Longitudinal waves P-waves. Like sound waves or acoustic wave.
S-Waves or shear waves travel slower than P-waves. The motion Of the wave disturbance is perpendicular to the waves motion.
If one know the speeds of the P-wave and S-wave (V p and V s ), then the difference between P-wave arrival (T p ) and S (T s )wave arrival can be used to figure out the distance to the Earth quakes. D= V p T p D= V s T s 3 stations need to locate the focus of the Earth quake.
Earths Radius 6400 km Depth to inner core 5000 km Depth to outer core 3000 km Depth to mantle 10 to 50 km (oceanic crust 10 km Continental crust 50 km) The lithosphere is hard / brittle The asthenosphere can deform like stiff putty.
There are approximately 12 lithospheric plates on Earths surface. Most scientists believe that convection within Earths lower and upper Mantle is the major driving force linked to plate motion. Convection is driven my temperature differences/density differences and gravity.
Juan de Fuca plate. Spreading and subduction Mt St Helens is part of the Cascade Arc Volcanoes
Hot Spots and Mantle plumes reaching the surface. Hot spots tend to be relatively stationary. As an oceanic plate moves over a hot spot new islands can be formed. Most think that the hawiian islands are a result of motion over a hot spot.