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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 ]
Seismic velocities within the Moon's approximately 60 km thick crust exhibit an initial low of 100 m/s at the surface, [53] which escalates to 4 km/s at 5 km depth, and then to 6 km/s at 25 km depth where velocities sharply increase to 7 km/s and stabilize, revealing a consistent composition and pressure conditions in deeper layers. [54] [55]
The thickness is heavily dependent on location. For oceanic crust, the seismogenic layer thickness can be 0 to 40 kilometres (0 to 25 mi), and for continental crust, it ranges from 0 to 25 kilometres (0 to 16 mi). [2] It is also important to note that at subduction zones, there is one seismogenic layer being pushed on top of another.
The thickness of Earth's crust (km). The continental crust consists of various layers, with a bulk composition that is intermediate (SiO 2 wt% = 60.6). [5] The average density of the continental crust is about, 2.83 g/cm 3 (0.102 lb/cu in), [6] less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm 3 (0.12 lb/cu in).
Continental crust is a tertiary crust, formed at subduction zones through recycling of subducted secondary (oceanic) crust. [17] The average age of Earth's current continental crust has been estimated to be about 2.0 billion years. [20] Most crustal rocks formed before 2.5 billion years ago are located in cratons.
Variation of strength with depth in continental crust and changes in dominant deformation mechanisms and fault rocks in a conceptual vertical fault zone.. The brittle-ductile transition zone (hereafter the "transition zone") is the zone of the Earth's crust that marks the transition from the upper, more brittle crust to the lower, more ductile crust. [1]
Only beneath mid-ocean ridges does it define the lithosphere–asthenosphere boundary (the depth at which the mantle becomes significantly ductile). The Mohorovičić discontinuity is 5 to 10 kilometres (3–6 mi) below the ocean floor , and 20 to 90 kilometres (10–60 mi) beneath typical continental crusts, with an average of 35 kilometres ...
Earthquakes are common along convergent boundaries. A region of high earthquake activity, the Wadati–Benioff zone, generally dips 45° and marks the subducting plate. Earthquakes will occur to a depth of 670 km (416 mi) along the Wadati-Benioff margin. [citation needed] Both compressional and extensional forces act along convergent boundaries.