Absolute strain determination from a calibrated seismic field experiment

David W. S. Eaton, Adam Pidlisecky, Robert James Ferguson, Kevin W. Hall

The concepts of displacement and strain are fundamental to our understanding of how elastic waves propagate in the subsurface, but accurate absolute determination of these quantities is rare. In August 2009, a field experiment was conducted on University of Calgary lands near Priddis, Alberta (Rothney Astrophysical Observatory) using various seismic sources (minivibe, weight drop) and receivers (geophones, accelerometers and broadband seismometers). A 3-component shot gather using a weight-drop source was recorded by 8 broadband seismometers and used to verify the absolute instrumental response of 80 3-C 10 Hz geophones, recorded using the university's ARAM-24 acquisition system. Although significant lateral amplitude variability is evident, an empirically derived average response for the ARAM system agrees with manufacturer specs to within < 4 in the frequency range 2-40 Hz, representing the bandwidth overlap between the geophone and seismometer systems. Based on this calibration, the strain associated with ground roll and refracted P- and S-wave energy is ~10-7.