Site characterization of the PIER-ICDP drill locations to understand the relation between earthquake swarms, mofette fields and crustal fluid pathways by imaging the electrical conductivity structure

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The area around Nový Kostel/NW-Bohemia is part of the geodynamically active Variscan orogenic belt in Europe, and experiences repeated occurrence of intra-plate earthquake swarms and is characterized by numerous mineral springs and CO2 emissions. These phenomena are usually related to volcanic activity. To better understand the underlying processes, the Eger rift and the Cheb Basin are favored as a possible location for several scientific drillings. Magnetotelluric (MT) data sense the electrical resistivity of the Earth, a physical parameter that is particularly sensitive to the presence of low-resistivity phases such as aqueous fluids, partial melts or metallic compounds. Fluid phases have electrical resistivities orders of magnitude lower than that of the rock matrix, and relatively small amount of fluids, when interconnected, can thus decrease bulk rock resistivity by several orders of magnitude. Measurements of electrical resistivity can therefore be used to constrain the volume of subsurface fluids, their interconnectivity and the rheology of the crust and mantle. I propose a passive MT experiment centred on the location where earthquake swarms occur and mofette fields are observed. The major objectives are (i) imaging the regional electrical conductivity on crustal scale, including tectonic features such as fault zones, (ii) providing a site characterization for drilling locations, (iii) studying the behavior of rocks and fluids from the surface down to the source region of earthquake swarms, (iv) imaging fluid pathways, their hydraulic properties and their interconnection, in particular in relation to mofette fields (v) investigate existence and characteristics of possible lower crustal magmatic sources.