Figure 4
From: Seismic imaging and petrology explain highly explosive eruptions of Merapi Volcano, Indonesia
Schematic illustration of Merapi’s magma plumbing system inferred from our arrival time tomography analysis and published petrological data. (a) Vp and (b) Vp/Vs taken from Fig. 3a,b, respectively, with vertical exaggeration by a factor of 5 to emphasize vertical features. The tomogram in (b) shows an extensive high-Vp/Vs structure that extends from Merapi’s summit to the uppermost mantle with three main (shallow, intermediate, deep) anomalies at <4 km, at ~10–20 km, and at >25 km depth. We interpret the shallow anomaly as a fluid-rich zone, while we interpret the intermediate and deep anomalies to outline magma storage zones. We posit that the 2010 magma was sourced from the top of the intermediate reservoir (below the dashed line) at a depth just below 10 km and thus below the carbonate-dominated upper crust, with a volume of ≥1 km3 (corresponding to the yellow ellipse). This estimate further constrains previous estimates based on phase-equilibrium experiments6. Magma in this zone has a temperature of ~925–950 °C, ~3–4 wt% H2O, and ~1000 ppm melt CO25,6, while magma deeper in the system may be significantly more volatile-rich and hazardous in case of ascent and eruption. We have assumed an average crustal density of 2242 kg/cm3 (cf.15) for the upper 10 km of the section, while we have estimated an average crustal density of 2900 kg/cm3 for the crust below (cf.33, for intermediate-mafic crust). Open dots depict relocated hypocenters of earthquakes recorded during the DOMERAPI experiment projected from a distance up to 20 km on both sides of the vertical section.
