Publications

Export 6 results:
Sort by: Author [ Title  (Asc)] Type Year
A B C D E F G H [I] J K L M N O P Q R S T U V W X Y Z   [Show ALL]
I
Forsyth, DW, Scheirer DS, Webb SC, Dorman LM, Orcutt JA, Harding AJ, Blackman DK, Morgan JP, Detrick RS, Shen Y, Wolfe CJ, Canales JP, Toomey DR, Sheehan AF, Solomon SC, Wilcock WSD, Team MS.  1998.  Imaging the deep seismic structure beneath a mid-ocean ridge: The MELT experiment. Science. 280:1215-1218.   10.1126/science.280.5367.1215   AbstractWebsite

The Mantle Electromagnetic and Tomography (MELT) Experiment was designed to distinguish between competing models of magma generation beneath mid-ocean ridges. Seismological observations demonstrate that basaltic melt is present beneath the East Pacific Rise spreading center in a broad region several hundred kilometers across and extending to depths greater than 100 kilometers, not just in a narrow region of high melt concentration beneath the spreading center, as predicted by some models. The structure of the ridge system is strongly asymmetric: mantle densities and seismic velocities are lower and seismic anisotropy is stronger to the west of the rise axis.

Tong, CH, Barton PJ, White RS, Sinha MC, Singh SC, Pye JW, Hobbs RW, Bazin S, Harding AJ, Kent GM, Orcutt JA.  2003.  Influence of enhanced melt supply on upper crustal structure at a mid-ocean ridge discontinuity: A three-dimensional seismic tomographic study of 9 degrees N East Pacific Rise. Journal of Geophysical Research-Solid Earth. 108   10.1029/2002jb002163   AbstractWebsite

[1] We present a three-dimensional upper crustal model of the 9degrees03'N overlapping spreading center (OSC) on the East Pacific Rise that assists in understanding the relationship between melt sills and upper crustal structure at a ridge discontinuity with enhanced melt supply at crustal levels. Our P wave velocity model obtained from tomographic inversion of similar to 70,000 crustal first arrival travel times suggests that the geometry of extrusive emplacement are significantly different beneath the overlapping spreading limbs. Extrusive volcanic rocks above the western melt sill are inferred to be thin ( similar to 250 m). More extensive accumulation of extrusives is inferred to the west than to the east of the western melt sill. The extrusive layer inferred above the eastern melt sill thickens from similar to 350 ( at the neovolcanic axis) to 550 m ( to the west of the melt sill). Volcanic construction is likely to be significant in the formation of ridge crest morphology at the OSC, particularly at the tip of the eastern limb. On the basis of our interpretation of the velocity model, we propose that enhanced magma supply at crustal levels at the OSC may provide an effective mechanism for the migration of ridge discontinuities. This "dynamic magma supply model'' may explain the commonly observed nonsteady migration pattern of ridge discontinuities by attributing this to the temporal fluctuations in melt availability to the overlapping spreading limbs.

Adair, RG, Orcutt JA, Farrell WE.  1988.  Infrasonic Seismic and Acoustic Measurements in the Deep Ocean. IEEE Journal of Oceanic Engineering. 13:245-253.   10.1109/48.9237   AbstractWebsite

The authors compare the signal-to-noise ratios obtained on bottomed seismometers, bottomed hydrophones, and buried seismometers from near-surface explosions in the Ngendei Expedition. The data were recorded in 5.5-km-deep water in the south central Pacific Ocean with a triaxial borehole seismograph and four triaxial ocean-bottom seismographs having externally mounted hydrophones. At ranges less than 35 km, the data indicate that the ocean bottom seismometer is a superior signal detector than the ocean-bottom hydrophone, and that the subbottom seismometer is superior in performance to the ocean-bottom seismometer. Above 4 Hz, the seismometer appears to have a 10-dB signal-to-noise advantage over the hydrophone for surface explosions at ranges less than 30 km.

Jordan, TH, Menard HW, Natland JH, Orcutt JA.  1987.  Introduction: Objectives and results of Deep Sea Drilling Project Leg 91 and the NGENDEI seismic experiment, and explanatory notes for Volume 91. Initial Reports of the Deep Sea Drilling Project. 91:185-203.   10.2973/dsdp.proc.91.101.1987   Abstract
n/a
Orcutt, JA, Dorman LM, Spudich PKP.  1977.  Inversion of seismic refraction data. The Earth's Crust. ( Heacock JG, Keller GV, Oliver JE, Simmons G, Eds.).:371-384., Washington, DC, United States (USA): American Geophysical Union, Washington, DC Abstract
n/a
Herzfeld, UC, Kim II, Orcutt JA.  1995.  Is the Ocean-Floor a Fractal. Mathematical Geology. 27:421-462.   10.1007/bf02084611   AbstractWebsite

The topographic structure of the ocean bottom is investigated at different scales of resolution to answer the question: Can the seafloor be described as a fractal process? Methods from geostatistics, the theory of regionalized variables, are used to analyze the spatial structure of the ocean floor at different scales of resolution. The key to the analysis is the variogram criterion: Self-similarity of a stochastic process implies self-similarity of its variogram. The criterion is derived and proved here; it also is valid for special cases of self-affinity (in a sense adequate for topography). It has been proposed that seafloor topography can be simulated as a fractal (an object of Hausdorff dimension strictly larger than its topological dimension), having scaling properties (self-similarity or self-affinity). The objective of this study is to compare the implications of these concepts with observations of the seafloor. The analyses are based on SEABEAM bathymetric data from the East Pacific Rise at 13 degrees N/104 degrees W and at 9 degrees N/104 degrees W and use tracks that run both across the ridge crest and along the ridge flank. In the geostatistical evaluation, the data are considered as a stochastic process. The spatial continuity of this process is described by variograms that are calculated for different scales and directions. Applications of the variogram criterion to scale-dependent variogram models yields the following results: Although the seafloor may be a fractal in the sense of the definition involving the Hausdorff dimension, it is not self-similar, nor self-affine (in the given sense). Mathematical models of scale-dependent spatial structures are presented, and their relationship to geologic processes such as ridge evolution, crust formation, and sedimentation is discussed.