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  • 1
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    Preserved history of global mean spreading rate: 83 Ma to present (2017)
    Oxford University Press
    Details
    Publication Date: 2017-01-07
    Description: Using an up-to-date global plate rotation model, applied to the endpoints of preserved major spreading ridge isochrons, we have calculated the explicitly reconstructable length-weighted mean global half-spreading rate (HSR), ridge length and area production as a function of time since the end of the Cretaceous Normal Superchron at 83.0 Ma. Our calculations integrate uncertainties in rotation parameters and chron boundary ages with the partial sampling uncertainties arising from progressive subduction of older oceanic lithosphere and its preserved spreading record. This record of directly reconstructable oceanic ridge production provides a well-constrained baseline that can be compared to reconstructions that include the largely unconstrained extrapolated histories of entirely subducted oceanic plates. The directly reconstructable global mean HSR has not varied by more than ±15 per cent about an average rate of 28.4 ± 4.6 mm a –1 since 83 Ma. No long-term secular trend is evident: a maximum global mean half-rate of 32 ± 6 mm a –1 occurred from 33.1 Ma to about 25.8 Ma, with minima of 26 ± 5 mm a –1 between about 56 and 40.2 Ma, and 24 ± 1 mm a –1 since 3.2 Ma. Only this most recent interval has a rate that differs significantly (at ±2) from the long-term mean. The global, reconstructable ridge length at 56 Ma decreases by less than 15 per cent relative to the modern ridge system; by 83 Ma it has decreased by 38 per cent. These relatively high preserved ridge fractions mean that the estimated uncertainty due to partial sampling stays roughly equivalent to the estimated rotation model uncertainties, allowing long-term spreading rate variations of 〉20 per cent since the Late Cretaceous to be ruled out. In contrast, prior to 83 Ma too little oceanic lithosphere is preserved to reliably reconstruct global spreading rates.
    Keywords: Geodynamics and Tectonics
    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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  • 2
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    The Value of Heterogeneous Property Rights and the Costs of Water Volatility (2017)
    Oxford University Press
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    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
    Published by Oxford University Press
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  • 3
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    Present-day velocity field and block kinematics of Tibetan Plateau from GPS measurements (2017)
    Oxford University Press
    Details
    Publication Date: 2017-01-01
    Description: In this study, we present a new synthesis of GPS velocities for tectonic deformation within the Tibetan Plateau and its surrounding areas, a combined data set of ~1854 GPS-derived horizontal velocity vectors. Assuming that crustal deformation is localized along major faults, a block modelling approach is employed to interpret the GPS velocity field. We construct a 30-element block model to describe present-day deformation in western China, with half of them located within the Tibetan Plateau, and the remainder located in its surrounding areas. We model the GPS velocities simultaneously for the effects of block rotations and elastic strain induced by the bounding faults. Our model yields a good fit to the GPS data with a mean residual of 1.08 mm a –1 compared to the mean uncertainty of 1.36 mm a –1 for each velocity component, indicating a good agreement between the predicted and observed velocities. The major strike-slip faults such as the Altyn Tagh, Xianshuihe, Kunlun and Haiyuan faults have relatively uniform slip rates in a range of 5–12 mm a –1 along most of their segments, and the estimated fault slip rates agree well with previous geologic and geodetic results. Blocks having significant residuals are located at the southern and southeastern Tibetan Plateau, suggesting complex tectonic settings and further refinement of accurate definition of block geometry in these regions.
    Keywords: Geodynamics and Tectonics
    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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    Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-22
    Description: Kinematics of divergent boundaries and Rift-Rift-Rift junctions are classically studied using long-term geodetic observations. Since significant magma-related displacements are expected, short-term deformation provides important constraints on the crustal mechanisms involved both in active rifting and in transfer of extensional deformation between spreading axes. Using InSAR and GPS data, we analyse the surface deformation in the whole Central Afar region in detail, focusing on both the extensional deformation across the Quaternary magmato-tectonic rift segments, and on the zones of deformation transfer between active segments and spreading axes. The largest deformation occurs across the two recently activated Asal-Ghoubbet (AG) and Manda Hararo-Dabbahu (MH-D) magmato-tectonic segments with very high strain rates, whereas the other Quaternary active segments do not concentrate any large strain, suggesting that these rifts are either sealed during interdyking periods or not mature enough to remain a plate boundary. Outside of these segments, the GPS horizontal velocity field shows a regular gradient following a clockwise rotation of the displacements from the Southeast to the East of Afar, with respect to Nubia. Very few shallow creeping structures can be identified as well in the InSAR data. However, using these data together with the strain rate tensor and the rotations rates deduced from GPS baselines, the present-day strain field over Central Afar is consistent with the main tectonic structures, and therefore with the long-term deformation. We investigate the current kinematics of the triple junction included in our GPS data set by building simple block models. The deformation in Central Afar can be described by adding a central microblock evolving separately from the three surrounding plates. In this model, the northern block boundary corresponds to a deep EW-trending trans-tensional dislocation, locked from the surface to 10–13 km and joining at depth the active spreading axes of the Red Sea and the Aden Ridge, from AG to MH-D rift segments. Over the long-term, this plate configuration could explain the presence of the en-échelon magmatic basins and subrifts. However, the transient behaviour of the spreading axes implies that the deformation in Central Afar evolves depending on the availability of magma supply within the well-established segments.
    Keywords: Geodynamics and Tectonics
    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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    Compound dislocation models (CDMs) for volcano deformation analyses (2016)
    Oxford University Press
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    Publication Date: 2016-12-22
    Description: Volcanic crises are often preceded and accompanied by volcano deformation caused by magmatic and hydrothermal processes. Fast and efficient model identification and parameter estimation techniques for various sources of deformation are crucial for process understanding, volcano hazard assessment and early warning purposes. As a simple model that can be a basis for rapid inversion techniques, we present a compound dislocation model (CDM) that is composed of three mutually orthogonal rectangular dislocations (RDs). We present new RD solutions, which are free of artefact singularities and that also possess full rotational degrees of freedom. The CDM can represent both planar intrusions in the near field and volumetric sources of inflation and deflation in the far field. Therefore, this source model can be applied to shallow dikes and sills, as well as to deep planar and equidimensional sources of any geometry, including oblate, prolate and other triaxial ellipsoidal shapes. In either case the sources may possess any arbitrary orientation in space. After systematically evaluating the CDM, we apply it to the co-eruptive displacements of the 2015 Calbuco eruption observed by the Sentinel-1A satellite in both ascending and descending orbits. The results show that the deformation source is a deflating vertical lens-shaped source at an approximate depth of 8 km centred beneath Calbuco volcano. The parameters of the optimal source model clearly show that it is significantly different from an isotropic point source or a single dislocation model. The Calbuco example reflects the convenience of using the CDM for a rapid interpretation of deformation data.
    Keywords: Geodynamics and Tectonics
    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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    Insights into pulverized rock formation from dynamic rupture models of earthquakes (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-18
    Description: Pulverized rocks (PR) are extremely incohesive and highly fractured rocks found within the damage zones of several large strike-slip faults around the world. They maintain their crystal structure, show little evidence of shearing or chemical alteration, and are believed to be produced by strong tensile forces. Several mechanisms for pulverization have been proposed based on simple qualitative analyses or laboratory experiments under simplified loading conditions. Numerical modelling, however, can offer new insights into what is needed to produce PR and likely conditions of formation. We perform dynamic rupture simulations of different earthquakes, varying the magnitude, the slip distribution, and the rupture speed (supershear and subshear), while measuring the stresses produced away from the fault. To contextualize our results, a basic threshold of 10 MPa is set as the tensile strength of the rock mass and recordings are made of where, when, and by how much this threshold is exceeded for each earthquake type. Guided by field observations, we discern that a large (〉 M w 7.1) subshear earthquake along a bimaterial fault produces a pulverized rock distribution most consistent with observations. The damage is asymmetric with the majority on the stiffer side of the fault extending out for several hundred metres. Within this zone there is a large and sudden volumetric expansion in all directions as the rupture passes. We propose that such an extreme tensile stress state, repeated for every earthquake, eventually produces the PR seen in the field.
    Keywords: Geodynamics and Tectonics
    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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  • 7
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    Rethinking the Water-Food-Climate Nexus and Conflict: An Opportunity Cost Approach (2016)
    Oxford University Press
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    Publication Date: 2016-12-07
    Description: Much attention has been paid to the potential role that climate and food security has on conflict, especially in the Middle East. However, there has been little critical examination beyond the statistical correlation of events, which demonstrates whether a causal link exists and if it does, what can be done about it. This paper explores the conceptual linkages between food and conflict and attempts to draw attention to the opportunity cost of conflict as the nexus for decision-making in this context.
    Keywords: D74 - Conflict ; Conflict Resolution ; Alliances, Q18 - Agricultural Policy ; Food Policy, 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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  • 8
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    What Is the Social Value of Second Generation Biofuels? (2016)
    Oxford University Press
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    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
    Published by Oxford University Press
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  • 9
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    A study of different fault slip modes governed by the gouge material composition in laboratory experiments (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-04
    Description: Described are results of laboratory experiments which revealed regularities of gradual transition from stick-slip mode to aseismic creep. The behaviour of model gouge-filled fault was investigated with experimental setup of the spring-bock model. It was experimentally proven that small variations of a percentage of materials with velocity strengthening and velocity weakening properties in the fault principal slip zone may result in significant variation of the portion of seismic energy radiated during a fault slip event. The tests simulated different modes of interblock sliding whose characteristic values of scaled kinetic energy varied by several orders of magnitude, while differences in contact strength and shear stress drop remained relatively small. The obtained results led to the conclusion that the earthquake radiation efficiency and the fault slip mode are governed by the ratio of two parameters—maximum fault slip-weakening rate and shear stiffness of the enclosing massif. The ratio can be essentially changed by small variations of the material composition of the fault principal slip zone.
    Keywords: Geodynamics and Tectonics
    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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  • 10
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    Dynamics of intracontinental convergence between the western Tarim basin and central Tien Shan constrained by centroid moment tensors of regional earthquakes (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-04
    Description: Among the outstanding tectonic questions regarding the convergence between the Tien Shan and Tarim basin in northwestern China are the manner in which deformation is accommodated within their lithospheres, and the extent that the Tarim lithosphere underthrusts the Tien Shan. In particular, the amount and type of deformation within the Tarim basin is poorly understood. It is also uncertain if the convergence between the Tarim and the Tien Shan takes place mainly along a discrete boundary, or if the Tarim lithosphere simply indents into the Kazach shield, forming the Tien Shan through crustal thickening accommodated by a distributed series of thrust faults. In this study we use hypocentres from published earthquake catalogues and waveforms recorded by regional seismic networks to determine earthquake source parameters through regional centroid moment tensor inversion. The entire dataset consists of 160 earthquakes that occurred between 1969 and 2009 and with moment magnitudes between 3.5 and 7 distributed throughout the central Tien Shan and northwestern Tarim Basin. The estimated focal depths of these earthquakes range from the near-surface to about 44 km. Focal mechanisms throughout much of the Tien Shan indicate active deformation accommodated by thrust faults from at least the upper crust to 30 km depth. South of the Tien Shan, the Jia-shi earthquake sequence within the Tarim basin suggests that both crustal shortening and localized flexure are part of a complicated process involving rotational convergence. Inside the Tarim basin, two earthquakes with thrust faulting mechanisms near the crust–mantle boundary beneath the Bachu uplift imply a brittle rheology of the lower crust. High-angle thrust events occur broadly across the Tien Shan, suggesting that the Tarim lithosphere as a whole is strong and indents into the Kazach shield to create the mountain range.
    Keywords: Geodynamics and Tectonics
    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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