Depth of focus (tectonics)

<p>In <a href="/facts/Seismology/Lony1LYX">seismology</a>, the depth of focus or focal depth is the depth at which an <a href="/facts/Earthquake/NGjIzagw">earthquake</a> occurs. Earthquakes occurring at a depth of less than 70 km (43 mi) are classified as shallow-focus earthquakes, while those with a focal depth between 70 km (43 mi) and 300 km (190 mi) are commonly termed mid-focus or intermediate-depth earthquakes. In <a href="/facts/Subduction/rkasNdTo">subduction zones</a>, where older and colder <a href="/facts/Oceanic_crust/0lGjI7jN">oceanic crust</a> sinks under another tectonic plate, <a href="/facts/Deep-focus_earthquake/LjrucCzQ">deep-focus earthquakes</a> may occur at much greater depths in the mantle, ranging from 300 km (190 mi) up to 700 km (430 mi).
</p><p>The cause of deep-focus earthquakes is still not entirely understood since subducted <a href="/facts/Lithosphere/1mqaxASd">lithosphere</a> at that pressure and temperature regime should not exhibit brittle behavior. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by <a href="/facts/Olivine/tLLL4rae">olivine</a> undergoing a <a href="/facts/Phase_transition/eLP2BY8R">phase transition</a> into a <a href="/facts/Spinel/Nb7K5ctV">spinel</a> structure, with which they are believed to be associated. Earthquakes at this depth of focus typically occur at oceanic-continental <a href="/facts/Convergent_boundary/rhgWhQx3">convergent boundaries</a>, along <a href="/facts/Wadati%25E2%2580%2593Benioff_zone/SWy7E56r">Wadati–Benioff zones</a>.
</p>

Depth of focus (tectonics) open-in-new

Depth of focus (tectonics)