Export 6 results:
Sort by: [ Author  (Asc)] Title Type Year
A B C D E F G H I J K L M N O P Q R [S] T U V W X Y Z   [Show ALL]
Hildebrand, JA, Stevenson JM, Hammer PTC, Zumberge MA, Parker RL, Fox CG, Meis PJ.  1990.  A Sea-Floor and Sea-Surface Gravity Survey of Axial Volcano. Journal of Geophysical Research-Solid Earth and Planets. 95:12751-12763.   10.1029/JB095iB08p12751   AbstractWebsite

Seafloor and sea surface gravity measurements are used to model the internal density structure of Axial Volcano. Seafloor measurements made at 53 sites within and adjacent to the Axial Volcano summit caldera provide constraints on the fine-scale density structure. Shipboard gravity measurements made along 540 km of track line above Axial Volcano and adjacent portions of the Juan de Fuca ridge provide constraints on the density over a broader region and on the isostatic compensation. The seafloor gravity anomalies give an average density of 2.7 g cm−3 for the uppermost portion of Axial Volcano, The sea surface gravity anomalies yield a local compensation parameter of 23%, significantly less than expected for a volcanic edifice built on zero age lithosphere. Three-dimensional ideal body models of the seafloor gravity measurements suggest that low-density material, with a density contrast of at least 0.15 g cm−3, may be located underneath the summit caldera. The data are consistent with low-density material at shallow depths near the southern portion of the caldera, dipping downward to the north. The correlation of shallow low-density material and surface expressions of recent volcanic activity (fresh lavas and high-temperature hydrothermal venting) suggests a zone of highly porous crust. Seminorm minimization modeling of the surface gravity measurements also suggest a low-density region under the central portion of Axial Volcano. The presence of low-density material beneath Axial caldera suggests a partially molten magma chamber at depth.

Johnson, HO, Wyatt F, Zumberge MA.  1988.  Stabilized Laser for Long Base-Line Interferometry. Applied Optics. 27:445-446.   10.1364/AO.27.000445   AbstractWebsite
Munk, W, Revelle R, Worcester P, Zumberge M.  1990.  Strategy for future measurements of very-low frequency sea-level change. National Research Council Report, Geophysics Study Committee. :221-227., Washington, D. C.: National Research Council Abstract
Nooner, SL, Sasagawa GS, Blackman DK, Zumberge MA.  2003.  Structure of oceanic core complexes: Constraints from seafloor gravity measurements made at the Atlantis Massif. Geophysical Research Letters. 30   10.1029/2003gl017126   AbstractWebsite

[1] Using the DSV Alvin, the relative seafloor gravimeter ROVDOG was deployed at 18 sites on the Atlantis Massif (located at the ridge-transform intersection of the Mid-Atlantic Ridge and the Atlantis Transform Fault near 30degreesN, 42degreesW). These data along with previously collected shipboard gravity and bathymetry provide constraints on the density structure of this oceanic core complex. A series of quasi 3-D forward models suggests that symmetric east and west-dipping density interfaces bound the core of the massif with dip angles of 16degrees-24degrees in the east and 16degrees-28degrees in the west, creating a wedge with a density of 3150-3250 kg/m(3). The dip angle in the east is steeper than that of the surface slope, suggesting that the detachment fault surface does not coincide with the density boundary. The resulting low-density layer is interpreted as a zone of serpentinization.

Sasagawa, G, Zumberge MA.  2013.  A self-calibrating pressure recorder for detecting seafloor height change. IEEE Journal of Oceanic Engineering. 38:447-454.   10.1109/joe.2012.2233312   AbstractWebsite

One method to detect vertical crustal deformation of the seafloor, where Global Positioning System (GPS) surveys are not possible, is to monitor changes in the ambient seawater pressure, whose value is governed primarily by depth. Modern pressure sensors based on quartz strain gauge technology can detect the pressure shift associated with subsidence or uplift of the seafloor by as little as 1 cm. Such signals can be caused by tectonic or volcanic activity, or by hydrocarbon production from an offshore reservoir. However, most gauges undergo a slow drift having unpredictable sign and magnitude, which can be misinterpreted as real seafloor height change. To circumvent this problem, we have developed an instrument that calibrates the pressure gauges in place on the seafloor. In this autonomous system, a pair of quartz pressure gauges recording ambient seawater pressure are periodically connected to a piston gauge calibrator. In a 104 day test off the California coast at 664-m depth, the contribution to the uncertainty in depth variation from gauge drift was 1.3 cm based on calibrations occurring for 20 min every ten days.

Zumberge, MA, Hildebrand JA, Stevenson JM, Parker RL, Chave AD, Ander ME, Spiess FN.  1991.  Submarine Measurement of the Newtonian Gravitational Constant. Physical Review Letters. 67:3051-3054.   10.1103/PhysRevLett.67.3051   AbstractWebsite

We have measured the Newtonian gravitational constant using the ocean as an attracting mass and a research submersible as a platform for gravity measurements. Gravitational acceleration was measured along four continuous profiles to depths of 5000 m with a resolution of 0.1 mGal. These data, combined with satellite altimetry, sea surface and seafloor gravity measurements, and seafloor bathymetry, yield an estimate of G = (6.677 +/- 0.013) x 10(-11) m3 s-2 kg-1; the fractional uncertainty is 2 parts in 1000. Within this accuracy, the submarine value for G is consistent with laboratory determinations.