The Passive Seismic Technique ‘HVSR’ as a Reconnaissance Tool for Mapping Paleo‐soils: The Case of the Pilastri Archaeological Site, Northern Italy

Abstract

Horizontal-to-vertical spectral ratio (HVSR) is a widely used geophysical technique in seismic microzonation studies. It is based on a specific analysis of seismic ambient noise. The method allows to obtain the frequency and amplitude of the resonance peaks of a layered earth with increasing acoustic impedance contrasts. The peaks can be interpreted to obtain an estimation of depth(s) of the impedance contrast horizon(s). Based on the assumption that long-term human trampling results in sediment's stiffening, which increased both density and velocity of seismic shear waves, the HVSR method was applied to investigate the shallow subsurface of an important, Middle Bronze Age, archaeological site called 'Pilastri Terramara' discovered at the end of the last century. Following recent excavations, archaeologists supposed that the settlement could extend outside the initially hypothesized borders, and decided to involve geophysicists to verify the truthiness of this new hypothesis and consequently to map the possible spatial extent of the paleo-surfaces frequented by ancient occupants. The purpose of the geophysical investigation was then to detect and possibly to map one or more anthropogenic paleo-surfaces over a relatively large area (about 12000 m 2 ). Unfortunately, direct evidences showed that the paleo-surfaces were embedded in clayey sediments and laying at depths ranging between 50 and 170 cm below ground level. Furthermore, the area to be investigated is occupied by a farm with glasshouses and other buildings. These obstacles constituted a real challenge that hindered the utilization of the most commonly used geophysical methods in archaeology, i.e. ground penetration radar (GPR), magnetometry and electrical resistivity tomography. For these reasons, we decided to use the HVSR method as a reconnaissance exploration tool, to confirm or rule out the presence of such paleo-surfaces. Spectral peaks related to acoustic horizons provided evidences about their presence and allowed to estimate their depths as was later confirmed by a new excavation.

Exploring the paleolithic cave of Fumane (Italy): Geophysical methods as planning tool for archaeology

“…While GPR is commonly used in archaeology, its application in paleolithic caves is very rare, perhaps because of the absence of those targets that are quite easily detected in archaeological sites. Further, despite the fact that HVSR is seldom used in such a context, successful applications of the method in archaeology exist (Abu Zeid et al 2016, 2017, so that we decided to investigate the use of these techniques to cross-check and possibly integrate ERT results, therefore producing more reliable result. The ERT has the power to reconstruct the vertical and horizontal electrical stratigraphy (i.e.…”

Coastal Groundwater Bodies Modelling Using Geophysical Surveys: The Reconstruction of the Geometry of Alluvial Plains in the North-Eastern Sicily (Italy)

“…Furthermore, the net of the actual cost of geophysical instrumentation, the relationship between the amount of data acquired and the economic evaluation of a geophysical survey make geophysical methodologies quite economical when compared to direct investigations. This approach had been often used in many studies regarding stratigraphic [1][2][3] and structural geology [4][5][6][7], the analysis of depositional sequences [8][9][10], archaeological [11][12][13] and civil engineering research [14][15][16]. In these studies, acquired geophysical data constrained by the information derived from direct investigation provide a fundamental tool for the integration and definition of subsurface models.…”

Multi-Scale Geophysical Methodologies Applied to Image Archaeological Ruins at Various Depths in Highly Terraneous Sites

“…In a In such challenging cases, the role of geophysical surveys over large areas could be decisive to fill the knowledge gap and explore the buried targets at different depths with sufficient resolution. In addition, information about the location, depth, and dimensions of buried archaeological remains may be determined by means of geophysical investigation, which is carried out easily and quickly on the surface without disturbing or damaging the buried archaeological structures [6][7][8][9][10][11][12][13][14][15]. However, the manifestation of buried archaeological features in geophysical surveys is complex.…”