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initial part of the TR04 and TR05 models, with resistivity resistivity values lower than 0.5 Ωm are to be expected.
values lower than 1.0 Ωm, attributable to highly These values are not found in the resistivity models,
fractured and karst areas. As also observed in the except for two small nuclei present in the ERT TR04
longitudinal models, in depth (25-27 m in the platform and TR05, in their initial portions, attributable to areas
area) there is a marked decrease in the resistivity of strong fracture and karst.
values, correlated with the increase in the frequency of
th
the marly intercalations. This paper was presented at the 15 OMC Med Energy
Conference and Exhibition in Ravenna, Italy, September
28-30, 2021. It was selected for presentation by OMC
Conclusions 2021 Programme Committee following review of
Geophysical surveys through geoelectric resistivity information contained in the abstract submitted by the
method (ERT) have been carried out in the nearshore author(s). The Paper as presented at OMC 2021 has
area of the Delimara Peninsula, where a microtunnel is not been reviewed by the Programme Committee.
planned to be realized for the offshore approach of the This paper has been published thanks to the
22” (Melita Transgas Pipeline). authorisation of the contracting company Interconnect
The measurements were carried out in extreme Malta.
conditions, from a technical point of view: the presence
of significant water depths, with high electrical
conductivity, limits the resolution capability of the
methods due to short circuiting in the water layer. References
However, these difficulties have, at least in part, been Pedley, H.M., The Oligo-Miocene sediment of the Maltese
avoided thanks to adequate equipment, careful Islands, Unpublished PhD thesis, University of Hull.
planning, and attention to details (precise positioning
on the seabed and measurement of sea water Micallef et al., The submerged paleolandscape of the
resistivity). The electrical resistivity models obtained Maltese Island: Morphology, evolution and relation to
have a good quality level (residual 7-8%) and are Quaternary environmental change, Marine Geology
consistent with the lithostratigraphic context of the (2012), http://dx.doi.org/10.1016/j.margeo.2012.10.017.
investigation area.
The correlation of the electrical resistivity values of the Dahlin T., Bjelm L. and Svensson C. 1999. Use of electrical
2D and 3D models with the lithologies, as reconstructed imaging in the site investigations for a railway tunnel
also in the executed coring, allowed to hypothesize the through the Hallandsås Horst, Sweden. Quarterly Journal
geometric arrangement of the lithologies up to depths of Engineering Geology and Hydrogeology 32, 163–173
that reach 50-60 from the seabed. In the offshore area,
the lithological structure is characterized by the Dahlin, T., & Loke, M. H. (2018). Underwater ERT
presence of a horizon with relatively high resistivity, surveying in water with resistivity layering with example of
attributable to the predominantly calcareous and marly application to site investigation for a rock tunnel in central
limestone lithologies (Upper Globigerina Limestone Stockholm. Near Surface Geophysics, 16(3), 230-237.
Member), with a thickness varying between about 22
and 30 m, in which a gradual decrease is observed of Loke M.H. 2020. Tutorial: 2D and 3D electrical imaging
the resistivity values in its lower portion, attributable to surveys (www.geotomosoft.com). Revision date 17 Agust
the presence of more frequent pelitic intercalations 2020.
(marly). Even deeper, resistivity values are observed to
decrease further, a condition attributable to a lithological Loke M.H. and Lane J.W. 2004. Inversion of data from
change (marls and clayey marls - Middle Globigerina electrical resistivity imaging surveys in water-covered
Limestone Member). areas. Exploration Geophysics 35(4), 266–271.
For the identification of the fractured and karst areas in
the rock mass, it was considered that they led to an Simyrdanis K., Papadopoulos N., Kim J.-H., Tsourlos P.
increase in porosity, and that in the presence of sea and Moffat I. 2015a. Archaeological investigations in the
water there was a reduction in the electrical resistivity shallow seawater environment with electrical resistivity
values. This condition is extreme in the presence of tomography. Near Surface Geophysics 13(6), 601–611.
cavities filled with sea water, in which calculated

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