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A
Aldrich, LT, Tamayo L, Beach L, Dorman LM, Casaverde M, Velasquez A, Rodriguez A, Simoni D, Salgueiro R, del Pozo S.  1971.  Electrical Conductivity Studies. Year Book - Carnegie Institution of Washington. 70:351-352., Washington, DC, United States (USA): Carnegie Institution of Washington, Washington, DCWebsite
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Bibee, DL, Dorman LM.  1995.  Full Waveform Inversion of Seismic Interface Wave Data. Full Field Inversion Methods in Ocean and Seismo-Acoustics. ( Diachok O, Caiti A, Gerstoft P, Schmidt H, Eds.)., Dordrecht: Klewer Academic Publishers Abstract

A technique for inverting marine seismic interface wave data for shear wave attenuation parameters of ocean sediments is presented. Because of the difficulty in estimating spectral ratios of seismograms in the case when multiple modes are present, a linear perturbation technique that uses the recorded time series seismogram or its envelope as input data is proposed. The technique is stable for tests using synthetic data. Application of the technique to data collected in the Gulf of Mexico yields a model producing a good fit to the data. However, a simple source model is insufficient to correctly predict modal excitations, and the source must be parameterized as part of the inversion process.

Bibee, DL, Dorman LM, in Sediments SWM.  1991.  Implications of Deep-water Seismometer Array Measurements for Scholte Wave Propagation. Shear Waves in Marine Sediments. ( Hovem JM, Richardson MD, Stoll RD, Eds.)., Dordrecht: Klewer Academic Publishers Abstract

A field exercise was conducted in March 1990 to make measurements of Scholte wave propagation characteristics in a deep ocean environment. Signals from a series of bottom explosive shots were recorded on an array of ocean bottom seismometers. Clear Scholte phases were observed on the vertical seismometers to ranges of 1.25 km, but were attenuated to noise levels by 2 km range. Collocated hydrophones did not detect the Scholte waves even at the closest ranges. The ratio of pressure (µPa) to vertical ground velocity (nm/s) was 68 dB in time windows dominated by body waves but only 20 dB in windows dominated by the Scholte wave. Group velocities were low (30-100 m/s) and showed considerable variability despite the expected uniformity of the seafloor in this abyssal environment.

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.

Brown, KM, Tryon MD, DeShon HR, Dorman LM, Schwartz SY.  2005.  Correlated transient fluid pulsing and seismic tremor in the Costa Rica subduction zone. Earth and Planetary Science Letters. 238:189-203.   10.1016/j.epsl.2005.06.055   AbstractWebsite

Continuous measurements of fluid flow were made over a six month period across the Nicoya Peninsula, Costa Rica (Pacific), convergent margin utilizing osmotically-driven fluid flow meters designed to quantify both inflow and outflow rates on the order of similar to 10(-5) to 3 cm/d. Significant transience in flow was observed through the surface of the forearc. Three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out-of-sequence thrust (OOST) zone over along-margin strike distances of similar to 30 km. Amplitudes of ground velocity recorded on collocated ocean bottom seismometers (OBS) increase during the three correlated flow events. The seismic signal has frequency characteristics that resemble volcanic and non-volcanic tremor. We hypothesize that repeated plate boundary slow slip events, potentially originating at the up dip limit of the seismogenic zone, generate the observed signals within the toe of the forearc. We propose a model in which the poro-elastic stress/strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments. The former generates the seismic tremor-like noise recorded by the OBSs and the latter generates the flow transients recorded by the fluid flow meters. We suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible. (c) 2005 Elsevier B.V. All rights reserved.

Brune, JN, Curray JR, Dorman LRM, Raitt R.  1992.  A proposed super-thick sedimentary basin, Bay of Bengal. Geophysical Research Letters. 19:565-568., Washington, DC, United States (USA): American Geophysical Union, Washington, DC   10.1029/91gl03134   AbstractWebsite

A super-thick ( approximately 22km) sedimentary basin under the northern Bay of Bengal is proposed. The hypothesis is based on data from surface wave dispersion, seismic refraction, S (sub n) attenuation, and geology. We present new high frequency S (sub n) data which indicate a cold upper mantle beneath the Bay of Bengal. We propose that the oceanic crust in this region is in fact nearly normal, and that the sedimentary section is at least 6 km thicker than previously thought, with velocities at the base of the sediments having been increased to near 6.5 km/sec by high pressure metamorphism. Reinterpretation of the refraction data indicate a post India-Asia collision thickness of over 16 km. Copyright 1992 by the American Geophysical Union.

C
Crawford, WC, Wiens DA, Dorman LM, Webb SC, Wiens DA.  2003.  Tonga Ridge and Lau Basin crustal structure from seismic refraction data. Journal of Geophysical Research-Solid Earth. 108   10.1029/2001jb001435   AbstractWebsite

[1] The crustal structure across the Tonga-Lau arc-back arc system from the Lau Ridge to the Pacific Plate (178degrees-170degreesW, 18degrees19degreesS) is modeled, using data from an 840-km-long air gun refraction line over 19 ocean bottom seismometers and one land station. The data reveal that the Pacific Plate crust is 5.5 km thick, with a velocity structure similar to that found at the present-day East Pacific Rise (EPR). Beneath Tonga Ridge, an intermediate velocity layer (6-7 km/s) is up to 7.5 km thick and has a velocity-depth distribution similar to andesitic rocks found in continental crust. The crust is abnormally thin (4 km) at the boundary between the Tonga Ridge and the Lau Basin. At the east end of Lau Basin, the crust is 5.5-6.5 km thick and resembles crust formed at the EPR except for a thicker sheeted-dike section (2-3 km) and thinner lower crust (2 km). The Lau Basin crust thickens to 7-8 km near the Central Lau Spreading Center (CLSC), mostly through thickening of the lower crust. The crust thickens again to 8.5-9.5 km at 50 km west of the CLSC, mostly through thickening of the midcrust. In the thick westernmost section, the crustal structure is uniform even though one part of this section formed through extension of arc-type crust while the rest was created at an oceanic spreading center. The relative homogeneity of these rocks suggests that their petrology may be dominated by postemplacement magmatic infilling from a mantle source west of the spreading center.

Creager, KC, Dorman LM.  1982.  Location of Instruments on the Seafloor by Joint Adjustment of Instrument and Ship Positions. Journal of Geophysical Research. 87:8379-8388.   10.1029/JB087iB10p08379   Website
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DeShon, HR, Schwartz SY, Bilek SL, Dorman LM, Gonzalez V, Protti JM, Flueh ER, Dixon TH.  2003.  Seismogenic zone structure of the southern Middle America Trench, Costa Rica. Journal of Geophysical Research-Solid Earth. 108   10.1029/2002jb002294   AbstractWebsite

[1] The shallow seismogenic portion of subduction zones generates damaging large and great earthquakes. This study provides structural constraints on the seismogenic zone of the Middle America Trench offshore central Costa Rica and insights into the physical and mechanical characteristics controlling seismogenesis. We have located similar to 300 events that occurred following the M-W 6.9, 20 August 1999, Quepos, Costa Rica, underthrusting earthquake using a three-dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers. We use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region. These events define a plane dipping at 19degrees that marks the interface between the Cocos Plate and the Panama Block. The majority of aftershocks occur below 10 km and above 30 km depth below sea level, corresponding to 30 - 35 km and 95 km from the trench axis, respectively. Relative event relocation produces a seismicity pattern similar to that obtained using absolute locations, increasing confidence in the geometry of the seismogenic zone. The aftershock locations spatially correlate with the downdip extension of the oceanic Quepos Plateau and reflect the structure of the main shock rupture asperity. This strengthens an earlier argument that the 1999 Quepos earthquake ruptured specific bathymetric highs on the downgoing plate. We believe that subduction of this highly disrupted seafloor has established a set of conditions which presently limit the seismogenic zone to be between 10 and 35 km below sea level.

DeShon, HR, Schwartz SY, Newman AV, Gonzalez V, Protti M, Dorman LRM, Dixon TH, Sampson DE, Flueh ER.  2006.  Seismogenic zone structure beneath the Nicoya Peninsula, Costa Rica, from three-dimensional local earthquake P- and S-wave tomography. Geophysical Journal International. 164:109-124.   10.1111/j.1365-246X.2005.02809.X   AbstractWebsite

The subduction plate interface along the Nicoya Peninsula, Costa Rica, generates damaging large (M-w > 7.5) earthquakes. We present hypocenters and 3-D seismic velocity models (V-P and V-P/V-S) calculated using simultaneous inversion of P- and S-wave arrival time data recorded from small magnitude, local earthquakes to elucidate seismogenic zone structure. In this region, interseismic cycle microseismicity does not uniquely define the potential rupture extent of large earthquakes. Plate interface microseismicity extends from 12 to 26 and from 17 to 28 km below sea level beneath the southern and northern Nicoya Peninsula, respectively. Microseismicity offset across the plate suture of East Pacific Rise-derived and Cocos-Nazca Spreading Center-derived oceanic lithosphere is similar to 5 km, revising earlier estimates suggesting similar to 10 km of offset. Interplate seismicity begins downdip of increased locking along the plate interface imaged using GPS and a region of low V-P along the plate interface. The downdip edge of plate interface microseismicity occurs updip of the oceanic slab and continental Moho intersection, possibly due to the onset of ductile behaviour. Slow forearc mantle wedge P-wave velocities suggest 20-30 per cent serpentinization across the Nicoya Peninsula region while calculated V-P/V-S values suggest 0-10 per cent serpentinization. Interpretation of V-P/V-S resolution at depth is complicated however due to ray path distribution. We posit that the forearc mantle wedge is regionally serpentinized but may still be able to sustain rupture during the largest seismogenic zone earthquakes.

Dorman, LM, Sauter AW.  2006.  A reusable implosive seismic source for midwater or seafloor use. Geophysics. 71:Q19-Q24.   10.1190/1.2335512   AbstractWebsite

We have developed a new implosive seismic or acoustic source for seafloor or midwater use. The fact that this device does not use pyrotechnics simplifies logistic and permitting problems. It produces relatively little high-frequency output, so it is wildlife friendly. This device enables us to place the source nearer to the image target compared to surface sources, which thus increases resolution. The simple 20-1 version we have constructed must be reset after each use by bringing it to the sea surface. We present measurements of seafloor shear velocity at a depth of about I km in the San Diego Trough. There the surficial shear velocity is 16 m/s, and the gradient is about 10 s(-1).

Dorman, LM.  1968.  Anelasticity and Spectra of Body Waves. Journal of Geophysical Research. 73:3877-&.   10.1029/JB073i012p03877   Website
Dorman, LM, Gehringer DD.  2002.  Web browser applet allows visualization of three-dimensional models. EOS, Transactions of the AGU. 83(18)   10.1029/2002EO000136   AbstractWebsite

A new, machine-independent Java Applet, a program that runs in a browser, downloads both byte code and three-dimensional models from a remote Web site and displays them on a local computer. The code is a few hundred kilobytes in size and allows the viewer to control a two-dimensional view of a three-dimensional array, which can be represented by files as small as one byte per node. This code allows both the angle of view and the color map to be controlled by the user.

Dorman, LM.  1975.  The gravitational edge effect. Journal of Geophysical Research. 80:2949-2950., Washington, DC, United States (USA): American Geophysical Union, Washington, DC   10.1029/JB080i020p02949   AbstractWebsite

The knowledge that a gravity anomaly is due to an edge effect is sufficient to resolve the inherent ambiguity of the inverse potential problem. Thus given the gravity field across the contact between two laterally uniform structures, the density difference between the adjacent sections can be calculated by means of integral transforms operating on the data. The Backus-Gilbert inversion technique allows a rational trade-off between accuracy and resolution. The kernels associated with the physics of the problem indicate a resolution comparable to that of surface waves.

Dorman, L, et al.  1993.  Deep-water sea-floor array observations of seismo-acoustic noise in the eastern Pacific and comparison with wind and swell. Natural Physical Sources of Underwater Sound. ( Kerman B, Ed.).:165-174., Holland: Kluwer Academic Publishers   10.1007/978-94-011-1626-8_14   Abstract

We report results from the analysis of data from an array of Ocean-Bottom Seismographs (OBSs) employed in an array of 150 meter aperture at a depth of 3800 meters off the California coast. The array recorded noise samples four times per day for a month using pressure and three-component inertial sensors.

Comparison of the month-long noise spectrograms with swell spectrograms and wind hind-casts shows marked similarities. In the 0.05–1.0 Hz range the frequency-doubling of swell energy into sea-floor noise predicted by the wave interaction theory is evident. In the 1–10 Hz range the wind-related effects dominate. Lulls in the wind produce deep notches in the noise level. During times of high wind, saturation of the wind wave spectrum causes limiting and reduces the size of the noise maxima.

The wind estimates are from the meteorological model of the U.S. Navy Fleet Numerical Oceanography Center and the swell estimates are from their Global Spectral Ocean Wave Model.

Dorman, LM.  1969.  Reply to Debremaecker,Jc Comments on Anelasticity and Spectra of Body Waves. Journal of Geophysical Research. 74:3304-&.   10.1029/JB074i012p03304   Website
Dorman, LM.  1979.  Linear Relationship between Earth Models and Seismic Body Wave Data. Geophysical Research Letters. 6:132-134.   10.1029/GL006i003p00132   Website
Dorman, LM.  2001.  Seismology Sensors. Encyclopedia of Ocean Sciences. ( Steele JH, Turekian KK, Thorpe SA, Eds.)., Amsterdam: Elsevier ScienceDirect   10.1016/B978-012374473-9.00334-9  
Dorman, LM.  1972.  Seismic Crustal Anisotropy in Northern Georgia. Bulletin of the Seismological Society of America. 62:39-&.Website
Dorman, LM, et al.  1991.  The effect of shear velocity structure on sea floor noise. Shera waves in marine sediments. ( Hovem JM, Richardson MD, Stoll RD, Eds.).:239-245., Holland: Kluwer academic publishers
Dorman, LM.  1983.  Modeling and Parameterization Errors in Body Wave Seismology. Geophysical Journal of the Royal Astronomical Society. 72:571-576.   10.1111/j.1365-246X.1983.tb02820.x   Website
Dorman, LRM.  1971.  Seismic Anisotropy in the Crust of the Southeastern U.S. Year Book - Carnegie Institution of Washington. 70:349-349., Washington, DC, United States (USA): Carnegie Institution of Washington, Washington, DCWebsite