Depth of focus

In geophysics, the depth of the rock formation that triggers the quake through a jerky movement of the layers is understood as the depth of an earthquake . It generally coincides with the depth of the hypocenter .

In most of the earthquake regions, the focus depths have characteristic values ​​that depend on the geological structure of the earth's crust there ; in the case of deeper earthquake centers, also on the border with the upper earth's mantle . For example are

• in plate tectonics focal depths of a few tens of kilometers are common, however
• can reach depths of more than 100 km in subduction zones ;
• in sedimentary basins , however, focus depths of a few kilometers prevail.

The focal depth can be determined through precise analyzes of the seismic waves, if these are recorded by simultaneous measurements of several far apart seismographs - see time of flight measurement . The depth of a quake focus can also be approximated from a mapping of the isoseists and a relationship that can be derived from this between the intensity of the quake and the radii of the shock areas.

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

Literature and web links

• BA Bolt: Earthquakes, Keys to Geodynamics , 226p. Spectrum Academic Publishing House, Heidelberg 1996
• D.Csomor, Z.Kiss: The seismicity of Hungary . Studia Geophysica et Geodaetica Vol.3 / 1, Eötvös-Inst.Budapest and Czech Academy of Science, Prague 1959
• László Egyed : Solid Earth Physics , 368p, Chapter IV The Earthquakes . Akadémiai Kiadó, Budapest 1969
• R. Gutdeutsch et al., Magnitude estimation ... and focus parameters from earthquake catalogs, DGG 2000

See also

• Continental plate , collision and subduction , volcanism
• geological fault , settlement , tectonics