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A deep-focus earthquake in seismology (also called a plutonic earthquake) is an earthquake with a hypocenter depth exceeding 300 km. They occur almost exclusively at convergent boundaries in association with subducted oceanic lithosphere .
In seismology, the depth of focus or focal depth is the depth at which an earthquake 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. [1]
The 2015 Ogasawara earthquake was a 7.8 magnitude earthquake which struck offshore Japan 189 km (117 mi) west northwest of Chichi-jima in the Ogasawara Islands on May 30 at a depth of 664.0 km (412.6 mi). [1] The shaking of the earthquake was observed almost all over Japan, [2] as it was one of the largest deep-focus earthquakes recorded worldwide.
Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure. [22]
The primary tectonic feature of the 1,200 km (750 mi) island chain is the New Hebrides Trench, the convergent boundary between the Australian and Pacific plates.Along the Wadati–Benioff zone, earthquake activity has been observed as shallow, intermediate, and deep-focus events at depths of up to 700 km (430 mi).
A strong 4.5-magnitude earthquake occurred in deep waters off the North Carolina coast Wednesday, April 19, according to the U.S. Geological Survey.. It happened shortly after noon and witnesses ...
A primary example of this is located along Japan's largest island of Honshu, where the Wadati–Benioff zone is characterized by two well-defined lines of earthquake foci, with a distance between each line of 30–40 kilometers. [11] A study of the global prevalence of double Benioff zones has found that they are common in subduction zones ...
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