercalli scale: these are ways of rating an earthquake, by magnitude or by damage. The seismograph is the instrument that records the waves.