How do we measure Earthquake?
There are two ways to measure an Earthquake, by magnitude and
intensity. Magnitude is measured using the Richter scale, the founder of the
Richter scale is Charles F. Richter. The Richter scale measures the amplitude
of the largest seismic wave recorded on a particular seismograph located 100Km
away from the Epicenter. The Richter scale has no limit on how high the
Intensity is measured using the modified Mercalli scale. The
scale shows the received damage from an Earthquake. These limitation are biased
they rely on the action of buildings and the suggestions of the observers. To
make the scale more objective, the US Geological Survey used measurements of the
ground movement to measure the earthquakes
Some earthquakes can not be felt because it's too far underground or because the earthquake is too light.
This includes Intensity 1, 2 and 3 they may be felt but certainly do not do any damage.
This also goes to magnitude 1,2 and 3 magnitudes 5 and over are reported globally and magnitudes 4 and under are reported nationally on the news they also report the people that had died by the earthquake and the people that are missing form there families usually the report is not excated but is close enough to be excated.
References : http://tremor.nmt.edu/faq/how.html