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). Standard SEG-Y uses the following:
Example of a 3200-byte EBCDIC reel identification header:

C 1 CLIENT U.S.G.S. COMPANY WHFC CREW NO 0
C 2 LINE l2f1.sgy REAL Fire Island, NY MAP ID None
C 3 REEL NO 1 DAY-START OF REEL 098 YEAR 1997 OBSERVER
C 4 INSTRUMENT: MODEL Mudseis SERIAL NO
C 5 DATA TRACES/RECORD 2 AUXILIARY TRACES/RECORD CDP FOLD
C 6 SAMPLE INTERVAL 500 SAMPLES/TRACE 8000 BITS/IN BYTES/SAMPLE 2
C 7 RECORDING FORMAT 3 FORMAT THIS REEL MEASUREMENT SYSTEM
C 8 SAMPLE CODE: Short Integers
C 9 GAIN TYPE:
C10 FILTERS: ALIAS HZ NOTCH HZ BAND HZ SLOPE DB/OCT
C11 SOURCE: NUMBER/POINT POINT INTERVAL
C12 PATTERN: LENGTH WIDTH
C13 SWEEP: HZ HZ LENGTH MS CHANNEL NO TYPE
C14 TAPER: MS MS TYPE
C15 SPREAD:
C16 GEOPHONES:
C17 PATTERN:
C18 TRACES SORTED BY: RECORD
C19 AMPLITUDE RECOVERY:
C20 MAP PROJECTION
C21 PROCESSING:
C22 ACOUSTIC SOURCE: Geopulse FIRE RATE: 0.5 SECS
C23
C24
C25
C26
C27
C28
C29
C30
C31
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The SEG-Y binary reel identification header. The values in red are assigned in the SEG-Y output.
 
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.
 
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., 1 975, Recommended standards for digital tape formats, Geophysics, v. 40, p. 344-352