* j.liu-4@tudelft.nl © 2018 European Association of Geoscientists & Engineers Near Surface Geophysics, 2018, 16, 372-382 doi:10.3997/1873-0604.2018013 372 Seismic interferometry facilitating the imaging of shallow shear-wave reflections hidden beneath surface waves Jianhuan Liu * , Deyan Draganov and Ranajit Ghose Department of Geoscience and Engineering, Delft University of Technology, Delft, The Netherlands Received September 2017, revision accepted April 2018 ABSTRACT High-resolution reflection seismics is a powerful tool that can provide the required resolution for subsurface imaging and monitoring in urban settings. Shallow seismic reflection data acquired in soil-covered sites are often contaminated by source-coherent surface waves and other linear moveout noises (LMON) that might be caused by, e.g., anthropogenic sources or harmonic distor- tion in vibroseis data. In the case of shear-wave seismic reflection data, such noises are particularly problematic as they overlap the useful shallow reflections. We have developed new schemes for suppressing such surface-wave noise and LMON while still preserving shallow reflections, which are of great interest to high-resolution near-surface imaging. We do this by making use of two tech- niques. First, we make use of seismic interferometry to retrieve predominantly source-coherent surface waves and LMON. We then adaptively subtract these dominant source-coherent surface waves and LMON from the seismic data in a separate step. We illustrate our proposed method using synthetic and field data. We compare results from our method with results from frequency–wave- number (f-k) filtering. Using synthetic data, we show that our schemes are robust in separating shallow reflections from source-coherent surface waves and LMON even when they share very similar velocity and frequency contents, whereas f-k filtering might cause undesirable artefacts. Using a field shear-wave reflection dataset characterised by overwhelming LMON, we show that the reflectors at a very shallow depth can be imaged because of significant suppression of the LMON due to the application of the scheme that we have developed. amount of (dispersive) surface waves, which generally camou- flage the very shallow reflections. The conventional techniques for suppression of surface waves, e.g., muting or spatial filtering (Yilmaz 2001), are ineffective or even detrimental to the target reflections in suppressing this source-generated noise, especially at near offsets. This is especially challenging in urban settings where the available source–receiver offset is often quite limited, and the velocity and frequency content of the surface waves largely overlap with those of the target shear-wave reflections (unlike compressional wave reflections, which usually have much higher velocities than the surface waves). The first goal of the present research is, therefore, to reduce the surface waves due to the active source (source-coherent surface waves) and reveal the very shallow reflections in the recorded data using seismic interferometry (SI) and adaptive subtraction (AS). Also, human activities (e.g., nearby traffic, construction works, or movement of people) are common during urban seis- mic surveys. When many such noise sources are excited simulta- neously in the crossline direction, the traveltime from these noise sources to all receivers depends on the distance between these sources and the receivers. In the urban settings, such noise sources are mainly linearly distributed (such as in construction INTRODUCTION Engineering and environmental problems (e.g., sinkhole and groundwater-related issues) in urban areas often require highly detailed information about the subsurface structure in depth to a few metres. Among all available geophysical methods, for soil- covered areas, high-resolution reflection seismics using shear or S-waves (e.g., Pullan, Hunter and Neave 1990; Hasbrouck 1991; Ghose, Brouwer and Nijhof 1996; Ghose and Goudswaard 2004; Pugin et al. 2004; Krawczyk, Polom and Beilecke 2013; Konstantaki et al. 2014) is one of the few options to accomplish the target resolution of the subsurface in an urban setting. For example, using specialised seismic vibratory sources and shear waves, it has been possible in the past to achieve decimetre-scale seismic resolution in the near-surface soils (e.g., Ghose et al. 1996; Brouwer et al. 1997; Ghose et al., 1998; Ghose 2002; Ghose and Goudswaard 2004). However, most cities are located in soil-covered plains or Quaternary basins overlying consolidated bedrock (Sinsakul 2000; Haworth 2003). Shallow shear-wave reflection data acquired in such soil-covered sites are characterised by a large