Earthquakes rupture on faults that cut through the Earth crustal layers (e.g. Fig. 1). Shallow earthquakes occur when seismic activity takes place within the top 30km of the earth's crust and they account for majority of the Earth's seismic activity. These earthquakes are also among the most destructive and violent natural disasters in history in the Pacific ‘ring-of-fire’. The Great Sumatra earthquake and associated tsunami that occurred on Boxing Day 2004, killed ~230,000 people in 14 countries.
This is a companion discussion topic for the original entry at https://www.geo-down-under.org.au/a-deep-dive-into-shallow-quakes/