On the acoustic detection of flint blade in soft sediment

A lot of Stone Age sites are known to be destroyed by the wave activity of risen and fallen sea level. A direct consequence of this destruction is a loss of environmental information about the relation of human culture and the changing environment. Even when this destruction occurs, there is still some remains of prehistoric landscapes which can provide useful information. With the relatively complex seawater environment, the use of acoustic methods to detect and map submerged Stone Age sites is of great importance for archaeological research. This paper presents a preliminary numerical study for the geoacoustic characterization of Stone Age cultural layers containing worked flints and blades in particular. Finite element modeling tools are used to investigate the feasibility of detecting acoustically a submerged flint. Since well preserved submerged settlement remains will often be related to areas with soft sediments, the acoustic response of a flint buried in soft sediment is here simulated. In classical environments, flints are also known to be submerged in a cultural layer surrounded by seawater, sand, mud and a substrate layer of Moraine. A theoretical calculation of flint resonance frequencies shows that depending on their characteristics, they can produce a wide range of frequencies beyond 2 kHz as it has been observed experimentally. In this study, a Ricker wavelet source is used to estimate the total and scattered pressure fields due to a flint blade sample. To detect the submerged flint, the source contains the determined fundamental resonance obtained at 10.6 kHz. Snapshots for different views around the flint are analyzed to detect the effect of the flint sample. In the frequency domain, it is observed a relatively detectable zone around the flint. The total pressure level is computed at a fixed distance of 5 cm above the flint blade buried inside 5 cm of a cultural layer environment. A sharp peak is noticed to appear for this latter result at the give- resonance of about 18% the emitting signal for the flint. In this preliminary study, the case of the flint buried inside 15 cm of cultural layer overlying 100 cm of sand is also computed and presented. In the time domain, the total pressure fields at the indicated fixed distance for both cases with and without the flint blade are compared in the case of an environment composed of 15 cm of cultural layer overlying 100 cm of sand layer. The result shows that although the sound pressure response amplitude is slightly increased for the case with the flint blade sample, the difference between these responses is about 10% of the incidence source amplitude. This first step modeling suggests a possibility to use an acoustic method to detect and localize worked flints buried inside soft sediment environment. The other results obtained are analyzed and discussed. The study support the development of a geoacoustic inverse method to characterize submerged flints cores and blades but also the accumulation of flakes.