Data Series 147

SEG-Y Format

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Note: The web version of this archive does not contain the SEG-Y trace files. These files are very large and would require extremely long download times. To obtain the complete DVD archive, contact USGS Information at 1-888-ASK-USGS or infoservices@usgs.gov.

The seismic data are stored in SEG-Y, integer, Motorola format. The SEG-Y files on this disc conform to the SEG-Y standard format (Barry and others, 1975) with the exception of the first 3,200 bytes of the reel identification header that are in ASCII format. Standard SEG-Y uses an EBCDIC format. The Delph Seismic version of SEG-Y consists of the following:


Example of a 3,200-byte ASCII reel identification header created with Delph Seismic.
C 1 CLIENT COMPANY CREW NO
C 2 LINE line1dS 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 1 AUXILIARY TRACES/RECORD 0 CDP FOLD
C 6 SAMPLE INTERVAL 333 SAMPLES/TRACE 1496 BITS/IN 16 BYTES/SAMPLE 2
C 7 RECORDING FORMAT FORMAT THIS REEL MEASUREMENT SYSTEM
C 8 SAMPLE CODE: FIXED PT
C 9 GAIN TYPE: FIXED
C10 FILTERS: ALIAS 1500 HZ NOTCH HZ BAND - HZ SLOPE - DB/OCT
C11 SOURCE: TYPE NUMBER/POINT POINT INTERVAL
C12 PATTERN: LENGTH WIDTH
C13 SWEEP: START HZ END HZ LENGTH MS CHANEL NO TYPE
C14 TAPER: START LENGTH MS END LENGTH 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: NONE
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 

Example of a 400-byte binary reel identification header.
The values in blue are assigned in the SEG-Y output from Delph Seismic.
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.

The SEG-Y defined 240-byte trace identification header values.
The values in blue are assigned in the SEG-Y output from Delph Seismic.

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 or longitude.
77 - 80 
Source coordinate - Y. UTM Northing coordinate or latitude.
81 - 84 
Group coordinate - X. UTM Easting coordinate or longitude.
85 - 88 
Group coordinate - Y. UTM Northing coordinate or latitude.
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.

Reference:
Barry, R.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats, Geophysics, v. 40, p. 344-352. Also available online at: http://www.seg.org/publications/tech-stand.

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