2.2.1. Ground Truth: Siljan, Sweden

Of special importance to inferring sills from reflection data is the multichannel seismic reflection profiling at the Siljan Ring in east central Sweden (Figures 1 and 3; [54–56]). The Siljan seismic profiles (Figure 3) reveal a distinctive sequence of strong reflections that have been identified as dolerite sills by drill holes (Figure 4). Analogy with the reflection character of the Siljan reflections (high amplitudes, subhorizontal orientation, linear extent) has been a primary argumen<sup>t</sup> for the interpretation of similar appearing reflections elsewhere in the world, including those discussed in this paper.

**Figure 3.** Strong subhorizontal reflections mapped in the upper 10 km of Proterozoic crust by seismic reflection profiling at the Siljan Ring Sweden [55]. Depth assuming the average velocity of 6 km/s. R1–R5 label individual reflectors in this stack.

**Figure 4.** Detail of the Siljan Ring reflections in Figure 3 correlated with the borehole observations of diabase intrusions (solid black lines, with indicated thicknesses [55]). The sills date from 850 to 1700 my. This clear identification of strong reflectivity with mafic sills [55,56] has served as a reference for the interpretation for similar appearing reflection sequences in other areas.
