Koehn, D., Meier, T., Fehr, M., De Nil, D. and Auras, M. (2016) Application of 2D elastic Rayleigh waveform inversion to ultrasonic laboratory and field data. Near Surface Geophysics, 14 (2139). DOI 10.3997/1873-0604.2016027.

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Abstract

In addition to geophysical applications from the near surface to a global scale, seismic full‐waveform inversion can be applied to ultrasonic data on the centimetre and decimetre scales for nondestructive testing of pavements, facades, plaster, sculptures, and load‐bearing structures such as pillars or core samples from boreholes, which can consist of geo‐materials and non‐geomaterials. Classical non‐destructive testing approaches are based on the inversion of body‐wave travel times to deduce P‐wave velocity models. In contrast, surface waves (especially Rayleigh waves) are well suited to quantify surficial alterations of material properties, e.g., due to weathering. Furthermore, ultrasonic measurements of test samples with known material parameters close the gap between synthetic tests or analytical solutions and field data applications to estimate the accuracy of seismic modelling and inversion codes. Due to the scale invariance of the problem, the full‐waveform‐inversion approaches developed on the ultrasonic scale are also applicable to larger scale geophysical problems. In this paper, we demonstrate the potential of two‐dimensional Rayleigh waveform inversion on the ultrasonic scale using two data examples acquired with a single‐fold, low‐coverage acquisition geometry. For a simple homogeneous Plexiglas block in a controlled laboratory environment, we discuss the accuracy of visco‐elastic Rayleigh wave modelling, as well as the sensitivity of two‐dimensional elastic full‐waveform inversion with respect to small data residuals. While the inversion is restricted to the recovery of the S‐wave velocity model, a passive visco‐elastic modelling approach with a homogeneous average ‐model is required in order to describe amplitude loss and dispersion of the Rayleigh wave. The applicability of this approach under field conditions is illustrated for an ultrasonic data example from the weathered sandstone facade of the Porta Nigra in Trier (Germany). In addition to a random medium resolution analysis of the full‐waveform‐inversion result, we particularly emphasise the importance of lateral model smoothing to mitigate small‐scale inversion artefacts and to avoid erroneous interpretations. The estimated two‐dimensional S‐wave velocity anomalies correlate well with prominent surficial weathering effects in the upper about 3 cm.

Document Type:	Article
Research affiliation:	OceanRep > The Future Ocean - Cluster of Excellence > FO-R09 Kiel University Kiel University > Kiel Marine Science OceanRep > The Future Ocean - Cluster of Excellence OceanRep > The Future Ocean - Cluster of Excellence > FO-R06
Refereed:	Yes
Open Access Journal?:	Yes
Publisher:	European Association of Geoscientists and Engineers
Projects:	Future Ocean
Date Deposited:	04 Oct 2017 13:46
Last Modified:	23 Sep 2019 20:55
URI:	https://oceanrep.geomar.de/id/eprint/39618

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