Figure 6: Schematic representation of the magmatic plumbing system beneath Toba and its relation to the IFZ.

(a) Three-dimensional view of the oblique subduction of the IFZ (red dotted line) beneath Toba. S-velocity anomalies (same as in Fig. 5) are shown in the mantle wedge beneath Toba. The red dotted line depicts the IFZ and the zone of slab tear. (b) Interpretation of the S-wave velocity model in the vertical section shown in Fig. 5. Exaggerated topography is shown above the section. The red triangle indicates the location of the volcanic complex identified in the coastal area. Green dots depict the earthquakes. Blue arrows indicate possible ascent of water from the slab dehydration zone at 80–90 km depth. Red arrows indicate the path of ascending fluids and melts that originated from the slab at ∼150 km depth. The crustal interfaces beneath Toba (solid lines) are shown based on receiver function results¹⁹. Surrounding the Toba Caldera, their shapes are extrapolated according to general knowledge about the crustal nature and isostasy (dotted lines). The location of the GSFZ with the displacement polarity and possible depth propagation is indicated.