Combined seismic tomographic and ultrashallow seismic reflection study of an Early Dynastic mastaba, Saqqara, Egypt

Abstract

Mastabas were large rectangular structures built for the funerals and burials of the earliest Pharaohs.One such mastaba was the basic building block that led to the first known stone pyramid, the >4600-yearoldStep Pyramidwithinthe Saqqaranecropolisof Egypt.Wehavetestedanumberofshallowgeophysical techniques for investigating in a non-invasive manner the subsurface beneath a large Early Dynastic mastabalocated closeto the Step Pyramid.Afterdiscoveringthat near-surface sedimentary rocks with unusually high electrical conductivities precluded the use of the ground-penetrating radar method, a very high-resolution seismic data set was collected along a profile that extended the 42.5 m length of the mastaba. A sledgehammer source was used every 0.2 m and the data were recordedusinga 48-channelarrayofsinglegeophonesspacedat 0.2 mintervals.Inversionsofthe directand refracted-wave travel times provided P-wave velocity tomograms of the shallow subsurface, whereas relatively standard processing techniques yielded a high-fold (50^80) ultrashallow seismic reflection section. The tomographic and reflection images were jointly interpreted in terms of loose sand and friable limestone layers with low P-wave velocities of150^650 m s À1 overlying consolidated limestoneandshalewithvelocities >1500 m s À1.The sharp contact betweenthelow-andhigh-velocity regimes was approximately horizontal at a depth of ca. 2 m. This contact was the source of a strong seismic reflection. Above this contact, the velocity tomogram revealed moderately high velocities at the surface location of a friable limestone outcrop and two low-velocity blocks that probably outlined sand-filled shafts.Below the contact, threeregularly spacedlow velocity blocksprobably represented tunnels and/or subsurface chambers

Detecting Trends in the Prediction of the Buried Past: A Review of Geophysical Techniques in Archaeology*

“…Seismic studies have provided much to the community by way of processing and visualization, but have had fewer applications over the years. Whereas the earlier papers used refracted waves (Goulty and Hudson 1994), the most recent have attempted to use ultra‐shallow reflected waves to identify cavities (Metwaly et al . 2005) and palaeochannels (Hildebrand et al .…”

Exploring the performances of the vibrating barriers for the seismic protection of the Zoser pyramid

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Non-Invasive Vibrating Control of the Zoser Pyramid

“…The Pyramid is made of polished white limestone modelled as an isotropic linear material defined by the elastic modulus, , Poisson's ratio, as well as unit density, , of 2900 . The position of the bedrock has been determined from previous studies available in the literature [13], [14] and it is considered to be located at 35m depth. The soil stratum between the bedrock and the base of the pyramid is assumed homogeneous with a shear wave velocity of 3000 m/sec considering the site investigation undertaken in the first 10m.…”