Search

This integrated study of deep earthquake locations and focal mechanisms investigates the relationship between the shape of subducting slabs and seismic behaviour in Wadati-Benioff zones. High quality earthquake locations are used to map the shapes of subducting slabs which have reached the upper-lower mantle boundary. The resulting slab models reveal the presence of large slab folds in the mantle transition zone. The distributions and focal mechanisms of deep earthquakes are analysed to determine whether these folds have a role in governing Wadati-Benioff zone seismicity.Bands or lineations of dense seismicity are associated with the hinge zones of identified folds. The focal mechanisms of earthquakes within these bands reveal that the mapped fold hinges are commonly perpendicular to the directions of maximum coseismic extension and compression. The hinges plunge at a variety of angles, resulting in systematic deviations from the downdip stress field expected within planar slabs. Slab synforms are typified by earthquake focal mechanisms indicating in-plane compression (e.g. Izu-Bonin, Tonga), while antiforms have earthquake focal mechanisms indicating in-plane extension (e.g. Solomons) or a mixture of in-plane compression and extension (e.g. Tonga).Slab buckling explains both the clustering of earthquakes and the observed focal mechanism orientations within fold hinges. The localization of strain within buckle zones results in several of the peaks observed in regional earthquake depth distributions. During buckling, the directions of maximum shortening and extension are expected to be perpendicular to the fold hinges, in agreement with deep earthquake moment tensors. Displacement of the minimum-strain surface away from the centre of each seismogenic zone can explain the predominance of in-plane compression within synforms and in-plane extension within antiforms. More complex local variation in focal mechanism orientations in the Tonga slab can be explained by a superposition of in-plane compression and bending strain.Buckling appears to be a common mechanism facilitating convergence between subducting slabs and the lower mantle. The consequent rotation and translation of fold limbs may explain the discrepancy between estimates of convergence based on subduction velocities and long-term coseismic strain. [ABSTRACT FROM AUTHOR]

We report on a series of analogue modeling experiments that study the oroclinal buckling process as a thick-skinned process involving the entire lithosphere. The results obtained in the experiments suggest that, during oroclinal buckling, extension in the outer arc and significant shortening in the inner arc are produced by tangential longitudinal strain as the main mechanism of deformation. The models also reveal that the mantle lithosphere thickens in different noncylindrical ways depending on the initial lithospheric mantle thickness: from almost recumbent to folding with subvertical axial planes for the thinnest to the thickest mantle lithosphere, respectively. The results provide useful insights into thick-skinned orocline buckling as it is interpreted to have happened in the Iberian-Armorican Arc. [ABSTRACT FROM AUTHOR]

The buckling orocline is generally formed by buckling of an originally straight or nearly straight orogenic belt, which formed in the first stage and was buckled in the second stage either by mountain-parallel/oblique compression (e.g. Cantabrian orocline [[12]]) or by mountain-perpendicular/oblique indentation (e.g. Adriatic Orocline [[13]], Peruvian and Bolivian oroclines [[3]]). Therefore, the orocline structure plays a key role in the development of accretionary orogen architecture and contributes to the formation of a huge orogenic belt, such as the CAOB. The term "orocline" was first proposed by Carey [[1]] to describe the structure as 'an orogenic system which has been flexed in plane to a horse-shoe or elbow shape'; it usually emphasizes that a previous straight mountain belt or tectonic units have been bended horizontally. [Extracted from the article]

Abstract: Peak lithospheric strength should reside in the rocks that, under the applied stress, cannot either creep (due to low temperature) or break (due to high confining pressure). The greatest resistance comes from dry olivine/pyroxene-rich upper mantle/lowermost crust at Moho conditions (400–600 °C and >1 GPa). We have conducted laboratory experiments to investigate the importance of the unbreakable core of the lithosphere in between its brittle and ductile parts and conclude that it can control the large-scale lithospheric deformation pattern under shortening. Regardless of the thickness of the unbreakable core, it acts as a restraining layer that is easily flexed but is unstretchable. This eliminates large scale brittle faulting or homogeneous thickening as available shortening modes and results in irregular wrinkling of the unbreakable layer. We discuss geodynamic implications of our laboratory experiments and advocate studies of large scale buckling of the lithosphere as a relevant shortening mode. [Copyright &y& Elsevier]

Bacteriophages are the most abundant biological life forms on Earth. However, relatively little is known regarding which bacteriophages infect and exploit which bacteria. A recent meta-analysis showed that empirically measured phage-bacteria infection networks are often significantly nested, on average, and not modular. A perfectly nested network is one in which phages can be ordered from specialist to generalist such that the host range of a given phage is a subset of the host range of the subsequent phage in the ordering. The same meta-analysis hypothesized that modularity, in which groups of phages specialize on distinct groups of hosts, should emerge at larger geographic and/or taxonomic scales. In this paper, we evaluate the largest known phage-bacteria interaction data set, representing the interaction of 215 phage types with 286 host types sampled from geographically separated sites in the Atlantic Ocean. We find that this interaction network is highly modular. In addition, some of the modules identified in this data set are nested or contain submodules, indicating the presence of multi-scale structure, as hypothesized in the earlier meta-analysis. We examine the role of geography in driving these patterns and find evidence that the host range of phages and the phage permissibility of bacteria is driven, in part, by geographic separation. We conclude by discussing approaches to disentangle the roles of ecology and evolution in driving complex patterns of interaction between phages and bacteria. [ABSTRACT FROM AUTHOR]

Abstract: The Sudbury Basin is a non-cylindrical fold basin occupying the central portion of the Sudbury Impact Structure. The impact structure lends itself excellently to explore the structural evolution of continental crust containing a circular region of long-term weakness. In a series of scaled analogue experiments various model crustal configurations were shortened horizontally at a constant rate. In mechanically weakened crust, model basins formed that mimic several first-order structural characteristics of the Sudbury Basin: (1) asymmetric, non-cylindrical folding of the Basin, (2) structures indicating concentric shortening around lateral basin termini and (3) the presence of a zone of strain concentration near the hinge zones of model basins. Geometrically and kinematically this zone corresponds to the South Range Shear Zone of the Sudbury Basin. According to our experiments, this shear zone is a direct mechanical consequence of basin formation, rather than the result of thrusting following folding. Overall, the models highlight the structurally anomalous character of the Sudbury Basin within the Paleoproterozoic Eastern Penokean Orogen. In particular, our models suggest that the Basin formed by pure shear thickening of crust, whereas transpressive deformation prevailed elsewhere in the orogen. The model basin is deformed by thickening and non-cylindrical synformal buckling, while conjugate transpressive shear zones propagated away from its lateral tips. This is consistent with pure shear deformation of a weak circular inclusion in a strong matrix. The models suggest that the Sudbury Basin formed as a consequence of long-term weakening of the upper crust by meteorite impact. [ABSTRACT FROM AUTHOR]

Abstract: Data from a western United States short-period seismic network are analyzed in order to investigate anomalous later phases within a time window from about 10 s to 120 s after direct P waves for deep and intermediate-depth earthquakes in circum-Pacific subduction zones. The anomalous phases are best interpreted as S-to-P scattered waves (wavelengths of ~10 km) from heterogeneities in the shallow lower mantle (depths ≤950 km). Several S-to-P scatterers where elastic properties of the rocks must substantially change within several kilometers are detected in the shallowest 300 km of the lower mantle beneath four circum-Pacific regions: Kuril, Bonin, Fiji, and Peru. Around most of the observed scatterers the seismic tomography models have delineated high seismic velocity anomalies which are associated with recently subducted Pacific slab or Nazca slab. The most likely origin of the scatterers would be basalt which used to form the oceanic crust. Interestingly enough the majority of the scatterers are located near the bottom boundaries of the slabs. Given rather moderate degrees of folding and/or buckling of the Pacific and Nazca slabs in the shallowest lower mantle at the study areas, the existence of the oceanic crust associated with the most recent slab subduction at the scattering sites is unlikely. Alternative and more likely explanations include: the presence of ancient basaltic rocks, localized dehydration of hydrous minerals, or a sharp boundary between different rock fabrics such as isotropic and anisotropic lower mantle rocks associated with mantle flow dragged by the slab subduction. [Copyright &y& Elsevier]

Abstract: Many papers have been published on engineering and economic aspects of the Space Elevator. The Elevator, however, is a very special and unusual astronomical body. Its behavior in space is affected not only by the attraction of the Earth and by the “centrifugal force” but also by the attraction of the Sun and the Moon, by the detailed shape of the Earth, by the presence of space debris, etc. Not all of the minor effects have been adequately studied. The size of the Space Elevator and its lack of resistance against buckling or bending require a detailed study of its stability, both in its initial phase as a geostationary (GEO) satellite as well as in its operational phase as a “sling”. Lunisolar perturbations and other minor forces may affect the stability in the initial phase and will cause oscillations in the operational phase. Station-keeping thrusters will have to be mounted at selected points along the cable in order to maintain stability. In addition, the thrusters will perform local maneuvers for avoiding collisions with passing space debris. The control system of thrusters has to be adaptive, reacting fast to actual situation and rectifying the attitude of the Elevator whenever necessary. A further advantage of the thrusters is a possibility to locate the Elevator at any longitude, possibly looking for a region with minimum traffic at GEO distance. Extensive numerical simulations will have to be performed in order to determine elements of the thrusters and their control system. [Copyright &y& Elsevier]

Slow-moving arctic soils commonly organize into striking largescale spatial patterns called solifluction terraces and lobes. Although these features impact hillslope stability, carbon storage and release, and landscape response to climate change, no mechanistic explanation exists for their formation. Everyday fluids--such as paint dripping down walls--produce markedly similar fingering patterns resulting from competition between viscous and cohesive forces. Here we use a scaling analysis to show that soil cohesion and hydrostatic effects can lead to similar largescale patterns in arctic soils. A large dataset of high-resolution solifluction lobe spacing and morphology across Norway supports theoretical predictions and indicates a newly observed climatic control on solifluction dynamics and patterns. Our findings provide a quantitative explanation of a common pattern on Earth and other planets, illuminating the importance of cohesive forces in landscape dynamics. These patterns operate at length and time scales previously unrecognized, with implications toward understanding fluid-solid dynamics in particulate systems with complex rheology. [ABSTRACT FROM AUTHOR]

Around the Nanga Parbat massif in the west and the Namche Barwa massif in the east, the trend of the Himalayan orogen exhibits an abrupt strike change from roughly E-W to N-S, forming two structural syntaxes. Within each syntaxis, exposed crystalline basement of the underthrust Indian plate exhibits metamorphism up to granulite-facies grade, and records some of the fastest exhumation rates on Earth (up to c. 10 mm/a), together with Plio-Pleistocene mineral (re)crystallisation and cooling ages (Bracciali et al., 2016; Crowley et al., 2009). The proposed cause(s) of this deep, rapid exhumation are controversial, and include: (1) structural buckling of a pre-existing indentor on the Indian plate (Burg et al., 1997); (2) geometrical stiffening driven by subduction geometry (Bendick & Ehlers, 2014); (3) focusing of exhumation by surface processes such as the capture of the major trans-Himalayan Indus and Yarlung-Tsangpo drainages (Zeitler et al., 2001); and (4) orogen-parallel strain partitioning (Whipp et al., 2014). Distinguishing between these hypotheses can in part be achieved by constraining the onset rapid syntaxial exhumation.Here, we report the first detrital rutile U-Pb data from the Indus catchment system: both from offshore samples collected during IODP expedition 355, and also from modern river sediment, which we use for source-area characterisation. We compare these data with previously reported zircon U-Pb data, and also with data from the Bengal Fan (Najman et al., In Press), and discuss the implications of these results for the exhumation history of the syntaxes. We consider the implications for future large-scale detrital provenance studies. Bendick, R., & Ehlers, T. A., Geophys. Res. Lett. 41, 5861–5867 (2014); Bracciali, L., et al., Earth-Science Rev. 160, 350–385 (2016); Burg, J., et al., Terra Nov. 9, 53–56 (1997); Crowley, J., et al., Earth Planet. Sci. Lett. 288, 408–420 (2009); Najman, Y., et al., GSA Bull., (In Press);Whipp, D., et al., J. Geophys. Res. Solid Earth 119, 5077–5096 (2014);Zeitler, K. et al., Tectonics 20, 712–728 (2001). [ABSTRACT FROM AUTHOR]

This cycle is characterized by the formation of pene-contemporaneous low and high I T/P i metamorphic rocks, exemplified by the low-temperature eclogite- and upper amphibolite-granulite-facies metamorphism, respectively (Fig. The Central Asian Orogenic Belt (CAOB) [[1]], which includes the Altaids in Central and Northern Asia [[2]], is the largest accretionary orogen formed during the subduction of the Paleo-Asian Ocean and the Panthalassa Ocean in the period of the Late Proterozoic to Late Paleozoic [[3]]. 1c), represented by Ordovician to Early Devonian orogenic events that initiated by ~460 Ma high-temperature eclogite-facies metamorphism in the Beishan Orogen and culminated with granulite-facies metamorphism of the Dunhuang block at ~412 Ma. [Extracted from the article]

This survey is devoted to some typical problems modeling technological processes of treatment of materials, rolling of a rigid body on a lubricated surface, the behavior of layers of the Earth's crust for continuous loading, and dynamical interaction of elements of viscoplastic constructions. [ABSTRACT FROM AUTHOR]

The article discusses the study on the use of open sidewalls for self-consistent lithosphere subduction dynamics modelling. It says that subduction modelling is commonly performed using closed vertical boundaries and the study could develop a flow-speed scaling based on energy dissipation to convert flow fields of different model aspect ratios. Results show that open boundaries with intraplate stress conditions are to be preferred for modelling subduction evolution.

SUMMARY In the eighties, the analysis of satellite altimetry data leads to the major discovery of gravity lineations in the oceans, with wavelengths between 200 and 1400 km. While the existence of the 200 km scale undulations is widely accepted, undulations at scales larger than 400 km are still a matter of debate. In this paper, we revisit the topic of the large-scale geoid undulations over the oceans in the light of the satellite gravity data provided by the GRACE mission, considerably more precise than the altimetry data at wavelengths larger than 400 km. First, we develop a dedicated method of directional Poisson wavelet analysis on the sphere with significance testing, in order to detect and characterize directional structures in geophysical data on the sphere at different spatial scales. This method is particularly well suited for potential field analysis. We validate it on a series of synthetic tests, and then apply it to analyze recent gravity models, as well as a bathymetry data set independent from gravity. Our analysis confirms the existence of gravity undulations at large scale in the oceans, with characteristic scales between 600 and 2000 km. Their direction correlates well with present-day plate motion over the Pacific ocean, where they are particularly clear, and associated with a conjugate direction at 1500 km scale. A major finding is that the 2000 km scale geoid undulations dominate and had never been so clearly observed previously. This is due to the great precision of GRACE data at those wavelengths. Given the large scale of these undulations, they are most likely related to mantle processes. Taking into account observations and models from other geophysical information, as seismological tomography, convection and geochemical models and electrical conductivity in the mantle, we conceive that all these inputs indicate a directional fabric of the mantle flows at depth, reflecting how the history of subduction influences the organization of lower mantle upwellings. [ABSTRACT FROM AUTHOR]

A ∼400 km long deep crustal reflection seismic survey was acquired in central Victoria, Australia, in 2006. It has provided information on crustal architecture across the western Lachlan Orogen and has greatly added to the understanding of the tectonic evolution. The east-dipping Moyston Fault is confirmed as the suture between the Delamerian and western Lachlan Orogens, and is shown to extend down to the Moho. The Avoca Fault, the boundary between the Stawell and Bendigo Zones, is a west-dipping listric reverse fault that intersects the Moyston Fault at a depth of about 22 km, forming a V-shaped geometry. Both the Stawell and Bendigo Zones can be divided broadly into a lower crustal region of interlayered and imbricated metavolcanic and metasedimentary rocks and an upper crustal region of tightly folded metasedimentary rocks. The Stawell Zone was probably part of a Cambrian accretionary system along the eastern Gondwanaland margin, and mafic rocks may have been partly consumed by Cambrian subduction. Much of the Early Cambrian oceanic crust beneath the Bendigo Zone was not subducted, and is preserved as a crustal-scale imbricate thrust stack. The seismic data have shown that a thin-skinned structural model appears to be valid for much of the Melbourne Zone, whereas the Stawell and Bendigo Zones have a thick-skinned structural style. Internal faults in the Stawell and Bendigo Zones are mostly west-dipping listric faults, which extend from the surface to near the base of the crust. The Heathcote Fault Zone, the boundary between the Bendigo and Melbourne Zones, extends to at least 20 km, and possibly to the Moho. A striking feature in the seismic data is the markedly different seismic character of the mid to lower crust of the Melbourne Zone. The deep seismic reflection data for the Melbourne Zone have revealed a multilayered crustal structure that supports the Selwyn Block model. [ABSTRACT FROM AUTHOR]

The uniaxial exponential law, , has been applied to experimental results for steady-state creep, including that of wet and dry olivine, pyroxenite and carbonates, at a deviatoric stress greater than ∼100 MPa. Such stress levels likely occur in the upper-mantle lithosphere and middle crust. In a layered rock, in layer-parallel extension or shortening, high deviatoric stress can occur in the stiffest layers, for example, a dolomite layer in fine-grained marble. Under assumptions of isotropy and incompressibility, the uniaxial law yields where is an invariant of the deviatoric stress tensor, . Linearization about a homogeneous basic-state of flow yields equations identical in form to those obtained for the familiar power law. This establishes expressions for an effective viscosity, and stress exponent, , where is an invariant of the basic-state deformation rate, . These results allow application of existing analytical folding and necking solutions for a rock layer of power-law fluid to a rock layer with an exponential flow law. The effective stress exponent for the exponential flow law increases with decreasing temperature, through the dependence of C on the latter and, weakly, with increasing deformation rate. For dry olivine, effective stress exponents are between 10 and 30 for temperatures between 400 and 600°C with little dependence on deformation rate. Finite element simulations employing full non-linear forms of the flow laws show that large strain necking is nearly identical for power law and exponential flow laws. The results suggest that the instability in necking and folding in ductile rock layers can be considerably stronger than inferred from results based on flow laws representing diffusion and dislocation creep. The large values of the effective stress exponent, n > ∼15, that may be attained for exponential flow laws can account for observed outcrop-scale ductile necking. [ABSTRACT FROM AUTHOR]

We present a joint inversion of gravity and teleseismic data to enlighten the lithospheric structures of the Baikal–Mongolia region, an area characterized by high topographic contrasts, sporadic Cenozoic volcanism, extension and large transcurrent faulting in the vicinity of the Baikal Rift, Central Asia. The study uses a 1000 km long seismic transect that cross-cuts the main tectonic structures from north to south (namely, the Siberian platform, Tunka basin, Hangay Dome and Gobi-Altai belt). The Siberian platform depicts a high-velocity lithosphere down to about 150 km. We evidence strong velocity contrasts within the crust below the Hangay Dome and the Tunka depression, interpreted as a thickened crust. A low-velocity/density region is located at various depths below the Hangay Dome. Thanks to the dense spatial coverage of gravity data, we are able to define the 3-D geometry of this particular low-velocity/density anomaly. The Hangay Dome anomalous body extends from 60 to 225 km depth at his largest point and slightly thins to no more than 40 km at its easternmost end. A deep low-velocity zone (below 150 km) with only a weak negative density contrast is observed on the eastern part of the transect. We propose that the late Cenozoic uplift of the whole Mongolian Plateau and associated rifting, magmatism, high heat flow and lithospheric thinning are not externally driven by the India–Asia collision, but results from the interaction of two mantle plumes with the overlying lithosphere. Conversely, recent faulting may be the major expression of the India–Asia collision in this region, as well as N–S striking rift basins that connect and interact with major strike-slip faults, such as the Bolnai fault. The comparison between time residuals of this experiment and the Baikal Rift seismic data shows an undeniable disproportion for the Hangay anomaly. The Hangay time residuals are far more positive than through the Baikal, arguing for an asthenospheric signature that is not seen beneath the Baikal Rift. Furthermore, the southern edge of the thick Siberian cratonic lithosphere may favour the rise of a sublithospheric mantle flow at the contact with the Baikal–Mongolia lithosphere. [ABSTRACT FROM AUTHOR]

Over the last decade, a number of applications have been developed which utilize ground-based hemispherical photography. The collection of such imagery can be described as 'upside-down' remote sensing as, instead of viewing the Earth from a platform in the sky, techniques are being employed to view the sky from the Earth. This paper reviews the current theory and potential applications of 'upside-down' remote sensing across the electromagnetic spectrum. To date, apparatus has been developed to detect various wavelengths between ultraviolet and infrared. Potential applications using these wavelengths are numerous and currently span urban climatology, forest climatology and transportation. [ABSTRACT FROM AUTHOR]

Broad-band data from South American earthquakes recorded by Californian seismic networks are analysed using a newly developed seismic wave migration method—the slowness backazimuth weighted migration (SBWM). Using the SBWM, out-of-plane seismic P-wave reflections have been observed. The reflection locations extend throughout the Earth's lower mantle, down to the core–mantle boundary (CMB) and coincide with the edges of tomographically mapped high seismic velocities. Modelling using synthetic seismograms suggests that a narrow (10–15 km) low- or high-velocity lamella with about 2 per cent velocity contrast can reproduce the observed reflected waveforms, but other explanations may exist. Considering the reflection locations and synthetic modelling, the observed out-of-plane energy is well explained by underside reflections off a sharp reflector at the base of the subducted lithosphere. We also detect weaker reflections corresponding to the tomographically mapped top of the slab, which may arise from the boundary between the Nazca plate and the overlying former basaltic oceanic crust. The joint interpretation of the waveform modelling and geodynamic considerations indicate mass flux of the former oceanic lithosphere and basaltic crust across the 660 km discontinuity, linking processes and structure at the top and bottom of the Earth's mantle, supporting the idea of whole mantle convection. [ABSTRACT FROM AUTHOR]

No two rocky bodies offer a better laboratory for exploring the conditions controlling interior dynamics than Venus and Earth. Their similarities in size, density, distance from the sun, and young surfaces would suggest comparable interior dynamics. Although the two planets exhibit some of the same processes, Venus lacks Earth’s dominant process for losing heat and cycling volatiles between the interior and the surface and atmosphere: plate tectonics. One commonality is the size and number of mantle plume features which are inferred to be active today and arise at the core mantle boundary. Such mantle plumes require heat loss from the core, yet Venus lacks a measurable interior dynamo. There is evidence for plume-induced subduction on Venus, but no apparent mosaic of moving plates. Absent plate tectonics, one essential question for interior dynamics is how did Venus obtain its young resurfacing age? Via catastrophic or equilibrium processes? Related questions are how does it lose heat via past periods of plate tectonics, has it always had a stagnant lid, or might it have an entirely different mode of heat loss? Although there has been no mission dedicated to surface and interior processes since the Magellan mission in 1990, near infrared surface emissivity data that provides information on the iron content of the surface mineralogy was obtained fortuitously from Venus Express. These data imply both the presence of continental-like crust, and thus formation in the presence of water, and recent volcanism at mantle hotspots. In addition, the study of interior dynamics for both Earth and exoplanets has led to new insights on the conditions required to initiate subduction and develop plate tectonics, including the possible role of high temperature lithosphere, and a renewed drive to reveal why Venus and Earth differ. Here we review current data that constrains the interior dynamics of Venus, new insights into its interior dynamics, and the data needed to resolve key questions. [ABSTRACT FROM AUTHOR]