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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.