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Zumberge, M, Alnes H, Eiken O, Sasagawa G, Stenvold T.  2008.  Precision of seafloor gravity and pressure measurements for reservoir monitoring. Geophysics. 73:WA133-WA141.   10.1190/1.2976777   AbstractWebsite

Changes with gravity over time have proven to be valuable for inferring subsurface density changes associated with production from oil and natural gas reservoirs. Such inferences allow the monitoring of moving fluid fronts in a reservoir and provide an opportunity to optimize production over the life of the reservoir. Our group began making time-lapse seafloor gravity and pressure measurements in 1998. To date, we have surveyed six fields offshore Norway; we have made three repeat surveys at one field and one repeat survey at another. We incorporated a land-gravity sensor into a remotely operated seafloor housing. Three such relative gravity sensors mounted in a single frame are carried by a remotely operated vehicle (ROV) to concrete benchmarks permanently placed on the seafloor. Reference benchmarks sited outside the reservoir boundaries are assumed to provide stable fiducial points. Typical surveys last from a few days to a few weeks and cover from 8 to 80 benchmarks, with multiple observations of each. In our earliest surveys, we obtained an intrasurvey repeatability of approximately 20 mu Gal, but recently we have been achieving 3-mu Gal repeatability in gravity and approximately 5 mm in benchmark depth (deduced from simultaneously recorded ambient seawater pressure). We attribute the improved precision to several operational factors, including the use of multiple gravity sensors, frequent benchmark reoccupation, precise relocation and orientation of the sensors, repeated calibrations on land, and minimization of vibrational and thermal perturbations to the sensors. We believe that high-precision time-lapse gravity monitoring can be used to track changes in the height of a gas-water contact in a flooded reservoir, with a precision of a few meters.

Faller, JE, Rinker RL, Zumberge M.  1979.  Progress on the development of a portable absolute gravimeter. Bulletin d'Information. 44 Abstract
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Blum, JA, Nooner SL, Zumberge MA.  2008.  Recording Earth strain with optical fibers. IEEE Sensors Journal. 8:1152-1160.   10.1109/jsen.2008.926882   AbstractWebsite

Optical fibers are well suited to measure Earth strain because they can be stretched over long distances to average strain over a large interval. This is important to reduce disturbances to the measurement from very local effects. We have installed optical fibers ranging in length from a few 10s of meters to 2 km in vertical boreholes on land and in an icesheet, and horizontally along the sea floor. Due to the high sensitivity of optical fibers to temperature change, an environment of stable temperature is important-this is often available in boreholes or on the sea floor. Longevity of fiber cables and the means to protect the glass fibers from environmental effects and the rigors of deployment are critical issues. Our experiences cover a broad range of success in this regard, with some deployments lasting for more than four years and others failing immediately.

Zumberge, MA, Berger J, Dzieciuch MA, Parker RL.  2004.  Resolving quadrature fringes in real time. Applied Optics. 43:771-775.   10.1364/ao.43.000771   AbstractWebsite

In many interferometers, two fringe signals can be generated in quadrature. The relative phase of the two fringe signals depends on whether the optical path length is increasing or decreasing. A system is developed in which two quadrature fringe signals are digitized and analyzed in real time with a digital signal processor to yield a linear, high-resolution, wide-dynamic-range displacement transducer. The resolution in a simple Michelson interferometer with inexpensive components is 5 X 10(-13) m Hz(-1/2) at 2 Hz. (C) 2004 Optical Society of America.

Zumberge, MA, Faller JE, Gschwind J.  1983.  Results from an Absolute Gravity Survey in the United-States. Journal of Geophysical Research. 88:7495-7502.   10.1029/JB088iB09p07495   AbstractWebsite

Using the recently completed JILA absolute gravity meter, we made an absolute gravity survey which covered 12 sites in the United States. Over a period of 8 weeks, the instrument was driven a total distance of nearly 20,000 km to sites in California, New Mexico, Colorado, Wyoming, Maryland, and Massachusetts. The time spent in carrying out a measurement at a single location was typically 1 day. A measurement accuracy of around 1×10−7 m/s2 (10 μGal) is believed to have been obtained at each of the sites.

Arnautov, G, Boulanger Y, Cannizzo L, Cerutti G, Faller J, Feng Y-Y, Groten E, Guo Y, Hollander W, Huang D-L, Kalish E, Marson I, Niebauer T, Sakuma A, Sasagawa G, Schleglov S, Stus Y, Tarasiuk W, Ahang G-Y, Zhou J-H, Zumberge M.  1987.  Results of the Second International Comparison of Absolute Gravimeters in Sevres 1985. Bull. D'Information. 59 Abstract
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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.

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.

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
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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
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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.

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.

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Ander, ME, Zumberge MA, Lautzenhiser T, Parker RL, Aiken CLV, Gorman MR, Nieto MM, Cooper APR, Ferguson JF, Fisher E, McMechan GA, Sasagawa G, Stevenson JM, Backus G, Chave AD, Greer J, Hammer P, Hansen BL, Hildebrand JA, Kelty JR, Sidles C, Wirtz J.  1989.  Test of Newtons Inverse-Square Law in the Greenland Ice Cap. Physical Review Letters. 62:985-988.   10.1103/PhysRevLett.62.985   AbstractWebsite

An Airy-type geophysical experiment was conducted in a 2-km-deep hole in the Greenland ice cap at depths between 213 and 1673 m to test for possible violations of Newton’s inverse-square law. An anomalous gravity gradient was observed. We cannot unambiguously attribute it to a breakdown of Newtonian gravity because we have shown that it might be due to unexpected geological features in the rock below the ice.

Zumberge, MA, Ridgway JR, Hildebrand JA.  1997.  A towed marine gravity meter for near-bottom surveys. Geophysics. 62:1386-1393.   10.1190/1.1444243   AbstractWebsite

Gravity is measured presently on the sea surface and on the sea floor. Surface gravity suffers from loss of resolution over the deep ocean because the perturbing source masses are far from the observer, Bottom measurements recover this resolution, but suffer from poor coverage because of the time needed for each measurement. We have constructed a gravimetry system that combines the rapid data collection capability of a moving platform with the high resolution gained by locating the observations near the bottom. This gravity sensor is tethered to a ship and towed just above the sea floor. The instrument consists of a LaCoste and Romberg shipboard gravity meter modified to fit inside a pressure case that is mounted on a platform designed for towing stability. We have tested it in a survey in the San Diego Trough, a 1000-m-deep sedimented valley in the Pacific Ocean in the California continental borderlands. Multiple gravity tracklines collected there at a depth of 935 m show a resolution of a few tenths of a mGal. The new instrument will be useful for surveys of features whose lateral extent is equal to or less than the ocean depth.

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Chadwick, WW, Nooner SL, Zumberge MA, Embley RW, Fox CG.  2006.  Vertical deformation monitoring at Axial Seamount since its 1998 eruption using deep-sea pressure sensors. Journal of Volcanology and Geothermal Research. 150:313-327.   10.1016/j.jvolgeores.2005.07.006   AbstractWebsite

Pressure measurements made on the seafloor at depths between 1500 and 1700 m at Axial Seamount, an active submarine volcano on the Juan de Fuca Ridge in the northeast Pacific Ocean, show evidence that it has been inflating since its 1998 eruption. Data from continuously recording bottom pressure sensors at the center of Axial's caldera suggest that the rate of inflation was highest in the months right after the eruption (20 cm/month) and has since declined to a steady rate of similar to 15 cm/year. Independent campaign-style pressure measurements made each year since 2000 at an array of seafloor benchmarks with a mobile pressure recorder mounted on a remotely operated vehicle also indicate uplift is occurring in the caldera at a rate up to 22 +/- 1.3 cm/year relative to a point outside the caldera. The repeatability of the campaign-style pressure measurements progressively improved each year from +/- 15 cm in 2000 to +/- 0.9 cm in 2004, as errors were eliminated and the technique was refined. Assuming that the uplift has been continuous since the 1998 eruption, these observations suggest that the center of the caldera has re-inflated about 1.5 +/- 0.1 m, thus recovering almost 50% of the 3.2 m of subsidence that was measured during the 1998 eruption. This rate of inflation can be used to calculate a magma supply rate of 14 x 10(6) m(3)/year. If this rate of inflation continues, it also suggests a recurrence interval of similar to 16 years between eruptions at Axial, assuming that it will be ready to erupt again when it has re-inflated to 1998 levels. (c) 2005 Elsevier B.V. All rights reserved.