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Ziegler, RE, Dorman LRM.  1976.  The Georgia Gravity Base Net. :1-33., Atlanta: State of Georgia
Zhao, DP, Xu YB, Wiens DA, Dorman L, Hildebrand J, Webb S.  1997.  Depth extent of the Lau back-arc spreading center and its relation to subduction processes. Science. 278:254-257.   10.1126/science.278.5336.254   AbstractWebsite

Seismic tomography and wave form inversion revealed that very slow velocity anomalies (5 to 7 percent) beneath the active Lau spreading center extend to 100-kilometer depth and are connected to moderately slow anomalies (2 to 4 percent) in the mantle wedge to 400-kilometer depth, These results indicate that geodynamic systems associated with back-are spreading are related to deep processes, such as the convective circulation in the mantle wedge and deep dehydration reactions in the subducting slab, The slow regions associated with the Tonga are and the Lau back are are separated at shallow levels but merge at depths greater than 100 kilometers, suggesting that slab components of back-are magmas occur through mixing at these depths.

Yildiz, S, Sabra K, Dorman LM, Kuperman WA.  2013.  Using hydroacoustic stations as water column seismometers. Geophysical Research Letters. 40:2573-2578.   10.1002/grl.50371   AbstractWebsite

Getting seismic data from the deep oceans usually involves ocean-bottom seismometers, but hydrophone arrays may provide a practical alternative means of obtaining vector data. We here explore this possibility using hydrophone stations of the International Monitoring System, which have been used to study icebergs and T-wave propagation among others. These stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2km sides. We use data from these stations in the very low-frequency regime (0.01-0.05Hz band) to demonstrate that these stations can also be used as water column seismometers. By differencing the acoustic pressure, we obtain vector quantities analogous to what a seismometer would record. Comparing processed hydrophone station records of the 2004 Great Sumatra-Andaman Earthquake with broadband seismograms from a nearby island station, we find that the differenced hydrophones are indeed a practical surrogate for seismometers.

Wiggins, SM, Dorman LM, Cornuelle BD.  1997.  Topography can affect linearization in tomographic inversions. Geophysics. 62:1797-1803.   10.1190/1.1444280   AbstractWebsite

Linearized inverse techniques commonly are used to solve for velocity models from traveltime data. The amount that a model may change without producing large, nonlinear changes in the predicted traveltime data is dependent on the surface topography and parameterization. Simple, one-layer, laterally homogeneous, constant-gradient models are used to study analytically and empirically the effect of topography and parameterization on the linearity of the model-data relationship. If, in a weak-velocity-gradient model, rays turn beneath a valley with topography similar to the radius of curvature of the raypaths, then large nonlinearities will result from small model perturbations. Hills, conversely, create environments in which the data are more nearly linearly related to models with the same model perturbations.

Wiggins, SM, Dorman LM, Cornuelle BD, Hildebrand JA.  1996.  Hess Deep rift valley structure from seismic tomography. Journal of Geophysical Research-Solid Earth. 101:22335-22353.   10.1029/96jb01230   AbstractWebsite

We present results from a seismic refraction experiment conducted across the Hess Deep rift valley in the equatorial east Pacific. P wave travel times between seafloor explosions and ocean bottom seismographs are analyzed using an iterative stochastic inverse method to produce a velocity model of the subsurface structure. The resulting velocity model differs from typical young, fast spreading, East Pacific Rise crust by approximately +/-1 km/s with slow velocities beneath the valley of the deep and a fast region forming the intrarift ridge. We interpret these velocity contrasts as lithologies originating at different depths and/or alteration of the preexisting rock units. We use our seismic model, along with petrologic and bathymetric data from previous studies, to produce a structural model. The model supports low-angle detachment faulting with serpentinization of peridotite as the preferred mechanism for creating the distribution and exposure of lower crustal and upper mantle rocks within Hess Deep.

Tryon, M, Brown K, Dorman LR, Sauter A.  2001.  A new benthic aqueous flux meter for very low to moderate discharge rates. Deep-Sea Research Part I-Oceanographic Research Papers. 48:2121-2146.   10.1016/s0967-0637(01)00002-4   AbstractWebsite

Significant quantities of fluids and dissolved geochemical components are expelled through the sediment surface in ocean margin and sedimented ridge environments. Recently, significant interest has been generated in constraining hydrological processes in these environments, but direct measurement of fluid flow in the marine environment has proven to be difficult and many aspects of marine hydrogeology remain poorly understood. To address the need for a means to make a significant number of direct measurements in a wide range of low to moderate flow environments, we have developed a new type of benthic aqueous flux meter that is capable of measuring diffuse fluid flow through the sediment surface on the order of 0.1 mm yr(-1)-15 m yr(-1) when the flow is through sediments with permeabilities of less than 10(-8) cm(2) (typical seafloor sediments). The instrument measures fluid flow by determining the degree of dilution of a chemical tracer that is injected by an osmotic pump at a known rate into the fluids venting into or out of a collection chamber situated on the sea bed. The pump also withdraws a subsample of this tracer/fluid mix into sample coils allowing a serial record of the flow rates to be determined. Both upward and downward flow can be measured and, when flux rates are high enough to effectively flush the collecting chamber, the instruments also act as geochemical samplers. Three years of laboratory testing and field use have constrained the effects of (1) temperature, pressure, and deployment duration on osmotic pump performance, (2) dispersion/diffusion in the sample coils, and (3) deflection of flow under a range of sediment permeabilities. Recent deployments on the Kodiak and Cascadia accretionary prisms document the range and capabilities of the instrument in the field. (C) 2001 Elsevier Science Ltd. All rights reserved.

Trehu, AM, Ballard A, Dorman LM, Gettrust JF, Klitgord KD, Schreiner A.  1989.  Structure of the Lower Crust beneath the Carolina Trough, United-States Atlantic Continental-Margin. Journal of Geophysical Research-Solid Earth and Planets. 94:10585-10600.   10.1029/JB094iB08p10585   Website
Smith, GP, Wiens DA, Fischer KM, Dorman LM, Webb SC, Hildebrand JA.  2001.  A complex pattern of mantle flow in the Lau backarc. Science. 292:713-716.   10.1126/science.1058763   AbstractWebsite

Shear-wave splitting analysis of Local events recorded on Land and on the ocean floor in the Tonga are acid Lau backarc indicate a complex pattern of azimuthal anisotropy that cannot be explained by mantle flow coupled to the downgoing plate. These observations suggest that the direction of mantle flow rotates from convergence-parallel in the Fiji plateau to north-south beneath the Lau basin and are-parallel beneath the Tonga are. These results correlate with helium isotopes that map mantle flow of the Samoan plume into the Lau basin through an opening tear in the Pacific plate.

Shen, Y, Forsyth DW, Conder J, Dorman LM.  1997.  Investigation of microearthquake activity following an intraplate teleseismic swarm on the west flank of the Southern East Pacific Rise. Journal of Geophysical Research-Solid Earth. 102:459-475.   10.1029/96jb02852   AbstractWebsite

Between February 1991 and May 1992, 33 intraplate earthquakes having body wave magnitudes between 4.3 and 6.0 were located on the west flank of the Southern East Pacific Rise by the International Seismological Center. Seven months after the last teleseismic event we deployed four ocean bottom seismometers at the site of the teleseismic swarm. One hundred and ninety-two microearthquakes were located using P and S travel times of events recorded by three or more instruments during the 16-day deployment. Most of the microearthquakes were in a band about 30 km long and 6 km wide between and parallel to seamount chains. In addition, several events were distributed along a line perpendicular to the main seismicity band and parallel to the ridge axis. The focal depths of the microearthquakes range from 1 to 15 km, and most are between 5 and 12 km, similar to the depth range of the teleseismic events [Hung and Forsyth, 1996]. The composite P wave polarities indicate that the microearthquakes had a variety of focal mechanisms. We developed a new grid-search, inversion technique that utilizes the P wave polarities and the empirically corrected ratios of P and S wave amplitudes to find the focal mechanisms of individual events. Within the acceptable travel time and amplitude misfits, focal solutions are fairly stable. Normal faulting is found in the ridge-parallel seismicity line. The thrust and strike-slip faulting in the main seismicity band is distinctly different from the exclusively normal faulting mechanisms of the teleseismic events. There is no apparent depth dependence of fault types. None of the existing models of the sources of stress (ridge push, thermoelastic stresses; loading by local topographic features, caldera collapse, and north-south extension of the Pacific Plate) provides a satisfactory explanation for both the teleseismic swarm and microearthquakes. We propose a pew tectonic scenario. In this scenario, the lithosphere is prestressed by the cooling of the plate. Magma rising from the deeper mantle induces normal faulting ahead of the dike tips in the lower lithosphere, which is already under extensional, thermal stress, producing the larger, teleseismically detected events. Once the dikes propagate into the lithosphere, the region surrounding the dikes behind the tips is compressed by the overpressure of magma. Depending on the geometry of the dikes, the local orientations of the minimum principal stress, and the local weaknesses in the lithosphere, thrust or strike-slip faulting (the microearthquakes) may occur.

Schreiner, AE, Dorman LM.  1990.  Coherence Lengths of Sea-Floor Noise - Effect of Ocean Bottom Structure. Journal of the Acoustical Society of America. 88:1503-1514.   10.1121/1.400307   Website
Schreiner, AE, Dorman LM, Bibee LD.  1991.  Shear wave velocity structure from interface at two deep sites in the Pacific Ocean. Shera waves in marine sediments. ( Hovem JM, Richardson MD, Stoll RD, Eds.).:231-238., Holland: Kluwer academic publishers
Schiffelbein, P, Dorman L.  1986.  Spectral Effects of Time-Depth Nonlinearities in Deep-Sea Sediment Records - a Demodulation Technique for Realigning Time and Depth Scales. Journal of Geophysical Research-Solid Earth and Planets. 91:3821-3835.   10.1029/JB091iB03p03821   Website
Sauter, AM, Dorman LM.  1986.  Instrument Calibration of Ocean Bottom Seismographs. Marine Geophysical Researches. 8:265-275.   10.1007/bf00305486   Website
Sauter, AW, Dorman LM, Schreiner AE.  1986.  A study of sea floor structure using ocean bottom shots and receivers. ( Akal T, Berkson JM, Eds.)., New York, NY, United States (USA): Plenum Press, New York, NYWebsite
Sacks, IS, Evertson D, Dorman LM.  1971.  Borehole strainmeters. Year Book - Carnegie Institution of Washington. 69:426-430., Washington, DC, United States (USA): Carnegie Institution of Washington, Washington, DCWebsite
Roth, EG, Wiens DA, Dorman LM, Hildebrand J, Webb SC.  1999.  Seismic attenuation tomography of the Tonga-Fiji region using phase pair methods. Journal of Geophysical Research-Solid Earth. 104:4795-4809.   10.1029/1998jb900052   AbstractWebsite

The anelastic structure of the region surrounding the Tonga slab and Lau back are spreading center in the southwest Pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs. Two differential attenuation methods determine delta t* over the frequency band 0.1 to 3.5 Hz for earthquakes in the Tonga slab. The S-P method measures the difference in spectral decay between P and S waves arriving at the same station. The P-P method measures the difference in spectral decay for P waves with different paths through the upper mantle. Eight hundred sixty phase pairs are used to invert for two-dimensional 1/Q(alpha), structure using a nonnegative least squares algorithm. A grid search method determines the Q(alpha)/Q(beta) ratio most compatible with both the S-P and P-P differential measurements. The highest attenuation (Q(alpha) = 90) is found within the upper 100 km beneath the active portions of the Lau Basin extending westward to the Lau Ridge. These regions probably delineate the source region for the back are spreading center magmas, expected to be within the upper 100 km based on petrological considerations. The high attenuation regions also correlate well with zones of low P wave velocity determined by regional velocity tomography. Somewhat lower attenuation is found beneath the Fiji Plateau than beneath the Lau Basin. The entire back are is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km. The slab is imaged as a region of low attenuation (Q(alpha) > 900) material. A Q(alpha)/Q(beta) ratio of 1.75 provides the best fit between the S-P and P-P data sets upon inversion. Spectral stacking shows no frequency dependence within the frequency band analyzed.

Rosendahl, BR, Dorman LRM, Hekinian R, Briqueu L, Dmitriev Y, Fodor RV, Goll RM, Hoffert M, Humphris SE, Mattey DP, Natland JH, Petersen N, Roggenthen W, Schrader EL, Srivastava RK, Warren N, Barron JA, Bukry D, Lynts GW.  1980.  Summary of the geology and geophysics of the East Pacific Rise in the vicinity of the Siqueiros fracture zone. Initial Reports of the Deep Sea Drilling Project. 54( Powell R, Ed.).:23-36., College Station, TX, United States (USA): Texas A & M University, Ocean Drilling Program, College Station, TX   10.2973/dsdp.proc.54.102.1980   Website
Rosendahl, BR, Raitt RW, Dorman LM, Bibee LD, Hussong DM, Sutton GH.  1976.  Evolution of Oceanic-Crust .1. Physical Model of East Pacific Rise Crest Derived from Seismic Refraction Data. Journal of Geophysical Research. 81:5294-5304.   10.1029/JB081i029p05294   Website
Pautet, L, Kuperman WA, Dorman L.  2001.  Using refracted shear waves for velocity estimation. Geophysical Prospecting. 49:281-286.   10.1046/j.1365-2478.2001.00252.x   AbstractWebsite

The most difficult parr of multicomponent processing is the estimation of the shear-wave velocity map for migration. We used refracted shear waves and a simple iterative method called wavefield continuation (WFC) to evaluate the shallow shear-wave velocity profile on a real data example. The WFC was developed in 1981 by Clayton and McMechan to determine compressional-wave velocity profiles from refracted compressional waves. The application to refracted shear waves is straightforward. The real data example shows that shear structure can be easily determined independently of the compressional structure.

Orcutt, JA, Kennett BLN, Dorman LM.  1976.  Structure of East Pacific Rise from an Ocean Bottom Seismometer Survey. Geophysical Journal of the Royal Astronomical Society. 45:305-320.   10.1111/j.1365-246X.1976.tb00328.x   Website
Orcutt, JA, Dorman LM, Spudich PKP.  1977.  Inversion of seismic refraction data. Geophysical Monograph. ( Heacock JG, Keller GV, Oliver JE, Simmons G, Eds.).:371-384., Washington, DC, United States (USA): American Geophysical Union, Washington, DCWebsite
Orcutt, J, Kennett B, Dorman L, Prothero W.  1975.  Evidence of Low Velocity Zone Underlying a Fast-Spreading Rise Crest. Nature. 256:475-476.   10.1038/256475a0   Website
Orcutt, JA, Dorman LM.  1977.  Oceanic Long-Range Explosion Experiment - Preliminary-Report. Journal of Geophysics-Zeitschrift Fur Geophysik. 43:257-263.Website
Norabuena, E, Dixon TH, Schwartz S, DeShon H, Newman A, Protti M, Gonzalez V, Dorman L, Flueh ER, Lundgren P, Pollitz F, Sampson D.  2004.  Geodetic and seismic constraints on some seismogenic zone processes in Costa Rica. Journal of Geophysical Research-Solid Earth. 109   10.1029/2003jb002931   AbstractWebsite

[1] New seismic and geodetic data from Costa Rica provide insight into seismogenic zone processes in Central America, where the Cocos and Caribbean plates converge. Seismic data are from combined land and ocean bottom deployments in the Nicoya peninsula in northern Costa Rica and near the Osa peninsula in southern Costa Rica. In Nicoya, inversion of GPS data suggests two locked patches centered at 14 +/- 2 and 39 +/- 6 km depth. Interplate microseismicity is concentrated in the more freely slipping intermediate zone, suggesting that small interseismic earthquakes may not accurately outline the updip limit of the seismogenic zone, the rupture zone for future large earthquakes, at least over the short (similar to 1 year) observation period. We also estimate northwest motion of a coastal "sliver block'' at 8 +/- 3 mm/yr, probably related to oblique convergence. In the Osa region to the south, convergence is orthogonal to the trench. Cocos-Caribbean relative motion is partitioned here, with similar to 8 cm/yr on the Cocos-Panama block boundary ( including a component of permanent shortening across the Fila Costena fold and thrust belt) and similar to 1 cm/yr on the Panama block - Caribbean boundary. The GPS data suggest that the Cocos plate - Panama block boundary is completely locked from similar to 10 - 50 km depth. This large locked zone, as well as associated forearc and back-arc deformation, may be related to subduction of the shallow Cocos Ridge and/or younger lithosphere compared to Nicoya, with consequent higher coupling and compressive stress in the direction of plate convergence.

Nolet, G, Dorman LM.  1996.  Waveform analysis of Scholte modes in ocean sediment layers. Geophysical Journal International. 125:385-396.   10.1111/j.1365-246X.1996.tb00006.x   AbstractWebsite

In an effort to determine the characteristics of seismic noise on the ocean bottom and its relationship to the structure of the sea-floor, we have adapted the method of nonlinear waveform fitting to accommodate multidimensional models (shear velocity beta and shear damping Q(s)), and have applied it to invert several records of interface waves (Scholte 1958) from the THUMPER experiment off southern California. Waveform fitting is a very powerful tool to determine the S velocity in the top few metres of the sediment. Starting from beta = 30 m s(-1) at the top clay layer, the S velocity increases with a gradient of 2.8 m s(-1) m(-1) over the first 150 m of sediment. A theoretical estimation of the source strength gives coherent estimates of Q(s) as a function of depth for distances between 400 and 1070 m from the source. The Q(s) models are characterized by very low values (10-20) in the top three metres, but by values in excess of 100 below that level. The results confirm the identification of the noise as harmonics of interface waves. In the area of this experiment, the largest noise amplitudes belong to the fundamental mode and penetrate to a depth of about 20 m into the sediment. The overtone energy can be appreciable too, and is noticeable to about 80 m depth. The Q(s) structure confirms the strong influence that the sea-floor structure has on the noise spectrum. The high attenuation at frequencies above 3-4 Hz suppresses noise propagation and produces low noise at higher frequencies. (Similarly, high attenuation in the asthenosphere suppresses noise propagation below 0.1 Hz.)