Earthquakes and Plate Subduction
- Geophysicists categorize earthquakes by focus depth.
- shallow earthquakes: 0 to 70 km depth.
- medium depth earthquakes: 70 to 300 km
- deep focus earthquakes: 300-700 km
- Geophysicists discovered an interesting pattern when the locations of earthquakes near ocean trenches were plotted.
- They saw that the depth of earthquakes changes with increasing distance from an ocean trench.
- Plotting the locations of earthquakes in three dimensions allowed them to "see" a subducting plate at a convergent plate boundary.
- This pattern helped support theories regarding subduction of tectonic plates and deep focus earthquakes.