V Value of Proportionality: a constant value that relates strain to stress. Vector: a quantity that represents both a magnitude and direction; often described by an arrow whose length represents a magnitude and its orientation describes its direction. Velocity Map: a map that uses vectors to show how fast and in what direction ground GPS stations are moving relative to one another. Volcanic Earthquakes: earthquakes that result from tectonic forces which occur in conjunction with volcanic activity. Volume: space occupied or enclosed by cubic units.