UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY DATA REPORT FOR THE 1983 U.S. GEOLOGICAL SURVEY EAST-CENTRAL OREGON SEISMIC REFRACTION EXPERIMENT JOSEPH A. COTTON AND R.D. CATCHINGS 1 1 OPEN-FILE REPORT 89-124 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S.G.S. ^.S.G.S. Menlo Park, California 1989
Transcript
UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY
DATA REPORT FOR THE 1983 U.S. GEOLOGICAL SURVEY
EAST-CENTRAL OREGON SEISMIC REFRACTION EXPERIMENT
JOSEPH A. COTTON AND R.D. CATCHINGS 1 1
OPEN-FILE REPORT 89-124
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S.G.S.
^.S.G.S. Menlo Park, California
1989
TABLES OF CONTENTS
PageIntroduction............................................... 1Description of Survey...................................... 1Instrumentation and Data Reduction......................... 3Acknowledgements........................................... 4References Cited........................................... 4Appendix A: Tape Grade Codes............................... 18Appendic B: Shotpoint and Recorder Locations............... 19Appendix C: Archive Data Tape Format....................... 29
FIGURES
1. Geologic Map of Study Area............................. 22. Schematic Diagram of the Seismic Recorder.............. 63. Schematic Diagram of the System Response Curve......... 74. Record Section of Shotpoint 1A, Shot 10................ 85. Record Section of Shotpoint IB, Shot 3................. 96. Record Section of Shotpoint 2, Shot 7................. 107. Record Section of Shotpoint 3, Shot 4................. 118. Record Section of Shotpoint 4, Shot 6................. 129. Record Section of Shotpoint 5A, Shot 2................. 13
10. Record Section of Shotpoint 5B, Shot 8................. 1411. Record Section of Shotpoint 6A, Shot 9................. 1512. Record Section of Shotpoint 6B, Shot 1................. 16
TABLES
1. Master Shot List (Shot Location and Time).............. 17
INTRODUCTION
In October of 1983, the U.S. Geological Survey conducted a long-range seismic refraction survey across east-central Oregon . A single east-west profile as recorded from the eastern High Cascades across Newberry Crater to the eastern High Lava Plains. The purpose of the investigation was to determine the sub-volcanic crustal and upper mantle velocity structure of Newberry Volcano and the surrounding region. East-central Oregon is of great geologic interest, as it includes the arc-to-back-arc transition zone between two major geologic provinces; the actively extending Basin and Range and the volcanic Cascade mountains. Furthermore, this area marks the southernmost terminus of the Columbia Plateau, the third largest continental flood basalt province on Earth, and an area in which similiar data has been acquired (Cotton and Catchings, 1988).
Included in this report are record sections (Figures 4- 12), lists of shot times, recorder and shotpoint locations (Table 1), data files and a tape grade scale (Appendix A & Appendix B). The data from this experiment have been archived at the National Oceanic and Atmospheric Adminstration (N.O.A.A.). Tapes may be obtained at the
National Geophysical Data CenterNational Oceanic and Atmospheric Adminstration325 BroadwayBoulder, CO., 80303
Appendix C contains a description of the tape formats. An interpretation of the data has been published in a report by Catchings and Mooney (1988).
DESCRIPTION OF SURVEY
The 1983 east-central Oregon profile consisted of a 180-km-long transect which originated in the High Cascades roughly 30 km west of Newberry Volcano and trended east across the High Lava Plains (Figure 1). The transect was recorded in two deployments: the Newberry deployment (the western half of the profile) which extended from Wickiup Dam, Oregon to Riley, Oregon and the Brothers Fault Zone deployment (the eastern half of the profile) which extended from the Riley, Oregon to Harney, Oregon. Each deployment consisted of 120 seismic cassette recorders (SCR), but the field parameters varied significantly for each deployment. Five seperate shotpoints, spaced approximately 15 km apart( 1, 2, 3, 4, 5, and the offset shotpoint #6), were situated along the 60-km long-Newberry deployment. SCR's were spaced at approximately 0.5 km intervals. These parameters were used in order to provide higher resolution of the subsurface beneath the Newberry Volcano. Three shotpoints, spaced approximately 60 km apart (shotpoints 1, 5, and 6), were recorded along the Brothers Fault Zone deployment with SCR's spaced at approximately 1.3 km intervals. These parameters for the Brothers Fault Zone deployment were utilized in order to provide deeper, large-scale crustal data.
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Sources were generated from a total of ten (See Table 1) 900-to 2000-kg explosions located at six different shotpoints . Explosions were detonated in 20-cm diameter drillholes ranging in depth from 40 to 60 meters The drillholes were loaded with ammonium nitrate explosives, boosters, and detonation cord and tamped with approximately 20 meters of gravel. Explosions were detonated with an automated shooting system described by Healy et al. (1982). A signal from a reference chronometer triggered the shooting system by igniting an electrical blasting cap. The cap break, and two time-code signals, WWVB and IRIG E, were recorded on paper strip charts from which origin times were subsequently determined. Assuming explosions and cap break were instantaneous, shot times were maintained to within an accuracy of + 2 milliseconds.
Recorder locations, shotpoint locations, and elevations, were determined from USGS orthophotos (1:24000) and topographic maps (1:24000 and 1:62500) and are estimated to be accurate to within 20 meters. Locations were checked using Brunton compass readings, precision odometers, and vehicle odometers.
Information pertaining to shot location and reference time can be found in Table 1 .
INSTRUMENTATION AND DATA REDUCTION
Seismic Recorders
The USGS seismic cassette recorders consist of an analog cassette tape recorder and a vertical-component, 2-Hz geophone (Figure 2). The seismic signal recieved by the geophone is diverted through three parrell amplifiers, each with an adjustable gain setting (0 to 104 db). The three amplified seismic signals, a constant reference frequency (FSK), and an internally generated time code (IRIG E) are recorded as a multiplexed signal in analog form on a 30-minute cassette tape. Each recorder contains a time code generator and memory circuitry which allows pre-programming of ten seperate time windows.
Prior to the recording of seismic data, a micro-processor within each recorder performs a geophone release test, an amplification step test, and then records a calibration sequence consisting of 10-Hz sine waves with amplitudes of 1, 10 , 100, and 1000 microvolts. The system measures velocity with a frequency response that peaks at 6 Hz and sharply rolls off beyond 20 Hz, avoiding 60 Hz contamination (Figure 3). The tests are recorded on cassette tapes and can be referenced during processing to evaluate the performance quality of the seismic recording system.
Data Reduction
Information pertaining to the perfomance of each SCR was recorded on field data sheets (Appendix B). Chronometer corrections were determine for each record assuming a linear drift rate. Twenty seconds of seismic data were then converted from analog to digital format at a sampling rate of 2 milliseconds. Digitization began at :
T - SHOT TIME - 2 SECONDS + X / 6.0 km/s
where X is the distance in kilometers from the shotpoint to the recorder in question. Following the digitization process, each trace was evaluated and assigned a tape grade (Appendix A ).
Seismic record sections (Figures 4-12) are plotted with all traces normalized to a common amplitude and with a standard reduction velocity of 6.0 km/s. Sections are presented using variable area shading at 65 % pulse width.
ACKNOWLEDGEMENTS
We wish to express our appreciation to U. S. Geological Survey's Geothermal Program for providing funding for the acquisition of these data. The efforts of Walter Mooney and the U.S. Geological Survey's seismic refraction field crew, Bob Colburn, Coyn Criley, Ed Criley, Phil Dawson, Wendy Grant, Ron Kaderabik, Will Kohler, Nan Scott-McGregor, Pat Meador, Janice Murphy, Thomas Reed, John Van Shack, Moses Smith, Vicki Sutton, and Al Walter are greatly appreciated.
REFERENCES CITED
Barry, K.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats, Geophysics 40, 344-352 p.
Catchings, R.D., and Mooney, W.D., 1988, Crustal structure of east central Oregon: Relation between Newberry volcano and regional crustal structure, Journ. Geophys. Res., v.93, 10,081-10,094 p.
Cotton, J.A., and Catchings, R.D., 1988, Data report for the 1984 U.S. Geological Survey Central Columbia Plateau Seismic Refraction Experiment, Washington-Oregon:, U.S. Geological Survey Open File Report 88-226, 56 p.
Dawson, P.B., Stauber, D.A., 1986, Data report for a three-dimensional high resolution P-velocity structural investigation of Newberry volcano, Oregon, using seismic tomography:, U.S. Geological Survey Open File Report 86-352, 77 P-
Healy, J.H., Mooney, W.D., Blank, H.R., Gettings, M.E., Kohler, W.M., Lamson, R.J., and Leone, L.E., 1982, Saudi Arabian seismic deep-refraction profile: Final project report:, U.S. Geological Survey Open File Report USGS-of-02-37, 429 p.
SEISMOMETER
AMPLIFIERS
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MASTER SHOT LIST (SHOT LOCATIONS AND TIMES)
EAST-CENTRAL OREGON 1983
SHOT SHOTPOINT DATE LATITUDE LONGITUDE SHOT TIMEDAY HR MN SEC
Table 1: Master Shot List. Contains shot number, shotpoint number, date (calendar, Julian), latitude/longitude (degree ,minute, and seconds), and shot time (GMT).
18
APPENDIX A
TAPE GRADE CODES
A performance status number is assigned to each field tape as it is digitized. These numbers appear in the last column of the field data file.
0 - GOOD1 - TAPE DID NOT RUN2 - TAPE RAN BUT NO SIGNAL3 - TAPE SKIPPED RECORDING TIME4 - TAPE RAN FAST FORWARD;NO SIGNAL5 - TAPE REWOUND AND ERASED6 - WEAK SIGNAL; CANNOT READ THE TIME CODE; LOW RECORD LEVEL7 - NOISE, CONTINOUS CALIBRATION OR PERIODIC OFFSETS8 - NOISE, SINUSOIDAL9 - NOISE, SPIKE
10 - NOISE, WWVB CROSS-FEED11 - NOISE, PERIODIC TICKS12 - NOISE, RANDOM13 - BAD CLOCKS14 - OFF FREQUENCY, TAPE SPEED PROBLEM16 - INCOMPLETE RECORD; RECORDER STOPPED17 - NOISY OR WEAK TIME CODE19 - TURNED ON TO EARLY20 - IN FOR REPAIR; NOT DEPLOYED21 - GEOPHONE DISCONNECTED OR SHORTED22 - WRONG UNIT NUMBER23 - WRONG GAIN SETTING24 - TURNED ON TOO LATE25 - BAD GEOPHONE TEST26 - ONE OR MORE CHANNELS MISSING27 - NOISY OR WEAK WWVB28 - INSTRUMENT OR TAPE MISSING29 - WRONG TIME DURING TURN-ON30 - DIGITIZED W/0 CALIBRATION31 - AMPLIFIER OUT OF BALANCE32 - LOCATION NOT ON MAP; WRONG LOCATION
19
APPENDIX B
FIELD DATA TABLES
Field data include information related to the seismic recorders. Each table contains shot number, shotpoint number and shot time given in Julian day, hour, minutes and seconds. Column heading for the table are explained below:
LOG -location number from the seismic recorder.
DIST -distance in kilometers from the shotpoint to the recorder.
AZIM -azimuth from the shotpoint to the recorder(degreesclockwise from north).
Db -attenuation of preferred recording channel (db).
TAPE GRADE -number corresponding to the performance of each instrument.
20
NEWBERRY CRATERShot Number 1 Shot Point 6
Shot Time (Julian day, hr, min, sec): 284:06:00:00.007
Dist Azim Tape Dist Azim Tape Dist Azim Tape Loc (km) (deg) Db Grade Loc (km) (deg) Db Grade Loc (km) (deg) Db Grade
Archive data tapes are written SEGY standard format (Barry et al,l975). Recording density is 1600 bpi, phase encoded (PE). In order to accomodate seismic refraction data, some minor changes have been made to the tape header fields. A complete list of the header fields is provided in the card image portion of the reel identification header, shown below:
C 1 REEL IDENTIFICATION HEADER BYTES:C 2 3217 -3218 sampling interval (microsecs).C 3 3221 -3222 number of the sample per trace.C 4 3225 -3226 data sample format code.C 5 3255 -3256 measurement system (1 meters; 2 « feet).C 6C 7C 8 TRACE IDENTIFICATION HEADERS BYTES:C 9CIOCllC12C13C14CISC16C17CISC19C20C21C22C23C24C25C26C27C28C29C30C31C32C33C34C35
trace sequence number within reel.trace sequence number within reels.station location numbers.trace ID code (1 " seismic data).shotpoint- receiver distance (M).station elevation (M) .shotpoint elevations (M) .source depth (M).scalar to be applied to all elevations.scalar to be applied to all coordinates.shotpoint coordinated -X.shotpoint coordinates -Y.receiver coordinates -X.receiver coordinates -Y.coordinate units (1 * meters; 2 * seconds of arc).number of samples in this trace.sample interval in microseconds for this trace.instrument attenuation in db.shot time - year.shot time - day of year.shot time - hour of the day( 24 hour clock) .shot time - minute of the hour.shot time - second of minute.time basis code (2 - GMT).shot time - milliseconds.shotpoint location number.recording instrument unit number.
30
C36 191 -192 distance weighting exponent (hundredths).C37 193 -194 shot sequence number (shot number).C38 195 -196 shot size (kg).C39 197 -200 shot point - station azimuth (second of arc).C40 201 -204 time of first point minus shot time (msec).
The data point format is "32 bit floating point", and the appropriate bytes (3225-3226) of the binary reel ID header contain a value of 1. The trace amplitudes have not been adjusted for the instrument gain, but the gain correction factor can be estimated from the instrument attenuation value(att) specified in bytes 121- 122. To correct for gain, the data should be demeaned and then multiplied by:
(att/20) 10
The measurement system (bytes 3225-3226 of the binary reel header) is set to 1, meters.
Shot point and receiver coordinates are in seconds of arc (byte field 89-90). The.coordinate scalar multiplier (bytes 71-72) is set to -100, so the coordinates (bytes 73-88) are in hundredths of a second of arc.
Bytes 157-166 and bytes 181-182 refer to the shot detonation time. The time of the first data sample is found by adding the shot detonation time to the time specified in bytes 201-204.
Since there is no weighting of amplitudes with distance for archive tapes, the distance weighting exponent (bytes 191-192) is not used.
Shot sequence number (bytes 193-194) refers to the order in which shots were fired during the field campaign.
