Geophysical Characteristics of Epikarst: Case Studies from Zagros Mts. (Iran) and the Koněprusy Region (Czech Republic)

Abstract

Značilnosti epikraške cone so bile preučevane s pomočjo geofizičnih metod, posebej s pomočjo refrakcijske seizmike, kombinirane z električno upornostjo in gravimetrijskimi meritvami. Enake metode so bile uporabljane na obeh področjih, kar omogoča primerljive izsledke. Interpretirane seizmične meje sledijo bazno ploskev epikrasa in z geofizičnega stališča omejujejo epikraško cono, to je cono s primerljivimi nizkimi seizmičnimi hitrostmi (najbolj pogosto 1 000 do 3 000 m s-1). Na Češkem, na devonskem področju Konìprusy, je debelina epikraške cone 5 do 60 m. Epikras v gorovju Zagors pa dosega debelino 180 m (kredni apnenci). Razlike v značaju in debelini epikraške cone so v celoti odvisne od geološke zgradbe in geomorfoloških danosti (reliefa) ter od razvoja obeh področij, v čemer je vzrok različnih možnosti sproščanja nekdanjih pritiskov v apniških pogorjih.

Characteristics of epikarst zone were studied by geophysical methods, especially refraction seismics, combined with electrical resistivity and gravimetry measurements. Applied methods were equal in both regions, so comparable results were obtained. The interpreted seismic boundaries follow the basal plane of epikarst (s.l.) and limit the epikarst zone from the geophysical point of view, i.e. zone with comparably low seismic velocities (mostly 1,000 to 3,000 m.s-1). The thickness of epikarst in the Czech Karst - the Konìprusy Devonian - is from 5 to about 60 m. The epikarst in Zagros Mts. reached up to 180 m (Cretaceous lmst.). The differences of character and vertical extent of epikarst zone depend on entirely different geological structure and geomorphological setting (relief) and evolution of both sites, which established different conditions for the release of residual stress in the limestone massifs.