Ocean Seismic Network Pilot Experiment
Stephen, Ralph A.
Spiess, Fred N.
Collins, John A.
Hildebrand, John A.
Orcutt, John A.
Peal, Kenneth R.
Vernon, F. L.
Wooding, Frank B.
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KeywordOcean Seismic Network Pilot Experiment (OSNPE); Seismology; Instruments and techniques; Body wave propagation; Surface waves and free oscillations
The primary goal of the Ocean Seismic Network Pilot Experiment (OSNPE) was to learn how to make high quality broadband seismic measurements on the ocean bottom in preparation for a permanent ocean seismic network. The experiment also had implications for the development of a capability for temporary (e.g., 1 year duration) seismic experiments on the ocean floor. Equipment for installing, operating and monitoring borehole observatories in the deep sea was also tested including a lead-in package, a logging probe, a wire line packer and a control vehicle. The control vehicle was used in three modes during the experiment: for observation of seafloor features and equipment, for equipment launch and recovery, and for power supply and telemetry between ocean bottom units and the ship. The OSNPE which was completed in June 1998 acquired almost four months of continuous data and it demonstrated clearly that a combination of shallow buried and borehole broadband sensors could provide comparable quality data to broadband seismic installations on islands and continents. Burial in soft mud appears to be adequate at frequencies below the microseism peak. Although the borehole sensor was subject to installation noise at low frequencies (0.6 to 50 mHz), analysis of the OSNPE data provides new insights into our understanding of ocean bottom ambient noise. The OSNPE results clearly demonstrate the importance of sediment borne shear modes in ocean bottom ambient noise behavior. Ambient noise drops significantly at high frequencies for a sensor placed just at the sediment basalt interface. At frequencies above the microseism peak, there are two reasons that ocean bottom stations have been generally regarded as noisier than island or land stations: ocean bottom stations are closer to the noise source (the surface gravity waves) and most ocean bottom stations to date have been installed on low rigidity sediments where they are subject to the effects of shear wave resonances. When sensors are placed in boreholes in basement the performance of ocean bottom seismic stations approaches that of continental and island stations. A broadband borehole seismic station should be included in any real-time ocean bottom observatory.
Author Posting. © American Geophysical Union, 2003. It is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 4 (2003): 1092, doi:10.1029/2002GC000485.
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Stephen, Ralph A.; Swift, Stephen A.; Bolmer, S. Thompson; Hoskins, Hartley (Copernicus Publications on behalf of the German Research Centre for Geosciences, 2007-11)The first borehole seismic experiments on DSDP and ODP were two-ship Oblique Seismic Experiments (Stephen, 1979; Stephen, et al., 1979, 1980; Swift, et al., 1988). By recording on the drill ship and shooting explosives out ...
Swift, Stephen A.; Stephen, Ralph A.; Hoskins, Hartley; Bolmer, S. Thompson (2003-12)Third party borehole seismic experiments on the Ocean Drilling Program began with an oblique seismic experiment on Leg 102 at Site 418 in the Western Atlantic. Upper ocean crust here is characterized by a normal seismic ...
The character of seafloor ambient noise recorded offshore New Zealand : results from the MOANA ocean bottom seismic experiment Yang, Zhaohui; Sheehan, Anne F.; Collins, John A.; Laske, Gabi (American Geophysical Union, 2012-10-16)We analyze the characteristics of ambient noise recorded on ocean-bottom seismographs using data from the 2009–2010 MOANA (Marine Observations of Anisotropy Near Aotearoa) seismic experiment deployed west and east of South ...