Plate Tectonics

Global tectonic activity, seafloor spreading rates, Earth’s interior structure, and volcanism.

Model of Earth’s Interior Structure

Layers of Earth (crust, rigid mantle, asthenosphere, stiffer mantle, outer core, inner core) showing density, temperature, and pressure with depth.

Reference Table p. 11

1
Temperature and pressure with depthBoth increase continuously toward Earth’s center
2
Inner core stateSolid iron and nickel due to immense pressure
3
Outer core stateLiquid (blocks S-waves from passing through)
4
Plate motion driverThermal convection currents in the plastic asthenosphere/mantle

Tectonic plate boundaries (divergent, convergent, transform), hotspots, and spreading rates in cm/year.

Reference Table p. 12

1
Divergent boundaryPlates move apart → Mid-ocean ridges, rift valleys, new crust
2
Convergent boundaryPlates collide → Deep trenches, volcanic arcs, subduction zones
3
Transform boundaryPlates slide horizontally past one another (e.g., San Andreas Fault)
4
Locating an epicenterRequires arrival-time differences from at least 3 seismic stations
5
Seafloor age trendCrust is youngest at mid-ocean ridges and progressively older with distance