Step 1: Result of 3D resistivity inversion < 1000m
From the 3D grid of MT data inversion, one can extract interpolated section of electrical resistivity. Here are presented horizontal map of the resistivity at 2 depths, in the layer n°5 (average resistivity between 351 to 621m) and layer n°6 (between 621 to 1081 m). Close to the surface, the volcanoes signatures are clearly visible as conductive zones. This pattern disappears with depth, except below the largest volcanoes.
Step 2: Result of 3D resistivity inversion > 1000m
Here are presented horizontal map of the resistivity at 2 depths, in the layer n°7 (average resistivity between 1081 to 1851m) and layer n°8 (between 1851 to 3051 m). At these depths, the volcanoes roots are less visible. A north-south elongated resistive body (purple) appears with a deep root dipping westward.
Step 3: Integrated geophysical interpretation
Here are presented vertical sections, along a north-south profile centered on the main resistive body. MT, gravity and magnetic data (not shown here) reveal a resistive, dense and magnetic body. Surrounding less magnetic zones correspond to the hydrothermalized margins of the magmatic body. Superficial conductive layer (< 10 Ω.m) correlated with hydrothermal mineralization’s is interpreted as a « cap rock » partly eroded on the northern part. A potential « contracting-aging » reservoir is interpreted south of the main resistor.
Step 4: Conceptual resistivity model
The figure represents a conceptual resistivity model (after Rahajo, 2012) associated with temperature, alteration processes and geothermal fluid in the case of a geothermal system in a recent volcano. Arrows indicate the geothermal fluid flows.
