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Sereno, TJ, Farrell WE, Orcutt JA, Adair RG.  1988.  VLF Propagation Loss to a Buried Seismometer. IEEE Journal of Oceanic Engineering. 13:254-262.   10.1109/48.9238   AbstractWebsite

The propagation loss from a shallow underwater explosion to a buried vertically polarized seismometer over the frequency band between 3 and 15 Hz was measured during the 1983 Ngendei Experiment. The data was recorded in 5.5-km-deep water in the southwest Pacific with a triaxial borehole seismograph emplaced 50 m within the basaltic basement. It is found that the average power decays as r-3 (r is slant range) beyond 30 km and that the propagation loss is minimal between 6-9 Hz. At shorter ranges, the propagation loss is more complicated and exhibits a stronger frequency dependence. Power in the first water wave is estimated for both buried and ocean-bottom sensors. The ocean-bottom power is approximately 7 dB higher than that recorded by the buried sensor, and both exhibit similar decay rates.

Kilb, D, Keen CS, Newman RL, Kent GM, Sandwell DT, Vernon FL, Johnson CL, Orcutt JA.  2003.  The Visualization Center at Scripps Institution of Oceanography: Education and Outreach. Seismological Research Letters. 74:641-648. AbstractWebsite

The immersive environment of the Visualization Center at Scripps, coupled with the presentation of current seismological research, has great education and outreach potential. Since its March 2002 opening, the Visualization Center at Scripps has had more than 2,500 visitors, and numerous virtual visitors have explored our Web pages, which include streaming QuickTime movies of geophysical data, tutorials on how to use SGI/Mac/Windows registered visualization software, and examples of visualizations developed by SIO researchers and faculty members (http://siovizcenter.ucsd.edu/library.shtml). We will continue to expand the use of the Visualization Center at Scripps for K-12 and informal education, and to use the center to supply geophysical data sets, movies, and research results to as large a group of educators as possible. Our goal is to develop more sustained K-12 educational programs and to generate assessments of the center's programs and the educational products created at the Center.

Bradley, CR, Stephen RA, Dorman LM, Orcutt JA.  1997.  Very low frequency (0.2-10.0 Hz) seismoacoustic noise below the seafloor. Journal of Geophysical Research-Solid Earth. 102:11703-11718.   10.1029/96jb03183   AbstractWebsite

The sources and propagation of VLF (0.2 --> 10 Hz) ambient noise on and within the deep ocean crust at Deep Sea Drilling Project (DSDP) Hole 534B in the Blake Bahama Basin are shown to be related to the surface sea state and local lithology. This study represents the first experiment where ambient noise is measured simultaneously at several depths below the seafloor. The low-frequency microseism power spectral density (PSD) peak at 0.3 Hz is nearly invariant with depth between 0 and 100 m below the seafloor. PSD levels of the peak are 65 and 75 dB (rel 1 (nm/s(2))(2)/Hz) for the vertical and horizontal components, respectively, and both horizontal and vertical components of the ocean bottom seismometer and borehole array compare favorably. Above 0.5 Hz the noise levels decrease with depth and increasing frequency. At 1.0 Hz, 100 m below the seafloor the noise level is 10 and 20 dB below the levels observed at the seafloor for vertical and horizontal components, respectively. There is evidence that amplification in some frequency bands may make deeper sites noisier than shallower sites in the same well. Temporal variation of the noise shows nonlinear interaction of local water-borne gravity waves to be the dominant source mechanism and that the passing of a local storm generates interface waves and increases the noise level (similar to 10 dB) from 0.3 to 1.5 Hz and 5 to 64 Hz. Between 1.5 and 5 Hz the spectrum is not strongly affected by the passing storm, indicating that the ocean wave spectrum may be saturated.

Begnaud, ML, McClain JS, Barth GA, Orcutt JA, Harding AJ.  1997.  Velocity structure from forward modeling of the eastern ridge-transform intersection area of the Clipperton Fracture Zone, East Pacific Rise. Journal of Geophysical Research-Solid Earth. 102:7803-7820.   10.1029/96jb03393   AbstractWebsite

In the spring of 1994, we undertook an extensive geophysical study of the Clipperton Fracture Zone (FZ) on the fast spreading East Pacific Rise. The Clipperton Area Seismic Study to Investigate Compensation experiment (CLASSIC) included surveys to examine the deep structures associated with the fracture zone and adjacent northern ridge segment. In this paper, we report the results from five seismic profiles acquired over the eastern ridge-transform intersection (RTI), including profiles over the RTI high, the northern ridge segment, and the eastern transform region. The travel time data for crustal phases, Moho reflections, and mantle phases were modeled using two-dimensional ray tracing. Seismic profiles reveal that the crust is similar in thickness north and south of the Clipperton FZ, despite differences in axial topography that have previously been interpreted in terms of differences in magma supply. When compared to older crust, the northern ridge axis is characterized by lower seismic velocities and higher attenuation. In our model, a low-velocity zone exists beneath the ridge axis, probably associated with a zone of partial melt and/or very high temperatures. Within the transform zone, we find that the southeastern trough is underlain by nearly normal crustal structure. The crust is slightly thinner than the adjacent aseismic extension but not enough to compensate for the depths of the trough. Toward the RTI, the trough is replaced by an intersection high which appears underlain by a thickened crust, and a thicker upper crustal section. Both characteristics indicate that the intersection high is a volcanic feature produced by excess volcanism at the intersection. The volcanism acts to ''fill in'' the transform trough, creating the thicker crust that extends under the eastern aseismic extension of the transform. Our results show that the northern ridge segment, often identified as magma-starved, displays the crustal thickness and apparent signal-attenuation characteristic of a plentiful, but perhaps episodic, magma supply.

Whitmarsh, RB, Orcutt JA, Jordan TH, Adair RG, Shearer PM.  1987.  Velocity Bounds on the Seismic Structure of Mesozoic Crust and Uppr Mantle in the Southwest Pacific Basin from Downhole Observations at Deep-Sea Drilling Project Hole-595B. Initial Reports of the Deep Sea Drilling Project. 91:437-444.   10.2973/dsdp.proc.91.111.1987   AbstractWebsite

The Marine Seismic System (MSS) was deployed during Leg 91 of the Deep Sea Drilling Project in order to assess the reduction in noise levels achievable through burying a seismic inertial sensor within the basaltic crust. The noise levels were significantly reduced and the usual coupling problems experienced by ocean bottom seismographs were essentially eliminated. This contribution reports on the results of early analyses of data collected while shooting two roughly orthogonal refraction lines. The data were processed at Scripps Institution of Oceanography and topographic corrections were applied to reduce the effects of roughness in the seafloor topography. The data were first corrected to the seafloor and the remaining correlations with topography were attenuated by a correction for the height of the seafloor above a datum. The corrections reduced traveltime scatter and significantly tightened extremal envelopes on acceptable velocity functions. The best constrained solutions were achieved over moderate topography while the presence of substantial seamounts always introduced scatter presumably due to unknown features off the ship's track. Velocity anisotropy was discovered within the oceanic upper mantle and the velocity structure of this old crust was found to berather "normal."

Kennett, BLN, Bunch AWH, Orcutt JA, Raitt RW.  1977.  Variations in Crustal Structure on East Pacific Rise Crest - Travel Time Inversion Approach. Earth and Planetary Science Letters. 34:439-444.   10.1016/0012-821x(77)90055-3   AbstractWebsite

Systematic travel time inversion techniques have been applied to first arrival travel times from a number of seismic refraction profiles on the crest and flanks of the East Pacific Rise to generate bounds on the possible velocity-depth distributions. The greatest variability in structure occurs within 5 Myr of the rise crest. The generally similar character of the bounds on the velocity distributions for ages greater than 5 Myr indicates that the most rapid aging occurs within 5 Myr of the crest, though the mantle velocity increases systematically with age. The nature of the bounds on the velocity distribution for the range of velocities associated with layer 3 requires that the velocity distribution within layer 3 increase with depth.