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U.S. Geological Survey Data Series 496

SEG-Y Format


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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, which 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 software.

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 bold 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 = M-1 sum (M = 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 bold 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 (in meters).
65 - 68  Water depth at group.
69 - 70  Scalar to be applied to all elevations and 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 that 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 the initiation time of the energy source. May be 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 (decibels).
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,...,32767).
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  Gap 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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