Which of the following monitors both vertical and horizontal movements along a fault?

a. seismograph

b. GPS satellite system

c. Richter scale

d. Mercalli Scale

The correct answer is a. seismograph. This is the instrument used to detect and measure seismic waves. During an earthquake the infromation is recorded on a seismogram, which is the seismograph's record of earthquake waves. The GPS would monitor and measure how far a tectonic plate moves with respect to time.