Performance of high-resolution impact and vibration sources for underground seismic exploration of clay formations at the scale of a rock laboratory

SUMMARY Low permeability, high retention capacity and self-sealing ability are advantageous characteristics that attributed to argillaceous rocks. In contrast, other properties of clay, such as internal heterogeneities, strong attenuation anisotropic behaviour, pose major challenges for underground exploration techniques. Although with regard the storage nuclear waste, seismic in itself is great importance fill gap between surface borehole investigations. Furthermore, prevent destruction host rock during this demands low non-invasive To approach these issues, a survey was carried out Mont Terri Underground Rock Laboratory (Switzerland) using gallery-based acquisition an operating range up several decametres. The campaign included three-component sensors two different source types (pneumatic impact magnetostrictive vibroseis source). An executed comparison analysed types, example frequency or amplitude behaviour generated wavefield, assess their performance under similar conditions at meso scale reveal strengths weaknesses clay. Based on findings, we performed traveltime reflection analyses demonstrate potential characterize clay formations map structures. highest velocities found carbonate-rich sandy facies (vPmax = 4000 m s?1, vSmax 2050 s?1), slower 3720 1840 s?1) slowest shaly 3220 1480 s?1). velocity anisotropy larger within (AvP 23 per cent, AvS 32 cent) compared 9 12 it more pronounced S-waves than P-waves. Thus, meso-scale techniques suited Opalinus Clay detail.