Magnetotelluric data file J-format: A.G. Jones; 5 October 1994 version: 2.0 ------------------------------------------------------------------------------- A file of MT data responses consists of a COMMENT BLOCK, followed by an INFORMATION BLOCK, followed by one or more DATA BLOCKs for that site. ------------------------------------------------------------------------------- COMMENT BLOCK: ============== At the beginning of a data file, as many comment lines as required can be written. Each line must begin with the hash (#) mark. None of this information is required or read by the reading routine. Example:- # MT & GDS estimates from LIMS codes version: v3.1 # # Site info: Phoenix site 401 # Ex length: 133 # Ey length: 135 # Ex azimuth: 12 True North # Ey azimuth: 102 True North # Hx azimuth: 12 True North # Coherence minimum: 0.650000 # Coherence maximum: 0.990000 # Maxtype:JKN # Ntype: 1 # Weight: Y # ------------------------------------------------------------------------------- INFORMATION BLOCK: ================== This block contains information about the site co-ordinates and site orientation. Each line must begin with a"greater-than" (>) sign, followed by a recognizes keyword. After the keyword must be an equals (=) sign, followed by the numeric value. The following keywords are currently supported:- AZIMUTH the orientation of the "X"-direction of the responses LATITUDE site latitude in degrees and decimals LONGITUDE site longitude in degrees and decimals ELEVATION site elevation in metres Example:- >AZIMUTH = 45.0 >LATITUDE = 57.7517 >LONGITUDE = -103.9600 >ELEVATION = 0.0 ------------------------------------------------------------------------------- DATA BLOCK: The data block follows the comment and information blocks. The data block contains the site responses in a variety of formats (either apparent resistivities and phases, or impedances - if impedances then units must be specified). MT data responses are stored in the following format: RECORD ENTRY FORMAT DESCRIPTION Record 1:XXX001 A6 6 alphanumeric STATION NAME (case insensitive) survey XXX, station 001 Record 2:RXY A3 3 alphanumeric DATA TYPE (case insensitive) 1st character must be: R - apparent resistivities and phases S - as "R" but upward-biased estimates Z - impedances Q - as "Z" but upward biased estimates C - "Z" expressed as Schmucker C function T - GDS transfer functions 2nd/3rd characters can be XX - xx MT impedance element XY - xy MT impedance element YX - yx MT impedance element YY - yy MT impedance element TE - TE MT impedance element TM - TM MT impedance element AV - Berdichevsky average DE - determinant average ZX - Tzx transfer function ZY - Tzy transfer function Convention: The convention used is for RXY to represent the E-polarization (TE) mode, and for RYX to represent the B-polarization mode. If the data are stored as impedances, then the units must be specified following the data type code. The two keywords are either "SI", for units of ohms, or "field", for units of mV/km/nT. The preferred usage is ohms. The following two examples are permitted:- ZXX SI units (ohms) ZXX field units (mV/km/nT) Only the keywords "SI" and "field" are used. The other words are for clarification and confirmation. Record 3: n 1I(free) number of points to follow For data type=R?? 9F(free) Record 4: period(1), rho, pha, rhomax, rhomin, phamax, phamin, wrho, wpha . . Record 4+n: period(n), rho, pha, rhomax, rhomin, phamax, phamin, wrho, wpha period: period in s, if negative then is frequency in Hz rho : apparent resistivity, if negative then rejected pha : phase in degrees rhomax: rho + 1 standard error rhomin: rho - 1 standard error phamax: pha + 1 standard error phamin: pha - 1 standard error wrho : weight for rho, if <0 then rejected wpha : weight for phase -999. : missing data marker The GSC responses are stored after the above in the following format: Record 4: period(1), real, imag, error, weight . . Record 4+n: period(n), real, imag, error, weight period: period in s, if negative then is frequency in Hz real : real part of the transfer function imag : imaginary part of the transfer function error : standard error weight: weight (Note: some weights are in error!) -999. : missing data marker Record 4+n+1: Repeat of 2 - 4+n for a different type from the same station Note: each type can have differing "n", but for MTREAD to construct RAV and RDE correctly, there must be the same number of periods in the same order for each of the two or four types respectively. Example:- PCSE04 RXY 40 0.2604E-02 -18.52 50.3 19.67 17.41 52.0 48.5 0.93 0.93 0.3472E-02 12.39 54.7 12.84 11.96 55.8 53.7 0.97 0.97 0.5208E-02 13.58 53.6 14.76 12.46 56.0 51.2 0.87 0.87 0.6944E-02 14.53 54.5 14.93 14.13 55.3 53.7 0.94 0.94 0.1042E-01 14.70 58.4 15.47 13.96 59.8 56.9 0.90 0.90 0.1389E-01 -999.0 -999.0 -999.0 -999.0 -999.0 -999.0 -999.00 -999.00 0.2083E-01 11.56 61.4 11.96 11.17 62.4 60.4 0.92 0.92 0.2778E-01 9.311 59.6 9.591 9.036 60.5 58.8 0.92 0.92