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The SEG-Y standard format (Barry and others, 1975) used by the U.S. Geological Survey for seismic data consists of the following:

  • A 3600-byte reel identification header with the first 3200 bytes consisting of a EBCDIC header block and a 400-byte binary header block. Both headers include information specific to line and reel number.
  • The trace data block follows the reel identification header. The first 240 bytes of each trace block is the binary trace identification header. The seismic data samples follow the trace identification header. The trace data are recorded in binary format. The format that follows is that used for many of our seismic data sets. There is a new revision 1 standard (www.seg.org/publications/tech-stand/seg_y_rev1.doc )

EBCDIC Headers

Example of a 3200-byte EBCDIC reel identification header.

Column Numbers Description
C 1 CLIENT COMPAGNY CREW NO
C 2 LINE AREA MAP ID
C 3 REEL NO DAY-START OF REEL YEAR OBSERVER
C 4 INSTRUMENT: DELPH MODEL xx SERIAL NO
C 5 DATA TRACES/RECORD AUXILIARY TRACES/RECORD CDP FOLD
C 6 SAMPLE INTERVAL SAMPLES/TRACE BITS/IN BYTES/SAMPLE
C 7 RECORDING FORMAT FORMAT THIS REEL MEASUREMENT SYSTEM
C 8 SAMPLE CODE:
C 9 GAIN TYPE:
C10 FILTERS: ALIAS NOTCH Hz Band - Hz SLOPE - DB/OCT
C11 SOURCE: TYPE NUMBER/POINT POINT INTERVAL
C12 PATTERN: LENGTH WIDTH
C13 SWEEP: START Hz END Hz LENGHT ms CHANEL NO TYPE
C14 TAPER: START LENGHT ms END LENGHT ms TYPE
C15 SPREAD: OFFSET MAX DISTANCE GROUP INTERVAL
C16 GEOPHONES: PER GROUP SPACING FREQUENCY MFG MODEL
C17 PATTERN: LENGTH WIDTH
C18 TRACES SORTED BY:
C19 AMPLITUDE RECOVERY:
C20 MAP PROJECTION ZONE ID COORDINATE UNITS
C21 PROCESSING:
C22 PROCESSING:
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
C37
C38
C39
C40 END EBCDIC

Binary Headers

The SEG-Y binary reel identification header.

Byte Numbers Header Value Description
3201 - 3204 Job identification number.
3205 - 3208 Line number.
3209 - 3212 Reel number.
3213 - 3214 Number of data traces per record.
3215 - 3216 Number of auxiliary traces per record.
3217 - 3218 Sample interval, microseconds, this file (reel).
3219 - 3220 Sample interval, microseconds, original field recording.
3221 - 3222 Number of samples per data trace, this file (reel).
3223 - 3224 Number of samples per data trace, original field recording.
3225 - 3226 Data sample format code: 1 = floating point (4 bytes) 2 = fixed point (4 bytes) 3 = fixed point (2 bytes) 4 = fixed point with gain code (4 bytes).
3227 - 3228 CDP fold.
3229 - 3230 Trace sorting code: 1 = as recorded (no) sorting) 2 = CDP ensemble 3 = single fold continuous profile 4 = horizontally stacked
3231 - 3232 Vertical sum code: 1 = no sum 2 = two sum ... N = N sum (N = 32,767)
3233 - 3234 Sweep frequency at start.
3235 - 3236 Sweep frequency at end.
3237 - 3238 Sweep length, ms.
3239 - 3240 Sweep type code: 1 = linear 2 = parabolic 3 = exponential 4 = other
3241 - 3242 Trace number of sweep channel.
3243 - 3244 Sweep trace taper length, ms, at start if tapered.
3245 - 3246 Sweep trace taper length, ms, at end.
3247 - 3248 Taper type: 1 = linear 2 = cos 3 = other
3249 - 3250 Correlated data traces: 1 = no 2 = yes
3251 - 3252 Binary gain recovered: 1 = yes 2 = no
3253 - 3254 Amplitude recovery method: 1 = none 2 = spherical divergence 3 = AGC 4 = other
3255 - 3256 Measurement system: 1 = meters 2 = feet
3257 - 3258 Impulse signal: 1 = Upward = negative number. 2 = Upward = positive number.
3259 - 3260 Vibratory polarity code - seismic signal lags pilot signal by: 1 = 337.5 - 22.5 degrees 2 = 22.5 - 67.5 degrees 3 = 67.5 - 112.5 degrees 4 = 112.5 - 157.5 degrees 5 = 157.5 - 202.5 degrees 6 = 202.5 - 247.5 degrees

Trace Identification Headers

Example of the SEG-Y defined 240-byte trace identification header values.

Byte Numbers

Header Value Description

1 - 4

Trace sequence number within line.

5 - 8

Trace sequence number within file (reel)

9 - 12

Original field record number

13 - 16

Trace number within original field record

17 - 20

Energy source point number.

21 - 24

CDP ensemble number.

25 - 28

Trace number within the CDP ensemble.

29 - 30

Trace identification code: 1 = seismic data

31 - 32

Number of vertically summed traces yielding this trace

33 - 34

Number of horizontally stacked traces yielding this trace

35 - 36

Data use: 1 = production 2 = test

37 - 40

Distance from source point to receiver group.

41 - 44

Receiver group elevation - above sea level are positive, below sea level are negative.

45 - 48

Surface elevation at source.

49 - 52

Source depth below surface (positive number).

53 - 56

Datum elevation at receiver group.

57 - 60

Datum elevation at source.

61 - 64

Water depth at source (this is the Fish depth below the sea surface in meters*10)

65 - 68

Water depth at group.

69 - 70

Scalar to be applied to all elevations & depths, specified in bytes 41 - 68 to give the real value. Scalar = 1, +/-10, +/-100, +/-1000, or +/-10,000. If positive, scalar is used as a multiplier; if negative, scalar is used as a divisor.

71 - 72

Scalar to be applied to all coordinate specified in bytes 73 - 88 to give the real value. Scalar = 1, +/-10, +/-100, +/-1000, or +/-10,000. If positive, scalar is used as a multiplier; if negative, scalar is used as a divisor.

73 - 76

Source coordinate - X. UTM Easting coordinate

77 - 80

Source coordinate - Y. UTM Northing coordinate

81 - 84

Group coordinate - X. UTM Easting coordinate

85 - 88

Group coordinate - Y. UTM Northing coordinate

89 - 90

Coordinate units: 1 = length (meters or feet) 2 = seconds of arc

91 - 92

weathering velocity.

93 - 94

Subweathering velocity.

95 - 96

Uphole time at source.

97 - 98

Uphole time at group.

99 - 100

Source static correction.

101 - 102

Group static correction.

103 - 104

Total static applied.

105 - 106

Lag time A. Time in ms between end of 240-byte trace identification header and time break. positive if time break occurs after end of header, negative if time break occurs before end of header. Time break is defined as the initiation pulse which may be recorded on an auxiliary trace or as otherwise specified by the recording system.

107 - 108

Lag time B. Time in ms between the time break and positive or negative.

109 - 110

Delay recording time. Time in ms between initiation time of energy source and time when recording of data samples begins.

111 - 112

Mute time - start.

113 - 114

Mute time - end.

115 - 116

Number of samples in this trace.

117 - 118

Sample interval, in microseconds, for this trace.

119 - 120

Gain type of field instruments: 1 = fixed, 2 = binary, 3 = floating point, 4 = --- N = optional use

121 - 122

Instrument gain constant.

123 - 124

Instrument early or initial gain (db).

125 - 126

Correlated: 1 = no 2 = yes

127 - 128

Sweep frequency at start.

129 - 130

Sweep frequency at end.

131 - 132

Sweep length, ms.

133 - 134

Sweep type: 1 = linear 2 = parabolic 3 = exponential 4 = other

135 - 136

Sweep trace taper length at start, ms.

137 - 138

Sweep trace taper length at end, ms.

139 - 140

Taper type: 1 = linear 2 = cos 3 = other

141 - 142

Alias filter frequency.

143 - 144

Alias filter slope.

145 - 146

Notch filter frequency.

147 - 148

Notch filter slope.

149 - 150

Low cut frequency.

151 - 152

High cut frequency.

153 - 154

Low cut slope.

155 - 156

High cut slope.

157 - 158

Year data recorded (four digit integer).

159 - 160

Day of year.

161 - 162

Hour of day (24 hour clock).

163 - 164

Minute of hour.

165 - 166

Second of minute.

167 - 168

Time basis code: 1 = local 2 = GMT 3 = other

169 - 170

Trace weighting factor - defined as 2-N volts for the least significant bit. (N=0, 1,...,32,767)

171 - 172

Geophone group number of roll switch position one.

173 - 174

Geophone group number of trace number one within original field record.

175 - 176

Geophone group number of last trace within original field record.

177 - 178

Gape size (total number of groups dropped).

179 - 180

Overtravel associated with taper at beginning or end of line: 1 = down (or behind) 2 = up (or ahead)

181 - 240 Unassigned - for optional information.

References

Barry, R.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats, Geophysics, v. 40, p. 344-352.

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