Recent Trends in Physics
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Earthquakes
- Earthquake is a form of energy of wave motion which originates in a limited region and spread out in all directions from the source of disturbance.
- The originated point of earthquake is called focus or hypocenter and time at which it occurs is called origin time. And point on surface vertically upward from focus is called epicenter.
- Hypo central path: The distance between the focus and earth’s surface directly above the focus.
- Foreshocks: A large shock is expected to be proceed by smaller shocks.
- Aftershock: The smaller shock after main shock.
- Earthquake swarms: A long series of small shocks with no main event is frequently occurred in certain location.
- The foreshock and aftershock are expected to occur in the epicenter area, this cause to more damage in epicenter surface than other area.
- The outermost shell of the earth is rigid and behaves as a brittle material. The top portion is divided into six large and many small thin layers called lithospheric plates.
- And below this is asthenosphere (composed of viscous material), the convectional process is responsible for motion of these plate.
Artificial Earthquake:
- The earthquake generated as a result of disturbance caused by artificial process like bomb explosion, blasting of the road works, geophysical explorations, test of explosive materials, etc.
Natural Earthquake:
Natural disturbance caused inside the earth are the
main cause of natural earthquake.
- Volcanic activity or induced effect from geodynamic process are responsible for volcanic earthquake.
- Earthquake caused by the release of elastic strain energy are called tectonic earthquake.
In terms of distance between the epicenter and
the recording station.
- If the epicentral distance is less than 1000 km from the station, such earthquake is called local earthquake.
- Those having epicentral distance between 1000 and 2000 km are regional earthquake.
- And those far from 2000 km are called tele seismic earthquake.
Earthquake Magnitude:
- Earthquake magnitude is the measurement of the amount of energy released during an earthquake.
- The elastic potential energy is transformed into kinetic energy in an earthquake, which is propagated into all direction from the focus in the form of seismic waves.
- In 1935, Charles F. Richter developed the first quantitative measure of relative earthquake size, the local magnitude (𝑀𝐿 ), now known as Richter magnitude.
