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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.

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.

Ander, ME, Zumberge MA, Lautzenhiser T, Parker RL, Aiken CLV, Gorman MR, Nieto MM, Ferguson JF, McMechan GA.  1989.  A New Field Experiment in the Greenland Ice Cap to Test Newton Inverse Square Law. Annals of the New York Academy of Sciences. 571:672-680.   10.1111/j.1749-6632.1989.tb50553.x   AbstractWebsite

Recent experimental evidence suggests that Newton’s law of gravity may not be precise. There are modern theories of quantum gravity that, in their attempts to unify gravity with other forces of nature, predict non-Newtonian gravitational forces that could have ranges on the order of 102-105 m. If they exist, these forces would be apparent as violations of Newton’s inverse square law. A geophysical experiment was carried out to search for possible finite-range, non-Newtonian gravity over depths of 213-1673 m in the glacial ice of the Greenland ice cap. The principal reason for this choice of experimental site is that a hole drilled through the ice cap already existed and the uniformity of the ice eliminates one of the major sources of uncertainty arising in the first of earlier namely, the heterogeneity of the rocks through which a mine shaft or drill hole passes. Our observations were made in the summer of 1987 at Dye 3, Greenland, in the 2033-m-deep borehole, which reached the basement rock.

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
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.

Blum, J, Igel H, Zumberge M.  2010.  Observations of Rayleigh-Wave Phase Velocity and Coseismic Deformation Using an Optical Fiber, Interferometric Vertical Strainmeter at the SAFOD Borehole, California. Bulletin of the Seismological Society of America. 100:1879-1891.   10.1785/0120090333   AbstractWebsite

We present observations from a vertical, optical fiber interferometric strainmeter in the San Andreas Fault Observatory at Depth borehole near Parkfield, California. The sensor detects both teleseismic earthquakes and local events, along with coseismic strain steps consistent with theoretical dislocation models. For teleseismic events, we investigate the possibility of determining local Rayleigh-wave phase velocities beneath the borehole by comparing the ratio of vertical ground acceleration from a nearby seismometer to vertical strain. While similar studies have used horizontal components and rotations, this is the first such attempt utilizing vertical measurements. We show that at periods from around 16-40 seconds, we can recover general dispersion characteristics that are within a few percent of models of realistic local structure.

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.

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.

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

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.

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.

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
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.

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.

DeWolf, S, Wyatt FK, Zumberge MA, Hatfield W.  2015.  Improved vertical optical fiber borehole strainmeter design for measuring Earth strain. Review of Scientific Instruments. 86   10.1063/1.4935923   AbstractWebsite

Fiber-based interferometers provide the means to sense very small displacements over long baselines, and have the advantage of being nearly completely passive in their operation, making them particularly well suited for geophysical applications. A new 250 m, interferometric vertical borehole strainmeter has been developed based completely on passive optical components. Details of the design and deployment at the Pinon Flat Observatory are presented. Power spectra show an intertidal noise level of -130 dB (re. 1 epsilon(2)/Hz), consistent within 1-3 dB between redundant components. Examination of its response to Earth tides and earthquakes relative to the areal strain recorded by an orthogonal pair of collocated, 730 m horizontal laser strainmeters yield a Poisson's ratio for local near surface material of 0.25 that is consistent with previous results. (C) 2015 AIP Publishing LLC.

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.

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.

Faller, JE, Rinker RL, Zumberge M.  1979.  Progress on the development of a portable absolute gravimeter. Bulletin d'Information. 44 Abstract
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.

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
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.

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.

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
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.