Does a meteorite impact affect the conductivity in Earth's crust?

摘要

N(o)rdlinger Ries is a 15 million year old impact crater with a diameter of 25 km, situated in southern Germany. Although it is relatively well examinated in the upper part, MT measurements took place rarely. Here we report Data were obtained from 21 sites, inside and outside the crater, in the period range16-1024s. Rotated by a phasesensitive strike angle of nearly 66° at all sites, there is a significant phase split in the period range 16-512s at all sites. However, the difference between phases in both directions inside the crater is smaller than outside for short periods. 1D-Models are used to show the existence of a high conductive anisotropic layer.Searching for changes of an impact in the conductivity in upper crust, three qualitatively different 3D-Forward-Models were calculated to explain this effect. For this purpose, results from geoelectric and drillhole examinations of sediments and crater filling have been used.It turns out, that neither the sediments nor an impact crater overlaid by sediments are able to explain the reduction of phase splits inside the crater. The best explanation is an interruption of the high conductive layer underneath the N(o)rdlinger Ries. The size of this interruption is comparable to the surface signature of the impact.