Rayleigh-wave Resonance Analysis: a Methodological Test on a Viking Age Pit House

摘要

Seismic surface-waves may show amplitude resonances at certain frequencies depending on the thickness and elastic parameters of near-surface layers. We investigate if resonance frequencies of Rayleigh-waves, (seismic surface-waves polarized in the vertical plane) can be used to prospect archaeological remains of small-scale buildings such as pit houses. Our test site is a newly detected Viking age village on the island of Fohr (north Germany) where we concentrated on one typical pit house. The results from resonance analysis are compared with magnetic data, ground penetrating radar (GPR) and classical seismic refraction measurements. The method of Rayleigh-wave resonance mapping used in this paper is based on the idea that Rayleigh-wave oscillations on top of anthropogenic structures will show different resonances than on undisturbed soil. We perform spectral analysis of these oscillations to provide information related to the seismic site response. We process single vertical component recordings and map the change in resonance frequency that can be related to the archaeological objects. The test showed that the pit house can be mapped by Rayleigh-wave resonance analysis with a horizontal resolution of similar to 0.6 m. Corresponding computations of the depth of the pit house agree with the results from GPR, magnetic modelling and refraction seismics. A modelling study helped to understand the connection between subsoil shear-wave velocity model and the signal generated by the pit house. The progress of seismic field measurement is slow compared to GPR and magnetometry. However, since seismic methods are based on elastic subsoil parameters, it can be applied in cases where magnetic contrasts are low or GPR fails because of high electromagnetic wave absorption. Copyright (C) 2015 John Wiley & Sons, Ltd.