Richter scale is used to measure

Answer: (a) Earthquakes

The Richter scale measures earthquake magnitude.

The idea

An earthquake scale and a weather scale measure different physical events. Richter magnitude uses seismic-wave amplitude with corrections for distance. It describes earthquake size, not the damage experienced at each location.

Why the others are wrong

(b) Ocean depth uses sonar (fathometer).

(c) Wind uses the Beaufort scale.

Elimination technique

Seismic-wave recordings belong to earthquakes. Ocean depth uses sounding, and wind has its own scales, leaving (a).

Also know

Modified Mercalli measures local earthquake intensity; moment magnitude is widely used to describe large earthquake sources. Beaufort describes wind force and Saffir-Simpson categorises hurricanes by sustained wind speed. Ocean depth is measured using echo sounding. Keep the event, the instrument and the scale as separate associations.