Along converging plate margins, the dip angle of the rupture plane is very shallow, typically about 10 degrees. Thus, the width of the plane within the top brittle crust of the Earth can become 50–100 km (31–62 mi) (Japan, 2011; Alaska, 1964), making the most powerful earthquakes possible. Shallow-focus and deep-focus earthquakes
The majority of tectonic earthquakes originate in the ring of fire at depths not exceeding tens of kilometers. 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 and 300 km (43 and 186 mi) are commonly termed "mid-focus" or "intermediate-depth" earthquakes. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 to 700 km (190 to 430 mi)). These seismically active areas of subduction are known as Wadati–Benioff zones. 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. Earthquakes and volcanic activity
Earthquakes often occur in volcanic regions and are caused there, both by tectonic faults and the movement of magma in volcanoes. Such earthquakes can serve as an early warning of volcanic eruptions, as during the 1980 eruption of Mount St. Helens. Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes.
Erythrocyanosis crurum is a skin condition, a variant  of acrocyanosis caused by chronic exposure to cold. See also
Chilblains
List of cutaneous conditions

References
Otto Braun-Falco; G. Plewig; H. H. Wolff; Walter H. C. Burgdorf (2000). Dermatology. Springer Verlag. p. 889. ISBN 3-540-59452-3. James, William D.; Berger, Timothy G.;  et al. (2006). Andrews Diseases of the Skin: Clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0. == External links ==