What you're probably thinking of is the ML scale which measures "potential energy" of the tsunami. Don't get this confused with electrical potential (or voltage). they are not the same. the "potential energy" of a tsunami, I would assume, would be measured in joules.
The usual measure of a tsunami is the height of the wave just as it reaches the beach.
yes
hydrophone
To measure voltages and voltage drops
the instrument used to to measure tsunami is seismograph.
A milli voltmeter is suitable for measuring voltage/potential difference in milli volts, thus they measure smaller voltages. A regular voltmeter is used to measure comparatively larger voltages.
the Richter scale
Digital Volt Meter (DMM)
it is used to measure very high voltages which can not be measured with volt meter.
A multimeter is the best tool for the job Set the voltage to 20 V. dc.
use a ruler
A tsunameter is an instrument used to detect and measure tsunamis. It works by monitoring changes in water level in the ocean and can provide early warning signals to coastal regions at risk of tsunami events.