An anomaly in our understanding of upper continental crustal structure is caused by conflicting observations from structural geologists and reflection seismologists. Near-surface structure in metamorphic terrain is frequently steeply dipping or vertical, but seismic reflection images display flat-lying reflectors below depths of a few kilometers. The seismic image of the topmost 2–3 km is usually blank. How can this be, when seismic reflections are supposed to represent primary geological structure?
Seismic measurements in and around a deep borehole could solve this dilemma. Surface seismic observations and physical samples collected from the hole by wireline logging, particularly by vertical seismic profiles (VSPs), could then be compared.