Patent ID: 8055446

Claim:
A method of processing magnetotelluric data to identify subterranean deposits, wherein said data comprise the amplitude of alternating magnetic or electrical fields recorded over time in at least two vector components at one or more locations in an area of interest, said method comprising: (a) identifying amplitude pulses in said data, said pulses being time segments comprising an amplitude peak meeting defined threshold criteria in at least one said vector component; (b) filtering said pulses at a set of predetermined frequencies to separate amplitude data at each said frequency from the remainder of the amplitude data in said pulses, wherein said frequencies correspond to subterranean depths over a range of interest; and (c) statistically analyzing a differential impedance ΔZ of said pulses at each said frequency at each said location to determine a value correlated to the resistance of the earth at each said frequency, the resistance being indicative of the presence or absence of deposits at the corresponding subterranean depth at the location; wherein differential impedances of a given pulse x, ΔZ x (f), are defined as follows: Δ ⁢ ⁢ Z x ⁡ ( f ) = ( A n ⁢ E x , n ⁡ ( f ) H x , n ⁡ ( f ) + A n + 1 ⁢ E x , n + 1 ⁡ ( f ) H x , n + 1 ⁡ ( f ) + … + A N ⁢ E x , N ⁡ ( f ) H x , N ⁡ ( f ) ) - ( A m ⁢ E x , m ⁡ ( f ) H x , m ⁡ ( f ) + A m + 1 ⁢ E x , m + 1 ⁡ ( f ) H x , m + 1 ⁡ ( f ) + … + A M ⁢ E x , M ⁡ ( f ) H x , M ⁡ ( f ) ) where ΔZ x (f) is the differential impedance of pulse x; E x,n (f) through E N (f) and E x,m (f) through E x,M (f) are the recorded or synthetic electric fields for vector components n through N and m through M of pulse x; H x,n (f) through H x,N (f) and H x,m (f) through H x,M (f) are the recorded or synthetic magnetic field for vector components n through N and m through M of pulse x; E x , n ⁡ ( f ) H x , n ⁡ ( f ) ⁢ ⁢ through ⁢ ⁢ E x , N ⁡ ( f ) H x , N ⁡ ( f ) ⁢ ⁢ and ⁢ ⁢ E x , m ⁡ ( f ) H x , m ⁡ ( f ) ⁢ ⁢ through ⁢ ⁢ E x , M ⁡ ( f ) H x , M ⁡ ( f ) are the impedances for vector components n through N and m through M of pulse x; and A n through A N and A m through A M are complex scaling factors applied to the impedances for vector components n through N and m through M of pulse x.