Hollinshead
C. B.
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Progress report on the development of the seafloor borehole array seismic system (phase II) : July 14, 1992 to January 31, 1996
Hollinshead
C. B.
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Working Paper
The Seafloor Borehole Array Seismic System (SEABASS) was originally developed to
record autonomously on the seafloor the signals received on a four-sonde three-component
borehole geophone array in the VLF band (2-50Hz)(Stephen eta!., 1994). The system is designed
to use the wireline re-entry capability (Spiess, 1993; Spiess eta!., 1992) to install and retrieve the
seafloor instrumentation (Figures 1 and 2). Following the successful demonstration of this
technology on the LFASE (Low Frequency Acoustic-Seismic Experiment) project in September
1989, it was decided to extend the capability to broadband (1000sec-5Hz) borehole seismometers
which could be used for permanent seafloor seismic observatories in the Ocean Seismic Network
(Orcutt and Stephen, 1993; Purdy and Dziewonski, 1988; Purdy and Orcutt, 1995; Stephen, 1995;
Sutton and Barstow, 1990; Sutton eta!., 1988; Sutton eta!., 1965).
The Broadband Borehole Seismic System (B3S2) is the prototype system for permanent
broadband borehole seismic observatories on the seafloor. It has three major components: i) a
broadband borehole seismometer, the Teledyne 54000, modified for seafloor operations by
Scripps-IGPP; ii) the re-entry system provided by Scripps-MPL; and iii) the seafloor recording
system developed by WHO I. Because of the similarity of the seafloor recording system to
SEABASS we have named this new system SEABASS-ll. This report discusses the development
of SEABASS-Il at WHOI in the period from July 14, 1992 to January 31, 1996. The motivation
for the project and a work statement are contained in WHOI proposals 7016 and 7016.1.
This report is a collection of documentation prepared while the work was being carried out.
Some of the issues discussed in early memos were subsequently changed. Modifications and
further testing of SEABASS-ll, as well as final system integration tests with the borehole andreentry
systems (both of which are also still being modified and tested) have still to be carried out in
preparation for the OSN Pilot Experiment Cruise in Spring 1997. This is a preliminary report only
and presents work in progress. It will be useful to the engineering team as a historical reference of
the sequence of events in the development of SEABASS-ll but it should not be considered as a
technical manual for the instrumentation.