Vectors are equal if they have the same magnitude and direction regardless of where they are. Triangle ABC is isosceles. X is the midpoint of AB, Y is the midpoint of BC and Z is the midpoint of AC.

Vectors are equal if they have the same magnitude and direction regardless of where they are. Triangle ABC is isosceles. X is the midpoint of AB, Y is the midpoint of BC and Z is the midpoint of AC.

These scales account for the distance between the earthquake and the recording seismometer so that the calculated magnitude should be about the same no matter where it is measured. Another scale is ...