Step 1: TEM sounding for static shift correction
At each MT station a Time Domain EM sounding has been performed to measure the shallow resistivity. Indeed, a shallow resistive body close to the MT station would generate a galvanic response on all the frequencies recorded. This would will be partly solved by a 3D inversion, but for 1D interpretation of a single sounding, it is mandatory to check this so called static effect, and correct it if necessary.
Step 2: Gravimetric prospecting
This area has been covered by previous geophysical campaign revealing some interesting features. The available gravimetric data (Baltassat, 2003) were re-analyzed and processed. The density variation in the ground affects the gravity recorded in surface, and after some corrections have been applied, a Bouguer anomaly map can be obtained. The average density which decorrelates the more the topographic effect (Nettleton, 1939) is close to 2, and was used to compute this map. A high pass filter was applied (cut length 8 km). Black dots are gravimetric measurements.
Step 3: Magnetic prospecting
During the previous survey (Baltassat et al. 2003), this area was covered by ground magnetic measurements. The magnetic anomaly after pole reduction is presented here. The volcanic material of various ages highlight generally various responses in link with the varying geomagnetic field.
