Crust movement
As a crustal or short crustal movements are in the earth sciences , particularly in Geodesy and Geodynamics metrological or geologically detectable movements of parts of the solid earth's crust called. They can be recent (active, currently noticeable) or fossil (i.e. long since decayed).
The spatial and temporal extension of such movements can be very different. Most movements are continuous and predominantly horizontal, typically with movement rates of a few mm to cm per year. However, in the wake of earthquakes , sudden or gradual dislocations up to the meter range are also possible.
Very rapid, but local, slope and rock movements ( landslide , mudslide ) and ground flow are not crustal movements because only the uppermost areas of the earth's crust are affected. Even if such events can be triggered by earthquakes, they are manifestations that can be assigned to the general terms weathering and erosion . In the geodynamic sense, they are also referred to as “mass movements”.
causes
The Hungarian geophysicist László Egyed (Lit.1, p.299) writes: Crustal movements occur where the stresses exceed the strength (or at least the plastic strength) of the layers.
The layers of lowest strength consist of sedimentary rocks. Although the fault lines in sedimentary areas are sometimes difficult to detect, the fault systems are mostly reflected in the watercourses in an area. Because they shape the fracture systems of the rock zones under the sediments , and the rivers dig themselves into the most resilient rock formations.
Adrian Scheidegger (Zurich / Vienna) has also statistically proven this in the rivers of Europe, and Franz Kohlbeck (1943–2016) at the TU Vienna found clear correlations between stress tensors and fissures in numerous rock formations. Crustal movements occur not only along recent geological faults , but also in areas whose rocks were tectonically heavily stressed in earlier times (often imprecisely referred to as weak zones ). An example of this is the Vienna Basin - at that point between the Eastern Alps and the Carpathian Mountains , where parts of the earth's crust have sunk up to 6 km.
Many crustal movements are also the result of supra-regional movements caused by global plate tectonics . They usually show up on the edges of the continents and are associated with phases of orogenesis .
Crustal movements along geological faults
Local and regional crust movements therefore mostly occur along geological faults . At the edge of sedimentary basins , these fault lines usually run as so-called fractures in the nearby subsurface, but sometimes they “break through” to the surface of the earth. Basin edges are typically even characterized by whole rows of parallel fractures ( relay fractures ), along which the basin floor slowly sinks and is in turn filled with sediments . Fault zones in sedimentary basins are particularly interesting for petroleum geology , as they can form “traps” in which the hydrocarbons collect in degradable quantities.
Regional crust movements are not infrequently related to mountain formation . In the alpine fold mountains this takes z. B. is still on, with movement rates of up to a few millimeters per year. An important, repeatedly moving main fault in the Alps is, for example, the Periadriatic Seam , which, as a 700 km long line structure, forms the geological boundary between the Eastern and Southern Alps . The movements at the periadriatic suture cause frequent earthquakes. During the earthquake in Friuli in 1976 there was a noticeable shift of a few centimeters.
Global plate tectonics
Earth crust movements also occur on a global scale, where they are summarized under the term plate tectonics . These shifts affect entire continents or larger parts of them, contribute significantly to the formation of mountains and are therefore also the cause of many regional crustal movements. Plate tectonic movements run smoothly - with annual movement rates of around 1 cm to 20 cm - and can also include slow rotations of the crustal parts. Most important for Europe is the collision zone of the African plate (including some small plates ) with the Eurasian plate . a. formed the Alpine arc and which is responsible for many earthquakes in southern Europe.
See also
literature
- László Egyed : Solid Earth Physics , 370 p., Akadémiai Kiadó, Budapest 1969
- Adrian Scheidegger : Morphotectonics , 205 S., Springer-Verlag Berlin-Heidelberg 2004
- Peter Steinhauser : About the equilibrium of the Eastern Alps (mostly vertical crust movements). Meeting reports of the Austrian Academy of Sciences, math.-naturwiss. Class, Vienna 1991
- B.Bauer: Mass Movements in Austria , in: Integrated Risk Assessment, pp. 305–313; Series Environmental Science 1999
- St.Müller, J.Ansorge et al .: A crustal cross section along the Swiss Geotraverse from the Rhinegraben to the Po plain . Eclogae Geol. Helv. Volume 73, p. 463-485, Zurich 1980
Individual evidence
- ↑ F.Kohlbeck, R.Lahodynski, A.Scheidegger: Mountain tensions and mass movements in the Bad Goisern area, Upper Austria . Interpraevent 1984
- ↑ F.Kohlbeck, A.Scheidegger: The power of parametric statistics orientation in the Earth sciences. Mitt. Österr.geol.Gesell. 78, Vienna 1985