Marine ert modeling for the detection of fracture zones

Resistivity measurements in marine environments have already been tested in Norwegian landscapes in in the detection of subsea fracture zones (Lile et al. 1994; Dalsegg, 2012). Yet, most of the produced data have been processed without taking into account the special conditions created by the presence of seawater. Similar studies outside of Norway (Tsourlos et al., 2001; Satriani et al., 2011; Rucker & Noonan, 2013; Dahlin et al., 2014) have also utilized ERT in marine conditions however, most of these studies had deal with brackish water which is less conductive than pure seawater and therefore more favorable to the method (figure 1). This study summarizes our efforts to establish basic rules when considering whether or not pure sea water ERT can satisfactorily detect weak zones inside resistive bedrock. It is also in close connection to related ERT measuring (Rønning et al., 2009; Ganerod et al., 2006; Dalsegg, 2012) and modeling work (Reiser et al., 2007) carried out at the Geological Survey of Norway (NGU) and funded by the Norwegian Public Roads Administration. All results presented here are part of published NGU reports which were made to supplement the construction of an underwater tunnel in western Norway. Based on the modeling results, we were able to improve interpretations of ERT measurements made across seawater straits at Kvitsoy island but also conduct new marine ERT measurements in a more sophisticated manner. Nevertheless, we were also able to detect further limitations to the method.