USGS
File Format
Seismic Data Format

The SEG-Y files on this CD-ROM conform to the SEG-Y standard format (Barry and others, 1975) as follows:
Example of a 3200-byte EBCDIC reel identification header created with Xseismics:

C 1 CLIENT Atlantic Mar Geo COMPANY USGS CREW NO 0
C 2 LINE 1 AREA Not specified MAP ID None
C 3 REEL NO 3 DAY-START OF REEL YEAR 1995 OBSERVER
C 4 INSTRUMENT: MODEL SERIAL NO
C 5 DATA TRACES/RECORD 2 AUXILIARY TRACES/RECORD 0 CDP FOLD
C 6 SAMPLE INTERVAL 250 SAMPLES/TRACE 2048 BITS/IN EXB BYTES/SAMPLE 4
C 7 RECORDING FORMAT SEGY FORMAT THIS REEL SEGY MEASUREMENT SYSTEM
C 8 SAMPLE CODE: 1 (4 BYTE FLOATING)
C 9 GAIN TYPE: FIXED
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 LENGTH 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: RECORD
C19 AMPLITUDE RECOVERY:
C20 MAP PROJECTION ZONE ID COORDINATE UNITS
C21 PROCESSING:
C22 ACOUSTIC SOURCE: Water FIRE RATE: 5 SECS:
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
C37
C38
C39
C40 END EBCDIC

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The SEG-Y binary reel identification header. The values in red are assigned in the SEG-Y output from Xseismics.

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

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The SEG-Y defined 240-byte trace identification header values. The values in red are assigned in the SEG-Y output from Xseismics.

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.

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References

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