P Plastic Deformation: an objects ability to change shape under an additional amount of stress beyond its elastic limit before it breaks. Plate: a large, relatively rigid segment of the Earth's lithosphere that moves in relation to other plates over the asthenosphere. Plate Tectonics: a geological model in which the Earth's lithosphere (crust and upper most mantle) is divided into a number of more-or-less rigid segments which move in relation to one another. Period: the time for one complete wave cycle to be completed. Precision: a measure of how well a result has been determined, without reference to its agreement with the true value; a measurement of the reproducibility of the result. P Wave: the primary body wave; the first seismic wave detected by seismographs; able to move through both liquid and solid rock; compressional waves, like sound waves, which compress and expand matter as they move through it.