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Santelli, CM, Orcutt BN, Banning E, Bach W, Moyer CL, Sogin ML, Staudigel H, Edwards KJ.  2008.  Abundance and diversity of microbial life in ocean crust. Nature. 453:653-U7.   10.1038/nature06899   AbstractWebsite

Oceanic lithosphere exposed at the sea floor undergoes seawater rock alteration reactions involving the oxidation and hydration of glassy basalt. Basalt alteration reactions are theoretically capable of supplying sufficient energy for chemolithoautotrophic growth(1). Such reactions have been shown to generate microbial biomass in the laboratory(2), but field- based support for the existence of microbes that are supported by basalt alteration is lacking. Here, using quantitative polymerase chain reaction, in situ hybridization and microscopy, we demonstrate that prokaryotic cell abundances on seafloor- exposed basalts are 3 - 4 orders of magnitude greater than in overlying deep sea water. Phylogenetic analyses of basaltic lavas from the East Pacific Rise ( 9 degrees N) and around Hawaii reveal that the basalt- hosted biosphere harbours high bacterial community richness and that community membership is shared between these sites. We hypothesize that alteration reactions fuel chemolithoautotrophic microorganisms, which constitute a trophic base of the basalt habitat, with important implications for deep- sea carbon cycling and chemical exchange between basalt and sea water.

Rajasekar, A, Lu S, Moore R, Vernon F, Orcutt J, Lindquist K.  2005.  Accessing sensor data using meta data: a virtual object ring buffer framework. Proceedings of the 2nd international workshop on Data management for sensor networks. :35-42., Trondheim, Norway: ACM   10.1145/1080885.1080892   Abstract
Albert, DG, Orcutt JA.  1990.  Acoustic Pulse-Propagation above Grassland and Snow - Comparison of Theoretical and Experimental Wave-Forms. Journal of the Acoustical Society of America. 87:93-100.   10.1121/1.398917   AbstractWebsite

Theoretical predictions are made of the effect of an absorbing ground surface on acoustic impulsive waveforms propagating in a homogeneous atmosphere for frequencies below 500 Hz. The lower frequencies of the pulse are enhanced as the effective flow resistivity of the ground surface decreases and as the propagation distance increases. The pulse waveforms and peak amplitude decay observed for propagation distances of 40 to 274 m over grassland were satisfactorily matched by calculations using an assumed effective flow resistivity of 200 kN s m^−4. Measurements over snow gave much greater amplitude decay rates, and the waveforms were radically changed in appearance, being dominated by the lower frequencies. These waveforms were satisfactorily matched only when a layered ground was incorporated into the calculations; then, an assumed surface effective flow resistivity of 20 kN s m^−4 gave good agreement with the observed waveforms and peak amplitude decay.

Orcutt, JA.  1998.  AGU's electronic publishing strategies. EOS Trans. AGU. 79:29-30. Abstract
Adair, RG, Orcutt JA, Jordan TH.  1984.  Analysis of Ambient Seismic Noise Recorded by Downhole and Ocean-Bottom Seismometers on Deep-Sea Drilling Project Leg-78B. Initial Reports of the Deep Sea Drilling Project. 78:767-781.   10.2973/dsdp.proc.78b.112.1984   AbstractWebsite

Ambient seismic noise at depth in the ocean crust is characterized using data from the Marine Seismic System (MSS), a vertical-component, digitally recording, short-period seismograph system which was part of the borehole instrumentation deployed on Deep Sea Drilling Project Leg 78B. The instrument package rested undamped in Hole395A, 516 m sub-basement. Reliable estimates of microseismic noise levels were obtained between 0.16 and 2.2 Hz; instrument noise dominated outside this band. The observed microseismic noise was quasi-stationary on a time scale of 1 hr., but not 10. Although spectral shapes were stable, noise amplitudes grew with time over the 26-hr, observation period by 3 to 5 dB. The borehole noise levels increased concurrently with local swell height, suggesting a causal relationship. An estimate of displacement power densities obtained early in the experiment had a peak value of 4 x 10^6 nm^2/Hz at 0.21 Hz, and decreased at 80 dB/decade from 1 × 10^6 nm^2/Hz at 0.33 Hz to 1 nm^2/Hz at 1.9 Hz. Noise levels observed at the seafloor near Hole 395A were greater than those observed in the borehole by a factor which increased with frequency from 10 dB at 0.2 Hz to 28 dB at 2 Hz. This is consistent with noise propagating as a fundamental-modeStoneley wave trapped near the sediment/seawater interface. If the relationship observed between noise at and below the seafloor during Leg 78B is a general one, ocean-bottom borehole noise levels could approach those at quiet continental sites.

Tong, CH, Pye JW, Barton PJ, White RS, Sinha MC, Singh SC, Hobbs RW, Bazin S, Harding AJ, Kent GM, Orcutt JA.  2002.  Asymmetric melt sills and upper crustal construction beneath overlapping ridge segments: Implications for the development of melt sills and ridge crests. Geology. 30:83-86.   10.1130/0091-7613(2002)030<0083:amsauc>;2   AbstractWebsite

A new three-dimensional tomographic velocity model and depth-converted reflection images of the melt sills beneath the 9degrees03'N overlapping spreading center on the East Pacific Rise show that the upper crustal construction at this ridge discontinuity is highly asymmetric with reference to the bathymetric ridge crests of the overlapping limbs. Despite the similarly curved ridge crests, the asymmetries are markedly different under the two limbs and appear to be related to the contrasting evolutionary history of the limbs. The overlap basin is closely related to the propagating eastern limb in terms of its seismic structure. By contrast, the western limb forms a distinct morphologic region that displays little structural relationship to the adjacent overlap basin and other relict basins. As the overlapping spreading center is migrating southward, the differential development of melt sills and ridge crests may be inferred from the results of this study. Ridge propagation appears to involve two major processes: the advancement of the melt sill at the ridge tip and the development of ridge-crest morphology and the neovolcanic axis to the north of the overlap basin region near the existing propagating limb. The latter process may result in the abandonment of the current neovolcanic axis, leading to the self-decapitation of the propagating limb. By contrast, the self-decapitation of the western limb is related to the receding melt sill, which lags behind the anticlockwise rotational motion of the ridge crest.

Laske, G, Markee A, Orcutt JA, Wolfe CJ, Collins JA, Solomon SC, Detrick RS, Bercovici D, Hauri EH.  2011.  Asymmetric shallow mantle structure beneath the Hawaiian Swell-evidence from Rayleigh waves recorded by the PLUME network. Geophysical Journal International. 187:1725-1742.   10.1111/j.1365-246X.2011.05238.x   AbstractWebsite

We present models of the 3-D shear velocity structure of the lithosphere and asthenosphere beneath the Hawaiian hotspot and surrounding region. The models are derived from long-period Rayleigh-wave phase velocities that were obtained from the analysis of seismic recordings collected during two year-long deployments for the Hawaiian Plume-Lithosphere Undersea Mantle Experiment. For this experiment, broad-band seismic sensors were deployed at nearly 70 seafloor sites as well as 10 sites on the Hawaiian Islands. Our seismic images result from a two-step inversion of path-averaged dispersion curves using the two-station method. The images reveal an asymmetry in shear velocity structure with respect to the island chain, most notably in the lower lithosphere at depths of 60 km and greater, and in the asthenosphere. An elongated, 100-km-wide and 300-km-long low-velocity anomaly reaches to depths of at least 140 km. At depths of 60 km and shallower, the lowest velocities are found near the northern end of the island of Hawaii. No major velocity anomalies are found to the south or southeast of Hawaii, at any depth. The low-velocity anomaly in the asthenosphere is consistent with an excess temperature of 200-250 degrees C and partial melt at the level of a few percent by volume, if we assume that compositional variations as a result of melt extraction play a minor role. We also image small-scale low-velocity anomalies within the lithosphere that may be associated with the volcanic fields surrounding the Hawaiian Islands.

Holmes, RC, Tolstoy M, Harding AJ, Orcutt JA, Morgan JP.  2010.  Australian Antarctic Discordance as a simple mantle boundary. Geophysical Research Letters. 37   10.1029/2010gl042621   AbstractWebsite

Several complex models require unique mantle conditions to explain the Australian Antarctic Discordance (AAD), an unusually deep and rugged section of the Southeast Indian Ridge (SEIR) between similar to 120 degrees-128 degrees E. Seismic evidence suggests the AAD is instead the manifestation of two contrasting mantle domains converging along its eastern edge. Variations in axial morphology and flanking topographic relief along the SEIR arise as ridge segments to the west (Indian mantle) grade into a cooler melting regime while those to the east (Pacific mantle) are more magmatically robust. Seismic refraction data show crustal thickness decreases from the west into the AAD at a rate of 0.1 km/100 km, then rapidly increases from 4.8 +/- 0.4 km to 7.3 +/- 0.2 km across the eastern border. The AAD thus appears to be the terminal end of a long-wavelength reduction in melt supply at what may be the simplest global example of a mantle boundary. Citation: Holmes, R. C., M. Tolstoy, A. J. Harding, J. A. Orcutt, and J. P. Morgan (2010), Australian Antarctic Discordance as a simple mantle boundary, Geophys. Res. Lett., 37, L09309, doi: 10.1029/2010GL042621.

Hedlin, MAH, Minster BJ, Orcutt JA.  1990.  An automatic means to discriminate between earthquakes and quarry blasts. Bulletin of the Seismological Society of America. 80:2143-2160. AbstractWebsite

In this article we discuss our efforts to use the NORESS array to discriminate between regional earthquakes and ripple-fired quarry blasts (events that involve a number of subexplosions closely grouped in space and time). The method we describe is an extension of the time versus frequency “pattern-based” discriminant proposed by Hedlin et al. (1989b). At the heart of the discriminant is the observation that ripple-fired events tend to give rise to coda dominated by prominent spectral features that are independent of time and periodic in frequency. This spectral character is generally absent from the coda produced by earthquakes and “single-event” explosions. The discriminant originally proposed by Hedlin et al. (1989b) used data collected at 250 sec−1 by single sensors in the 1987 NRDC network in Kazakhstan, U.S.S.R. We have found that despite the relatively low digitization rate provide by the NORESS array (40 sec−1) we have had good success in our efforts to discriminate between earthquakes and quarry blasts by stacking all vertical array channels to improve signal-to-noise ratios.We describe our efforts to automate the method, so that visual pattern recognition is not required, and to make it less susceptible to spurious time-independent spectral features not originating at the source. In essence, we compute a Fourier transform of the time-frequency matrix and examine the power levels representing energy that is periodic in frequency and independent of time. Since a double Fourier transform is involved, our method can be considered as an extension of “cepstral” analysis (Tribolet, 1979). We have found, however, that our approach is superior since it is cognizant of the time independence of the spectral features of interest. We use earthquakes to define what cepstral power is to be expected in the absence of ripple firing and search for events that violate this limit. The assessment of the likelihood that ripple firing occurred at the source is made automatically by the computer and is based on the extent to which the limit is violated.

Shearer, PM, Toy KM, Orcutt JA.  1988.  Axi-Symmetric Earth Models and Inner-Core Anisotropy. Nature. 333:228-232.   10.1038/333228a0   AbstractWebsite

Seismic waves passing through the middle of the Earth travel slightly faster in a N – S direction than in an E – W direction. A comparison of travel times for different P-wave phases shows that most of this anomaly is within the inner core, and that uniform anisotropy of the inner core is the most likely cause.