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Sasagawa, GS, Zumberge MA, Stevenson JM, Lautzenhiser T, Wirtz J, Ander ME.  1989.  The 1987 Southeastern Alaska Gravity Calibration Range - Absolute and Relative Gravity Measurements. Journal of Geophysical Research-Solid Earth and Planets. 94:7661-7666.   10.1029/JB094iB06p07661   AbstractWebsite

In June 1987 a gravimeter calibration range was set up in southeastern Alaska and the Yukon territory, as part of a geophysical determination of the Newtonian gravitational constant. Absolute gravity measurements were made between the range endpoints using the Institute of Geophysics and Planetary Physics absolute gravity meter. The calibration range spans 171.841±0.014 mGal, with a midpoint g value of 9.81746500 ms−2. Relative gravity meters, including a LaCoste and Romberg borehole gravity meter, were read along this range. A scale factor correction (SFC) for borehole meter 14 was found to be (8.1 ± 1.5) × 10−4, and for meter G-349 the correction was (−3.3 ± 1.7) × 10−4. The SFC for meter D-85 has an upper bound of ±1.0 × 10−4.

Sasagawa, GS, Zumberge MA.  1989.  5-Year Frequency Stability of a Zeeman Stabilized Laser. Applied Optics. 28:824-825.   10.1364/AO.28.000824   AbstractWebsite

A five-year record of the lockpoint frequency of a Zeeman stabilized laser shows an observed drift rate of 0.3 ± 0.5 MHz/yr following an initial drift of 5.7 ± 2.2 MHz/yr in the first eighteen months of intermittent operation. A second Zeeman laser drifted at a rate of -0.8 ± 1.0 MHz/yr over the last 2.5 yr; the frequency drift was -0.2 ± 0.6 MHz/yr over the last 3.3yr. Empirical temperature correctionsto laser frequency measurements produce a slight variance reduction in the data but no effective bias in the drift estimates.

Zumberge, MA.  1989.  Absolute gravity measurements. The Encyclopedia of solid earth geophysics. ( James DE, Ed.).:5-9., New York: Van Nostrand Reinhold Abstract
Zumberge, MA, Sasagawa G, Kappus M.  1986.  Absolute Gravity Measurements in California. Journal of Geophysical Research-Solid Earth and Planets. 91:9135-9144.   10.1029/JB091iB09p09135   AbstractWebsite

We have constructed an absolute gravity meter that determines the local gravitational acceleration by timing a freely falling mass with a laser interferometer. The instrument has made measurements at 11 sites in California, four in Nevada, and one in France. The uncertainty in the results is typically 10μGal (1 Gal ≡ 1 cm/s2; 1 μGal = 10−6 Gal = 10−8 m/s2). Repeated measurements have been made at several of the sites; only one shows a substantial change in gravity.

Sasagawa, G, Zumberge MA.  1991.  Absolute Gravity Measurements in California, 1984-1989. Journal of Geophysical Research-Solid Earth and Planets. 96:2501-2513.   10.1029/90jb02283   AbstractWebsite

Repeated absolute gravity measurements have been made at 12 sites in California between 1984.3 and 1989.7. As determined in laboratory tests, the instrument used has an estimated accuracy of 10-mu-Gal (approximately 10(-8) g). The repeatability of the measurements is consistent with this accuracy assessment. No gravity changes above the limits set by instrumental uncertainty and environmental noise are observed in California during this period; the field observations provide upper limits on the rates of secular gravity changes which could be attributed to crustal deformation with a resolution corresponding to vertical displacement rates of 1-2 cm/yr.

Canuteson, E, Zumberge M, Hanson J.  1997.  An absolute method of vertical seismometer calibration by reference to a falling mass with application to the measurement of the gain. Bulletin of the Seismological Society of America. 87:484-493. AbstractWebsite

We measure the gain of a vertical seismometer by simultaneously recording the output of the seismometer and repeatedly measuring the displacement between the seismometer and a free-falling mass in a vacuum. The falling object provides an inertial reference frame. By comparing the ground motion measured by the seismometer with the independent record of displacement between the seismometer and inertial space, we obtain the gain. It is an absolute measurement of the gain relative to the local Lorentz reference frame, Bootstrap error estimates show that a high precision in the estimate of the gain can be obtained with a small number of individual drops. The method derived can be extended to multi-parameter searches of the vertical response function. The technique is also shown to reduce noise in absolute gravity measurements due to ground noise, Finally, we discuss the potential for replacing vibration isolation schemes in absolute gravity systems with digital noise reduction.

Ander, ME, Kerr W, Aiken CLV, Glover CC, Zumberge MA.  1990.  An Absolute Wireline Calibration to Support a Test of Newtons Inverse Square Law. Geophysics. 55:920-923.   10.1190/1.1442907   AbstractWebsite

As part of a Greenland ice cap experiment to measure possible scale length violations of Newton’s inverse square law over geophysical scales of 200 to 1500 m, it was necessary to locate the depth of a gravity meter attached to a wireline down a borehole to about 1 part in 10 000. In order to do this, the wireline and cable length measuring system had to be calibrated both before and after the Greenland expedition. The measuring system used a combination of a mechanical wheel measuring device and a magnetic mark counter. The calibration was conducted in a 1200 m vertical mine shaft at the Consolidated Silver Mine in Osborn, Idaho. Distances in the mine shaft were first calibrated to a precision of about 0.005 m using a geodetic laser system model 4L Geodimeter operating at 30 MHz. To calibrate the wireline, it was run up the mine shaft five times before and five times after the Greenland experiment. The calibration before the experiment was good to about 4 parts in 10 000 and the calibration after was accurate to about 1 part in 10 000. A total inelastic stretch of only 0.102 m occurred during the Greenland operation.

Parker, RL, Zumberge MA.  1989.  An Analysis of Geophysical Experiments to Test Newton Law of Gravity. Nature. 342:29-32.   10.1038/342029a0   AbstractWebsite

Signals reported as evidence for a non-newtonian 'fifth' force at a North Carolina television tower and elsewhere can be explained in a conventional way by postulating small density variations underground. The assumptions employed in earlier analyses which pointed to a failure of the inverse square law are examined and found to be difficult to justify.

Blum, JA, Chadwell CD, Driscoll N, Zumberge MA.  2010.  Assessing slope stability in the Santa Barbara Basin, California, using seafloor geodesy and CHIRP seismic data. Geophysical Research Letters. 37   10.1029/2010gl043293   AbstractWebsite

Seafloor slope instability in the Santa Barbara Basin, California, poses risk to the region. Two prominent landslides, the Goleta and Gaviota slides, occupy the northern flank, with a scarp-like crack extending east from the headwall of the Gaviota slide towards the Goleta complex. Downslope creep across the crack might indicate an imminent risk of failure. Sub-bottom CHIRP profiles with <1 m accuracy across the crack exhibit no evidence of internal deformation. Daily seafloor acoustic range measurements spanning the crack detected no significant motion above a 99% confidence level of +/- 7 mm/yr over two years of monitoring. These disparate data over different timescales suggest no active creep and that the crack is likely a relict feature that formed concomitantly with the Gaviota slide. Citation: Blum, J. A., C. D. Chadwell, N. Driscoll, and M. A. Zumberge (2010), Assessing slope stability in the Santa Barbara Basin, California, using seafloor geodesy and CHIRP seismic data, Geophys. Res. Lett., 37, L13308, doi: 10.1029/2010GL043293.

Nooner, SL, Eiken O, Hermanrud C, Sasayawa GS, Stenvold T, Zumberge MA.  2007.  Constraints on the in situ density of CO2 within the Utsira formation from time-lapse seafloor gravity measurements. International Journal of Greenhouse Gas Control. 1:198-214.   10.1016/s1750-5836(07)00018-7   AbstractWebsite

At Sleipner, CO2 is being separated from natural gas and injected into an underground saline aquifer for environmental purposes. Uncertainty in the aquifer temperature leads to uncertainty in the in situ density of CO2. In this study, gravity measurements were made over the injection site in 2002 and 2005 on top of 30 concrete benchmarks on the seafloor in order to constrain the in Situ CO2 density. The gravity measurements have a repeatability of 4.3 mu Gal for 2003 and 3.5 mu Gal for 2005. The resulting time-lapse uncertainty is S.3 mu Gal. Unexpected benchmark motions due to local sediment scouring contribute to the uncertainty. Forward gravity models are calculated based on both 3D seismic data and reservoir simulation models. The time-lapse gravity observations best fit a high temperature for-ward model based on the time-lapse 3D seismics, suggesting that the average in Situ CO2 density is about to 530 kg/m(3). Uncertainty in determining the average density is estimated to be 65 kg/m(3) (95% confidence), however, this does not include uncertainties in the modeling. Additional seismic surveys and future gravity measurements will put better constraints on the CO2 density and continue to map out the CO2 flow. (C) 2007 Elsevier Ltd. All rights reserved.

Pettit, EC, Waddington ED, Harrison WD, Thorsteinsson T, Elsberg D, Morack J, Zumberge MA.  2011.  The crossover stress, anisotropy and the ice flow law at Siple Dome, West Antarctica. Journal of Glaciology. 57:39-52.   10.3189/002214311795306619   AbstractWebsite

We used observations and modeling of Sip le Dome, West Antarctica, a ridge ice divide, to infer the importance of linear deformation mechanisms in ice-sheet flow. We determined the crossover stress (a threshold value of the effective deviatoric stress below which linear flow mechanisms dominate over nonlinear flow mechanisms) by combining measurements of ice properties with in situ deformation rate measurements and a finite-element ice flow model that accounts for the effects of viscous anisotropy induced by preferred crystal-orientation fabric. We found that a crossover stress of 0.18 bar produces the best match between predicted and observed deformation rates. For Sip le Dome, this means that including a linear term in the flow law is necessary, but generally the flow is still dominated by the nonlinear (Glen; n = 3) term. The pattern of flow near the divide at Sip le Dome is also strongly affected by crystal fabric. Measurements of sonic velocity, which is a proxy for vertically oriented crystal fabric, suggest that a bed-parallel shear band exists several hundred meters above the bed within the Ice Age ice.

Gee, JS, Webb SC, Ridgway J, Staudigel H, Zumberge MA.  2001.  A deep tow magnetic survey of Middle Valley, Juan de Fuca Ridge. Geochemistry Geophysics Geosystems. 2   10.1029/2001GC000170   AbstractWebsite

We report here results from a deep tow magnetic survey over Middle Valley, Juan de Fuca Ridge. A series of track lines are combined to generate a high-resolution map of the magnetic field anomaly within a 10 x 12 km region surrounding the Bent Hill massive sulfide (BHMS) deposit. A uniformly magnetized body (5 A/m) with a cross section approximating the body inferred from Ocean Drilling Program (ODP) drilling can account for the observed near-bottom magnetic anomaly amplitude. Assuming this magnetization is entirely induced, the average susceptibility (0.11 SI) corresponds to similar to3.5% magnetite + pyrrhotite by volume, consistent with the abundance of these phases observed in drill core samples. However, this uniform magnetization model significantly underestimates the magnetic anomaly measured a few meters above the seafloor by submersible, indicating that the upper portion of the sulfide mound must have a significantly higher magnetization (similar to 10% magnetite + pyrrhotite) than at deeper levels. On a larger scale, the near-bottom magnetic anomaly data show that basement magnetizations are not uniformly near zero, as had been inferred from analysis of the sea surface anomaly pattern. We interpret this heterogeneity as reflecting primarily differences in the degree of hydrothermal alteration. Our results highlight the potential of magnetic anomaly data for characterizing hydrothermal deposits where extensive drill core sampling is not available.

Ridgway, JR, Zumberge MA.  2002.  Deep-towed gravity surveys in the southern California Continental Borderland. Geophysics. 67:777-787.   10.1190/1.1484521   AbstractWebsite

We surveyed two sites in the southern California continental borderland with a newly developed instrument, a towed deep ocean gravimeter-a gravity sensor that can be towed a few tens of meters above the sea floor. During its development phase, we used the instrument to survey two regions off the coast of southern California. The first was along two tracks in the San Diego Trough. The second was over a seamount-like feature named Emery Knoll. Results of the trough survey reveal a basin with a geometry consistent with seismic data. We observed no significant density contrast across the San Diego Trough fault in the near-surface sediments. The survey of Emery Knoll shed light on the question of the origin of this structure; modeling the knoll to determine its bulk density suggested a nearly uniform structure surrounded by sedimentary basins with a more massive central intrusive body. Derived densities of 2850 kg/m(3) for the knoll and 3050 kg/m(3) for the central intrusion assume that no deep unmodeled sources exist directly underneath the knoll. The gravity data favor a model of metamorphic basement rock uplifted and containing igneous intrusives.

Elsberg, DH, Harrison WD, Zumberge MA, Morack JL, Pettit EC, Waddington ED, Husmann E.  2004.  Depth- and time-dependent vertical strain rates at Siple Dome, Antarctica. Journal of Glaciology. 50:511-521.   10.3189/172756504781829684   AbstractWebsite

As part of a project to investigate the flow of ice at low effective stress, two independent strain-gauge systems were used to measure vertical strain rate as a function of depth and time at Siple Dome, Antarctica. The measurements were made from January 1998 until January 2002 at the ice divide and a site 7km to the northeast on the flank. The strain-rate profiles place constraints on the rheology of ice at low stress, show the expected differences between divide and flank flow (with some structure due to firn compaction and probably ice stratigraphy), and suggest that the flow of the ice sheet has not changed much in the last 8.6kyr. The strain rates show an unexpected time dependence on scales ranging from several months to hours, including discrete summer events at the divide. Time dependence in strain rate, water pressure, seismicity, velocity and possibly basal motion has been seen previously on the Siple Coast ice streams, but it is especially surprising on Siple Dome because the bed is cold.

Thun, R, Akerlof CW, Alley P, Koltick D, Loveless RL, Meyer DI, Zumberge M, Bintinger D, Lundy RA, Yovanovitch DD, Ditzler WR, Finley DA, Loeffler FJ, Shibata EI, Stanfield KC.  1976.  Description of Drift Chambers Used in a Fermilab Experiment. Nuclear Instruments & Methods. 138:437-444.   10.1016/0029-554x(76)90308-6   AbstractWebsite

We give a detailed description of the drift chamber system used in a charm search at Fermilab. All important aspects of design and performance are discussed.

Fisher, E, McMechan GA, Gorman MR, Cooper APR, Aiken CLV, Ander ME, Zumberge MA.  1989.  Determination of Bedrock Topography beneath the Greenland Ice-Sheet by 3-Dimensional Imaging of Radar Sounding Data. Journal of Geophysical Research-Solid Earth and Planets. 94:2874-2882.   10.1029/JB094iB03p02874   AbstractWebsite

In the summer of 1987, approximately 42,600 radar reflections were obtained along 124 radial lines, 5 km long, centered at Dye 3 in southern Greenland. Processing of these data using a three-dimensional kinematic migration algorithm produces a high-resolution image of the rock surface topography beneath the ice sheet. Estimated uncertainties in the position of the rock surface increase where sampling is less dense, such as toward the edges of the survey, but are less than 5 m over most of the survey area. The main structure revealed is a northwest-southeast trending valley in the bedrock that crosses the westward regional dip of the rock surface. Ice thickness increases from approximately 1800 m in the east to approximately 2100 m in the west.

DeWolf, S, Walker KT, Zumberge MA, Denis S.  2013.  Efficacy of spatial averaging of infrasonic pressure in varying wind speeds. Journal of the Acoustical Society of America. 133:3739-3750.   10.1121/1.4803891   AbstractWebsite

Wind noise reduction (WNR) is important in the measurement of infrasound. Spatial averaging theory led to the development of rosette pipe arrays. The efficacy of rosettes decreases with increasing wind speed and only provides a maximum of similar to 20 dB WNR due to a maximum size limitation. An Optical Fiber Infrasound Sensor (OFIS) reduces wind noise by instantaneously averaging infrasound along the sensor's length. In this study two experiments quantify the WNR achieved by rosettes and OFISs of various sizes and configurations. Specifically, it is shown that the WNR for a circular OFIS 18m in diameter is the same as a collocated 32-inlet pipe array of the same diameter. However, linear OFISs ranging in length from 30 to 270m provide a WNR of up to similar to 30 dB in winds up to 5m/s. The measured WNR is a logarithmic function of the OFIS length and depends on the orientation of the OFIS with respect to wind direction. OFISs oriented parallel to the wind direction achieve similar to 4 dB greater WNR than those oriented perpendicular to the wind. Analytical models for the rosette and OFIS are developed that predict the general observed relationships between wind noise reduction, frequency, and wind speed.

Landro, M, Zumberge M.  2017.  Estimating saturation and density changes caused by CO2 injection at Sleipner - Using time-lapse seismic amplitude-variation-with-offset and time-lapse gravity. Interpretation-a Journal of Subsurface Characterization. 5:T243-T257.   10.1190/int-2016-0120.1   AbstractWebsite

We have developed a calibrated, simple time-lapse seismic method for estimating saturation changes from the CO2-storage project at Sleipner offshore Norway. This seismic method works well to map changes when CO2 is migrating laterally away from the injection point. However, it is challenging to detect changes occurring below CO2 layers that have already been charged by some CO2. Not only is this partly caused by the seismic shadow effects, but also by the fact that the velocity sensitivity for CO2 change in saturation from 0.3 to 1.0 is significantly less than saturation changes from zero to 0.3. To circumvent the seismic shadow zone problem, we combine the time-lapse seismic method with time-lapse gravity measurements. This is done by a simple forward modeling of gravity changes based on the seismically derived saturation changes, letting these saturation changes be scaled by an arbitrary constant and then by minimizing the least-squares error to obtain the best fit between the scaled saturation changes and the measured time-lapse gravity data. In this way, we are able to exploit the complementary properties of time-lapse seismic and gravity data.

De Groot-Hedlin, CD, Hedlin MAH, Walker KT, Drob DP, Zumberge MA.  2008.  Evaluation of infrasound signals from the shuttle Atlantis using a large seismic network. Journal of the Acoustical Society of America. 124:1442-1451.   10.1121/1.2956475   AbstractWebsite

Inclement weather in Florida forced the space shuttle "Atlantis" to land at Edwards Air Force Base in southern California on June 22, 2007, passing near three infrasound stations and several hundred seismic stations in northern Mexico, southern California, and Nevada. The high signal-to-noise ratio, broad receiver coverage, and Atlantis' positional information allow for the testing of infrasound propagation modeling capabilities through the atmosphere to regional distances. Shadow zones and arrival times are predicted by tracing rays that are launched at right angles to the conical shock front surrounding the shuttle through a standard climatological model as well as a global ground to space model. The predictions and observations compare favorably over much of the study area for both atmospheric specifications. To the east of the shuttle trajectory, there were no detections beyond the primary acoustic carpet. Infrasound energy was detected hundreds of kilometers to the west and northwest (NW) of the shuttle trajectory, consistent with the predictions of ducting due to the westward summer-time stratospheric jet. Both atmospheric models predict alternating regions of high and low ensonifications to the NW. However, infrasound energy was detected tens of kilometers beyond the predicted zones of ensonification, possibly due to uncertainties in stratospheric wind speeds. (C) 2008 Acoustical Society of America.

Canuteson, EL, Zumberge MA.  1996.  Fiber-optic extrinsic Fabry-Perot vibration-isolated interferometer for use in absolute gravity meters. Applied Optics. 35:3500-3505.   10.1364/ao.35.003500   AbstractWebsite

In an absolute gravity meter, a laser interferometer measures the position of a test mass that is falling in a vacuum. The calculated value of gravity is the average acceleration of the mass during a set of drops, Since systematic accelerations of the optical system will bias the measured value of gravity, various interferometar geometries have been implemented in the past to isolate the optical system from ground motion. We have developed and tested a low-finesse fiber-optic extrinsic Fabry-Perot interferometer that is fixed to the mass of a critically damped seismometer in which the effects of systematic ground motion and acoustic vibrations are reduced. (C) 1996 Optical Society of America

Zumberge, MA.  1985.  Frequency Stability of a Zeeman-Stabilized Laser. Applied Optics. 24:1902-1904.   10.1364/AO.24.001902   AbstractWebsite

The frequency of a commercial hard-sealed He-Ne laser has been stabilized to the center of the discharge gain profile using the mode splitting caused by an axial magnetic field. The absolute frequency has been measured repeatedly during intermittent operation over 20 months. Its drift over most of this period has been 2.6 ± 0.7 MHz/yr. The lock point has been found to depend slightly on the laser tube’s temperature.

Eiken, O, Stenvold T, Zumberge M, Alnes H, Sasagawa G.  2008.  Gravimetric monitoring of gas production from the Troll field. Geophysics. 73:WA149-WA154.   10.1190/1.2978166   AbstractWebsite

Four surveys of relative gravity and depth measurements have been conducted over the Troll field since gas production began in 1996. Precision in gravity (intrasurvey repeatability measured as standard deviation) has improved from 26 mu Gal to 4-5 mu Gal in two surveys in 2002 and 2005. The scatter of 74 station depth differences (standard deviation) has improved to 1.0 cm (with modeled subsidence removed) for the same two surveys. Subsidence of up to 3 cm is observed above the thickest reservoir of Troll East between 2002 and 2005. Time-lapse gravity shows a general slight average increase in Troll East (95% confidence for the interval centered at 5.2 +/- 4.4 mu Gal), which is likely caused by edgewater influx. One gravity station close to Troll A shows a 9-mu Gal gravity increase, indicating 2.2-m water rise. Repeated logging in a nearby well indicates 2.8-m rise. These two observations agree within uncertainty bounds. Gravity decrease in Troll West is explained by oil production and a downward-moving gas-oil contact. Gravity increases in two areas in the easternmost part appear statistically significant and are likely to have been caused by edgewater influx. This has not been confirmed by other data, but aquifers located near these areas make the results plausible. The gravity and subsidence data give estimates of total mass influx and pore compaction; these data have been used in and agree with material-balance calculations.

Zumberge, M.  2011.  Gravity Measurements, Absolute. Encyclopedia of Solid Earth Geophysics. ( Gupta HK, Ed.).:494-497., Dordrecht: Springer Abstract
Zumberge, M.  1995.  Gravity Meter. McGraw Hill Encyclopedia of Science & Technology. Abstract
Zumberge, MA, Ander ME, Lautzenhiser TV, Parker RL, Aiken CLV, Gorman MR, Nieto MM, Cooper APR, Ferguson JF, Fisher E, Greer J, Hammer P, Hansen BL, McMechan GA, Sasagawa GS, Sidles C, Stevenson JM, Wirtz J.  1990.  The Greenland Gravitational Constant Experiment. Journal of Geophysical Research-Solid Earth and Planets. 95:15483-15501.   10.1029/JB095iB10p15483   AbstractWebsite

An Airy-type geophysical experiment was conducted in a 2-km-deep hole in the Greenland ice cap at depths between 213 m and 1673 m to test for possible violations of Newton's inverse square law. The experiment was done at Dye 3, the location of a Distant Early Warning Line radar dome and the site of the deepest of the Greenland Ice-Sheet Program (GISP) drill holes. Gravity measurements were made at eight depths in 183-m intervals with a LaCoste&Romberg borehole gravity meter. Prior to the experiment the borehole gravity meter was calibrated with an absolute gravity meter, and the wireline depth-rinding system used in the borehole logging was calibrated in a vertical mine-shaft against a laser geodimeter. The density of the ice in the region was calculated from measurements taken from ice cores obtained from earlier drilling observations. Ice penetrating radar was employed in order to correct the gravity data for the topography of the ice-rock interface. Surface gravity observations were made to assess the extent to which density variations in the sub-ice rock could affect the vertical gravity gradient. The locations of the gravity observation points were determined with a combination of GPS recording, first-order leveling, and EDM surveying. An anomalous variation in gravity totaling 3.87 mGal (3.87×10−5 m/s2) in a depth interval of 1460 m was observed. This may be attributed either to a breakdown of Newtonian gravity or to unexpected density variations in the rock below the ice.