Trenches are formed by subduction, a geophysical process in which two or more of Earth's tectonic plates converge and the older, denser plate is pushed beneath the lighter plate and deep into the mantle, causing the seafloor and outermost crust (the lithosphere) to bend and form a steep, V-shaped depression.
At divergent plate boundaries, earthquakes tend to be weak and shallow. Transform plate boundaries, have shallow, but very powerful earthquakes. At convergent plate boundaries, where two continental plates collide earthquakes are deep and also very powerful.
Recall that there are three types of plate boundaries: convergent, divergent, and transform. Volcanism occurs at convergent boundaries (subduction zones) and at divergent boundaries (mid-ocean ridges, continental rifts), but not commonly at transform boundaries.
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