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Blackman, DK, Orcutt JA, Forsyth DW.  1995.  Recording teleseismic earthquakes using ocean-bottom seismographs at mid-ocean ridges. Bulletin of the Seismological Society of America. 85:1648-1664. AbstractWebsite

Existing teleseismic data recorded by ocean-bottom seismographs (OBS) are sparse, but they are sufficient for analysis of earthquake detection thresholds under various background noise conditions. Long-period P, S, and surface waves are consistently recorded by OBS's for magnitude 5.7 to 6+ events at ranges greater than 100 degrees. Both Love and Rayleigh waves are recorded for very large events, with high coherence in the 15- to 70-sec period range; high coherence in the 15- to 35-sec range is typical for events of magnitude 5.5 to 6+. Short-period body-wave arrivals (1 Hz), on the other hand, have only been clearly recorded by OBS's in the North Atlantic, during calm-weather periods or, by OBS's in the Pacific, for very large events at ranges less than a few tens of degrees. Seismograms recorded at the East Pacific Rise (EPR) and at the Mid-Atlantic Ridge (MAR) illustrate the high signal coherence between instruments deployed in an array of OBS's. Recordings of the pressure field as well as the vertical and horizontal displacement fields are used to assess the capabilities of OBS sensors and the frequency range of high signal-to-noise arrivals. Contamination of long-period, body-wave arrivals by secondary phases, due to reverberation in the water column, can significantly hinder investigation of relative travel-time anomalies across an OBS array on rough seafloor, particularly at low signal-to-noise ratios. The nature of the reverberations is illustrated in short-period data, and the basic physics behind the differences between the pressure and displacement signals is discussed. A bias of about 0.5 sec can be introduced to relative arrival times, with deeper stations appearing erroneously late, for an array where seafloor depths vary by about 1 km. Reflectivity synthetics provide the basis for designing optimum filters for removing the reverberation bias in long-period, P-wave data from the Mid-Atlantic Ridge, 34 degrees S. The resulting relative travel-time anomaly is 0.4 to 0.6 sec with delays with distance from the axis on the east flank of the spreading center.

Schofield, O, Kohut J, Glenn S, Morell J, Capella J, Corredor J, Orcutt J, Arrott M, Krueger I, Meisinger M, Peach C, Vernon F, Chave A, Chao Y, Chien S, Thompson D, Brown W, Oliver M, Boicourt W.  2010.  A Regional Slocum Glider Network in the Mid-Atlantic Bight Leverages Broad Community Engagement. Marine Technology Society Journal. 44:185-195. AbstractWebsite

Autonomous underwater gliders have proven to be a cost-effective technology for measuring the 3-D ocean and now represent a critical component during the design and implementation of the Mid-Atlantic Regional Ocean Observing System (MARCOOS), a Region of the U.S. Integrated Ocean Observing System. The gliders have been conducting regional surveys of the Mid-Atlantic (MA) Bight, and during the 3 years of MARCOOS, the glider fleet has conducted 22 missions spanning 10,867 km and collecting 62,824 vertical profiles of data. In addition to collecting regional data, the gliders have facilitated collaboration for partners outside of MARCOOS. The existence of the MA glider observatory provided a unique test bed for cyber-infrastructure tools being developed as part of the National Science Foundation's Ocean Observatory Initiative. This effort allowed the Ocean Observatory Initiative software to integrate the MARCOOS assets and provided a successful demonstration of an ocean sensor net. The hands-on experience of the MA glider technicians supported training and provided assistance of collaborators within the Caribbean Regional Association, also a region of the U.S. Integrated Ocean Observing System, to assess the efficacy of gliders to resolve internal waves. Finally, the glider fleet has enabled sensor development and testing in a cost-effective manner. Generally, new sensors were tested within the MARCOOS domain before they were deployed in more extreme locations throughout the world's oceans. On the basis of this experience, the goal of the MARCOOS glider team will be to expand the MA network in coming years. The potential of how an expanded network of gliders might serve national needs was illustrated during the 2010 Macondo Gulf of Mexico oil spill, where gliders from many institutions collected subsurface mesoscale data to support regional models and oil response planning. The experience gained over the last 5 years suggests that it is time to develop a national glider network.

Babcock, JM, Kirkendall BA, Orcutt JA.  1994.  Relationships Between Ocean-Bottom Noise and the Environment. Bulletin of the Seismological Society of America. 84:1991-2007. AbstractWebsite

Observations of ocean bottom low-frequency noise and surface environmental data over a period of 27 days in the northern Atlantic during the SAMSON and SWADE experiments reveal how closely related the noise is to meteorological conditions. Double-frequency microseisms produced by nonlinear interactions of storm-induced surface gravity waves are especially evident in the frequency band 0.16 to 0.3 Hz and show a high variability in both amplitude and peak frequencies. Bifurcated at times, the peak that characterizes the microseism band contains local and distant or ''teleseismic'' components, which are generated at different locations. Weather and storm fetch appear to be the major contributions to the size and shape of microseism spectra. Storm development on the sea surface is associated with progressively lower microseism frequencies along with a concurrent increase in amplitude. The single-frequency microseism peak is a continuous feature and is observed to portray the same time-dependent spectral characteristics as the portion of the double-frequency peak associated with distant storms. Coherence studies confirm that both peaks (single and teleseismic double) originate at a distant source. These peaks are generated at roughly the same location with some storm component over the coastline.

Hedlin, MAH, Minster JB, Orcutt JA.  1994.  Resolution of Prominent Crustal Scatterers Near the Noress Small-Aperture Array. Geophysical Journal International. 119:101-115.   10.1111/j.1365-246X.1994.tb00916.x   AbstractWebsite

Our goal is to identify prominent scatterers near seismic arrays so that the secondary phases they generate can be anticipated and recognized as being of local, not teleseismic, origin. Toward this end we have developed a technique to scan seismic coda recorded by arrays for phases generated locally by scattering of teleseismic energy from large topographical and crustal heterogeneities. In this paper we test the technique by using the NORESS small-aperture array in southern Norway to image free surface secondary R(g) sources excited by incoming teleseismic P waves. In essence, our technique suppresses the teleseismic energy and migrates the residual array records to image-coherent local sources. To assess the azimuthal and radial resolution that the NORESS array provides we have analysed point-source synthetics. A preliminary analysis of recorded data provides an initial view of the scatterers in the vicinity of NORESS and identifies limitations of imaging using the full coda of individual events. Single events can be used to image scatterers but more robust images, with higher azimuthal resolution, can be obtained by using a broadly distributed suite of events. Radial resolution of scatterers can be enhanced by deconvolution. A composite image generated by simultaneously considering a suite of 31 deconvolved teleseisms indicates that two secondary R(g) sources are present at, or near, the free surface near NORESS. One, 27 km to the south-west of the array, appears to be related to dramatic topographic relief at the south-west edge of Lake Mjosa. Another, roughly 10 km to the east of the array is judged by a bootstrap-resampling analysis to be only marginally significant. This apparent source does not coincide with obvious topography and is likely buried. Although the time delay that separates the scattered and 'parent' phases depends somewhat on the angle of approach of the incoming waves, in general these secondary sources are contributing wave trains to the seismic coda that begin approximately 4 and 11 s, respectively, after the primary onset.

Sutherland, FH, Vernon FL, Orcutt JA, Collins JA, Stephen RA.  2004.  Results from OSNPE: Improved teleseismic earthquake detection at the seafloor. Bulletin of the Seismological Society of America. 94:1868-1878.   10.1785/012003088   AbstractWebsite

Earthquake data from three ocean seismic network (OSN) sensors, located (1) on the seafloor, (2) buried in seafloor sediments and (3) in a borehole, together with those from Hawaiian Island stations, were compared by calculating threshold-detection magnitudes for P-, S-, Rayleigh-, and Love-wave arrivals. Our results show that the borehole seismometer had noise levels similar to those of the Island stations and produced high-quality high- and low-frequency body- and surface-wave data. Shallow burial of the seismometer in the sediments had no effect on higher frequencies but significantly reduced low-frequency noise levels so that data for S and Rayleigh waves were of high quality. In fact, the buried seismometer was characterized by the lowest noise levels at very low frequencies (<20 mHz; Collins et al., 2001). The ocean-floor seismometer was consistently noisy, and the data produced were of lower quality. Both observed magnitudes and calculated threshold magnitudes were lower by more than an order of magnitude than those observed in previous studies. Results for short-period body waves at the borehole instrument in particular were much better than those that were previously found for any ocean-bottom recording.

Orcutt, JA, Mackenzie K, McClain J.  1980.  The Role of X(P) Constraints in Linear, Extremal Inversion of Explosion Profile Data. Bulletin of the Seismological Society of America. 70:2103-2116. AbstractWebsite
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