Tag: our changing earth

Duration is the vibration of earthquakes which can be felt by human beings that last from a few seconds to several minutes. Generally, the greater the intensity of the shocks, the longer they last. The average duration of shocks of sufficient intensity to produce much damage is perhaps from one to two minutes.

There are annually 8,000 - 10,000 earthquakes in the world, which comes to about an earthquake every hour. And there are many more that go undetected because there are no stations to record them over the oceans covering a very large surface of our earth. This is known as the Earthquake Frequency

The epicenter is the point on the earth's surface vertically above the focus of the earthquake. Maximum damage is caused at the epicenter.

Isoseismic Line is the line connecting all points on the surface of the earth where the intensity is the same. These lines show great irregularity in their form. 

During an earthquake, surface waves are the seismic waves that cause the most damage. Unlike other seismic waves that move deep inside the Earth, surface waves move along just under the surface of the Earth like waves in water. Surface waves are the slowest seismic waves and are the final waves to hit an area after an earthquake. First, P-waves move through compression through the deep layers of the Earth. They result in minimal damage. The second group of waves is S-waves. They move up and down starting deeper in the Earth. Stronger S-waves do some damage when they reach the surface. Surface waves move in last. Their slow roll just under the surface provides the greatest risk for damage to man-made structures and changes to natural landforms

Earthquake is a movement of tremor of the earth's crust. It originated naturally and below the surface. An earthquake produces infrasound before the mainshock wave begins. Infrasound is low-frequency sound less than 20hz. It can travel hundreds of km through the earth's surface. So by detecting this sound, we can predict an earthquake.