(a) Station corrections (colour-coded triangles) obtained from the VELEST inversion, along with the retrieved epicentral locations. (b) Improved station corrections, obtained by fixing the location of well-constrained reference hypocentres. Epicentral locations with this new set of station corrections are shifted back towards SE. (c) Histograms of the differences along latitude, longitude and depth between 1-D and 3-D hypocentral locations. 1-D locations are obtained either with station corrections shown in (a) yellow histogram, or with the improved station corrections shown in (b) blue histogram. 3-D locations are obtained in the model shown in Fig. 7.