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Depth of focus (tectonics) 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 ...
The strongest deep-focus earthquake in seismic record was the magnitude 8.3 Okhotsk Sea earthquake that occurred at a depth of 609 km (378 mi) in 2013. [21] The deepest earthquake ever recorded was a small 4.2 earthquake in Vanuatu at a depth of 735.8 km (457.2 mi) in 2004. [22]
They form an important part of the macroseismic approach, i.e. that part of seismology dealing with noninstrumental data. The shape and size of the isoseismal regions can be used to help determine the magnitude, focal depth, and focal mechanism of an earthquake. [1] [2]
The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault -related event, it refers to the orientation of the fault plane that slipped, and the slip vector and is also known as a fault-plane solution. Focal mechanisms are derived from a solution of the moment ...
Hypocenter (Focus) and epicenter of an earthquake. An earthquake's hypocenter or focus is the position where the strain energy stored in the rock is first released, marking the point where the fault begins to rupture. [3] This occurs directly beneath the epicenter, at a distance known as the hypocentral depth or focal depth. [3]
Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic ...
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.
An earthquake occurred in the province of Sichuan, China at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 M s [5] [14] [15] (7.9–8.3 M w), [1] [6] the earthquake's epicenter was located 80 kilometres (50 mi) west-northwest of Chengdu, the provincial capital, with a focal depth of 19 km (12 mi). [6]