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ID G-1-95-SF
Abstract Chief Scientists: Jill McCarthy, Pat Hart. Deep-Crustal Seismic data (seismic) of field activity G-1-95-SF in San Francisco Bay from 04/17/1995 to 04/28/1995
Project/Theme Central California Earthquake Hazards (CENCAL)
National Plan Hazards
Chief Scientist Jill McCarthy
Pat Hart
Activity Type Deep-Crustal Seismic
Platform Robert Gray
Area of Operation San Francisco Bay, San Francisco Bay, CA
Bounding Coordinates
38.01217
-122.45324    -122.11396
37.49946
Dates 04/17/1995 (JD 107) to 04/28/1995 (JD 118)
Analog Materials list
Crew
Jill McCarthy Chief Scientist, USGS Western Region
Pat Hart Chief Scientist, USGS Western Region
Dennis Mann Geophysicist, USGS Western Region
Jon Childs Geophysicist, USGS Western Region
Mike Marlow Geologist, USGS Western Region
Ray Sliter Geophysicist, USGS Western Region
Mike Boyle Electronic Tech, USGS Western Region
Hal Williams Mechanical Tech, USGS Western Region
Equipment Used
seismic
Purpose
The purpose of this study (co-funded by the Marine
and Coastal Surveys Program and the National Earthquake Hazards Reduction
Program) was to test a new method for acquiring deep crustal seismic
reflection data in San Francisco Bay.  In contrast to the earlier 1991
BASIX experiment, which deployed single hydrophones at a spacing of 100 m,
the Bay Cable experiment deployed a continuous, 2400-m-long cable with
several hundred hydrophones directly onto the seafloor.  Our goal was to
determine whether an increased number of hydrophones and a decrease in the
level of water-born noise would combine to provide improved images of the
deep crust.
Summary
Deep seismic reflection data were acquired at three separate localities
in San Francisco Bay.  Data were acquired in a two-step process.  First the
48-channel, 2400-m streamer was deployed onto the sea floor and anchored in a
fixed position; the recording system was stationed with the streamer, separate
from the sound source. Once the streamer was in place, the Robert Gray towed the
12-element, 5858 cubic inch airgun array past the receiver array, achieving
shot-receiver offsets of 10-25 km.  Shots were fired approximately every 90
seconds, and 14 seconds of two-way traveltime data were recorded.  The three
streamer deployments were located in central and south San Francisco bays and
provide approximately 50 km of deep crustal seismic reflection profiling along
the north-south axis of the bay. The streamer was deployed three times; the most
northerly of these deployments was positioned over an area where the 1991 BASIX
survey had experienced particularly good success in imaging a deep crustal
reflector at 6 seconds two-way traveltime.  The goal of the 1995 Bay Cable study
was to reoccupy this site and see if an even better image of the 6-s arrival
could be provided using the new methodology.  The second and third deployments
were designed to provide further testing of this technique and to help constrain
the north-south extent of the 6-s reflector along the length of the San
Francisco Bay Block.
Notes
"BAY CABLE" CRUISE NEWS: The bay cable flotilla has been
successfully working through problems asthey arise (or drift away).
Mike, Jon, Pat, and Co. are seeing great first break arrivals on the
recorders that seem to be stronger than BASIX 1991. They believe
this means the very deep reflections will be that much more
resolvable. Working with the variable winds and rough chop have
presented difficulties, but nothing unexpected as of yet. The
streamer was deployed on Wed.; shooting began on Thurs.; and
retrieval begins today. Jill reports that the radio trigger is
experiencing interference as they approach the San Francisco
waterfront causing some missed shots. Curious sailboats are
understandably keeping their distance. Kevin's MARFAC team and
Curtis' Gray team are doing an outstanding job keeping everything
"safe and sane".- Ray Sliter

For more information about G195SF -- check out the
BASIX homepage.
Publications
McCarthy, J., Hart, P., and Childs, J.R., 1995, Deep reflective character of the 
San
Francisco Bay block; results from the 1995 BASIX Bay cable experiment: 
Geological Society
of America Abstracts with Programs, v. 27, no. 6, p. 287. 

Brocher, Thomas M., McCarthy, Jill, and Holbrook, W. Steven, 1996, Imaging the transform plate boundary in the San Francisco Bay area, California: Geological Society of America Abstracts with Programs, v. 28, no. 7, p. 216.
Got Help? For G-1-95-SF, we would appreciate any information on -- contract, days at sea, dive count, funding, information specialist, information to be derived, kms of navigation, NGDC Info, organization, owner, ports, project number, scanned materials, seismic description, station count, station description, submersible, tabulated info.
Type Webpage KMZ Arc         Metadata        
Metadata data     txt  data  FAQ  xml
Navigation data nav    
Seismic data seis    
Times   061.times    

G-1-95-SF location map of where navigation 

equipment operated

 
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