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  • Articles  (73)
  • Land Reform  (38)
  • Mineral Physics, Rheology, Heat Flow and Volcanology  (35)
  • Oxford University Press  (73)
  • American Physical Society
  • Economics  (38)
  • Geosciences  (35)
  • Geography
  • Natural Sciences in General
  • Electrical Engineering, Measurement and Control Technology
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  • Articles  (73)
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  • Oxford University Press  (73)
  • American Physical Society
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  • 1
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    Supply Response, Marginal Cost, and Soil Erosion Implications of Stover-based Biofuels (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-11
    Description: Existing economic analysis of corn stover as an energy feedstock has not considered potential changes in land use associated with different stover prices. We estimate the response of corn stover supply density to its price driven by changes in land use and examine its implications for a processing plant's pricing strategy and marginal cost, as well as associated changes in soil erosion. We find that plants will exploit the intensive margin as well as the extensive margin to secure additional amounts of stover. Our results show, counterintuitively, that a market for stover may result in lower soil erosion due to reallocations of land to continuous corn with removal, which, combined with no-till farming, results in lower soil erosion than the baseline without stover removal. Also contrary to expectations, using cover crops with stover removal may result in higher soil erosion due to land use changes within the fuel shed associated with optimal pricing.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q42 - Alternative Energy Sources
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 2
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    Quantitative reconstruction of thermal and dynamic characteristics of lava flow from surface thermal measurements (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-05
    Description: We study a model of lava flow to determine its thermal and dynamic characteristics from thermal measurements of the lava at its surface. Mathematically this problem is reduced to solving an inverse boundary problem. Namely, using known conditions at one part of the model boundary we determine the missing condition at the remaining part of the boundary. We develop a numerical approach to the mathematical problem in the case of steady-state flow. Assuming that the temperature and the heat flow are prescribed at the upper surface of the model domain, we determine the flow characteristics in the entire model domain using a variational (adjoint) method. We have performed computations of model examples and showed that in the case of smooth input data the lava temperature and the flow velocity can be reconstructed with a high accuracy. As expected, a noise imposed on the smooth input data results in a less accurate solution, but still acceptable below some noise level. Also we analyse the influence of optimization methods on the solution convergence rate. The proposed method for reconstruction of physical parameters of lava flows can also be applied to other problems in geophysical fluid flows.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
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    Seismic-acoustic energy partitioning during a paroxysmal eruptive phase of Tungurahua volcano, Ecuador (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-06
    Description: Studies of discrete volcanic explosions, that usually last less than 2 or 3 min, have suggested that the partitioning of seismic-acoustic energy is likely related to a range of physical mechanisms that depend on magma properties and other physical constraints such as the location of the fragmentation surface. In this paper, we explore the energy partition of a paroxysmal eruptive phase of Tungurahua volcano that lasted for over 4 hr, on 2006 July 14–15, using seismic-acoustic information recorded by stations on its flanks (near field). We find evidence of a linear scaling between seismic and acoustic energies, with time-dependent intensities, during the sustained explosive phase of the eruption. Furthermore, we argue that this scaling can be explained by two different processes: (1) the fragmentation region ultimately acts as the common source of energy producing both direct seismic waves, that travel through the volcanic edifice, and direct acoustic waves coming from a disturbed atmosphere above the summit; (2) the coupling of acoustic waves with the ground to cause seismic waves. Both processes are concurrent, however we have found that the first one is dominant for seismic records below 4 Hz. Here we use the linear scaling of intensities to construct seismic and acoustic indices, which, we argue, could be used to track an ongoing eruption. Thus, especially in strong paroxysms that can produce pyroclastic flows, the index correlation and their levels can be used as quantitative monitoring parameters to assess the volcanic hazard in real time. Additionally, we suggest from the linear scaling that the source type for both cases, seismic and acoustic, is dipolar and dominant in the near field.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 4
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    The collapse of Bartharbunga caldera, Iceland (2015)
    Oxford University Press
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    Publication Date: 2015-05-10
    Description: Lying below Vatnajökull ice cap in Iceland, Bárðarbunga stratovolcano began experiencing wholesale caldera collapse in 2014 August 16, one of the largest such events recorded in the modern instrumental era. Simultaneous with this collapse is the initiation of a plate boundary rifting episode north of the caldera. Observations using the international constellation of radar satellites indicate rapid 50 cm d –1 subsidence of the glacier surface overlying the collapsing caldera and metre-scale crustal deformation in the active rift zone. Anomalous earthquakes around the rim of the caldera with highly nondouble-couple focal mechanisms provide a mechanical link to the dynamics of the collapsing magma chamber. A model of the collapse consistent with available geodetic and seismic observations suggests that the majority of the observed subsidence occurs aseismically via a deflating sill-like magma chamber.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 5
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    Melt-band instabilities with two-phase damage (2015)
    Oxford University Press
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    Publication Date: 2015-03-11
    Description: Deformation experiments on partially molten rocks in simple shear form melt bands at 20° to the shear plane instead of at the expected 45° principal compressive stress direction. These melt bands may play an important role in melt focusing in mid-ocean ridges. Such shallow bands are known to form for two-phase media under shear if strongly non-Newtonian power-law creep is employed for the solid phase, or anisotropy imposed. However laboratory experiments show that shallow bands occur regardless of creep mechanism, even in diffusion creep, which is nominally Newtonian. Here we propose that a couple of forms of two-phase damage allow for shallow melt bands even in diffusion creep.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Is there a term structure in land lease rates? (2015)
    Oxford University Press
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    Publication Date: 2015-12-29
    Description: This article applies the concept of a term structure to agricultural land rental prices. Based on theoretical considerations, we develop a hedonic pricing model that allows for different shapes of the term structure curve while controlling for other price-relevant characteristics. We apply this model to land lease contracts in Saxony-Anhalt. We find an upward-sloping term structure during the agricultural price boom in 2007 and 2008, where market participants expected increasing rental prices. For the subsequent years, however, we detect a single-humped term structure. Hence, market participants revised their expectations and assumed a decline of land rental prices in the long term.
    Keywords: D44 - Auctions, E43 - Determination of Interest Rates ; Term Structure of Interest Rates, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 7
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    Irrigation Decisions for Major West Coast Crops: Water Scarcity and Climatic Determinants (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-13
    Description: This article uses the 2007 Farm and Ranch Irrigation Survey database developed by the U.S. Department of Agriculture to assess the impact of water scarcity and climate on irrigation decisions for producers of specialty crops, wheat, and forage crops. We estimate an irrigation management model for major crops in the West Coast (California, Oregon, and Washington), which includes a farm-level equation of irrigated share and crop-specific equations of technology adoption and water application rate (orchard/vineyard, vegetable, wheat, alfalfa, hay, and pasture). We find that economic and physical water scarcity, climate, and extreme weather, such as frost, extreme heat, and drought, significantly impact producers’ irrigation decisions. Producers use sprinkler technologies or additional water applications to mitigate risk of crop damage from extreme weather. Water application rates are least responsive to surface water cost or groundwater well depth for producers of orchard/vineyard. Water supply institutions influence producers’ irrigation decisions. Producers who receive water from federal agencies use higher water application rates and are less likely to adopt water-saving irrigation technologies for some crops. Institutional arrangements, including access to distinct water sources (surface or ground) and whether surface water cost is fee based, also affect the responsiveness of water application rates to changes in surface water cost. The analysis provides valuable information about how producers in irrigated agricultural production systems would respond and adapt to water pricing policies and climate change.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q16 - R&D ; Agricultural Technology ; Agricultural Extension Services, Q18 - Agricultural Policy ; Food Policy, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 8
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    Analytical parametrization of self-consistent polycrystal mechanics: Fast calculation of upper mantle anisotropy (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-29
    Description: Progressive deformation of upper mantle rocks via dislocation creep causes their constituent crystals to take on a non-random orientation distribution (crystallographic preferred orientation or CPO) whose observable signatures include shear-wave splitting and azimuthal dependence of surface wave speeds. Comparison of these signatures with mantle flow models thus allows mantle dynamics to be unraveled on global and regional scales. However, existing self-consistent models of CPO evolution are computationally expensive when used with 3-D and/or time-dependent convection models. Here we propose a new method, called ANPAR, which is based on an analytical parametrization of the crystallographic spin predicted by the second-order (SO) self-consistent theory. Our parametrization runs 2–6  x  10 4 times faster than the SO model and fits its predictions for CPO and crystallographic spin with a variance reduction 〉99 per cent. We illustrate the ANPAR model predictions for the deformation of olivine with three dominant slip systems, (010)[100], (001)[100] and (010)[001], for three uniform deformations (uniaxial compression, pure shear and simple shear) and for a corner-flow model of a spreading mid-ocean ridge.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    The Economic Costs of Environmental Regulation in U.S. Dairy Farming: A Directional Distance Function Approach (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-10
    Description: Analyses of the costs of regulating greenhouse gas emissions from dairy production, which could be used to assess the effectiveness of alternative policy measures, is a missing link in the literature. This article addresses this gap by establishing the economic impact associated with a hypothetical greenhouse gas environmental regulatory regime across major dairy producing counties in the United States. In doing so, the article makes three important contributions to the literature. First, it develops a comprehensive pollution index based on Environmental Protection Agency methodologies, which contrasts with previous studies that rely on partial measures based only on surplus nitrogen stemming from the over-application of fertilizer. Second, the article uses a directional output distance function, an approach that has not been employed previously to evaluate polluting technologies in the U.S. dairy sector. Third, the article incorporates a four-way error approach that accounts for unobserved county heterogeneity, time-invariant persistent technical efficiency, time-varying transient technical efficiency, and a random error. The results indicate that regulating greenhouse gas emissions from dairy farming would induce a 5-percentage point increase in average technical efficiency. In addition, the economic costs of implementing this hypothetical regulatory framework exhibit significant spatial variation across counties in the United States.
    Keywords: D22 - Firm Behavior: Empirical Analysis, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q52 - Pollution Control Costs ; Distributional Effects ; Employment Effects
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 10
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    Imaging volcanic infrasound sources using time reversal mirror algorithm (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-11
    Description: We investigate the capability of Time Reversal Mirror (TRM) algorithm to image local acoustic sources (〈3.5 km) associated with complex, sustained volcanic eruptions. Accurate source localization for volcano infrasound (low-frequency acoustic waves) is often challenging due to pronounced volcanic topography and emergent arrivals of infrasound signals. While the accuracy of the conventional approaches (e.g. triangulation and semblance method) can be severely compromised by the complex volcanic settings, a TRM-based method may have the potential to properly image acoustic sources by the use of full waveform information and numerical modelling of the time-reversed wavefield. We apply the TRM algorithm to a pyroclastic-laden eruption (sustained for ~60 s) at Santiaguito Volcano, Guatemala, and show that an ordinary TRM operation can undergo significant reduction of its focusing power due to strong topographic propagation effects (e.g. reflection and diffraction). We propose a weighted imaging condition to compensate for complicated transmission loss of the time-reversed wavefield and demonstrate that the presented condition significantly improves the focusing quality of TRM in the presence of complex topography. The consequent TRM source images exhibit remarkable agreement with the visual observation of the eruption implying that the TRM method with a proper imaging condition can be used to localize and track acoustic sources associated with complex volcanic eruptions.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 11
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    Drought Index Insurance for the Central Valley Project in California (2016)
    Oxford University Press
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    Publication Date: 2016-08-20
    Description: A multi-year drought has taken a severe toll on the agricultural economy of California’s Central Valley. Index insurance is an instrument with the potential to protect water users from economic losses due to periodic water shortages. An index insurance product based on the Sacramento Index and adapted to the Central Valley Project water supply is proposed. To address the potential for intertemporal adverse selection, three product designs are suggested: (1) "early bird" insurance; (2) variable premium insurance; and (3) variable deductible insurance. The performance of the designs are assessed using loss functions from the Westlands Water District in the San Joaquin Valley.
    Keywords: Q14 - Agricultural Finance, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 12
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    The thermal regime around buried submarine high-voltage cables (2016)
    Oxford University Press
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    Publication Date: 2016-06-19
    Description: The expansion of offshore renewable energy infrastructure and the need for trans-continental shelf power transmission require the use of submarine high-voltage (HV) cables. These cables have maximum operating surface temperatures of up to 70 °C and are typically buried 1–2 m beneath the seabed, within the wide range of substrates found on the continental shelf. However, the heat flow pattern and potential effects on the sedimentary environments around such anomalously high heat sources in the near-surface sediments are poorly understood. We present temperature measurements from a 2-D laboratory experiment representing a buried submarine HV cable, and identify the thermal regimes generated within typical unconsolidated shelf sediments—coarse silt, fine sand and very coarse sand. We used a large (2 x 2.5 m 2 ) tank filled with water-saturated spherical glass beads (ballotini) and instrumented with a buried heat source and 120 thermocouples to measure the time-dependent 2-D temperature distributions. The observed and corresponding Finite Element Method simulations of the steady state heat flow regimes and normalized radial temperature distributions were assessed. Our results show that the heat transfer and thus temperature fields generated from submarine HV cables buried within a range of sediments are highly variable. Coarse silts are shown to be purely conductive, producing temperature increases of 〉10 °C up to 40 cm from the source of 60 °C above ambient; fine sands demonstrate a transition from conductive to convective heat transfer between cf. 20 and 36 °C above ambient, with 〉10 °C heat increases occurring over a metre from the source of 55 °C above ambient; and very coarse sands exhibit dominantly convective heat transfer even at very low ( cf. 7 °C) operating temperatures and reaching temperatures of up to 18 °C above ambient at a metre from the source at surface temperatures of only 18 °C. These findings are important for the surrounding near-surface environments experiencing such high temperatures and may have significant implications for chemical and physical processes operating at the grain and subgrain scale; biological activity at both microfaunal and macrofaunal levels; and indeed the operational performance of the cables themselves, as convective heat transport would increase cable current ratings, something neglected in existing standards.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 13
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    Who Really Benefits from Agricultural Subsidies? Evidence from Field-level Data (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-09
    Description: If agricultural subsidies are largely capitalized into farmland values through their effect on rental rates, then expanding support for agriculture may not benefit farmers who rent the land they farm. Existing evidence on the incidence of subsidies on cash rental rates is mixed. Identification is obscured by unobserved or imprecisely measured factors that tend to be correlated with subsidies, especially land quality and time-varying factors like commodity prices and adverse weather events. A problem that has received less attention is the fact that subsidies and land quality on rented land may differ from owned land. Since most farms possess both rented and owned acreage, farm-level measures of subsidies, land values, and rental rates may bias estimated incidence. Using a new, field-level data set that, for the first time, precisely links subsidies to land parcels, we show that this bias is considerable: where farm-level estimates suggest an incidence of 42–49 cents of the marginal subsidy dollar, field-level estimates from the same farms indicate that landlords capture just 20–28 cents. The size of the farm and the duration of the rental arrangement have substantial effects. Incidence falls by 5–15 cents when doubling total operated acres, and the incidence falls by 0.1–0.8 cents with each additional year of the rental arrangement. Low incidence of subsidies on rents combined with the farm-size and duration effects suggest that farmers renting land have monopsony power.
    Keywords: H22 - Incidence, Q14 - Agricultural Finance, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 14
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    What Drives the Global "Land Rush"? (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-21
    Description: We review evidence regarding the size and evolution of the "land rush" in the wake of the 2007–8 boom in agricultural commodity prices, and we study the determinants of foreign land acquisition for large-scale agricultural investment. The use of data on bilateral investment relationships to estimate gravity models of transnational land-intensive investments confirms the central role of agro-ecological potential as a pull factor. However, this finding contrasts the standard literature insofar as the quality of the destination country's business climate is insignificant, and weak tenure security is associated with increased interest for investors to acquire land in the country. Policy implications are discussed.
    Keywords: F21 - International Investment ; Long-Term Capital Movements, O13 - Agriculture ; Natural Resources ; Energy ; Environment ; Other Primary Products, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q34 - Natural Resources and Domestic and International Conflicts
    Print ISSN: 0258-6770
    Electronic ISSN: 1564-698X
    Topics: Economics
    Published by Oxford University Press
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  • 15
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    A strategy to explore the topography-driven distortions in the tilt field induced by a spherical pressure source: the case of Mt Etna (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-12
    Description: We present a strategy to thoroughly investigate the effects of prominent topography on the surface tilt due to a spherical pressure source. We use Etna's topography as a case of study and, for different source positions, we compare the tilt fields calculated through (i) a 3-D boundary element method and (ii) analytical half-space solutions. We systematically determine (i) the source positions leading to the strongest tilt misfits when numerical and analytical results are compared and (ii) the surface areas where the strongest distortions in the tilt field are most likely to be observed. We also demonstrate that, under critical circumstances, in terms of respective positions of pressure source and observation points, results of inversion procedures aimed at retrieving the source parameters can be misleading, if tilt data are analysed using models that do not account for topography.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 16
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    Irrigated Agricultural Adaptation to Water and Climate Variability: The Economic Value of a Water Portfolio (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-18
    Description: Increasing aridity, more frequent and intense drought, and greater degrees of water scarcity create unique challenges for agriculture. In response to these challenges, which often manifest themselves as lower and more variable surface water supplies, as well as depleted and degraded ground water supplies, growers tend to seek opportunities to adapt. One option for growers to reduce their exposure to water scarcity and heightened uncertainty is to diversify. Indeed, access to a portfolio of supplies is one way in which water and irrigation districts, as well as individual growers, are responding to the changing landscape of water resource availability. This article evaluates the benefits to irrigated agriculture from having access to multiple sources of water. With farm-level information on 1,900 agricultural parcels across California, we use the hedonic property value method to investigate the extent that growers benefit from having access to multiple sources of water (i.e., a water portfolio). Our results suggest that while lower quality waters, less reliable water, and less water all negatively impact agricultural land values, holding a water portfolio has a positive impact on land values through its role in mitigating the negative aspects of these factors and reducing the sensitivity of agriculture to climate-related factors. From a policy perspective, such results identify a valuable adaptation tool that irrigation districts may consider to help offset the negative impacts of climate change, drought, and population increases on water supply availability and reliability.
    Keywords: Q10 - General, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, Q50 - General, Q51 - Valuation of Environmental Effects
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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  • 17
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    The elastic properties and stability of fcc-Fe and fcc-FeNi alloys at inner-core conditions (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-24
    Description: The agreement between shear wave velocities for the Earth's inner core observed from seismology with those derived from mineral physics is considerably worse than for any other region of the Earth. Furthermore, there is still debate as to the phase of iron present in the inner core, particularly when alloying with nickel and light elements is taken into account. To investigate the extent to which the mismatch between seismology and mineral physics is a function of either crystal structure and/or the amount of nickel present, we have used ab initio molecular dynamics simulations to calculate the elastic constants and seismic velocities ( V p and V s ) of face centred cubic (fcc) iron at Earth's inner core pressures (360 GPa) and at temperatures up to ~7000 K. We find that V p for fcc iron (fcc-Fe) is very similar to that for hexagonal close packed (hcp) iron at all temperatures. In contrast, V s for fcc-Fe is significantly higher than in hcp-Fe, with the difference increasing with increasing temperature; the difference between V s for the core (from seismology) and V s for fcc-Fe exceeds 40 per cent. These results are consistent with previous work at lower temperatures. We have also investigated the effect of 6.5 and 13 atm% Ni in fcc-Fe. We find that Ni only slightly reduces V p and V s (e.g. by 2 per cent in V s for 13 atm% Ni at 5500 K), and cannot account for the difference between the velocities observed in the core and those of pure fcc-Fe. We also tried to examine pre-melting behaviour in fcc-Fe, as reported in hcp-Fe by extending the study to very high temperatures (at which superheating may occur). However, we find that fcc-Fe spontaneously transforms to other hcp-like structures before melting; two hcp-like structures were found, both of hexagonal symmetry, which may most easily be regarded as being derived from an hcp crystal with stacking faults. That the structure did not transform to a true hcp phase is likely as a consequence of the limited size of the simulation box (108 atoms). At 360 GPa, in pure fcc-Fe, we find that the transition from fcc to the hcp-like structure occurs at 7000 K, whereas in the Ni bearing system, the transition occurs at higher temperature (7250 K). This reinforces previous work showing that fcc-Fe might transform to hcp-Fe just before melting, and that Ni tends to stabilize the fcc structure with respect to hcp.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 18
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    Time-dependent displacement and stress fields due to shear and tensile faults in a transversely isotropic viscoelastic half-space (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-25
    Description: Viscoelastic behaviour of materials in nature is observed in post-event deformations due to seismic or volcanic activities. In this paper, by adopting the correspondence principle, we propose an inelastic model to predict first the Laplace-domain response of a transversely isotropic viscoelastic half-space due to a shear or tensile fault of polygonal shape. The displacement and stress fields in the time domain are then obtained using an efficient and accurate algorithm for the inverse Laplace transform. Numerical examples are presented to validate the proposed solution and to show the viscoelastic displacement and stress fields due to a strike-slip, dip-slip and tensile fault of rectangular shape. The obtained results indicate that both viscoelasticity and transverse isotropy play significant roles in the viscoelastic response of the half-space due to faults, which could be used as benchmarks for the future numerical analysis of realistic post-seismic or volcanic event.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 19
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    Scaling of viscous shear zones with depth-dependent viscosity and power-law stress-strain-rate dependence (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-26
    Description: One of the unresolved questions concerning fault deformation is the degree and cause of localization of shear at depth beneath a fault. Geologic observations of exhumed shear zones indicate that while the motion is no longer planar, it can still be localized near the down-dip extension of the fault; however, the degree of localization is uncertain. We employ simple analytic and numerical models to investigate the structural form of distributed shear beneath a strike-slip fault, and the relative importance of the physical mechanisms that have the potential to localize a shear zone. For a purely depth dependent viscosity, = 0 exp (– z / z 0 ), we find that a shear zone develops with a half-width $\delta _w\sim \sqrt{z_0}$ for small z 0 at the base of the layer, where lengths are non-dimensionalized by the layer thickness ( d km). Including a non-linear stress–strain-rate relation ( $\dot{\epsilon }\propto \sigma ^n$ ) scales w by $1/\sqrt{n}$ , comparable to deformation length scales in thin viscous sheet calculations. We find that the primary control on the shear-zone width is the depth dependence of viscosity that arises from the temperature dependence of viscosity and the increase in temperature with depth. As this relationship is exponential, scaling relations give a dimensional half-width that scales approximately as $$ \tilde{\delta }_w\approx T_{\frac{1}{2}}\sqrt{\frac{Rd}{nQ\beta }}\text{ km}, $$ where $T_{\frac{1}{2}}$ (K) is the temperature at the midpoint of the layer, R (J mol –1 K –1 ) the gas constant, Q (J mol –1 ) the activation energy and β (K km –1 ) the geothermal gradient. This relation predicts the numerical results for the parameter range consistent with continental rheologies to within 2–5 per cent and shear-zone half-widths from 2 to 6 km. The inclusion of shear-stress heating reduces w by only an additional 5–25 per cent, depending on the initial width of the shear zone. While the width of the shear zone may not decrease significantly, local temperature increases from shear-stress heating range from 50 to 300 °C resulting in a reduction in viscosities beneath the fault of several orders of magnitude and a concomitant reduction in the stresses needed to drive the motion.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    On the use of thermal equations of state and the extrapolation at high temperature and pressure for geophysical and petrological applications (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-09
    Description: The equation that relates pressure, temperature and volume and is described by parameters that are function of temperature at 1 bar (hereafter called thermal equation of state, TEOS), has practical computational advantages for petrological and geophysical applications over the equation that considers explicitly a thermal pressure. Some considerations that justify the use of the TEOS are discussed here. (1) The assumption that the parameters are function of temperature is perhaps better understood by looking at the Helmholtz energy function that is implicitly assumed in the case of an equation of state (EOS) derived from interatomic potentials. A test case shows that the Helmholtz energy related to the Vinet EOS and the Helmholtz energy from the Debye model are very similar. (2) The TEOS should be able to reproduce thermal expansion (α), isothermal bulk modulus ( K T ) and heat capacity ( C p and C v ) at high P , T computed from a lattice vibration model. The generalized Rydberg EOS applied to MgO is able to fit reasonably well the properties computed using Jacobs’ lattice dynamics formulation ( T range = 300–3000 K, P range = 1 bar–1500 kbar). (3) It is shown that in the case of MgO, the TEOS can be used quite successfully for extrapolation that goes beyond the P , T range of the measured/given data. Some physical constraints need to be applied to the derivation of the volume, bulk modulus and derivative of the bulk modulus with pressure at 1 bar. (4) The pressure dependence of the reference parameters in the TEOS that was inferred several decades ago is only apparent. A numerical computation demonstrates that the combined pressure effect in the terms defining the partial derivative of the reference V and K (and K') over temperature cancels out, making the reference parameters independent of pressure at any condition.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 21
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    On the use of thermal equations of state and the extrapolation at high temperature and pressure for geophysical and petrological applications (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-17
    Description: The equation that relates pressure, temperature and volume and is described by parameters that are function of temperature at 1 bar (hereafter called thermal equation of state, TEOS), has practical computational advantages for petrological and geophysical applications over the equation that considers explicitly a thermal pressure. Some considerations that justify the use of the TEOS are discussed here. (1) The assumption that the parameters are function of temperature is perhaps better understood by looking at the Helmholtz energy function that is implicitly assumed in the case of an equation of state (EOS) derived from interatomic potentials. A test case shows that the Helmholtz energy related to the Vinet EOS and the Helmholtz energy from the Debye model are very similar. (2) The TEOS should be able to reproduce thermal expansion (α), isothermal bulk modulus ( K T ) and heat capacity ( C p and C v ) at high P , T computed from a lattice vibration model. The generalized Rydberg EOS applied to MgO is able to fit reasonably well the properties computed using Jacobs’ lattice dynamics formulation ( T range = 300–3000 K, P range = 1 bar–1500 kbar). (3) It is shown that in the case of MgO, the TEOS can be used quite successfully for extrapolation that goes beyond the P , T range of the measured/given data. Some physical constraints need to be applied to the derivation of the volume, bulk modulus and derivative of the bulk modulus with pressure at 1 bar. (4) The pressure dependence of the reference parameters in the TEOS that was inferred several decades ago is only apparent. A numerical computation demonstrates that the combined pressure effect in the terms defining the partial derivative of the reference V and K (and K') over temperature cancels out, making the reference parameters independent of pressure at any condition.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Decoupling of agricultural support payments: the impact on land market participation decisions (2012)
    Oxford University Press
    Details
    Publication Date: 2012-08-03
    Description: This paper analyses the impact of the recent decision by the European Union to ‘decouple’ agricultural support payments from agricultural production on Irish farmers' land market decisions. The land market participation decisions of Irish farmers are modelled using a dynamic probit model, while the extent of participation decisions is modelled using a dynamic tobit model. Decoupling does not appear to have significantly altered farmers' land market decisions. One likely explanation for this is the cross-compliance obligation for farmers to maintain land in a state fit for agricultural production in order to receive their full payments.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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  • 23
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    The influence of normal stress and sliding velocity on the frictional behaviour of calcite at room temperature: insights from laboratory experiments and microstructural observations (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-03
    Description: The presence of calcite in and near faults, as the dominant material, cement, or vein fill, indicates that the mechanical behaviour of carbonate-dominated material likely plays an important role in shallow- and mid-crustal faulting. To better understand the behaviour of calcite, under loading conditions relevant to earthquake nucleation, we sheared powdered gouge of Carrara Marble, 〉98 per cent CaCO 3 , at constant normal stresses between 1 and 100 MPa under water-saturated conditions at room temperature. We performed slide-hold-slide tests, 1–3000 s, to measure the amount of static frictional strengthening and creep relaxation, and velocity-stepping tests, 0.1–1000 μm s –1 , to evaluate frictional stability. We observe that the rates of frictional strengthening and creep relaxation decrease with increasing normal stress and diverge as shear velocity is increased from 1 to 3000 μm s –1 during slide-hold-slide experiments. We also observe complex frictional stability behaviour that depends on both normal stress and shearing velocity. At normal stresses less than 20 MPa, we observe predominantly velocity-neutral friction behaviour. Above 20 MPa, we observe strong velocity-strengthening frictional behaviour at low velocities, which then evolves towards velocity-weakening friction behaviour at high velocities. Microstructural analyses of recovered samples highlight a variety of deformation mechanisms including grain size reduction and localization, folding of calcite grains and fluid-assisted diffusion mass transfer processes promoting the development of calcite nanograins in the highly deformed portions of the experimental fault. Our combined analyses indicate that calcite fault gouge transitions from brittle to semi-brittle behaviour at high normal stress and slow sliding velocities. This transition has important implications for earthquake nucleation and propagation on faults in carbonate-dominated lithologies.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    A Green's function approach for assessing the thermal disturbance caused by drilling deep boreholes in rock or ice (2015)
    Oxford University Press
    Details
    Publication Date: 2015-10-30
    Description: A knowledge of subsurface temperatures in sedimentary basins, fault zones, volcanic environments and polar ice sheets is of interest for a wide variety of geophysical applications. However, the process of drilling deep boreholes in these environments to provide access for temperature and other measurements invariably disturbs the temperature field around a newly created borehole. Although this disturbance dissipates over time, most temperature measurements are made while the temperature field is still disturbed. Thus, the measurements must be ‘corrected’ for the drilling-disturbance effect if the undisturbed temperature field is to be determined. This paper provides compact analytical solutions for the thermal drilling disturbance based on 1-D (radial) and 2-D (radial and depth) Green's functions (GFs) in cylindrical coordinates. Solutions are developed for three types of boundary conditions (BCs) at the borehole wall: (1) prescribed temperature, (2) prescribed heat flux and (3) a prescribed convective condition. The BC at the borehole wall is allowed to vary both with depth and time. Inclusion of the depth dimension in the 2-D solution allows vertical heat-transfer effects to be quantified in situations where they are potentially important, that is, near the earth's surface, at the bottom of a well and when considering finite-drilling rates. The 2-D solution also includes a radial- and time-dependent BC at the earth's surface to assess the impact of drilling-related infrastructure (drilling pads, mud pits, permanent shelters) on the subsurface temperature field. Latent-heat effects due to the melting and subsequent refreezing of interstitial ice while drilling a borehole through ice-rich permafrost can be included in the GF solution as a moving-plane heat source (or sink) located at the solid–liquid interface. Synthetic examples are provided illustrating the 1-D and 2-D GF solutions. The flexibility of the approach allows the investigation of thermal drilling effects in rock or ice for a wide variety of drilling technologies. Numerical values for the required radial GFs G R are available through the Advanced Cooperative Arctic Data and Information Service at doi:10.5065/D64F1NS6.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Responsiveness of Crop Yield and Acreage to Prices and Climate (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-13
    Description: We investigate the effect of crop price and climate variables on rainfed corn and soybean yields and acreage in the United States using a large panel dataset for the 1977–2007 period. Instrumental variables are used to control for endogeneity of prices in yield and acreage regressions, while allowing for spatially auto-correlated errors. We find that an increase in corn price has a statistically significant positive impact on corn yield, but the effect of soybean price on soybean yields is not statistically significant. The estimated price elasticities of corn yield and acreage are 0.23 and 0.45, respectively. Of the increase in corn supply caused by an increase in corn price, we find that 33.8% is due to price-induced yield enhancement and 66.2% is due to price-induced acreage expansion. We also find that the impact of climate change on corn production ranges from $-$ 7% to $-$ 41% and on soybean ranges from $-$ 8% to $-$ 45%, depending on the climate change scenarios, time horizon, and global climate models used to predict climate change. We show that the aggregate net impact of omitting price variables is an overestimation of the effect of climate change on corn yield by up to 9% and on soybean yield by up to 15%.
    Keywords: Q11 - Aggregate Supply and Demand Analysis ; Prices, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Dynamic elastic moduli during isotropic densification of initially granular media (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-03
    Description: The elastic properties of homogeneous, isotropic materials are well constrained. However, in heterogeneous and evolving materials, these essential properties are less well-explored. During sintering of volcanic ash particles by viscous processes as well as during compaction and cementation of sediments, microstructure and porosity undergo changes that affect bulk dynamic elastic properties. Here using a model system of glass particles as an analogue for initially granular rock-forming materials, we have determined porosity and P -wave velocity during densification. Using these results, we test models for the kinetics of densification and the resultant evolution of the elastic properties to derive a quantitative description of the coupling between the kinetics of isotropic densification and the evolving dynamic elastic moduli. We demonstrate the power of the resultant model on a wide range of data for non-coherent sediments as well as sedimentary and volcanic rocks. We propose that such constraints be viewed as an essential ingredient of time-dependent models for the deformation of evolving materials in volcanoes and sedimentary basins.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Cooperation against theft: A test of incentives for water management In Tunisia (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-22
    Description: Water theft carried out by manipulating water meters constrains volumetric pricing in semi-arid regions. Cooperative management can reduce theft and improve incentives for efficient water use by inducing peer monitoring. Using a theoretical model, we show that theft is more likely when prices are high, punishments are weak, and cooperatives are large. We also show how cooperative membership and punishment levels are determined endogenously by constraints on monitoring. We test the model on data from Tunisia for the years 2001–2003, relying on instruments that proxy for unobservable monitoring costs. The results confirm that well-designed incentives can reduce theft, and that constraints on monitoring costs affect institutional design.
    Keywords: D82 - Asymmetric and Private Information, Q13 - Agricultural Markets and Marketing ; Cooperatives ; Agribusiness, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q25 - Water
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    A Natural Resource Theory of U.S. Crop Insurance Contract Choice (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-22
    Description: A large variety of subsidized crop insurance products are available to U.S. crop growers. Distinct and perhaps puzzling patterns in the choices of insurance products and coverage levels can be discerned. Where production conditions are better and yields are less risky then ( a ) higher insurance coverage levels are chosen; and ( b ) revenue insurance is preferred over yield insurance. Also, ( c ) the extent of preference for revenue insurance is stronger in more productive areas. Assuming, as many do, that growers seek to maximize subsidy transfers, point ( a ) can be explained by the interaction between yield technology and natural resource endowments. Points ( b ) and ( c ) can be explained by location in conjunction with the "natural hedge" and a contract design bias in how revenue insurance guarantees are computed. Empirical study of Risk Management Agency data on corn, soybean, and wheat yields, and insurance contract choices lend support to our model inferences.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, Q24 - Land
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Capitalized Costs of Habitat Conservation Easements (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-05
    Description: Perpetual conservation easements permanently remove the option to convert existing habitat to more intensive agricultural production. If existing habitat is at threat of conversion, removing the option to convert will reduce land values. In this article, we estimate the land value discount resulting from perpetual habitat conservation easements by using propensity score matching. We find that on the average eased parcel, land values fall by approximately $86 per acre for every acre of eased habitat. On average, our results suggest that landowners have been adequately compensated and conservation agencies have successfully secured habitat at risk of conversion.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Agri-environmental Policy and Urban Development Patterns: A General Equilibrium Analysis (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-05
    Description: This paper investigates the spatial effects that the provision of environmental public goods have on residential location choices in a suburban context. Specifically, a spatial general equilibrium framework is developed to analyze the consequences of adopting an agri-environmental policy promoting the provision of positive farming externalities. We use a static monocentric model of an open city where agricultural bid-rents and agricultural amenities vary endogenously in space, and where the positive externalities associated with agricultural production are valued by households. Consistent with empirical evidence of the potential side effects that conservation policies may have in terms of urbanization patterns and land price changes, we show that under certain conditions implementing an agri-environmental policy may promote additional suburban development. Moreover, we demonstrate that the emergence of disconnected suburban areas may be significantly influenced by the location of land regulated by an agri-environmental policy. Finally, we discuss distributional aspects and show that while introducing an agri-environmental policy has a negative impact on most residential land value, it can have positive effects on farmland and residential land located within the regulated areas, suggesting the non-neutrality of such policies regarding the agents’ assets.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, R13 - General Equilibrium and Welfare Economic Analysis of Regional Economies, R14 - Land Use Patterns, R21 - Housing Demand
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Agricultural Rodent Control Using Barn Owls: Is It Profitable? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-05
    Description: We develop a model to evaluate the profitability of controlling rodent damage by placing barn owl nesting boxes in agricultural areas. The model incorporates the spatial patterns of barn owl predation pressure on rodents, and the impact of this predation pressure on nesting choices and agricultural output. We apply the model to data collected in Israel and find the installation of nesting boxes profitable. While this finding indicates that economic policy instruments to enhance the adoption of this biological control method are redundant, it does support stricter regulations on rodent control using rodenticides.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    How do agricultural policies influence farm size inequality? The example of France (2011)
    Oxford University Press
    Details
    Publication Date: 2011-12-27
    Description: We investigate farm size inequality in France using agricultural censuses and farm structure surveys at the NUTS3 level (‘départements’) during the period 1970–2007. Using calculated Gini coefficients, we show that farm size inequality has not systematically increased in France. An econometric analysis of the determinants of farm size inequality reveals that policy measures significantly affected farm size inequality, with most of the measures considered decreasing it. Empirical results suggest that the main contributor was the activity of the SAFER (Société d'Aménagement Foncier et d'Etablissement Rural), a specific feature of the French farm structural policy aimed at regulating rural land management. Besides, this research highlights the great complexity of the dynamics underlying the evolution of farm size distribution.
    Keywords: D30 - General, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Optimisation of implementation policies of environmental quota trade (2011)
    Oxford University Press
    Details
    Publication Date: 2011-12-27
    Description: This paper analyses implementation policies of environmental quota trade, with the Flemish nutrient production rights as an example. Implementation policies concern the transaction quantity, quota reduction and prevention of speculation. They are analysed with a static and a dynamic multi-agent quota trade model. The static model with discrete non-auctioned quota trade shows that the obligation for quota sellers to entirely stop their production stimulates structural change. The dynamic model version indicates that a flat rate reduction on traded quota and measures taken to prevent speculation combined with too low penalties for overuse stimulate the total production.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Intensive and extensive margin adjustments to water scarcity in France's Cereal Belt (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-11
    Description: Efficient water management in agriculture is becoming critical due to increasing environmental constraints and global food and bio-energy demands. Farmers may respond to increased water scarcity along three main adjustment margins: a move towards rain-fed agriculture (super-extensive margin) or towards less water-intensive crops (extensive margin), and a reduction in water intensity for irrigated crops (intensive margin). Using a positive mathematical programming model of regional supply calibrated to economic and agronomic information, we decompose the total effect of reduced water availability on these adjustment margins in Beauce, a productive cereal region that relies on a groundwater resource to meet its irrigation needs. For realistic water scarcity scenarios, 57 per cent of the total response is attributable to super-extensive margin adjustments. The extensive margin represents 28 per cent of the total response, while the intensive margin accounts for 15 per cent. Crop-level analysis reveals more subtle adaptation patterns.
    Keywords: Q11 - Aggregate Supply and Demand Analysis ; Prices, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q25 - Water
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Encouraging Reductions in Nonpoint Source Pollution through Point-nonpoint Trading: The Roles of Baseline Choice and Practice Subsidies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-06
    Description: Water quality regulations in the United States apply almost exclusively to point sources. In impaired watersheds where both point and nonpoint sources contribute to pollution, the U.S. Environmental Protection Agency (EPA) is encouraging the use of point-nonpoint trading to reduce the cost of point sources to meet their permit requirement, and to encourage nonpoint sources to voluntarily contribute more towards meeting overall water quality goals. The EPA guidance encourages trading programs to set a nonpoint source eligibility baseline that extracts some "extra" abatement from nonpoint sources. Research has shown that setting an eligibility baseline that is substantially more stringent than current management could discourage nonpoint source participation and significantly hinder trading. In this paper we examine how choosing the eligibility baseline for agricultural sources affects the efficiency goal of trading (reducing costs to point sources), as well as how it affects the EPA goal of encouraging nonpoint abatement. Using data from the Chesapeake Bay Watershed we find that eligibility baselines set to encourage additional nonpoint source abatement reduce the supply of credits in a market; the more stringent the baseline, the fewer the trades and the smaller the overall abatement from nonpoint sources. A subsidy to farmers for reducing the cost of meeting a baseline encourages greater nonpoint source abatement, but may not benefit the trading market.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q20 - General, Q58 - Government Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Vertical variation in heat flow on the Kola Peninsula: palaeoclimate or fluid flow? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-07
    Description: Following earlier studies, we present forward and inverse simulations of heat and fluid transport of the upper crust using a local 3-D model of the Kola area. We provide best estimates for palaeotemperatures and permeabilities, their errors and their dependencies. Our results allow discriminating between the two mentioned processes to a certain extent, partly resolving the non-uniqueness of the problem. We find clear indications for a significant contribution of advective heat transport, which, in turn, imply only slightly lower ground surface temperatures during the last glacial maximum relative to the present value. These findings are consistent with the general background knowledge of (i) the fracture zones and the corresponding fluid movements in the bedrock and (ii) the glacial history of the Kola area.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    In situ frictional properties of San Andreas Fault gouge at SAFOD (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-11
    Description: Along the central segment of the San Andreas Fault (SAF) near Parkfield, California, displacement occurs by a combination of aseismic creep and micro-earthquake slip. To constrain the strength and parametrize a constitutive relation for the creeping behaviour of the central segment of the SAF, we conducted friction experiments on clay-rich gouge retrieved by coring the Central Deforming Zone (CDZ) of the SAF at 2.7 km vertical depth. The gouge was flaked rather than powdered to preserve the natural scaly microfabric, and formed into 2-mm-thick layers that were sheared using a triaxial deformation apparatus. Experiments were conducted at in situ effective normal stress (100 MPa), pore pressure (25 MPa) and temperature (80–120 °C) conditions using brine pore fluid with the ionic composition of the in situ formation fluid. Velocity-stepping (0.006–0.6 μm s –1 ) and temperature-stepping experiments were conducted on brine-saturated gouge, and slide-hold-slide experiments were conducted on brine-saturated and room-dry gouge. Results are used to quantify the effects of rate, state, temperature and pore fluid on the strength of the CDZ gouge. We find that the gouge is extremely weak ( μ  〈 0.13) and rate-strengthening, consistent with findings of previous studies on the CDZ gouge. We also find that, in a rate and state friction framework, slip history has a negligible effect on strength ( b 0) under both saturated and dry conditions. The CDZ gouge is temperature-weakening from 80 to 120 °C and weakens 17 per cent when saturated with brine compared to room-dry conditions. Employing the laboratory-derived friction constitutive parameters, and including the temperature weakening and the strain-rate strengthening effects, we determine an approximate in situ friction coefficient of μ 0.11. For μ 0.11, aseismic creep under normal pore fluid conditions is permitted for angles up to 79° between the maximum horizontal stress and the plane of the SAF, consistent with nearby stress orientation measurements.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Individual and Cooperative Management of Invasive Species in Human-mediated Landscapes (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-13
    Description: As a bioinvasion spreads across a landscape from its point of introduction, damages rise roughly with the square of the distance from the original invasion. It is thus generally beneficial, at the landscape scale, to apply eradication or containment controls early if not immediately upon discovery. However, an individual property owner only has incentives to consider the costs and benefits of control on his/her own property rather than potential landscape-scale damages. Bioinvasions will therefore generally be under-controlled in a landscape of independent owners operating under a laissez-faire system. A mechanism is thus needed to induce early cooperative contributions to control costs from beneficiaries who would, without them, be invaded later. We develop a spatially-explicit, integrated model of invasion spread and human behavior to examine how different degrees of spatial cooperation affect patterns of invasion spread and the total costs and damages imposed. We compare individual laissez-faire, cooperative control by adjacent neighbors, and cooperative control by groups including more distant but nearby neighbors. As expected, private laissez-faire control decisions tend to under-control the invasion relative to socially optimal control under most circumstances. But a reasonably high fraction of first best payoffs can be achieved with only a modest geographical reach of cooperation. We also find that less extensive cooperation is needed to control invasions whose costs and damages otherwise lead to the largest externalities (circumstances with costs that are relatively low compared with damages). This suggests that even small amounts of cooperation to control bioinvasions can provide large social benefits.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Farmland Protection and Agricultural Land Values at the Urban-Rural Fringe: British Columbia's Agricultural Land Reserve (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-13
    Description: Farmland conservation policies typically use zoning and differentiated taxes to prevent urban development of farmland, but little is known about the effectiveness of these policies. This study adds to current knowledge by examining the impact of British Columbia's Agricultural Land Reserve (ALR), established in 1973, which severely restricts subdivision and nonagricultural uses for more than 4.7 million hectares of farmland. To determine the extent to which the ALR preserves farmland by reducing or removing the development option, a multilevel hedonic pricing model is used to estimate the impact of land use, geographic, and zoning characteristics on farmland value near the capital city of Victoria on Vancouver Island. Using sales data from 1974 through 2008, the model demonstrates a changing ALR impact over time that varies considerably by improved and unimproved land types. In 2008, landowners paid 19% less for the typical improved farmland parcel within the ALR versus that outside it. This suggests that would-be developers expect permanency in the zoning law, and prefer non-ALR zoned land. However, ALR land that is unimproved has a premium of 55%, suggesting that this land is more valuable for agriculture than for development. Farmland located closer to the city or the commuting highway commands a premium if it has a residence on it, with a residence also explaining why smaller agricultural properties sell at higher prices. However, it appears that zoning by itself is insufficient to protect farmland; other policies likely need to be implemented in conjunction with zoning to protect agricultural land.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q28 - Government Policy, R14 - Land Use Patterns
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Capitalized Amenity Value of Native Vegetation in a Multifunctional Rural Landscape (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-13
    Description: In many parts of the world, natural vegetation has been cleared to allow agricultural production. To ensure a long-term flow of ecosystem services without compromising agricultural activities, restoring the environment requires a balance between public and private benefits and costs. Information about private benefits generated by environmental assets can be utilized to identify conservation opportunities on private lands, evaluate environmental projects, and design effective policy instruments. We use a spatio-temporal hedonic model to estimate the private benefits of native vegetation on rural properties in the state of Victoria, Australia. Specifically, we estimate the marginal value of native vegetation on private land and examine how it varies with the extent of vegetation on a property and across a range of property types and sizes. Private benefits of native vegetation are greater per unit area on small and medium-sized properties and smaller on large production-oriented farms. Native vegetation exhibits diminishing marginal benefits as its proportion of a property increases. The current extent of native vegetation cover is lower than the extent that would maximize the amenity value to many landowners. There is scope for improved targeting of investment in the study region by incorporating private benefits of environmental projects into environmental planning processes. Landowners with high marginal private benefits from revegetation would be more willing to participate in a revegetation program. Targeting these landowners would likely provide higher value for money because such projects could be implemented at lower public cost.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    New heat flow determination in northern Tarim Craton, northwest China (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-08
    Description: Tarim Craton is a Precambrian block situated in northwest China, just north of the Tibetan Plateau, where a large sedimentary basin with abundant hydrocarbon potential has developed. Accurate heat flow data for Tarim is vital for understanding the lithospheric evolution and hydrocarbon generation in this area; however, there were unavailable until now, due to a lack of high quality steady-state temperature logging data. Here, we report 10 new heat flow values derived from steady-state temperature logging and measured thermal conductivity data. New heat flow values range from 40.1 to 49.4 mW m –2 , with a mean of 43.1 ± 3.0 mW m –2 . In addition, radiogenic heat production from the sediments accounts for 20 per cent of the observed surface heat flow, whilst the mantle heat flow is estimated to be as low as 6–15 mW m –2 ; this indicates a dominant contribution from crustal heat, to the observed heat flow. The average heat flow and crustal temperature in the Tarim Craton are markedly lower than those in the Tibetan Plateau, whilst the calculated rheological strength of the lithosphere, beneath Tarim, is sufficiently large to resist the elevation-induced gravitational potential energy difference between Tarim and Tibet. This inherited thermal and rheological contrast, between the craton and Plateau, can be traced back to before the India–Asia collision; this accounts for the differential active deformation pattern in the Tarim Craton and adjacent areas.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Pipe Poiseuille flow of viscously anisotropic, partially molten rock (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-17
    Description: Laboratory experiments in which synthetic, partially molten rock is subjected to forced deformation provide a context for testing hypotheses about the dynamics and rheology of the mantle. Here our hypothesis is that the aggregate viscosity of partially molten mantle is anisotropic, and that this anisotropy arises from deviatoric stresses in the rock matrix. We formulate a model of pipe Poiseuille flow based on theory by Takei & Holtzman and Takei & Katz. Pipe Poiseuille is a configuration that is accessible to laboratory experimentation but for which there are no published results. We analyse the model system through linearized analysis and numerical simulations. This analysis predicts two modes of melt segregation: migration of melt from the centre of the pipe towards the wall and localization of melt into high-porosity bands that emerge near the wall, at a low angle to the shear plane. We compare our results to those of Takei & Katz for plane Poiseuille flow; we also describe a new approximation of radially varying anisotropy that improves the self-consistency of models over those of Takei & Katz. This study provides a set of baseline, quantitative predictions to compare with future laboratory experiments on forced pipe Poiseuille flow of partially molten mantle.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    The Eyjafjallajokull volcanic system, Iceland: insights from electromagnetic measurements (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-25
    Description: Electromagnetic (EM) measurements were performed 1 yr after the most recent eruption of the Eyjafjallajökull volcano (2010 March–May), southern Iceland, to investigate the geometries of structures of the volcano system through imaging lateral and vertical electrical resistivity variations. High quality magnetotelluric (MT) and transient EM data were acquired at 26 sites around Eyjafjallajökull and the southern part of Myrdalsjökull (the glacier covering the Katla volcano). For some locations the steep topography has influence on the MT responses, but this can be compensated by static shift correction using the transient EM data and/or including topography in the modelling mesh. As expected, qualitative indicators, such as phase tensor ellipses and induction arrows, infer a concentration of conductive material beneath Eyjafjallajökull. 2-D resistivity models are presented from data along three profiles: Along the river valley of Markarfljót in the north, along the coast to the south of Eyjafjallajökull and across the mountain ridge Fimmvörðuháls between Eyjafjallajökull and Katla. In numerous previous studies elsewhere in Iceland a conductive layer at about 10–30 km depth was identified. From our data, such a conductor is also present in the northeastern part of the investigated area. Additionally, all profiles show a conductive, near-surface layer at about 1–2 km depth, as seen previously for example at the Hengill geothermal region. A connection between those two conductive layers is indicated by the resistivity models, and the dyke (flank eruption) and the conduit (summit eruption) appear as vertical conductive structures. It is uncertain if the vertical connection is permanent or a transient feature as consequence of the eruptive sequences. Subsequent measurements are required when the volcano system is quiescent.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Simultaneous retrieval of volcanic sulphur dioxide and plume height from hyperspectral data using artificial neural networks (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-22
    Description: Artificial neural networks (ANNs) are a valuable and well-established inversion technique for the estimation of geophysical parameters from satellite images; once trained, they help generate very fast results. Furthermore, satellite remote sensing is a very effective and safe way to monitor volcanic eruptions in order to safeguard the environment and the people affected by those natural hazards. This paper describes an application of ANNs as an inverse model for the simultaneous estimation of columnar content and height of sulphur dioxide (SO 2 ) plumes from volcanic eruptions using hyperspectral data from remote sensing. In this study two ANNs were implemented in order to emulate a retrieval model and to estimate the SO 2 columnar content and plume height. ANNs were trained using all infrared atmospheric sounding interferometer (IASI) channels between 1000–1200 and 1300–1410 cm –1 as inputs, and the corresponding values of SO 2 content and height of plume, obtained from the same IASI channels using the SO 2 retrieval scheme by Carboni et al. , as target outputs. The retrieval is demonstrated for the eruption of the Eyjafjallajökull volcano (Iceland) for the months of 2010 April and May and for the Grimsvotn eruption during 2011 May. Both neural networks were trained with a time series consisting of 58 hyperspectral eruption images collected between 2010 April 14 and May 14 and 16 images from 2011 May 22 to 26, and were validated on three independent data sets of images of the Eyjafjallajökull eruption, one in April and the other two in May, and on three independent data sets of the Grímsvötn volcanic eruption that occurred in 2011 May. The root mean square error (RMSE) values between neural network outputs and targets were lower than 20 Dobson units (DU) for SO 2 total column and 200 millibar (mb) for plume height. The RMSE was lower than the standard deviation of targets for the Grímsvötn eruption. The neural network had a lower retrieval accuracy when the target value was outside the values used during the training phase.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    The Effects of Energy Prices on Agricultural Groundwater Extraction from the High Plains Aquifer (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-02
    Description: We examine the effects of energy prices on groundwater extraction using an econometric model of a farmer's irrigation water pumping decision that accounts for both the intensive and extensive margins. Our results show that energy prices have an effect on both types of margins. Increasing energy prices would affect crop selection decisions, crop acreage allocation decisions, and farmers’ demand for water. Our estimated total marginal effect, which sums the effects on the intensive and extensive margins, suggests that a $1 per million btu increase in the energy price would decrease water extraction by an individual farmer by 5.89 acre-feet per year, a decrease of 3.6 percent of the average annual extraction rate. Our estimated elasticity of water extraction with respect to energy price is –0.26.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q40 - General
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Do Wealth Gains from Land Appreciation Cause Farmers to Expand Acreage or Buy Land? (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-02
    Description: Recent increases in farm real estate values in the United States have increased farm equity. By exploiting periods of high and low appreciation that caused various increases in wealth for farmers owning various shares of their farmland, we examine whether U.S. grain farmers expanded their acres harvested or acres owned in response to an increase in their land wealth. We find that land wealth had little effect on farm size. However, for similarly-sized farms, a larger ownership share (10 percentage points) led to an increase in the growth of land owned (2 percentage points). Because older farmers own more of the land that they farm, greater land appreciation slows the rate at which younger farmers acquire land relative to older farmers.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    The role of crop land during economic development: evidence from rural Vietnam (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-02
    Description: Under economic structural changes, some households intensify farming while others reduce it, resulting in significant changes in landholding. This paper studies the link between such changes in landholding and household well-being during a period of rapid economic transformation in Vietnam. Using a rural household panel data set, we find a U-shaped relationship between landholding and well-being: both accumulating crop land and moving out of farming are associated with higher household income and expenditure. Notably, these relationships are greater in communes that are less developed, suggesting that the benefits of structural transformation may diminish at higher levels of development.
    Keywords: I30 - General, I32 - Measurement and Analysis of Poverty, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Velocity variations associated with the large 2010 eruption of Merapi volcano, Java, retrieved from seismic multiplets and ambient noise cross-correlation (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-14
    Description: We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12–25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of volcanic eruptions in andesitic volcanoes, without taking their sign into account.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Linear stability analysis for hydrothermal alteration of kimberlitic rocks (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-06
    Description: The influx of groundwater into hot kimberlite deposits results in the reaction of water with olivine-rich rocks. The products of the reaction are serpentine and release of latent heat. The rise of temperature due to the heat release increases the rate of the reaction. Under certain conditions, this self-speeding up of the reaction can result in instabilities associated with a significantly higher final serpentinization in slightly warmer regions of the kimberlite deposit. We conduct linear stability analysis of serpentinization in an isolated volume of porous kimberlitic rocks saturated with water and an inert gas. There is a counteracting interplay between the heat release tending to destabilize the uniform distribution of parameters and the heat conduction tending to stabilize it by smoothing out temperature perturbations. We determine the critical spatial scale separating the parameters where one phenomenon dominates over another. The perturbations of longer-than-critical length grow, whereas the perturbations of shorter-than-critical length fade. The analytical results of the linear stability analysis are supported by direct numerical simulations using a full nonlinear model.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Brittle and semi-brittle behaviours of a carbonate rock: influence of water and temperature (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-22
    Description: Inelastic deformation can either occur with dilatancy or compaction, implying differences in porosity changes, failure and petrophysical properties. In this study, the roles of water as a pore fluid, and of temperature, on the deformation and failure of a micritic limestone (white Tavel limestone, porosity 14.7 per cent) were investigated under triaxial stresses. For each sample, a hydrostatic load was applied up to the desired confining pressure (from 0 up to 85 MPa) at either room temperature or at 70 °C. Two pore fluid conditions were investigated at room temperature: dry and water saturated. The samples were deformed up to failure at a constant strain rate of ~10 –5 s –1 . The experiments were coupled with ultrasonic wave velocity surveys to monitor crack densities. The linear trend between the axial crack density and the relative volumetric strain beyond the onset of dilatancy suggests that cracks propagate at constant aspect ratio. The decrease of ultrasonic wave velocities beyond the onset of inelastic compaction in the semi-brittle regime indicates the ongoing interplay of shear-enhanced compaction and crack development. Water has a weakening effect on the onset of dilatancy in the brittle regime, but no measurable influence on the peak strength. Temperature lowers the confining pressure at which the brittle–semi-brittle transition is observed but does not change the stress states at the onset of inelastic compaction and at the post-yield onset of dilatancy.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Dynamics of Farmland Ownership and Leasing: Implications for Young and Beginning Farmers (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-19
    Description: This study considers the transition into farming and growth of new farmers in U.S. agriculture by examining land ownership and leasing trends. Our approach is to characterize the entire distribution by farmer age and farmer experience rather than using young versus old and beginning versus established farmer categories. We also use a linked-farms longitudinal approach to show trends over time in farmland expansion and contraction. We find that farms operated by older beginning farmers tend to be smaller and do not tend to grow over time. Our results show that it is mostly young farmers as opposed to all beginning farmers who rapidly expand their farm operations after entering agriculture. Our findings inform policy makers about the strategies that young and beginning farmers use to start their businesses and expand over time, and suggest more effective approaches for targeting loan programs to both young and beginning farmers.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Corn Area Response to Local Ethanol Markets in the United States: A Grid Cell Level Analysis (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-24
    Description: We measure corn and total agricultural area response to the biofuels boom in the United States from 2006 to 2010. Specifically, we use newly available micro-scale grid cell data to test whether a location's corn and total agricultural cultivation rose in response to the capacity of ethanol refineries in their vicinity. Based on these data, acreage in corn and overall agriculture not only grew in already-cultivated areas but also expanded into previously uncultivated areas. Acreage in corn and total agriculture also correlated with proximity to ethanol plants, though the relationship dampened over the time period. A formal estimation of the link between acreage and ethanol refineries, however, must account for the endogenous location decisions of ethanol plants and areas of corn supply. We present historical evidence to support the use of the US railroad network as a valid instrument for ethanol plant locations. Our estimates show that a location's neighborhood refining capacity exerts strong and significant effects on acreage planted in corn and total agricultural acreage. The largest impacts of ethanol plants were felt in locations where cultivation area was relatively low. This high-resolution evidence of ethanol impacts on local agricultural outcomes can inform researchers and policy-makers concerned with crop diversity, environmental sustainability, and rural economic development.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q16 - R&D ; Agricultural Technology ; Agricultural Extension Services
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Exchanging Land for Solidarity: Solidarity Transfers among Voluntarily Resettled and Non-resettled Land-Reform Beneficiaries (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-24
    Description: Mutual aid among villagers in developing countries is often the only means of insuring against economic shocks. We use "lab-in-the-field experiments" in Cambodian villages to study solidarity in established and newly resettled communities. Our experimental participants were part of an agricultural land-distribution project for which they signed up voluntarily. Half of our sample voluntarily resettled one and a half years before this study. Playing a version of the "solidarity game," we identify the effect of voluntary resettlement on willingness to help anonymous fellow villagers. We find that resettled farmers transfer substantially less money to their fellow villagers than farmers who have not resettled. Our experimental results indicate greater vulnerability on the part of resettled households in the initial years after resettlement.
    Keywords: C93 - Field Experiments, D03 - Behavioral Economics ; Underlying Principles, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Does the Minimum Lot Size Program Affect Farmland Values? Empirical Evidence Using Administrative Data and Regression Discontinuity Design in Taiwan (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-24
    Description: This study empirically assesses the causal effect of the minimum lot size program on farmland values in Taiwan. A unique dataset of 4,032 parcels of farmland drawn from administrative foreclosure auction profiles between 2000 and 2008 and regression discontinuity design were applied to cope with the endogeneity issue of land use regulations. The results of the parametric and nonparametric estimations indicate that the minimum lot size program significantly increases farmland value by approximately 18% and 15%, respectively. Moreover, the program effect is more pronounced for farmland located in urban/suburban areas. In the absence of a tax effect and externality resulting from non-agricultural activities, the significant program effect on farmland values is likely to result from the effect of the program on farmland's option value for future development.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, R52 - Land Use and Other Regulations
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    A Novel, Spatiotemporally Explicit Ecological-economic Modeling Procedure for the Design of Cost-effective Agri-environment Schemes to Conserve Biodiversity (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-31
    Description: Agri-environment schemes (AES) compensate farmers for land use measures that are costly to them but beneficial to biodiversity and the environment. We present an ecological-economic modeling procedure for the design of cost-effective AES to conserve grassland biodiversity, which is applicable to large areas, covers many endangered species and grassland types, and includes several hundred different types of mowing regimes, grazing regimes, and combinations of mowing and grazing regimes as land use measures. The modeling procedure also accounts for the spatial variations in the land use measures' costs and in the effects on species and grassland types. The procedure's main novelty is that it considers variations of the costs and impacts on species and grassland types that arise from different timings of the land use measures. Considering the spatial and the temporal dimension of land use measures makes the modeling procedure spatiotemporally explicit. We demonstrate the power of the modeling procedure by evaluating an existing grassland AES in Saxony, Germany, and identify substantial improvements in terms of cost-effectiveness.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q57 - Ecological Economics: Ecosystem Services ; Biodiversity Conservation ; Bioeconomics
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
    Published by Oxford University Press
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    Influence of pre-existing topography on downflow lava discharge rates estimated from thermal infrared airborne data (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-12
    Description: Remote sensing thermal data of active lava flows allow the evaluation of effusion rates. This is made possible by a simple formula relating the lava effusion rate to the heat flux radiated per unit time from the surface of the flow. Due to the assumptions of the model, this formula implies that heat flux, surface temperature and lava temperature vary as a function of the flow thickness. These relationships, never verified or validated before, have been used by several authors as a proof of the weakness of the model. Here, multispectral infrared and visible imaging spectrometer (MIVIS) high spatial resolution (5–10 m) thermal data acquired during Etna's 2001 eruption were used to investigate downflow heat flux variations in the lava flow emitted from a vent located at 2100 m a.s.l. A high correlation between the downflow heat flux and the lava flow thickness (measured from a pre-existing digital elevation model) was found. Topography beneath the flow appears to play an important role both in lava emplacement mechanisms and flow dynamics. MIVIS-derived downflow effusion rates are consistent with the law of conservation of mass assessing the reliability of remote sensing techniques.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Profit-Maximizing Land-Use Revisited: The Testable Implications of Non-joint Crop Production Under Land Constraint (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-22
    Description: This article derives new implications for the land allocation and production decisions of profit-maximizing farm-firms where production of different crops is non-joint but subject to a constraint on the total land area. These implications are observable and thus subject to empirical scrutiny. An estimable model of crop production, land allocation, and input-use decisions is derived that permits joint production and enables the implications of non-joint but land-constrained production to be tested. This may improve econometric estimates of cross-price elasticities of supply by linking models of land use and production decisions, and allowing non-jointness to be imposed where appropriate.
    Keywords: Q11 - Aggregate Supply and Demand Analysis ; Prices, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Comparison of GHG-Emission Indicators for Dairy Farms with Respect to Induced Abatement Costs, Accuracy, and Feasibility (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-22
    Description: There is broad debate about including agriculture in greenhouse gas (GHG) reduction efforts such as the European Emissions Trading Scheme. Since most agricultural GHG emissions originate from non-point sources, they cannot be directly measured, and therefore have to be derived by calculation schemes (indicators). We designed five such GHG indicators for dairy farms and analyzed the trade-offs between their feasibility, measurement accuracy, and level of induced abatement costs. Analyses of induced abatement costs and calculation accuracy are based on emission reduction simulations with a highly-detailed single-farm optimization model. Feasibility is discussed in a qualitative manner. Our results indicate that the trade-offs depend on both farm characteristics and the targeted reduction level. In particular, the advantages of detailed indicators decrease for higher abatement levels. Only the least feasible indicator led to abatement costs that would result in emission efforts at given prices in the European Emissions Trading Scheme, although with a rather small potential. Our results thus suggest little potential for including dairy production into market-based reduction policies.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Production Incentives from Static Decoupling: Land Use Exclusion Restrictions (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-22
    Description: Many agricultural support payments are based on past production with restrictions on how land may currently be used. When support payments to field crops are analyzed in a static framework, they do not directly impact current production decisions. However, over time, as relative profits change, these payments affect current output. The payments may keep land in less profitable production of program crops through restrictions prohibiting potentially more profitable endeavors such as cultivating fruits and vegetables. These payments have the potential to lead to production and trade distortions similar in magnitude to the distortions associated with direct production subsidies.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q17 - Agriculture in International Trade, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Induced polarization of volcanic rocks - 1. Surface versus quadrature conductivity (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-22
    Description: We performed complex conductivity measurements on 28 core samples from the hole drilled for the Humu'ula Groundwater Research Project (Hawai'i Island, HI, USA). The complex conductivity measurements were performed at 4 different pore water conductivities (0.07, 0.5, 1.0 or 2.0, and 10 S m –1 prepared with NaCl) over the frequency range 1 mHz to 45 kHz at 22 ± 1 °C. The in-phase conductivity data are plotted against the pore water conductivity to determine, sample by sample, the intrinsic formation factor and the surface conductivity. The intrinsic formation factor is related to porosity by Archie's law with an average value of the cementation exponent m of 2.45, indicating that only a small fraction of the connected pore space controls the transport properties. Both the surface and quadrature conductivities are found to be linearly related to the cation exchange capacity of the material, which was measured with the cobalt hexamine chloride method. Surface and quadrature conductivities are found to be proportional to each other like for sedimentary siliclastic rocks. A Stern layer polarization model is used to explain these experimental results. Despite the fact that the samples contain some magnetite (up to 5 per cent wt.), we were not able to identify the effect of this mineral on the complex conductivity spectra. These results are very encouraging in showing that galvanometric induced polarization measurements can be used in volcanic areas to separate the bulk from the surface conductivity and therefore to define some alteration attributes. Such a goal cannot be achieved with resistivity alone.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Induced polarization of volcanic rocks. 2. Influence of pore size and permeability (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-22
    Description: We investigate the relationship between complex conductivity spectra and both permeability and pore mean size and distribution of 22 core samples (21 volcanic rocks and 1 clayey sandstone). The volcanic core samples were extracted from a wellbore drilled for the Humu‘ula Groundwater Research Project in the Humu‘ula saddle region between Mauna Kea and Mauna Loa volcanoes (Hawaii). The quadrature conductivity spectra of volcanic rocks exhibit a subtle, but generally detectable, relaxation frequency in the range 0.3 Hz to 45 kHz similar to the relaxation frequency observed for clayey sandstones. We find a fair relationship between this relaxation frequency and the pore size determined by mercury porosimetry. Combined with the intrinsic formation factor of the core samples, the relaxation frequency can be used as an indicator of the permeability of the material. The predicted values of the permeability are grossly consistent with the permeability values to air (in the range 0.001–100 mD) within two orders of magnitude. The measured permeability values are highly correlated to the peak of the pore size distribution determined from mercury porosimetry divided by the intrinsic formation factor. By fitting the complex conductivity spectra with the pore size distribution, we obtain the normalized chargeability of the core samples, which is, in turn, highly correlated to the measured cation exchange capacity.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Strength and failure characteristics of Jurassic Red-Bed sandstone under cyclic wetting-drying conditions (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-28
    Description: Due to cyclic fluctuations of reservoir water levels, bank slopes in drawdown areas are subjected to wetting–drying cycles. In order to reasonably evaluate the stabilities of sandstone slopes in the drawdown area of the Three Gorges Reservoir, it is a primary premise to obtain the strength and failure characteristics of the sandstones undergoing wetting–drying cycles. In this paper, the conventional triaxial compression tests, ultrasonic velocity and porosity measurements and microstructural observations were conducted on Jurassic Red-Bed sandstone (JRS) specimens undergoing wetting–drying cycles. The results from the triaxial experiments indicate that the peak strengths of the JRS are dramatically reduced after the first wetting–drying cycle, and then remain approximately constant with increasing number of wetting–drying cycles. The failure modes of the JRS samples undergoing different wetting–drying cycles are all brittle failures under low confining pressures ( ≤ 15 MPa). The decrease in P -wave velocity and increase in porosity with increasing number of wetting–drying cycles reveals the raise of damage level of the sandstone specimens, which is the main reason for the decline of peak strength. Detailed microstructural analysis has shown obvious argillization phenomena after undergoing wetting–drying cycles, which weakens the cements between grains in the sandstone and increases the damage of the sandstone.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Land Markets and the Value of Water: Hedonic Analysis Using Repeat Sales of Farmland (2014)
    Oxford University Press
    Details
    Publication Date: 2014-07-23
    Description: The lack of robust water markets makes it difficult to value irrigation water. Because water rights are appurtenant to land, it is possible to infer the value of water from observed differences in the market price of land. We use panel data on repeat farmland sales in California's San Joaquin Valley to estimate a hedonic regression equation with parcel fixed effects. This controls for sources of omitted variables bias and allows us to recover the value of irrigation water to landowners in our sample. We show that a more traditional cross-sectional regression results in an artificially low value of irrigation water.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q24 - Land, Q25 - Water
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    When Is Reliance on Voluntary Approaches in Agriculture Likely to Be Effective? (2013)
    Oxford University Press
    Details
    Publication Date: 2013-12-05
    Description: Voluntary approaches have been used in a variety of contexts and for a variety of purposes in agriculture, including voluntary conservation programs and product labeling. This paper provides an overview of some of the general principles that emerge from the literature on voluntary approaches and their application in agriculture. The literature suggests that, to be effective, voluntary approaches must provide sufficiently strong participation incentives to a targeted population, clearly identify standards for behavior or performance that ensure additionality and avoid slippage, and monitor outcomes. Thus, reliance on voluntary approaches in agriculture is likely to be effective only if there is sufficient market demand for certain product characteristics, significant public funds are committed to pay for voluntary actions, or the political will exists to impose regulations if voluntary approaches fail.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q20 - General, Q50 - General
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Possible structural control on the 2011 eruption of Puyehue-Cordon Caulle Volcanic Complex (southern Chile) determined by InSAR, GPS and seismicity (2016)
    Oxford University Press
    Details
    Publication Date: 2016-11-10
    Description: The Puyehue-Cordón Caulle Volcanic Complex (PCCVC) is one of the best examples of tectonic control on volcanism at the Southern Volcanic Zone of the Andes (southern Chile). The PCCVC comprises several volcanic centres that erupted dominantly SiO 2 -rich magmas at the intersection of the trench-parallel Liquiñe-Ofqui Fault Zone (LOFZ) and an inherited NW–SE basement structure. The PCCVC began an explosive and later effusive eruption on 2011 June 4 causing decimetre- to metre-scale surface deformation that was observed by a series of Envisat ASAR satellite scenes. We modelled this data and complemented it with time-series of two continuous GPS stations and seismicity recorded by a local network. Deformation during the first 3 days of the eruption can be modelled either by two point sources aligned with the NW–SE Cordón Caulle graben or by a closing dyke with a significant component of left-lateral motion along the graben. These models are discussed with respect to their implications on the estimated rheology and the eruption mechanism. GPS observations near the volcanic complex reveal an additional, more localised effect related to the LOFZ in the south of the complex. Coeruptive deformation at the main geological structures of the PCCVC is further supported by relocated seismicity, which is concentrated along the Cordón Caulle graben and to the western side of the LOFZ.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    The dynamics of dairy land use change with respect to the milk quota regime (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-29
    Description: This article analyses the sequence of changes in land used for milk production on dairy farms before, during and towards the abolition of milk quotas. Using a unique dataset comprising farm level data of the Netherlands between 1971 and 2011 we estimate two duration models, analysing the time period between increases and decreases in dairy land use. The impact of milk quota, socio-economic, farm income and economic-political variables on the likelihood of a farm changing its land use are assessed. Results show that changes are highly farm specific, but that quota abolition will lead to a more dynamic dairy sector.
    Keywords: Q12 - Micro Analysis of Farm Firms, Farm Households, and Farm Input Markets, Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q18 - Agricultural Policy ; Food Policy
    Print ISSN: 0165-1587
    Electronic ISSN: 1464-3618
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    Calculation of thermal conductivity, thermal diffusivity and specific heat capacity of sedimentary rocks using petrophysical well logs (2015)
    Oxford University Press
    Details
    Publication Date: 2015-11-05
    Description: In this study, equations are developed that predict for synthetic sedimentary rocks (clastics, carbonates and evapourates) thermal properties comprising thermal conductivity, specific heat capacity and thermal diffusivity. The rock groups are composed of mineral assemblages with variable contents of 15 major rock-forming minerals and porosities of 0–30 per cent. Petrophysical properties and their well-logging-tool-characteristic readings were assigned to these rock-forming minerals and to pore-filling fluids. Relationships are explored between each thermal property and other petrophysical properties (density, sonic interval transit time, hydrogen index, volume fraction of shale and photoelectric absorption index) using multivariate statistics. The application of these relations allows computing continuous borehole profiles for each rock thermal property. The uncertainties in the prediction of each property vary depending on the selected well-log combination. Best prediction is in the range of 2–8 per cent for the specific heat capacity, of 5–10 per cent for the thermal conductivity, and of 8–15 for the thermal diffusivity, respectively. Well-log derived thermal conductivity is validated by laboratory data measured on cores from deep boreholes of the Danish Basin, the North German Basin, and the Molasse Basin. Additional validation of thermal conductivity was performed by comparing predicted and measured temperature logs. The maximum deviation between these logs is 〈3 °C. The thermal-conductivity calculation allowed an evaluation of the depth range in which the palaeoclimatic effect on the subsurface temperature field can be observed in the North German Basin. This effect reduces the surface heat-flow density by 25 mW m –2 .
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Electrical resistivity of coal-bearing rocks under high temperature and the detection of coal fires using electrical resistance tomography (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-02
    Description: Coal fires are severe hazards to environment, health and safety throughout the world. Efficient and economical extinguishing of these fires requires that the extent of the subsurface coal fires should be delineated. Electrical and electromagnetic methods have been used to detect coal fires in recent years. However, the resistivity change of coal-bearing rocks at high temperature is rarely investigated. The resistivity characteristics of coal fires at different temperatures and depths are seldomly researched as well. In this paper, we present the results of measurements of several coal-bearing rocks’ resistivity and permeability under high temperature. Two major causes for the change in resistivity with increasing temperature are recognized, there are the increase of charge carriers and thermal fracturing, of which the first one is probably the dominant cause. A set of 2-D simulations is carried out to compare the relation of resolution and efficiency of coal fires detection to temperature and depth when adopting the electrical resistance tomography. The simulation results show that the resolution and efficiency decrease with the decrease of temperature and the increase of depth. Finally, the electrical resistance tomography is used to delineate coal fires in the Anjialing Open Pit Mine. Most low-resistivity regions are verified as coal-fire areas according to the long-term monitoring of borehole temperature. The results indicate that the electrical resistance tomography can be used as a tool for the detection of coal fires.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    What Is the Social Value of Second Generation Biofuels? (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-07
    Description: What are second-generation (2G) biofuel technologies worth to global society? A dynamic, economic model is used to assess the impact that introducing 2G biofuels technology has on crops, livestock, biofuels, forestry, and environmental services, as well as greenhouse gas emissions. Under baseline conditions, this amounts to $64 billion and is $84 billion under the optimistic technology case, suggesting that investing in 2G technology could be appropriate. Under greenhouse gas regulation, global valuation more than doubles to $139 and $174 billion, respectively. A flat energy price scenario eliminates the value of 2G technology to society.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q42 - Alternative Energy Sources, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 2040-5790
    Electronic ISSN: 2040-5804
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    The Value of Heterogeneous Property Rights and the Costs of Water Volatility (2017)
    Oxford University Press
    Details
    Publication Date: 2017-01-05
    Description: The system of prior appropriation in the Western Unites States prioritizes property rights for water based on the establishment of beneficial use, creating a hierarchy where rights initiated first are more secure. I estimate the demand for security in water rights through their capitalization in agricultural property markets in the Yakima River Basin, a major watershed in Washington State. All water rights are satisfied in an average year, so the relative value of secure property rights is a function of water supply volatility and the costs of droughts are predominantly born by those with weak rights. In aggregate, security in water rights does not capitalize into property values at the irrigation district level; however, there is heterogeneity in the premium for secure water rights. The lack of a premium for district-level water security is robust to a variety of econometric methods to account for correlated district unobservables, and the null result produces an economically significant upper bound on the value to water security for the district. The ability for farmers to adapt to water supply volatility, as well as expectations about water markets and government infrastructure investment, are leading explanations for the lack of an aggregate premium. These explanations are supported by the pattern of heterogeneity in the water security premium.
    Keywords: Q15 - Land Ownership and Tenure ; Land Reform ; Land Use ; Irrigation, Q21 - Demand and Supply, Q24 - Land, Q25 - Water, Q54 - Climate ; Natural Disasters ; Global Warming
    Print ISSN: 0002-9092
    Electronic ISSN: 1467-8276
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Economics
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    The transient divided bar method for laboratory measurements of thermal properties (2016)
    Oxford University Press
    Details
    Publication Date: 2016-10-21
    Description: Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Several methods, including the classical divided bar technique, are available for laboratory measurements of thermal conductivity, but much fewer for thermal diffusivity. We have generalized the divided bar technique to the transient case in which thermal conductivity, volumetric heat capacity and thereby also thermal diffusivity are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity can also be determined. The finite element formulation provides a flexible forward solution for heat transfer across the bar, and thermal properties are estimated by inverse Monte Carlo modelling. This methodology enables a proper quantification of experimental uncertainties on measured thermal properties and information on their origin. The developed methodology was applied to various materials, including a standard ceramic material and different rock samples, and measuring results were compared with results applying traditional steady-state divided bar and an independent line-source method. All measurements show highly consistent results and with excellent reproducibility and high accuracy. For conductivity the obtained uncertainty is typically 1–3 per cent, and for diffusivity uncertainty may be reduced to about 3–5 per cent. The main uncertainty originates from the presence of thermal contact resistance associated with the internal interfaces in the bar. These are not resolved during inversion and it is imperative that they are minimized. The proposed procedure is simple and may quite easily be implemented to the many steady-state divided bar systems in operation. A thermally controlled bath, as applied here, may not be needed. Simpler systems, such as applying temperature-controlled water directly from a tap, may also be applied.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Electrokinetic experimental study on saturated rock samples: zeta potential and surface conductance (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-18
    Description: It is important to know the electrokinetic properties of crustal rocks for interpreting the conductivity mechanisms and seismoelectric phenomena during earthquakes and seismoelectric well logging. In this study, electrokinetic experiments are conducted using a special core-holder by employing an AC lock-in technique. A series of experiments are conducted on 10 sandstone samples to measure the streaming potentials and streaming currents, and the experiments on each sample are done at six different salinities. The streaming potential coefficient and streaming current coefficient are calculated from the measured streaming potentials and streaming currents. The experimental results show that streaming potential coefficient and streaming current coefficient decrease as the salinity increases. The dependence of these two coefficients on permeability and pore radius are analysed and compared with previous works. At low salinities, the streaming potential coefficient and streaming current coefficient increase with the increasing permeability and pore radius. At high salinities, the streaming potential coefficient (streaming current coefficient) almost share a same value for 10 different samples. This conclusion indicates that the differences of rock parameters can only be well recognized at lower salinities, and the electrokinetic signals are invalid at high salinities, which offers a restrictive condition for using the amplitude of electrokinetic signals to estimate rock parameters. The zeta-potential have also been estimated through combined measurements of streaming potential and streaming current. The surface conductivity and its contribution to electrokinetic effects are determined from a comparison of zeta-potentials by two different methods, and then the validation of the Helmholz–Smoluchowski equation for a capillary tube is tested in rocks. We also compare our date with theoretical and experimental works, and set up an expression about the relationship between zeta potential and salinity, which fits the experimental data well.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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    Elastic properties of ferrous bearing MgSiO3 and their relevance to ULVZs (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-04
    Description: We used ab initio molecular dynamics to calculate the elastic constants of MgSiO 3 , FeSiO 3 and (Fe 0.5 Mg 0.5 )SiO 3 perovskite under lower-most mantle conditions (136 GPa, 2000–4000 K). At 0 K, V p and V s for FeSiO 3 perovskite are 12 and 18 per cent lower, respectively than those for MgSiO 3 , in agreement with previous work. The difference in velocity, however, increases with temperature for high spin (but not low spin) states and at 4000 K, V p and V s for the end-member FeSiO 3 are, respectively, 19 and 34 per cent lower than those of MgSiO 3 . We find that (dln V s /dln V p ) T,P of Fe x Mg 1- x O 3 remains below 2 for all relevant iron concentrations and lower than the value of 3 seen in most ultralow velocity zones (ULVZ). Moreover, we are unable to match simultaneously the observed density increase and shear wave velocity reduction shown by ULVZs by increasing the ferrous iron content in perovskite except for the largest density increases and the smallest shear wave decreases observed in ULVZs. Assuming that current seismic estimates of ULVZ properties are accurate, our results suggest that ferrous iron enrichment alone cannot explain ULVZs.
    Keywords: Mineral Physics, Rheology, Heat Flow and Volcanology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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