A seismogragh and/or seismometer.
Seismometer
intensity
An earthquakes intensity
to measure what is the intensity of the earthquake.From :Lyssa
The strainmeter, by which its seismometer component detects the vibrations or shock waves that its seismograph records, is the scientific instrument that's used to predict and measure earthquakes.
Richter scale is used to measure earthquakes magnitude Shake intensity is measured on the Mercalli scale
It depends on what substance/object you are trying to determine the intensity.
A seismograph is an instrument used to measure the strength of earthquakes.
Seismograph
They use a richter scale to measure intensity and magnitude.
Mercalli and Richter scales
The Richter Scale is used to measure the intensity of earthquakes.