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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.

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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.

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.

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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.

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.

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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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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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.

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.

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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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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.

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.

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.

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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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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.

Zumberge, MA.  1997.  Precise optical path length measurement through an optical fiber: Application to seafloor strain monitoring. Ocean Engineering. 24:531-542.   10.1016/s0029-8018(96)00029-7   AbstractWebsite

An optical tiber strainmeter intended for measuring tectonic strains on the seafloor is under development. In this instrument, an optical fiber is stretched between two points fixed to the ocean bottom; relative displacement of these points causes a change in the elongation of the fiber. This associated change in optical path length is monitored by an electronic distance meter. The dominant sources of noise in determining the optical path length of the fiber stem from the dependence of the fiber's index of refraction on both wavelength and temperature. In a 50 day long experiment performed in the shallow ocean, a test fiber was installed along a 210 m long baseline on the bottom. The RMS Variation in length was 5 mm except for two displacements of order 10 cm caused by known effects. (C) 1997 Elsevier Science Ltd.

Zumberge, MA, Rinker RL, Faller JE.  1982.  A Portable Apparatus for Absolute Measurements of the Earths Gravity. Metrologia. 18:145-152.   10.1088/0026-1394/18/3/006   AbstractWebsite

We have developed a new and portable apparatus for making absolute measurements of the acceleration due to the Earth's gravity. We use the method of free fall, and interferometrically determine the acceleration of a freely falling cube corner. In the design and development of this instrument, particular attention was paid to those aspects which would affect its performance in the field. The resulting instrument, we believe, provides a viable new tool for the study of tectonic motions. The system is very small; it can be transported in a small van and requires only two hours for assembly. A high rate of data acquisition is available; if necessary, a single measurement can be made every two seconds. Further, we have made a concerted effort to detect and (we hope) eliminate systematic errors. The results of extensive tests indicate that the achievable accuracy for g is about six parts in 109. This instrument therefore provides a sensitivity to vertical motions (e.g., of the Earth's crust) as small as 2 cm.

Chave, AD, Zumberge MA, Ander ME, Hildebrand JA, Spiess FN.  1987.  Polar Ice Test of the Scale Dependence of G. Nature. 326:250-251.   10.1038/326250b0   AbstractWebsite
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Faller, JE, Rinker RL, Zumberge M.  1978.  Plans for the development of a portable absolute gravimeter: A tool for studying non-tidal variations in gravity. Boll. Geofis.Teor. Appl. 20:355-362. Abstract
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Faller, JE, Rinker RL, Zumberge MA.  1979.  Plans for the Development of a Portable Absolute Gravimeter with a Few Parts in 109 Accuracy. Tectonophysics. 52:107-116.   10.1016/0040-1951(79)90212-9   AbstractWebsite

Successful development of a few parts in 109 portable g apparatus (which corresponds to a height sensitivity of about 1 cm) would have an impact on large areas of geodynamics as well as having possible application to earthquake prediction. Furthermore, the use of such an instrument in combination with classical leveling or extraterrestrially determined height data would yield information on internal mass motions. The plans for the development of such an instrument at JILA using the method of free fall will be given. The proposed interferometric method uses one element of an optical interferometer as the dropped object. Recent work has resulted in substantial progress towards the development of a new type of long-period (T > 60 sec) suspension for isolating the reference mirror (corner cube) in the interferometer. Improvements here over the isolation methods previously available, together with state-of-the-art timing and interferometric techniques, are expected to make it possible to achieve a few parts in 109 accuracy with a field-type instrument.

Berger, J, Davis P, Widmer‐Schnidrig R, Zumberge M.  2014.  Performance of an optical seismometer from 1 μHz to 10 Hz. Bulletin of the Seismological Society of America. 104:2422-2429.   10.1785/0120140052   AbstractWebsite

We compare the performance of four different instruments that measure the vertical component of motion of an inertial mass—an STS1 seismometer, an STS2 seismometer, a superconducting gravity meter, and an optical seismometer—operating inside the mine at the Black Forest Observatory near Schiltach in southwest Germany. Simultaneous, collocated operation of these sensors offers an opportunity to test the calibration, response, and performance of each instrument. We estimate noise floors from the tidal bands to 10 Hz. We note small nonlinearities in the suspension of the STS1, which are normally suppressed by analog signal processing and feedback or, in the optical version, by digital signal processing alone. The results demonstrate that the optical seismometer utilizing an STS1 suspension can provide observatory‐quality data over a bandwidth from tidal frequencies to at least 10 Hz and over a large dynamic range.

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Zumberge, M, Berger J, Otero J, Wielandt E.  2010.  An Optical Seismometer without Force Feedback. Bulletin of the Seismological Society of America. 100:598-605.   10.1785/0120090136   AbstractWebsite

We are developing a new vertical seismometer, motivated by a desire to have an instrument whose performance is similar to that of observatory sensors yet can operate within a borehole without electronics. This has led us to an all-optical seismometer consisting of a spring-suspended mass whose position is monitored interferometrically. We use a Michelson interferometer illuminated with a 1 mW laser that can be linked to the seismometer with optical fibers only. A digital signal processor samples the interference fringe signal and produces a 400 samples/sec record of the seismometer mass displacement with a root mean square noise per octave band that varies from about 4 x 10(-12) m at 0.001 Hz to 4 x 10(-13) m at 1 Hz. The maximum displacement is limited by mechanical issues to a few millimeters at present, providing a dynamic range of at least 109, equivalent to 30 bits (180 dB). Experiments to test this idea have been performed on a modified STS1 vertical seismometer whose electronics have been replaced with an optical system. Comparisons with other seismometers show that, in terms of both noise and signal fidelity, the optical approach is quite viable.

Zumberge, MA, Wyatt FK, Yu DX, Hanada H.  1988.  Optical Fibers for Measurement of Earth Strain. Applied Optics. 27:4131-4138.   10.1364/AO.27.004131   AbstractWebsite

We report on laboratory experiments on single-mode optical fibers for use in measuring earth strain. We have monitored the long-term stability of 25-m long tensioned fibers and found their rates of fractional change in optical path lengths to be no more than 2 × 10-6/yr. The optical temperature coefficients for several fibers whose physical lengths were held constant were found to be within 4% of 1.17 × 10-5 apparent strain/°C. The strain sensitivity (the ratio of observed optical path change to physical path change) was determined to be within 1% of 1.16 for all the fibers tested. Initial field tests indicate that fibers are suitable for earth strain measurements of moderate precision.

Zumberge, MA, Wyatt FK.  1998.  Optical fiber interferometers for referencing surface benchmarks to depth. Pure and Applied Geophysics. 152:221-246.   10.1007/s000240050152   AbstractWebsite

We have developed and operated optical fiber interferometers for monitoring displacements within boreholes, as part of a program of crustal deformation measurement. These optical tiber strainmeters-a total of twelve instruments at two sites in southern California-were installed to sense the motion of the end-monuments of much longer baseline strainmeters and tiltmeters, allowing correction for any near-surface ground movement. One of the installations was specifically designed to investigate the distribution of deformation with depth, measuring over several borehole length-intervals from 5 m to 50 m. The displacements recorded over year-long time scales along these length intervals range up to 6 mm and show internal consistency and stability at the 50 mu m level. The use of these interferometers to provide correction signals for kilometer-scale crustal strain measurements has resulted in greatly improved records.

Zumberge, MA, Berger J, Hedlin MAH, Husmann E, Nooner S, Hilt R, Widmer-Schnidrig R.  2003.  An optical fiber infrasound sensor: A new lower limit on atmospheric pressure noise between 1 and 10 Hz. Journal of the Acoustical Society of America. 113:2474-2479.   10.1121/1.1566978   AbstractWebsite

A new distributed sensor for detecting pressure variations caused by distant sources has been developed. The instrument reduces noise due to air turbulence in the infrasound band by averaging pressure along a line by means of monitoring strain in a long tubular diaphragm with an optical fiber interferometer. Above 1 Hz, the optical fiber infrasound sensor (OFIS) is less noisy than sensors relying on mechanical filters. Records collected from an 89-m-long OFIS indicate a new low noise limit in the band from 1 to 10 Hz. Because the OFIS integrates pressure variations at light-speed rather than the speed of sound, phase delays of the acoustical signals caused by the sensor are negligible. Very long fiber-optic sensors are feasible and hold the promise of better wind-noise reduction than can be achieved with acoustical-mechanical systems. (C) 2003 Acoustical Society, of America.