U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY MARINE, HIGH-RESOLUTION, MULTICHANNEL, SEISMIC-REFLECTION DATA COLLECTED DURING CRUISE G3-95-PS, NORTHWESTERN WASHINGTON By Shawn V. Dadisman (1), Samuel Y. Johnson(2), and Jonathan R. Childs(1) (with software contributions by F.N. Zihlman(3)) OPEN-FILE REPORT 97-735 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. (1) U.S. Geological Survey, 345 Middlefield Rd. MS 999, Menlo Park, CA 94025 (2) U.S. Geological Survey, P.O. Box 25046 MS 966, Denver Federal Center, Denver, CO 80225 (3) U.S. Geological Survey, P.O. Box 25046 MS 939, Denver Federal Center, Denver, CO 80225 1997 INTRODUCTION In June of 1995, the U.S. Geological Survey collected about 1500 km of high-resolution, multichannel, seismic- reflection data across the submerged portions of known and proposed upper crustal faults in central and northern Puget Sound, Lake Washington, the eastern Strait of Juan de Fuca, and adjacent inland waterways of northwestern Washington. Cruise G3-95-PS was designed to image the upper 1 km of active or possibly active fault zones within the Puget Lowland. Detailed surveys (1-3 km spacing) of the Seattle and Southern Whidbey Island fault zones were conducted. Reconnaissance scale surveys at roughly 5-km or greater spacing were completed over the Devils Mountain fault and potential fault zones in Hood Canal, offshore of the northern Olympic Peninsula, and local offshore areas adjacent to the San Juan Islands. Cruise G3-95-PS was conducted aboard the R/V Robert Gray, a 120-ft research vessel, operating 24-hrs/day for 12 days. Six-fold data were acquired using a source consisting of two 40 cubic-inch airguns, and received by a 24-channel, 150-m long streamer. These data imaged the upper 1 to 2-km subbottom. Final stacked sections of these data are presented here in SEG-Y format along with details about processing parameters, CDP locations, scanned observers logs, and PC-based software for viewing SEG-Y data files. INSTRUMENTATION The high-resolution multichannel reciever system consisted of a 24-channel (6.25-meter group interval; 150 meters active length) solid-core streamer with "thin-film" hydrophones. The streamer was manufactured by Innovative Transducers, Inc. and utilizes cylindrical hydrophones constructed from poly-vinylidene fluoride (PVDF) plastic, which are characterized by high sensitivity and broad band (5-5000 Hz) frequency response. The seismic data were recorded with a Geometrics Strataview seismograph recorder, which uses a PC-based floating point computer system. Field sampling rate was 1 msec, and field record length 2 seconds. The air gun source consisted of two Bolt air guns with 40 cubic-inch chambers, fired at a 12.5-meter interval. Factors limiting the firing interval were air compressor capacity and the time required by the recording system to process each shot. At speeds of 3.5 knots or less the 12.5- meter fire interval could be maintained at full capacity resulting in common-depth-point (CDP) data that were 6- fold, with a 3.125-meter CDP interval. Navigation fixes were based on a single Global Positioning System (GPS) receiver. Because this GPS system was not operational in differential mode, absolute position accuracy was approximately + or - 100 m. However, relative positions from fix to fix, are accurate to within a few meters. Shots were fired at 12.5-meter intervals based on relative GPS fixes. DATA REDUCTION Data were originally recorded in SEG-2 format but were converted to SEG-Y formatted files at sea. To simplify processing, multiple navigation tracklines were recorded to a single SEG-Y file and processed together. Therefore, CDPs and FFIDs may not start with 1 for every seismic line. These data were processed using a Landmark Graphic Promax processing system, Versions 5 and 6.1. The processing routine is shown in Table 1 (below). Extensive editing of bad shots was necessary due to random misfires of the air guns. Geometry was then defined, and top mutes picked. The data were then desampled to 2 ms, gained, deconvolved using a minimum phased predictive filter, bandpass filtered and sorted into CDPs. Determination of accurate normal moveout (NMO) velocity was difficult because very little NMO was observed due to the limited offset and the low fold of the data. After extensive velocity analysis, the decision to apply a standard velocity function to all the data was made. The standard function was derived from velocity functions applied to conventional industry seismic reflection data collected in the region (Table 1). The function was modified for differences in the waterbottom travel time for each line. TABLE 1. Processing Sequence for G3-95-PS seismic data 1. SEGY input 2. Header Statics (-10 ms) 3. Trace Header Math (offset = (chan-1) * 6.25 + 23.0) 4. Trace Header Math (ffid-1) * 4 + (25-chan) 5. Trace Header Math (sin=ffid) 6. Resample (1ms to 2 ms) 6. Trace Kill (channel 22 plus any bad shots) 7. Automatic Gain Control (150 ms) 8. Predictive decon (minimum phase) 9. Bandpass Filter (12-18-150-190 Hz) 10. In-line sort (CDP sort) 11. Normal Moveout Correction (velocity function = 50ms*-1450m/sec, 1000ms-2000m/sec, 2000ms-2500m/sec; *Varied with water bottom depth) 12. CDP/Ensemble Stack 13. Trace Mute (water bottom mute) 14. SEGY output TABLE OF DISC CONTENTS Each volume or disc contains both 1_README files and all of the contents of each subdirectory with the exception of the SEGYDATA subdirectory. The contents of each SEGYDATA subdirectory are listed below. 1_README.TXT- a guide to the CD-ROM set in DOS format. 1_README.UNIX- a guide to the CD-ROM set in Unix format. DOCS subdirectory- all contents are on each volume TITLE.TXT = Title Page TABLE.TXT = Table of Contents DISCLAIM.TXT = Disclaimer INTRO.TXT = Introduction GEAR.TXT = Instrumentation PROCESS.TXT = Data Reduction Table 1: Processing Sequence for G3-95-PS seismic data THANKS.TXT = Acknowledgments REF.TXT = References LOCATION subdirectory- all contents are on each volume 1README.TXT- an explanation of the ASCII location files by line number (PXXX.NAV). Every disc contains all location files for the entire cruise. LOGS subdirectory- all contents are on each volume 1README.TXT-explanation of the logs Scanned cruise logs (CLOGXX.GIF or CLOGXX.PCX) Scanned seismic logs (SLOGXX.GIF or SLOGXX.PCX) SEGYDATA subdirectory-see below for a list of contents on each volume. 1README.TXT-Quick instructions on how to use PLOTSEGY and DUMPSEGY programs on DOS systems included on each volume. Executables for both PLOTSEGY and DUMPSEGY included on each volume. Stacked seismic lines in SEG-Y format (PXXX.SGY) Volume 1 contains lines P1.SGY to P87.SGY Volume 2 contains lines P88.SGY to P145.SGY Volume 3 contains lines P146.SGY to P186.SGY SOFTWARE subdirectory provided by F.N. Zihlman (1992a and b)-contents included on each volume. The executables are included in the SEGYDATA subdirectory for convenience. 1README.TXT PLOTSEGY.TXT- the original Open-file Report of PLOTSEGY program DUMPSEGY.TXT- the original Open-file Report of DUMPSEGY program PSGYV2.TXT- upgrades to PLOTSEGY in version 2 ACKNOWLEDGMENTS The authors wish to express their appreciation to the Captain and crew of the R/V Robert Gray, Larry Kooker, Kevin O'Toole and Fred Payne of the Coastal and Marine Geology Marine Facility, and Guy Cochrane (WRCMGT) who assisted in the collection of the data. We also wish to thank John Miller (CRERT) and Bill Stephenson (CRGHT) for assistance and advice in processing the data. Nick Zihlman (CRERT), Carl Abston (CRMRT) and Ray Sliter (WRCMGT) provided guidance in producing the CD-ROMs. Nick Zihlman allowed us to include his DOS software for viewing the data (Zihlman, 1992a and b). Guy Cochrane provided a helpful review of this manuscript. Eleanor Omdahl designed the artwork on the discs and jewel case cover. Funding for this work was received from the Coastal and Marine Geology Program and the National Earthquake Hazard Reduction Program of the U.S. Geological Survey. CONTACTS For further information contact: JON CHILDS OR SHAWN DADISMAN U.S. GEOLOGICAL SURVEY, M/S 999 345 MIDDLEFIELD RD. MENLO PARK, CALIFORNIA 94025 (650) 329-5195 email jchilds@usgs.gov or sdadisman@usgs.gov FOR SALE BY USGS INFORMATION SERVICES BOX 25286, BUILDING 810 DENVER FEDERAL CENTER DENVER, CO 80225 (303) 202-4200 DISCLAIMER This 3-volume Compact Disc-Read Only Memory (CD- ROM) publication were prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of the information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Although all data and software published on these CD-ROMs have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or functioning of the software. The act of distribution shall not constitute any such warranty and no responsibility is assumed by the USGS in the use of this data, software, or related materials. REFERENCES Zihlman, F.N., 1992a, DUMPSEGY V1.0: A program to examine the contents of SEG-Y disk-image seismic data; U.S. Geological Survey Open File 92-590. Zihlman, F.N., 1992b, PLOTSEGY V1.0: A DOS graphics program to display SEG-Y disk-image seismic data; U.S. Geological Survey Open File 92-349A and 92-349B.