Patrick Fulton on the 2011 Tōhoku Earthquake

Glossary

accretionary prism – a wedge of marine sediments scraped off from a subducting plate onto a non-subducting tectonic plate at a convergent plate boundary

asthenosphere — the upper layer of Earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and where convection is thought to occur

Cascadia – the Pacific northwest region of North America stretching from northern California to British Columbia and including Washington, Oregon, and parts of Idaho, Montana, and southeast Alaska

graben — an elongated block of the earth's crust lying between two faults and displaced downward relative to the blocks on either side, as in a rift valley

horst — a raised elongated block of the earth's crust lying between two faults.

mud stone placid — lens-shaped pieces of mudstone, which are seen in the borehole core near the fault zone

platy mineral – minerals, such as mica, that develop crystals as thin sheet-like layers

seismogenic zone — the depths within the crust or lithosphere within which most earthquakes originate

smectite clay — a family of non-metallic clays primarily composed of hydrated sodium calcium aluminum silicate

trench axis – a line marking a long depression in the seafloor where plates converge at a subduction zone