Tectonic Plates

• Geophysical imaging techniques are used to model what is going on below our feet.
• Seismologists measure the time it takes for waves to reach seismic monitoring stations set up around the globe.
• A seismometer is the machine used to measure seismic waves.
• The different layers in the Earth have been inferred using the time of travel of refracted and reflected seismic waves created by an earthquake.
• Changes in seismic velocity occur as the waves pass through different materials.
• Measuring these changes tell seismologists how many layers there are and the thickness and physical properties of each layer.
• Geophysical methods, for example measuring different gravity, magnetic and electrical anomalies by air and/or satellite, can help reconstruct shallow crystal features.
• Plate tectonics is a process where the land masses that were once joined together have pulled apart.
• The Earth's crust is divided into 12 major plates which are moved in various directions.
• This plate motion causes them to collide, pull apart, or scrape against each other.
• Each type of interaction causes a characteristic set of Earth structures to form or tectonic" features.
• The word tectonic refers to the formation of the crust as a consequence of plate interaction.
• The plates are made of rigid lithosphere.
• Lithosphere is made up of the crust and the upper mantle.
• The asthenosphere, beneath the lithosphere, is part of the upper mantle and is so hot that it is 1-5% liquid.
• Plates of lithosphere are moved around by the underlying hot mantle convection cells.
• Divergent boundaries are linear features that exist between 2 tectonic plates that are moving away from each other.
• Divergent boundaries can form in the middle of the continent on the ocean floor, spreading ridges.
• Convergent boundaries are where the plate moves towards each other.
• There are 3 styles of convergent plate boundaries: continent-continent collision, continent-oceanic crust collision, and oceanic-oceanic collision.
• Continent-continent collision is when continental crust pushes against continental crust.
• Continent-oceanic crust collision is where continental crust pushes against oceanic crust, the oceanic crust which is thinner and more denser than the continental crust called as subduction.
• Oceanic crust is called the subducting slab.
• Ocean-ocean plate collision is when two oceanic plates collide, one runs the other which causes it to sink into the mantle forming a subduction zone.
• The subducting plate is bent downward to form a very deep depression in the ocean floor called trench.
• The world's deepest part of the ocean are found along trenches, for example, the Mariana Trench is 11km deep.
• Transform boundaries are along which plates slide past each other.
• Pacific Ring of Fire is a region of area where active volcanism and earthquakes frequently occur.
• Volcanoes and Earthquakes are not randomly distributed, they occur at the boundaries between plates due to friction causing them to stick together when built up energy causes them to break, earthquakes occur.
• Earthquakes and volcanic activities occur in linear patterns associated with plate boundaries.