FAQs: What is an earthquake and other key questions answered

In less than three months, Delhi and its adjoining national capital region (NCR) felt a second earthquake that lasted a few seconds and forced residents to leave their homes on Tuesday evening. The National Centre for Seismology informed via a tweet that the tremor was measured with a magnitude of 6.6 on the Richter Scale with epicentre in Afghanistan's Fayzabad. Earlier, Delhi-NCR had felt tremors on January 25. The 5.9-magnitude earthquake jolted Western Nepal on January 24 (Tuesday) afternoon with tremors also being felt in parts of Delhi, the national capital region and Jaipur.

Here are a few key questions related to earthquakes:

Why do earthquakes happen?

Earthquakes result when rock beneath the ground suddenly breaks and rapidly moves along a fault, releasing sudden energy in the form of seismic waves that shake the ground. During and after an earthquake, the plates continue to move until they are stuck again. The place right above the underground spot where the rock breaks first is called the epicentre of the earthquake.

What are aftershocks?

They are a sequence of earthquakes that happen after a larger one on a fault.

How are earthquakes measured?

For starters, most scales are based o the amplitude of seismic waves recorded on seismometers. The most widely used method is the Richter scale, developed by Charles F, Richter in 1934.