Contribution of the resistivity method to characterize mud walls in a very dry region and comparison with GPR

BONGIOVANNI, MARÍA V.; DE LA VEGA, MATÍAS; BONOMO, NÉSTOR

JOURNAL OF ARCHAEOLOGICAL SCIENCE

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2011 vol. 38 p. 2243 - 2250

0305-4403

Mud walls are frequent in many archaeological sites, including sites located in semi-desertregions. In cases with buried walls, the geophysical methods can be useful tools for their investigation,since they provide maps of the subsoil in a non-invasive way and in relatively short times. This articledeals with the characterization of mud walls in very dry soils through the resistivity method,discussing a methodology to satisfactorily apply the method in this kind of adverse environment andhow to interpret the results. The case of the Palo Blanco archaeological site, a pre-Incaic village locatedin the NW region of Argentina, is analyzed.In very dry soils, it is frequent that the electrical current cannot be injected due to the high values ofelectrical resistivity at the shallowest portions of soil, which makes the resistivity method useless. Herewe show how this problem can be systematically overcome by wetting a shallow thread between eachpair of injection electrodes, and the manner in which the resulting profiles can be analyzed. Weperform numerical simulations of the resistivity profiles considering 3D models of mud walls andwetted threads that reproduce experimental situations, and compare them to 2D field data. Theresistivity profiles are analyzed for different orientations and distances between the wall and profile,and fluctuations of the soil parameters. The experimental profiles are interpreted from thesesimulations and compared to ground penetrating radar (GPR) profiles. The resistivity methodologyshows effective for characterizing the size and depth of the mud walls, even in cases with collapsed ormuch eroded walls, for which GPR often fails.