In this paper we analyze the applicability of seismic full-waveform inversion (FWI) for investigation of tells, which are often characterized by heterogeneous and small-scale stratigraphy. Major aim is to identify location and shape of settlement layers and house remains. Furthermore, a paleochannel, which is important to understand the interaction between tell and the surrounding landscape, was found at the tell flank

Dreibrodt, Stefan

Erkul, Ercan

Hofmann, Robert

Köhn, Daniel

Lazar, Catalin

Müller, Johannes

Pickartz, Natalie

Rabbel, Wolfgang

Serbanescu, Adrian

Wilken, Dennis

Zolchow, Manuel

English

MACAU: Open Access Repository of Kiel University

KIEL-UP • DOI: https://doi.org/10.38072/978-3-928794-83-1/p63 315 ADVANCES IN ON- AND OFFSHORE ARCHAEOLOGICAL PROSPECTION  Proceedings of the 15th International Conference on Archaeological Prospection  ICAP 2023First results from stratigraphic investigation  of Chiselet tell (Romania) using seismic full  waveform inversionManuel Zolchow   1*, Natalie Pickartz   2, Adrian Serbanescu   3, Ercan Erkul   1, Daniel Köhn   1, Dennis Wilken   1, Stefan Dreibrodt 4, Robert Hofmann   5, Johannes Müller 5, Catalin Lazar   3, Wolfgang Rabbel   11 Institute of Geosciences, Kiel University, Kiel, Germany2 State Office for Cultural Heritage Baden-Württemberg, Ludwigsburg, Germany 3 Research Institute of the University of Bucharest (ICUB), University of Bucharest, Bucharest, Romania4 Institute for Ecosystem Research, Kiel University, Kiel, Germany 5 Institute of Pre- and Protohistoric Archaeology, Kiel University, Kiel, Germany *Corresponding author: Email: manuel.zolchow@ifg.uni-kiel.deAbstractIn this paper we analyze the applicability of seismic full-waveform inversion (FWI) for investigation of tells, which are often characterized by heterogeneous and small-scale stratigraphy. Major aim is to identify location and shape of settle-ment layers and house remains. Furthermore, a paleochannel, which is important to understand the interaction between tell and the surrounding landscape, was found at the tell flank.  Keywordsarchaeological prospection; full-waveform inversion (FWI); seismic; stratigraphy; tell  IntroductionNeolithic tell settlements are, due to their size, topogra-phy and heterogeneity, challenging targets in the field of archaeological prospection. Since traditional geophysical prospection methods are often limited by penetration depth or resolution, a sufficient 3D reconstruction of an entire tell is often unachievable. To overcome these issues seismic full-waveform inversion (FWI) has been proven as promising method and is therefore increasingly integrated to multi-method approaches for geophysical prospection of heterogeneous stratified archaeological targets like set-tlement mounds. For a case study we performed measurements at a Chalco-lithic tell (Fig. 1d) from Gumelnița culture (4600 – 4250 BC) in the lower Danube basin near Chiselet in Romania (Fig. 1a) to prove the applicability of our seismic FWI integrated multi-method strategy to geophysical investigation of pre-historic settlement mounds. Aim of our investigation was to reconstruct stratigraphic units of different settlement phases, to identify archaeological features like house re-mains, pits or trenches and to analyze the relation between tell and the surrounding paleo landscape. MethodsThe seismic data were recorded using a GEOMETRICS seismic system in SH-configuration along two profiles (Fig. 1b, c) of 95 m length with 10 Hz horizontal compo-nent geophones in 1 m distance. Whereas profile 1 is cross-ing the entire tell in direction from west to east, profile 2 is running down the southern tell flank into the surround-ing plane. For excitation of shear waves a sledge hammer source was positioned along the profiles in intervals of 2 m.The data was analyzed using two-dimensional, elas-tic FWI in time-domain based on inversion of disper-sive Love- and refracted SH-waves. For this purpose, we ADVANCES IN ON- AND OFFSHORE ARCHAEOLOGICAL PROSPECTION  Proceedings of the 15th International Conference on Archaeological Prospection  ICAP 2023316  KIEL-UP • DOI: https://doi.org/10.38072/978-3-928794-83-1/p63used the FWI-code DENISE (Köhn et al. 2012). The data fit was improved by inverting for shear wave velocity vs and density ρ simultaneously, while seismic quality fac-tor Qs was assumed to be constant. The required initial model of the shear wave velocity was determined using ray-based first arrival traveltime tomography (FATT) on the basis of refracted SH-waves with the software Reflexw (Fig. 2a, 3a). Proceeding from this initial seismic velocity model, a density model was calculated via an empirical relation (Ulugergerli and Uyanik 2007) valid for uncon-solidated sands. The constant value of the quality factor Qs = 30 was optimized by best data fit after multiple for-ward modeling runs with different quality factors. Since the existing code is based on rectangular grids, we used an oversampled spatial discretization of 0.05 m together with the improved vacuum formulation (Pan et al. 2018) Fig. 1: a) Location of Chiselet; b) Map of Chiselet tell including measured seismic / ERT profiles (orange lines) (base map: Goo-gle ©2023 CNES / Airbus, Imagery; ©2023 CNES / Airbus, Maxar Technologies); c) Photo of seismic and ERT setup (M. Zolchow); d) Aerial photo of Chiselet tell (G. Bilotti).ADVANCES IN ON- AND OFFSHORE ARCHAEOLOGICAL PROSPECTION  Proceedings of the 15th International Conference on Archaeological Prospection  ICAP 2023KIEL-UP • DOI: https://doi.org/10.38072/978-3-928794-83-1/p63 317 to implement accurate free-surface boundary conditions in the presence of strong topography. In order to obtain stable and interpretable results despite the strong non-linearity of the full-waveform inversion, a multi-stage inversion strate-gy was implemented. This combines a sequential lowpass filter strategy including alternating offset windowing with a high frequency bandpass filter strategy (Köhn et al. 2019) in order to ensure a similar waveform-adaptation of Love- and SH-wave. To enhance and verify interpretation, the FWI results are compared to results of electrical resistivity tomography (ERT), down-hole measurements of magnetic susceptibili-ty, corings and small-scale archaeological excavations.Results and discussionThe results of seismic FWI (Fig. 2b) at profile 1 show sev-eral horizontal layers of alternating low (< 200 m/s) and high (> 200 m/s) shear wave velocity with thickness of 1 - 2 m, while the uppermost layer is characterized by comparatively very low (< 120 m/s) velocity. The layer boundaries correlate with peaks of increased magnetic sus-ceptibility in 1D - depth curves, measured with down-hole probes at five positions along the profile. The anomalies of positive magnetic susceptibility can be related to settle-ment layers known from coring and excavation. Therefore, it remains open, whether the high shear wave velocities are caused by consolidated leveling layers or by massive layers of house remains and ceramics, which could be identified in a small test excavation trench. Furthermore, the FWI result shows no clear layer boundary or velocity difference between anthropogenic settlement layers and underlying natural sediments, which was identified by corings in a depth of 7 – 8 m. Therefore, both units must be assumed to feature comparable seismic material parameters. ERT mea-surements on profile 1 (Fig. 2c) are interfered by a high degree of dehydration at the ground surface resulting in low penetration and weak depth resolution.On profile 2 at the southern tell flank anomalies of low seismic velocity (Fig. 3a) and electric resistivity (Fig. 3b) may refer to a former paleochannel. A vertical bound-ary between high seismic velocities (> 250 m/s) of the tell and lower velocities (< 150 m/s) of the surrounding plane sediments indicate an erosional impact of the paleo-channel at the tell flank. Fig. 2: a) Comparison of seismic FATT (a), seismic FWI (b) including 1D-depth curves of magnetic susceptibility (black curves) and marked layer boundaries (dashed lines) and ERT (c) of profile 1. ADVANCES IN ON- AND OFFSHORE ARCHAEOLOGICAL PROSPECTION  Proceedings of the 15th International Conference on Archaeological Prospection  ICAP 2023318  KIEL-UP • DOI: https://doi.org/10.38072/978-3-928794-83-1/p63ConclusionAlthough further investigations including seismic cross pro-files and intensified bore-hole geophysics are necessary to verify the current results and enhance interpretation, the presented seismic FWI results illustrate the potential of the method for archaeological prospection of settlement mounds. AcknowledgmentsThis research was funded by the Deutsche Forschungs-gemeinschaft (DFG, German Research Foundation, Project number 290391021, SFB 1266: Scales of Transformation: Human-environmental Interaction in Prehistoric and Ar-chaic Societies). ReferencesKöhn D, De Nil D, Kurzmann A, Przebindowska A, Bohlen T. On the influence of model parametrization in elastic full waveform tomo-graphy. Geophys J Int. 2012;191 (1):325-345. doi: 10.1111/j.1365-246X.2012.05633.x Köhn D, Wilken D, De Nil D, Wunderlich T, Rabbel W, Werther L, et al. Comparison of time-domain SH waveform inversion strate-gies based on sequential low and bandpass filtered data for im-proved resolution in near-surface prospecting. J Appl Geophys. 2019;160:69–83. doi: 10.1016/j.jappgeo.2018.11.001 Pan Y, Gao L, Bohlen T. Time-domain full-waveform inversion of Rayleigh and Love waves in presence of free-surface topo-graphy. J Appl Geophys. 2018;152:77–85. doi: 10.1016/j.japp-geo.2018.03.006Ulugergerli E, Uyanik O. Statistical correlations between seismic wave velocities and SPT blow counts and the relative density of soils. J Test Eval. 2007;35(2):187–191. doi: 10.1520/JTE100159  Open AccessThis paper is published under the Creative Commons Attri-bution 4.0 International license (https://creativecommons.org/licenses/by/4.0/deed.en). Please note that individual, appropriately marked parts of the paper may be excluded from the license mentioned or may be subject to other co-pyright conditions. If such third party material is not under the Creative Commons license, any copying, editing or pu-blic reproduction is only permitted with the prior consent of the respective copyright owner or on the basis of rele-vant legal authorization regulations.Fig. 3: a) Comparison of seismic FATT (a), seismic FWI (b) including interpretation (black lines) and ERT (c) of profile 2.

First results from stratigraphic investigation of Chiselet tell (Romania) using seismic full waveform inversion

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First results from stratigraphic investigation of Chiselet tell (Romania) using seismic full waveform inversion

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