geometry definition - Shot spacing was calculated and loaded into a database together with channel offsets.

resample - GI gun data were desampled to a 1 millisecond sample rate. Minisparker data were desampled to a 0.5 millisecond sample rate.

shot edit - Noisy shots or channels within shots were omitted. System crashes and shutdowns were cleaned up by blanking "no data" traces and inserting blank shots as appropriate.

CMP sort - Data were sorted from shot gathers into common-mid-point (CMP) gathers.

velocity picking - Stacking velocities were analysed and assigned interactively using semblance displays and constant velocity stacking panels.

bandpass filter - Hanning bandpass filter - GI gun: (12-24-400-450), minisparker: (18-36-800-1000).

deconvolution - Full trace, operator length 20 samples, gap length 56 milliseconds, white noise 10%.

dip filter - Coherency energy rejection, filter length 101 samples, width 11 traces, dip 1.5 milliseconds per trace.

normal moveout - Using stacking velocities.

stack - 5 to 22 fold depending on shot rate.

migration - Finite difference time migration at 85% of stacking velocity.

display - Waterbottom mute and a 500 millisecond AGC was applied. Image files are positive-only, variable-density profiles. Vertical scale is in milliseconds two-way travel time, horizontal scale bar is provided at bottom of each section. Shotpoints and line crossings are annotated along the horizontal axis.