Fathometer is used to measure

A) Earthquakes
B) Rainfall
C) Ocean depth
D) Sound intensity

Fathometer is used to measure Ocean depth. Fathometer is a depth finder that uses sound waves to determine the depth of water.
The Richter Scale is used to measure the intensity of Earthquakes.
A rain gauge (also known as an odometer, pluviometer, or an ombrometer) is an instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation over a set period of time.
A sound level meter is used to measure acoustic/Sound intensity.

c)ocean depth