Why can the focus of earthquakes be very deep at subduction boundaries?

1 Answer
Jul 8, 2017

See answer below


A subduction boundary is where one plate pushes under another plate.

The crust varies in thickness form about 5 km (3 mi) to about 50 km (30mi) with the thinner crust under the ocean and the continental crust from 30 km (20 mi) to 50 km (30 mi).

Since the focus is the exact place where the earthquake occurs, subduction earthquakes can be up to 50 km (30mi) deep (it occurs at the bottom of one plate when another plate is pushing under it).

50 km (30mi) is usually the thickness nearer the center of a plate so at the edge of a plate boundary where the subduction occurs is more like 30 km (20 mi).