If you find a well-exposed fault that moved before seismographs were available,you can infer the approximate magnitude of earthquake by measuring the:

Question

Quizplus · Accepted Answer

The total length of the fault break during the event is the most appropriate measurement to infer the approximate magnitude of the earthquake. This is because the length of the fault break is directly related to the amount of energy released during the earthquake, which is a main factor in determining the magnitude of the earthquake. The other options are not reliable indicators of the earthquake's magnitude. The largest size tree snapped off or average size of the largest rock moved may depend on factors other than the earthquake, and the strength of rocks may not necessarily be related to the energy released during an earthquake. The total area affected by the tsunami wave produced by the event is also not a reliable indicator as it may depend on the location and topography of the affected area.

If You Find a Well-Exposed Fault That Moved Before Seismographs