Heat flow and tectonics of the Ligurian Sea basin and margins

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1988Heat flow, tectonic subsidence and crustal thickness distributions in the Ligurian Basin are best explained by asymmetric lithospheric thinning mechanisms. Over 150 heat flow measurements are made on several transects between Nice, France and Calvi, Corsica on continental slope and rise settings. Thermal gradient determinations are improved using an optimization technique. Piston core data and surface sediment 3.5 kHz reflectivity patterns help constrain thermal conductivity obtained from over 100 in situ stations. Plio-Quaternary stratigraphy is revised using new seismic reflection profiles: a boundary fault system associated with postrift margin uplift, a Pleistocene-age Var Fan construction, and recent diapirism of Messinian salt are indicated. After assessing local thermal disturbances (mass-wasting, microtopography, and salt refraction), positive heat flow corrections are made for multi-lithologic sedimentation histories and glacial paleotemperatures. Using boundary-layer cooling models, equilibrium heat flow estimates support geologic evidence for Oligocene and early Miocene rifting. Heat flow maxima correlate well with two "oceanic" sub-basins, suggesting that the southeastern trough near Corsica is ~5 Myr younger, consistent with the southeastern progression of volcanism and back arc rifting in the Western Mediterranean. Tectonic subsidence-crustal thickness trends indicate lithospheric stretching, with heat flow supporting asymmetric sub-crustal lithospheric thinning during the conjugate margin formation

Technological Innovation and Adaption: Tyndrum Lead Mine and the German Managers, 1838 to 1865

In 1838 the second Marquis of Breadalbane, having failed to lease the mineral rights at Tyndrum lead mine on the Campbell family estate in the southern Scottish highlands, made a decision to work the mine himself. When he began his operation, the mine was nearing exhaustion and what little productivity remained was hindered by increasingly complex mineralisation. The Marquis, however, was convinced that the mine could still produce great wealth; he looked to Germany for expertise and employed a succession of German mining engineers to manage his ailing operation. The survival of their monthly progress reports and other documentation offers a unique perspective on the Scottish lead mining industry and the adaptive strategies, in terms of technological innovation and mining practices, that the Germans employed to prolong the venture's economic survival

Treatment with lamivudine, zidovudine, or both in hiv-positive patients with 200 to 500 cd4+ cells per cubic millimeter

Background. The reverse-transcriptase inhibitor lamivudine has in vitro synergy with zidovudine against the human immunodeficiency virus (HIV). We studied the activity and safety of lamivudine plus zidovudine as compared with either drug alone as treatment for patients with HIV infection, most of whom had not previously received zidovudine. Methods. Three hundred sixty-six patients with 200 to 500 CD4+ cells per cubic millimeter who had received zidovudine for four weeks or less were randomly assigned to treatment with one of four regimens: 300 mg of lamivudine every 12 hours; 200 mg of zidovudine every 8 hours; 150 mg of lamivudine every 12 hours plus zidovudine; or 300 mg of lamivudine every 12 hours plus zidovudine. The study was double-blind and lasted 24 weeks, with an extension phase for another 28 weeks. Results. Over the 24-week period, the low-dose and high-dose regimens combining lamivudine and zidovudine were associated with greater increases in the CD4+ cell count (P=0.002 and P=0.015, respectively) and the percentage of CD4+ cells (P<0.001 for both) and with greater decreases in plasma levels of HIV type 1 (HIV-1) RNA (P<0.001 for both) than was treatment with zidovudine alone. Combination therapy was also more effective than lamivudine alone in lowering plasma HIV-1 RNA levels and increasing the percentage of CD4+ cells (P<0.001 for all comparisons), and these advantages persisted through 52 weeks. Adverse events were no more frequent with combination therapy than with zidovudine alone. Conclusions. In HIV-infected patients with little or no prior antiretroviral therapy, treatment with a combination of lamivudine and zidovudine is well tolerated over a oneyear period and produces more improvement in immunologic and virologic measures than does treatment with either agent alone. (N Engl J Med 1995;333:1662-9.

Heat flow from the Southeast Indian Ridge flanks between 80°E and 140°E: Data review and analysis

International audienceWe analyze available heat flow data from the flanks of the Southeast Indian Ridge adjacent to or within the Australian-Antarctic Discordance (AAD), an area with patchy sediment cover and highly fractured seafloor as dissected by ridge- and fracture-parallel faults. The data set includes 23 new data points collected along a 14-Ma old isochron and 19 existing measurements from the 20- to 24-Ma old crust. Most sites of measurements exhibit low heat flux (from 2 to 50 mW m−2) with near-linear temperature-depth profiles except at a few sites, where recent bottom water temperature change may have caused nonlinearity toward the sediment surface. Because the igneous basement is expected to outcrop a short distance away from any measurement site, we hypothesize that horizontally channelized water circulation within the uppermost crust is the primary process for the widespread low heat flow values. The process may be further influenced by vertical fluid flow along numerous fault zones that crisscross the AAD seafloor. Systematic measurements along and across the fault zones of interest as well as seismic profiling for sediment distribution are required to confirm this possible, suspected effect

Depth-varying seismogenesis on an oceanic detachment fault at 13°20'N on the Mid-Atlantic Ridge

Extension at slow- and intermediate-spreading mid-ocean ridges is commonly accommodated through slip on long-lived faults called oceanic detachments. These curved, convex-upward faults consist of a steeply-dipping section thought to be rooted in the lower crust or upper mantle which rotates to progressively shallower dip-angles at shallower depths. The commonly-observed result is a domed, sub-horizontal oceanic core complex at the seabed. Although it is accepted that detachment faults can accumulate kilometre-scale offsets over millions of years, the mechanism of slip, and their capacity to sustain the shear stresses necessary to produce large earthquakes, remains subject to debate. Here we present a comprehensive seismological study of an active oceanic detachment fault system on the Mid-Atlantic Ridge near 13°20′N, combining the results from a local ocean-bottom seismograph deployment with waveform inversion of a series of larger teleseismically-observed earthquakes. The unique coincidence of these two datasets provides a comprehensive definition of rupture on the fault, from the uppermost mantle to the seabed. Our results demonstrate that although slip on the deep, steeply-dipping portion of detachment faults is accommodated by failure in numerous microearthquakes, the shallow, gently-dipping section of the fault within the upper few kilometres is relatively strong, and is capable of producing large-magnitude earthquakes. This result brings into question the current paradigm that the shallow sections of oceanic detachment faults are dominated by low-friction mineralogies and therefore slip aseismically, but is consistent with observations from continental detachment faults. Slip on the shallow portion of active detachment faults at relatively low angles may therefore account for many more large-magnitude earthquakes at mid-ocean ridges than previously thought, and suggests that the lithospheric strength at slow-spreading mid-ocean ridges may be concentrated at shallow depths

Heat Pumps and Household Energy Consumption in Norway: An actor-network and practice theory approach

The aim of this project is to determine how heat pumps, as technical objects, impact energy consumption in Norwegian homes. Much of the previous research on energy consumption has focused on what motivates users to reduce their energy use, for example better billing information or knowledge of the environmental benefits. This study approaches the question of domestic energy consumption by bringing the technology that actually uses the energy to the foreground. The study uses actor-network theory in conjunction with practice theory to examine the role of heat pumps in the network of household energy-using practices, with a particular focus on home-heating. The aim is to shed light on how these practices might be shaped by heat pump technology, and vice-versa. The study utilises key concepts from ANT, namely the concepts of technological scripts and agency, to conceptualise heat pump technology. This conceptualisation is then employed in an examination of the role of heat pumps in the network of household activities, which is approached from a practice theory perspective. Members from 15 households in the Oslo/Akershus area were interviewed about the use of their heat pump and the other methods used for heating their home. The research questions guiding these interviews were: How do heat pumps, as technical objects, influence the way people use them? Are heat pumps used in the ways intended by their design? And how do homes with heat pumps use other forms of heating? The interaction between the user and the heat pump is discussed with a focus on how the nature of this interaction affects energy consumption. The study also incorporates an examination of the wider context of this energy use, namely the heating related practices taking place in the households studied