Depth of focus (tectonics)

As a focal depth of an earthquake is understood in geophysics, the depth of that rock formation that triggers the quake by a jerky movement of the layers. She falls i.a. with the depth of the hypocenter together.

In most areas of the earth quake have the stove depths characteristic values ​​which depend on the geological structure of the earth's crust there, at lower epicentres also from the border to the upper mantle. For example,

• In plate tectonics stove depths of a few tens of kilometers frequently, but
• To over 100 km depth can range in subduction zones;
• In sedimentary basins, however, prevail stove depths present in the range of several kilometers.

The focal depth can be determined by accurate analysis of seismic waves when they are recorded by simultaneous measurements of several widely separated seismographs - see transit time measurement. Approached the depth of a quake cooker also from a mapping of Isoseisten and a derivable relationship between the intensity of the quake and the radii of the shock regions are calculated.

The term " focal depth " is occasionally used for the starting point of a volcanic eruption, called magma chamber.

Literature and links

• B. A. Bolt: Earthquake, key to the geodynamics, 226p. Spektrum Akademischer Verlag, Heidelberg, 1996
• D.Csomor, Z.Kiss: The seismicity of Hungary. Studia et Geophysica Geodaetica Vol.3 / 1, Eötvös Inst.Budapest and Czech Academy d.Wiss. , Prague 1959
• Laszlo Egyed: Physics of the solid earth, 368P, Chapter IV The earthquake. Akadémiai Kiadó, Budapest 1969
• R.Gutdeutsch et al., Magnitudenschätzung ... and stove parameters from earthquake catalogs, DGG 2000