Figure 11. 3-D deformation field modeling at Merapi on the 1996-1997 period: GPS displacements (red arrows), computed tilt field at the surface of the volcano (contour lines) and location of the tilt station (DEL). Deep magma chamber is deduced from both displacements and tilt observations. Because in elasticity, dP ÷ dV ÷ displacements, we avoid the difficult task of Young’s modulus estimation, and resolve only the volume variation of the source. Superficial magma chamber has been proposed from seismic observations but is not compatible with our deformation data. The computed volume variation is 3 times larger than the observed volume at the summit (3.2 ± 0.2 106 m3).

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