Publications

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2010
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.

1997
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.

1991
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.

1990
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.

1989
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.

Zumberge, MA.  1989.  Absolute gravity measurements. The Encyclopedia of solid earth geophysics. ( James DE, Ed.).:5-9., New York: Van Nostrand Reinhold Abstract
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1986
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.