There are two instruments, which are basically the same thing. There is the seismograph , and a more specific tool measures the waves on what is called the Richter scale. Earthquakes are given a number from one to ten, ten being the strongest. The strongest earthquake that their ever was, was measured a 9.3.
The Seismic Moment Scale is the most accurate measurement of an earthquake's magnitude.
an earthquake hazard
9.0
a seismographic flow
7.4
6.6-6.7
6.3
The 2011 Tohoku earthquake measured 9.0 on the Richter scale.
200 miles
Mercalli is a scale for the measurement of earthquake intensities.
an earthquake hazard
An earthquake's magnitude is a measure of how strong it is