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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]
For example, in the 2004 Indian Ocean earthquake, the moment tensor solution gives two nodal planes, one dipping northeast at 6 degrees and one dipping southwest at 84 degrees. In this case, the earthquake can be confidently associated with the plane dipping shallowly to the northeast, as this is the orientation of the subducting slab as ...
Preliminary evidence for the existence of deep-focus earthquakes was first brought to the attention of the scientific community in 1922 by Herbert Hall Turner. [2] In 1928, Kiyoo Wadati proved the existence of earthquakes occurring well beneath the lithosphere, dispelling the notion that earthquakes occur only with shallow focal depths.
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.
Given the proximity between source and receivers, a precise earthquake focus location must be known. This requires the simultaneous iteration of both structure and focus locations in model calculations. [14] Teleseismic tomography uses waves from distant earthquakes that deflect upwards to a local seismic array. The models can reach depths ...
The temblor, which measured 4.8 on the Richter scale, was considered a shallow earthquake by the U.S. Geological Survey, meaning that it occurred at a depth of zero to 70 kilometers below ground.
As an example, in the magnitude 7.9 Denali earthquake of 2002 in Alaska, the epicenter was at the western end of the rupture, but the greatest damage was about 330 km (210 mi) away at the eastern end. [7] Focal depths of earthquakes occurring in continental crust mostly range from 2 to 20 kilometers (1.2 to 12.4 mi). [8]
These include the length of the fault, magnitude, the depth of the quake, the distance from the epicentre, the duration (length of the shake cycle), and the geology of the ground (subsurface). Shallow-focused earthquakes generate stronger shaking (acceleration) than intermediate and deep quakes, since the energy is released closer to the ...