METHODS OF PROCESSING MAGNETOTELLURIC SIGNALS

Methods for processing magnetotelluric signals to identify subterranean deposits are provided for. The methods comprise obtaining magnetotelluric data from an area of interest. The magnetotelluric data comprises the amplitude of magnetotelluric signals recorded over time at defined locations in the area of interest. The data for each location then is filtered through a set of frequency filters. The frequencies of the frequency filters correspond to subterranean depths over a range of interest. Amplitude peaks in the filtered data then are identified and analyzed to determine a value correlated to the resistance of the earth at each frequency at each location. The resistance values are indicative of the presence or absence of deposits at the corresponding subterranean depth. Preferably, the amplitude data is power is normalized across all locations in the survey, a gain factor is applied to the resistance values to scale the values for depth variation, and the resistance values are displayed as a depth-location plot for interpretation. The amplitude peaks may be analyzed by a number of different statistical approaches. For example, a subset of the peaks falling within defined thresholds or bins within such thresholds may be analyzed, and it has been observed that accurate relative resistivity values may be derived based on the number of peaks, the amplitudes of those peaks, or a combination thereof. Alternate embodiments comprise obtaining magnetotelluric data sampled over relatively long periods of time at defined locations in the area of interest. The magnetotelluric data for each location is then filtered through a set of frequency filters and analyzed to determine a value correlated to the resistance of the earth at each frequency at each location. L'invention concerne des procédés de traitement de signaux magnétotelluriques permettant d'identifier des dépôts souterrains. Ces procédés consistent à obtenir des données magnétotelluriques d'une zone d'intérêt. Ces données magnétotelluriques comprennent l'amplitude de signaux magnétotelluriques enregistrés dans le temps à des endroits précis de la zone d'intérêt. Les données de chaque endroit sont ensuite filtrées à travers un ensemble de filtres de fréquence. Les fréquences des filtres de fréquence correspondent aux profondeurs souterraines d'une gamme d'intérêt. Des pics d'amplitude des données filtrées sont identifiés et analysés afin de déterminer une valeur en corrélation avec la résistance de la terre