Shallow reflection seismic evidence of tectonic activity in the Cheb Basin, NW Bohemia

Abstract

With a high-resolution seismic survey, we targeted the shallow structural features of the Cheb Basin, Northwest Bohemia. The aim of this study was to evaluate these features’ relation to seismic activity below the Cheb Basin with the first reflection seismic image of parts of the basin. We recorded a densely sampled, 3200 m long seismic survey stretching from Kopanina towards SE, into the basin. From the recordings of 170 shots at 192 geophones with 384-m total spread, we obtained a reflection seismic image down to the basement at 300-m depth, supplemented by a shallow tomographic velocity model for the uppermost 40 m. Strong lateral velocity contrasts indicate Quaternary river terraces, into which the Plesna river incises. We observe reverse faults in the lower basin sediments, which we interpret as signs of a push-up structure related to the N-S oriented Pocatky-Plesna Zone (PPZ). However, we do not observe any vertical fault offsets in the younger sedimentary layers, which suggests that any normal or reverse faulting must be older than 20 Ma. The image agrees well with previous lithostratigraphic borehole data and previous sedimentological and tectonic models. Our explanation for the formation of the escarpment at the eastern bank of the Plesna valley, previously interpreted as outcrop of the PPZ, relies solely on incision of the Plesna river into weak sediments.