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Richter Scale
Earthquake
they only rarely determine when they happen, but they can measure how bad they are when or after they happen.
the instrument used to to measure tsunami is seismograph.
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.
A seismograph.
Scientists use seismographs.
Seismographs are used to measure earthquakes, and how violent they are.
Richter Scale
Since a seismograph is a device used to measure the magnitude earthquakes, someone who studies earthquakes would use it.
They use a richter scale to measure intensity and magnitude.
The Beaufort scale
They use seismographs and the richter scale to determine their size.
Earthquake
If for ancient China, (i am assuming because you said did) it is seismograph
they use the pH scale
Seismograph