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Newman, AV, Schwartz SY, Gonzalez V, DeShon HR, Protti JM, Dorman LM.  2002.  Along-strike variability in the seismogenic zone below Nicoya Peninsula, Costa Rica. Geophysical Research Letters. 29   10.1029/2002gl015409   AbstractWebsite

[1] At the subduction zone in northwestern Costa Rica, the seismogenic zone lies directly beneath the Nicoya Peninsula, allowing for near source seismic studies of earthquake activity. We located 650 earthquakes along the seismogenic plate interface using a dense seismic network in the vicinity of the Nicoya Peninsula. Using these data we constrained the updip limit of the seismogenic zone there and found a transition in depth, 10 km in the south to 20 km in the north, that occurs where the subducting oceanic crust changes from warmer Cocos-Nazca Spreading center (CNS) origin to colder East Pacific Rise (EPR) origin. We argue that the temperature of the incoming oceanic crust controls the seismogenic updip limit beneath Nicoya, Costa Rica; subducting colder oceanic crust deepens the seismogenic updip limit.

Dorman, LM.  1968.  Anelasticity and Spectra of Body Waves. Journal of Geophysical Research. 73:3877-&.   10.1029/JB073i012p03877   Website
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
McGowan, JA, Cayan DR, Dorman LM.  1998.  Climate-ocean variability and ecosystem response in the northeast Pacific. Science. 281:210-217.   10.1126/science.281.5374.210   AbstractWebsite

The role of climatic variation in regulating marine populations and communities is not well understood. To improve our knowledge, the sign, amplitude, and frequency of climatic and biotic variations should be compared as a necessary first step. it is shown that there have been large interannual and interdecadal sea-surface temperature changes off the West Coast of North America during the past 80 years. Interannual anomalies appear and disappear rather suddenly and synchronously along the entire coastline. The frequency of warm events has increased since 1977. Although extensive, serial, biological observations are often incomplete, it is clear that climate-ocean variations have disturbed and changed our coastal ecosystems.

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
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.

Koper, KD, Wiens DA, Dorman L, Hildebrand J, Webb S.  1999.  Constraints on the origin of slab and mantle wedge anomalies in Tonga from the ratio of S to P velocities. Journal of Geophysical Research-Solid Earth. 104:15089-15104.   10.1029/1999jb900130   AbstractWebsite

We examine two prominent upper mantle Velocity anomalies in the southwest Pacific, the Tongs slab anomaly and the corresponding overlying mantle wedge anomaly, using data collected during a combined land-sea deployment of temporary seismometers. The linear geometry and small interstation spacing of the instruments yield high-resolution data along a cross section of the Tonga subduction zone, including the actively spreading Lau back are basin. We estimate the relative variation of P and S velocity, often described as v = delta lnV(s)/delta lnV(p), for the slab and mantle wedge anomalies using two distinct methods: a linear regression of the P and S travel time residuals, and detailed modeling of the velocity structure using a three-dimensional finite difference travel time algorithm. The two methods yield similar results, with v of the slab being 1.1-1.5 and v of the mantle wedge being 1.2-1.3. These values are consistent with experimental data concerning the effect of temperature on P and S wave velocities in the upper mantle and are lower than what is expected for velocity anomalies generated by the presence of partial melt. These observations imply that either the theoretical estimates of v for partial melt are too large or very little partial melt is present beneath the Lau basin. In the latter case, melt must be quickly removed from the rock matrix, such that the velocity anomalies are due to increased temperature, and not melt. The bulk of the velocity anomaly in the mantle wedge can be explained by temperature anomalies of 400-600 degrees C because of the amplification of temperature derivatives of seismic velocity by anelastic effects. Such large thermal anomalies, generated by decreased lithospheric thickness and mantle upwelling beneath the fast spreading Lau back are basin, can still leave the mantle near the solidus, even after accounting for the effect of increased volatile content in the mantle wedge. The lower-amplitude velocity reductions in the deeper wedge are likely related to an increased concentration of volatiles from the subducting slab.

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.

Goodman, D, Bibee LD, Dorman LM.  1989.  Crustal Seismic Structure beneath the West Philippine Sea, 17-Degrees-18-Degrees North. Marine Geophysical Researches. 11:155-168.Website
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.

Menard, HW, Dorman LM.  1977.  Dependence of Depth Anomalies Upon Latitude and Plate Motion. Journal of Geophysical Research. 82:5329-5335.   10.1029/JB082i033p05329   Website
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.

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
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
Mammerickx, J, Herron E, Dorman L.  1980.  Evidence for 2 Fossil Spreading Ridges in the Southeast Pacific. Geological Society of America Bulletin. 91:263-271.   10.1130/0016-7606(1980)91<263:eftfsr>;2   Website
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
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
Lewis, BTR, Dorman LM.  1970.  Experimental Isostasy .2. An Isostatic Model for USA Derived from Gravity and Topographic Data. Journal of Geophysical Research. 75:3367-&.   10.1029/JB075i017p03367   Website
Dorman, LM, Lewis BTR.  1972.  Experimental Isostasy .3. Inversion of Isostatic Green-Function and Lateral Density Changes. Journal of Geophysical Research. 77:3068-&.   10.1029/JB077i017p03068   Website
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.

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.

Ziegler, RE, Dorman LRM.  1976.  The Georgia Gravity Base Net. :1-33., Atlanta: State of Georgia
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.

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.