Compilation of SKS splitting data. Red: measurements from Barruol et al. (2004), dark blue: measurements from Bokelmann et al. (2013), purple: measurements from Bonnin et al. (2017), pink: measurements from Bormann et al. (1993), brown: measurements from Judenherc et al. (2003), green: measurements from Vinnik et al. (1994), light blue: measurements from (Walker et al. (2005), orange: measurements from Walther et al. (2014). SKS splitting data have good lateral but poor vertical resolution and constrain the upper mantle anisotropy (Wüstefeld et al., 2009; Vauchez et al., 2012; Tommasi and Vauchez, 2015). The high surface heat flow areas are defined from Figure 3B.