M Magma: molten rock material that is liquid or pasty which originated within the earth. Magnitude: greatness or extent of size. Mantle: the layer in Earth's interior between the crust and the core. Mechanical Wave: disturbance of a mechanical medium such as air, water, earth, and space. Model: a representation or simulation of something that cannot be directly observed Moment Magnitude: the preferred measure of earthquake size (magnitude) in which the stiffness of the rock, the average slip on the rupture plane, and the area of the rupture plane are taken into account (the "moment" of the earthquake).