A most public of musical performances: the English art of change-ringing

Bells were installed in churches throughout much of the western world to announce upcoming services when there was no other means of transmitting such information over long distances and few people had watches. Their initial raison d’être is now obsolete but bell-ringing has been sustained, and significantly expanded, in England as a particular art-form, dependent on a peculiar technology, associated in large part with the established church there. The nature of the technology has strongly influenced the development of that art-form, whereas the resources that had to be invested in the installation of a ring of bells in a stable tower created a long-lasting geography of the practice.     

Possible role for dust or other northern forcing of ice-age carbon dioxide changes

A simple impulse-decay model driven by the history of atmospheric dust loading from Greenland can match the history of glacial–interglacial changes in atmospheric carbon dioxide concentration rather accurately, if model parameters are tuned within physically possible ranges; forcing with the Greenland temperature record produces a similarly good match. Calculations using southern forcing do not match as accurately. These results leave open the possibility of northern control of glacial–interglacial carbon dioxide changes.     

Sulfur isotope insights into microbial sulfate reduction: When microbes meet models

Metabolic models for fractionations produced by sulfate-reducing Bacteria and Archaea derived from experimental observations are the cornerstone of our interpretation of ancient and modern biogeochemical cycles. Although recent studies have called into question a traditionally accepted model, experimental evidence has been lacking for such a claim. We present data from all four sulfur isotopes that suggest that the internal fractionations associated with the sulfate reduction network are larger than previous estimates. Models of a traditional sulfate reduction network, as well as a more recent incarnation of the sulfate reduction network (with multiple sulfur intermediates) are constructed to aid in the understanding of new experimental data. These data also allow for the further development of additional minor isotope relationships, one of which is easily measurable in geologic settings and accurately depicts the net effect of an environment, whereas the other is more applicable to modern environments and may better illuminate the specific process(es) controlling the fractionation in those environments. This approach illustrates the uses of systems containing more than two isotopes.     

Anglo‐American Electoral Geography: Same Roots and Same Goals,but Different Means and Ends?*

Electoral geographers in the United States and the United Kingdom have similar goals but pursue these through different means. In part, these reflect differences between the two countries' electoral and political systems, but they also reflect different methodological strategies and desired ends. Drawing on the U.K. experience, this article identifies areas for possible expansion in studies of the electoral geography of the United States, which are expressed as five challenges.     

Refinement of thrust faulting models for the Central New Madrid seismic zone

We present the results of the joint relocation of events recorded during 1989–1992 by the PANDA network in the central New Madrid seismic zone. The near-surface material in the study area is a gently-dipping layer of poorly consolidated sediments with low P-wave velocity and high V_p/V_s (estimated values: 1.8 km s⁻¹ and 3). The sediments are underlain by high-velocity Paleozoic rocks. Under the network the difference in sediment thickness is only 0.6 km, but because of the low velocities the location of the events using layered models is affected by errors. Application of the joint hypocentral determination (JHD) technique to a subset of 580 events shows that the single-event locations may be in error by as much as 1 km in depth, depending on where the events are located. Analysis of synthetic data generated for a realistic 3-D velocity model supports the JHD results. The analysis of synthetic data also suggests that a V_p/V_s≤ 2.3 is more appropriate for the post-Paleozoic Mississippi embayment sediments. Based on the JHD locations we present a new interpretation of the seismicity, with two en-echelon SW-dipping thrust faults connected by a west-dipping thrust fault. These faults appear associated with the Reelfoot scarp and its northern extension, the Kentucky bend scarp.     

Marine seismic sources: QC of wavefield computation from near-field pressure measurements

A commercial marine seismic survey has been completed with the wavefield from the n-element (single guns and clusters) airgun array measured for every shot using an array of n + 2 near-field hydrophones, n of which were required to determine the source wavefield, the remaining two providing a check on the computation. The source wavefield is critical to the determination of the seismic wavelet for the extraction of reflection coefficients from seismic reflection data and for tying the data to wells. The wavefield generated by the full array of interacting airguns can be considered to be the superposition of n spherical pressure waves, or notional source signatures, the n hydrophone measurements providing a set of n simultaneous equations for each shot. The solution of the equations for the notional source signatures requires three ingredients: the geometry of the gun ports and near-field hydrophones; the sensitivity of each hydrophone recording channel; and the relative motion between the near-field hydrophones and the bubbles emitted by the guns. The geometry was measured on the back deck using a tape measure. A calibration data set was obtained at the approach to each line, in which each gun was fired on its own and the resulting wavefield was measured with the near-field hydrophones and recorded. The channel sensitivities, or conversion from pressure at the hydrophones to numbers on the tape, were found for each near-field hydrophone channel using the single gun calibration data, the measured geometry, and the peak pressure from each gun, known from the manufacturer’s calibration. The relative motion between the guns and hydrophones was obtained from the same calibration data set by minimizing the energy in the computed notional source signatures at the guns which did not fire. The full array data were then solved for the notional source signatures, and the pressure was computed at the two spare hydrophones and compared with the actual recordings. The rms errors were 5.3% and 2.8% and would have been smaller if the hydrophone channel sensitivities had been properly calibrated beforehand and if the movement of the guns with respect to the hydrophones had been more restricted. This comparison of the predicted and measured signatures at spare hydrophones can, in principle, be done on every shot and we recommend that this be implemented as a standard quality control procedure whenever it is desired to measure the wavefield of a marine seismic source.