Evolving force balance during incipient subduction

Nearly half of all active subduction zones initiated during the Cenozoic. All subduction zones associated with active back arc extension have initiated since the Eocene, hinting that back arc extension may be intimately associated with an interval (several tens of Myr) following subduction initiation. That such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates. Subduction initiation is known to have occurred in a variety of tectonic settings: old fracture zones, transform faults, and extinct spreading centers and through polarity reversal behind active subduction zones. Although occurring within different tectonic settings, four known subduction initiation events (Izu-Bonin-Mariana (IBM) along a fracture zone, Tonga-Kermadec along an extinct subduction boundary, New Hebrides within a back arc, and Puysegur-Fiordland along a spreading center) were typified by rapid uplift within the forearc followed by sudden subsidence. Other constraints corroborate the compressive nature of IBM and Tonga-Kermadec during initiation. Using an explicit finite element method within a two-dimensional domain, we explore the evolving force balance during initiation in which elastic flexure, viscous flow, plastic failure, and heat transport are all considered. In order to tie theory with observation, known tectonic settings of subduction initiation are used as initial and boundary conditions. We systematically explore incipient compression of a homogeneous plate, a former spreading center, and a fracture zone. The force balance is typified by a rapid growth in resisting force as the plate begins bending, reaching a maximum value dependent on plate thickness, but typically ranging from 2 to 3 × 1012 N/m for cases that become self-sustaining. This is followed by a drop in stress once a shear zone extends through the plate. The formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall. Cumulative convergence, not the rate of convergence, is the dominant control on the force balance. Viscous tractions influence the force balance only if the viscosity of the asthenosphere is >1020 Pa s, and then only after plate failure. Following plate failure, buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction. The total work done is also influenced by the rate of lithospheric failure. A self-sustaining subduction zone does not form from a homogeneous plate. A ridge placed under compression localizes subduction initiation, but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate. The large initial bending resistance can be entirely eliminated in ridge models, explaining the propensity for new subduction zones to form through polarity reversals. A fracture zone (FZ) placed in compression leads to subduction initiation with rapid extension of the overriding plate. A FZ must be underthrust by the older plate for ~100–150 km before a transition from forced to self-sustaining states is reached. In FZ models the change in force during transition is reflected by a shift from forearc uplift to subsidence. Subduction initiation is followed by trench retreat and back arc extension. Moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of Pacific subduction zones. The models provide an explanation for the compressive state of western Pacific margins before and during subduction initiation, including IBM and Tonga-Kermadec in the Eocene, and the association of active back arcs with young subduction zones. On the basis of our dynamic models and the relative poles of rotation between Pacific and Australia during the Eocene, we predict that the northern segment of the Tonga-Kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self-sustaining states

Testing the P-Map: Lenition and Position

This study tests the P-Map's (Steriade, 2001) hypothesis that attested phonological patterns vary depending on phonological context due to differences in the perceptual similarity of two phonological contrasts in different contexts, and that the knowledge of these relative perceptibilities are used to explain cross-linguistic patterns of phonological typology. Specifically, the phenomena in focus are spirantization and devoicing. The study investigates if preference for spirantization of voiced stops in intervocalic position and devoicing of voiced stops in word-final position across languages is correlated with perceptual similarity. Using perceptual similarity tests with native Michigan English speakers on pairs of contrasts in nonsense words, the results show that continuancy contrasts are significantly more similar in intervocalic position than in word-final position, explaining the preference for spirantization intervocalically while voicing contrasts are significantly more similar word-finally, explaining the preference for devoicing word-finally. The results thus support the P-Map's claim and support a phonetics-based approach to phonology. In addition, since neither phenomenon is a process that happens in Michigan English, the lack of bias in these similarity judgements lends weight to the idea that these results reflect the universal perception of phonological processes

Strength of fracture zones from their bathymetric and gravitational evolution

Fracture zone evolution is investigated using dynamic models that allow the fault zones to freely slip. This is an improvement over past formulations where bathymetric offsets were imposed kinematically. The models use a viscoelastoplastic rheology that incorporates the influence of fault friction on fracture zone slip history. Using viscoelastic plates, we assess the role of small-scale convection on removal of the lowermost thermal lithosphere beneath fracture zones. Through a comparison of synthetic gravity to free-air gravity across fracture zones we find that the amplitude of the gravity jump across fracture zones is best fit by models with weak faults that have depth-averaged yield strengths <10 MPa. Fracture zones with such low strengths can convert to subduction zones with ∼100 km of convergence. Many fracture zones do not fit plate subsidence models with locked or slipping faults but are better fit by systems that are tectonically deformed by modest amounts of extension

Uncovering a focused Lebanese American English ethnolect in Dearborn Michigan

This study presents findings from a quantitative analysis of inter- and intraspeaker phonetic variability in the realization of /t/ and /d/ from second- and third- generation Lebanese American speakers from Dearborn, Michigan. The realization of /t/ and /d/ as either alveolar or dental (a substrate feature from Lebanese Arabic) is the focus of the analysis. The data, which come from 2006 corpus recordings, are also subject to diagnostics for a focused ethnolect i.e. the retention of distinctive features into the third and later generations of a speech community. These diagnostics are derived from new-dialect formation and ethnolect formation models. Evidence is found for a focused Lebanese American English ethnolect in Dearborn though the findings are tentative due to a small dataset. The results of the study lay the foundation for future work, which will seek to confirm these findings in greater detail.Ope

The Rhotic Pronunciation of Anglo-English and Punjabi-English Bilingual Speakers in West Yorkshire

In this paper, the /r/ production of adolescent Anglo-English and Punjabi-English Bilingual speakers in West Yorkshire was analysed from speech data collected in 2000. A clear difference was found between Anglo-English speakers who used the standard British rhotic, the postalveolar approximant [ɹ̠], exclusively, and the Punjabi-English Bilingual speakers who used both British rhotics and a number of different variants influenced by the Punjabi retroflex flap /ɽ/. The influence of the retroflex flap /ɽ/ was proven by formant and duration results, as well as qualitative observations of the speaker spectrograms. It is predicted that Punjabi-English speaker preference for either Punjabi influenced rhotics or British rhotics depended on if they identify as culturally integrated “British Asians” or culturally alienated “Asians”. This study also considers the possibility of a progression in rhotic production of West Yorkshire Punjabi-English speakers over the last fifteen years.Este trabajo analizó la producción del fonema /r/ de los adolescentes anglo-ingleses y punjabí-ingleses bilingües en el oeste de Yorkshire a partir de los datos recogidos en el año 2000. Se encontró una clara diferencia entre los hablantes anglo-ingleses que usan exclusivamente el /r/ británico estándar, [ɹ̠], y los hablantes bilingües punjabí-ingleses que usan el fonema /r/ británico tanto como otras variantes influenciadas por la vibrante retrofleja Punjabi /ɽ/. La influencia de esta última se demuestra en el movimiento formántico y la duración resultantes, así como por las observaciones cualitativas de los espectrogramas de los hablantes. Se predice que la preferencia de los hablantes punjabíes hacia los róticos punjabíes o los róticos británicos depende de si se identifican como "británicos asiáticos" integrados culturalmente o como asiáticos alienados culturalmente. Este estudio también considera la posibilidad de una progresión en la producción del rótico punjabi en los angloparlantes del oeste de Yorkshire en los últimos quince años

Reduction of a Vehicle Multibody Dynamic Model Using Homotopy Optimization

The original publication is available at: Hall, A., Uchida, T., Loh, F., Schmitke, C., & Mcphee, J. (2013). Reduction of a Vehicle Multibody Dynamic Model Using Homotopy Optimization. Archive of Mechanical Engineering, LX(1). https://doi.org/10.2478/meceng-2013-0002Despite the ever-increasing computational power of modern processors, the reduction of complex multibody dynamic models remains an important topic of investigation, particularly for design optimization, sensitivity analysis, parameter identification, and controller tuning tasks, which can require hundreds or thousands of simulations. In this work, we first develop a high-fidelity model of a production sports utility vehicle in Adams/Car. Single-link equivalent kinematic quarter-car (SLEKQ, pronounced “sleek”) models for the front and rear suspensions are then developed in MapleSim. To avoid the computational complexity associated with introducing bushings or kinematic loops, all suspension linkages are lumped into a single unsprung mass at each corner of the vehicle. The SLEKQ models are designed to replicate the kinematic behaviour of a full suspension model using lookup tables or polynomial functions, which are obtained from the high-fidelity Adams model in this work. The predictive capability of each SLEKQ model relies on the use of appropriate parameters for the nonlinear spring and damper, which include the stiffness and damping contributions of the bushings, and the unsprung mass. Homotopy optimization is used to identify the parameters that minimize the difference between the responses of the Adams and MapleSim models. Finally, the SLEKQ models are assembled to construct a reduced 10-degree-of-freedom model of the full vehicle, the dynamic performance of which is validated against that of the high-fidelity Adams model using four-post heave and pitch tests.The authors gratefully acknowledge the financial support provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the NSERC/Toyota/Maplesoft Industrial Research Chair program

A Statistical Method for Estimating Luminosity Functions using Truncated Data

The observational limitations of astronomical surveys lead to significant statistical inference challenges. One such challenge is the estimation of luminosity functions given redshift $z$ and absolute magnitude $M$ measurements from an irregularly truncated sample of objects. This is a bivariate density estimation problem; we develop here a statistically rigorous method which (1) does not assume a strict parametric form for the bivariate density; (2) does not assume independence between redshift and absolute magnitude (and hence allows evolution of the luminosity function with redshift); (3) does not require dividing the data into arbitrary bins; and (4) naturally incorporates a varying selection function. We accomplish this by decomposing the bivariate density into nonparametric and parametric portions. There is a simple way of estimating the integrated mean squared error of the estimator; smoothing parameters are selected to minimize this quantity. Results are presented from the analysis of a sample of quasars.Comment: 30 pages, 9 figures, Accepted for publication in Ap

Crop response to amelioration of agricultural soils are mediated by contraint combinations and soil type

Over the past decade alternative strategic deep tillage approaches have been developed to complement more established soil amelioration methods. Strategic tillage takes the form of a one-off or occasional intervention, implemented to overcome a number of soil and biotic constraints. Deep ripping can effectively remove subsoil hardpans and potentially delve up some subsoil to the surface depending on tine design. Deep soil mixing, using rotary spaders or large disc ploughs, can mix and incorporate topsoil and amendments deeper into the soil profile and reduce topsoil repellence. Soil inversion, using mouldboard, square or one-way disc ploughs, can bury surface-applied amendments, as well as repellent topsoil and weed seeds. While these techniques principally address soil constraints, some also improve weed control and reduce frost damage

Crop Response to Amelioration of Agricultural Soils are Mediated by Constraint Combinations and Soil Type

Over the past decade alternative strategic deep tillage approaches have been developed to complement more established soil amelioration methods. Strategic tillage takes the form of a one-off or occasional intervention, implemented to overcome a number of soil and biotic constraints