Periods 3 and 4 Even
This lab uses earthquake data to construct profiles of two convergent boundaries: the Tonga Trench and the Peru-Chile Trench. Where two tectonic plates converge, if one or both of the plates is an oceanic lithosphere, a subduction zone will form. When crust is formed at a mid-ocean ridge, it is hot and buoyant meaning it has a low density. As it spreads away from the ridge and cools and contracts, or becomes denser, it is able to sink into the hotter underlying mantle. When two oceanic plates collide, the younger of the two plates, because it is less dense will ride over the edge of the older plate. The density of the rock that makes up the subducting plate determines the way in which a plate behaves. A plate with a greater density subducts into the mantle faster and at a steeper angle than a plate with a lower density. The age of the crust involved in the subduction also affects the rate at which it subducts. Older crust is cooler and denser therefore it suducts at a steeper angle and faster than new crust at a subduction zone. The three key features associated with a subduction zone are a deep ocean trench, a volcanic arc on the overriding plate parallel to the trench, and a plane of earthquakes, shallow near the trench and descending beneath and beyond the volcanic arc. Most earthquakes occur at tectonic plate boundaries. The largest earthquakes are associated with subduction zones because they have long continuous fault lines. The depth of its focus can classify an earthquake. Earthquake depth range is divided into three zones: shallow, intermediate, and deep. Shallow earthquakes are between 0 to 70 km deep, intermediate earthquakes are between 70 to 300 km deep, and deep focus earthquakes have foci at more than 300 km.
Terms Introduced and Defined:
- Subduction zone: the place where two lithospheric plates come together, one riding