Seismic Waves and Earth's Layers

• Seismic waves are energy waves travelling through Earth's layers, commonly from volcanoes and earthquakes.

P-waves (Primary)

• P-waves are faster longitudinal waves.
• These waves travel through all mediums.

S-waves (Secondary)

• S-waves are slower transverse waves.
• These waves only travel through solids.
• The lithosphere is the uppermost mantle and crust of the earth.
• The asthenosphere is the solid, flowing upper mantle on which the lithosphere rests.
• The magnetic field protects Earth from radioactive rays and is used for navigation.
• Convection currents in Earth's layers result from temperature differences.
• Convection currents are responsible for moving tectonic plates.

Earth Layers

• The crust is the thinnest (30 km), uppermost layer, made of continental and oceanic crust.
• Continental crust is older, more stable, lighter, and does not sink; it contains sediments, granite, and basalt.
• Oceanic crust is younger, less stable, heavier, and sinks; it contains sediments and basalt.
• Seismic waves travel faster in oceanic crust.
• The mantle is 2900 km thick, a solid silicate layer denser than the crust, with temperatures between 500-4000C.
• The Mantle drives convection currents and causes earthquakes, continental drift, and volcanoes.
• The upper mantle is melted, allowing tectonic plates to move, while the lower mantle is rigid due to pressure.
• The outer core is 2200 km thick, made of liquid iron and nickel, with a temperature around 4000C.
• Convection in the liquid outer core creates Earth's magnetic field, and S-waves cannot travel through it, influencing seismic wave activity.
• The inner core is 1200 km thick, made of solid iron and nickel, with a temperature around 5000C.
• High pressure keeps the inner core solid, providing a stable center, helping maintain convection, creating magnetic fields.

Plate Boundary Types

• In convergent boundaries, plates move in the same direction, creating mountains, trenches, and volcanoes, such as the Himalayas and Mariana Trench.
• At divergent boundaries, plates move in opposite directions, forming mid-ocean ridges and rift valleys, like the East African Rift.
• At transform boundaries, plates slide across each other, causing large earthquakes, like the San Andreas Fault.

Plate Interactions

• At constructive boundaries, plates move apart, magma rises, solidifies, and creates new crust.
• At collision boundaries, two plates collide, forming mountains.
• At subduction zones, two plates collide, the oceanic crust moves under the continental crust and breaks down.
• At conservative boundaries, nothing is created or destroyed, but strong earthquakes occur.

Volcano Types

• Fissure volcanoes have a long streak of magma escaping from cracks, producing basaltic lava.
• Shield volcanoes have a shield form, with a very small slope, and basaltic lava.
• Dome volcanoes have steep sides, concave interiors, and mound shapes with Andesitic lava.
• Ash-cinder volcanoes are small and steep, like dome volcanoes, but without the dome mound, and do not flare out at the top.
• Composite volcanoes are very tall and cone-shaped, with Andesitic lava.
• Caldera volcanoes form after an eruption when the magma chamber collapses, leaving a large crater called the caldera.