IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS007 Oral Presentation 1952
Three - Dimensional resistivity model of the Volcano Elbrus (Northern
Caucasus) revealed from MT and satellite data
Prof. Viacheslav Spichak
EM data interpretation methodology Geoelectromagnetic Research Center IPE RAS IAVCEI
Borisova Valeriya, Fainberg Edward, Khalezov Alex, Goidina Aleksandra
Construction of the 3D resistivity model of the volcano requires array EM survey provided over the
whole surface, which is often difficult due to its relief surface and inaccessibility of some zones
surrounding the summit. This problem could be overcome by using a new approach, which combines
analysis of both ground and satellite data. It is based on the method of the correlation similitude, which
enables to fill the gaps in the EM data using other geological and/or geophysical data, correlating with
the resistivity values. In particular, the latter ones could consist from the tectonic fragmentation of the
rocks obtained by analysis of the satellite photographs of the surface using the method developed in
(Nechaev, 1999). In turn, it is based on the estimation of the coefficient of the tectonic fragmentation
(CTF) from the specific lineaments' lengths determined by the photographs of the studied area. The
approach mentioned above was used in order to construct a 3D resistivity model of the Elbrus volcano
(northern Caucasus) by MT data measured along one longitudinal profile crossing its summit. Twodimensional
inversion of the MT data resulted in a resistivity values in the same nodes of the grid,
where the CTF was determined. A special neural network based technique was used in order to extract
the subset of these nodes, which supports the biggest correlation ratio between these two parameters.
At the next step an artificial neural network was taught to correspondence of these parameters
determined only in the selected nodes followed by reconstruction of the resistivity distribution in the
whole area from the CTF values. The analysis of the constructed resistivity model resulted in detection
of the relatively conductive body at the depth 40 km (conductivity - 0.04 S/m, dimensions in vertical
axis, latitude and longitude being equal to 20 km, 35km and 15km, accordingly), which can be treated
as a magma chamber. The model of the Elbrus volcano can be used for solution of two important tasks
related to the monitoring of its activity: optimization of the EM survey network and determination of the
background level for detection of the time and spatial variations of the manifestations of the tectonic
activity leading to the eruptions.
Keywords: magnetotelluric, volcano, three dimensional