Seismology is the study of earthquakes. More specifically, it is the study of tremors in the Earth's crust that result from the movement of plate tectonics. The lithosphere of the Earth (the crust) is divided into numerous plates that essentially "float" on the underlying asthenosphere. These plates move very slowly over time and can collide, move apart from, or have shearing forces with each other. These movements of the plates (called plate tectonics) cause tremors in the Earth's crust which manifest themselves on the surface as earthquakes. A seismologist is a scientist (specifically a geologist) who studies seismology, or earthquakes. Probably the biggest area of study for a seismologist is trying the predict earthquakes in order to help save people's lives.