Potential Application of Environmental Noise Recordings in Geoarchaeological Site Characterization

Abstract:

Environmental noise recordings are commonly applied in seismic microzonation studies. By calculating the H/V spectral ratio, the fundamental frequency of soft terrains overlying a rigid bedrock can be determined (Nakamura (1989). In such a simple two-layer system, equation f = n Vs/4H (1) links the resonance frequency "f" to the thickness “H” and shear waves velocity “Vs “of the resonating layer.

In recent years, this methodology has been applied generally to obtain information on the seismostratigraphy of an investigated site in different environmental context. In this work, its potential application in the characterization of archaeological features hosted in shallow geological levels is discussed.

Field cases are identified in the Appia Antica archaeological site which is placed in central Italy. Here, acknowledged targets correspond to: i) empty tanks carved by the Romans into Cretaceous limestone in the IV-III cen. BC and ii): the basaltic stone paving of the ancient road track which is locally buried beneath colluvial deposits. Narrowly-spaced recordings of environmental noise were carried using a portable digital seismograph equipped with three electrodynamic orthogonal sensors (velocimeters) responding in the band 0.1 ÷1024 Hz and adopting a sampling frequency of 256 Hz..

Results are discussed in terms of absolute H/V values and related distribution maps in the very high-frequency interval of 10-40Hz. In the tanks hosting area, interpolation of H/V maximum values around 13Hz matches caves location and alignment, which is also evidenced by clear inversions (H/V<1) at lower frequencies (10-1Hz). Correlation between H/V peaks and the top surface of the buried stone paving along the prosecution of the road track is even more straightforward. Finally, the depth variations of the tank roofs and the basaltic paving were reconstructed combining in equation (1) results of noise recordings with borehole data and geophysical surveys (SASW analysis).