Geodynamics articles within Nature

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  • News |

    The movement of oxygen and sulphur at the heart of the planet may drive its magnetic field.

    • Geoff Brumfiel

  • Brief Communications Arising |

    • T. L. Grove
    • , C. B. Till
    •  & E. Médard

  • Letter |

    Here, the seismic anisotropy of the Earth's lowermost mantle between North and Central America has been measured, using shallow and deep earthquakes to increase the azimuthal coverage. The findings show that the previously assumed vertical transverse isotropy — where wave speed should show no azimuthal variation — is not possible, and that more complicated mechanisms must be involved.

    • Andy Nowacki
    • , James Wookey
    •  & J-Michael Kendall

  • Letter |

    These authors use a scaling argument derived from a model of heat transfer in subduction zones to argue that the locations of volcanic arcs cannot be explained by the release of fluids in reactions taking place near the top of the slab. Instead, they conclude that the sharpness of the volcanic fronts, together with the systematics of their locations, require that arcs be located above the place where the boundary defined by the anhydrous solidus makes its closest approach to the trench.

    • Philip C. England
    •  & Richard F. Katz

  • Letter |

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. It has recently been argued that the decay of aftershocks with distance from the main earthquake could be explained only by dynamic triggering. This hypothesis has now been tested, the conclusion being that the observed decay can be better explained by static triggering.

    • Keith Richards-Dinger
    • , Ross S. Stein
    •  & Shinji Toda

  • Letter |

    Earthquake instability has long been attributed to fault weakening during accelerated slip, but what are the mechanisms that control this weakening? Here laboratory evidence is presented for the dynamic weakening of faults that are sheared at velocities approaching earthquake slip rates. The experimental faults, made from solid granite blocks, quickly wore to form a fine-grain rock powder, known as gouge, which reduced the faults' strength. It is concluded that only newly formed gouge can weaken the experimental faults.

    • Ze’ev Reches
    •  & David A. Lockner

  • Letter |

    These authors show evidence for a high coherence between the slip distribution inferred from the 2010 Maule earthquake, Chile, and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade. Their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes, which thus might be anticipated by geodetic observations.

    • Marcos Moreno
    • , Matthias Rosenau
    •  & Onno Oncken

  • Letter |

    Cratons, the ancient cores of continents, extend laterally for hundreds of kilometres, and are underlain to depths of 180–250 km by mantle roots that are chemically and physically distinct from surrounding mantle. But how can these roots stay so isolated from mantle convection? Here it is shown that olivine in peridotite xenoliths from the lithosphere–athenosphere boundary region of the Kaapvaal craton mantle root is water-poor, providing sufficient viscosity contrast with the underlying asthenosphere to explain the root's stability.

    • Anne H. Peslier
    • , Alan B. Woodland
    •  & Marina Lazarov

  • Letter |

    At the end of the last ice age, rising atmospheric CO2 levels coincided with a decline in radiocarbon activity, suggesting the release of highly radiocarbon-depleted CO2 from the deep ocean to the atmosphere. These authors present radiocarbon records of surface and intermediate-depth waters from two sediment cores and find an decrease in radiocarbon activity that precedes and roughly equals in magnitude the decrease in the atmospheric radiocarbon signal during the early stages of the glacial–interglacial climatic transition.

    • Kathryn A. Rose
    • , Elisabeth L. Sikes
    •  & Howard J. Spero

  • Article |

    These authors show that changes in seismic anisotropy with depth across the stable part of North America reveal the presence of two lithospheric layers. The top layer, which is chemically depleted, is ∼150 km thick under the ancient core of the continent and tapers out along its younger borders. The bottom of the lithosphere is relatively flat, in agreement with the presence of a thermal conductive root that subsequently formed around the depleted chemical layer.

    • Huaiyu Yuan
    •  & Barbara Romanowicz

  • News |

    Recent measurements of gravitational constant increase uncertainty over accepted value.

    • Eugenie Samuel Reich

  • Letter |

    On 29 September 2009, a tsunami devastated the Samoan and northern Tongan islands. Here, an unusual earthquake sequence that preceded this tsunami is analysed. A magnitude-8.1 intraplate faulting event in the outer trench-slope at the northern end of the Tongan subduction zone was followed by extensive interplate faulting, with total moment equivalent to that of a magnitude-8.0 earthquake. Overlap of the seismic signals had obscured the fact that distinct faults had ruptured with different geometries.

    • Thorne Lay
    • , Charles J. Ammon
    •  & Alexander R. Hutko

  • Letter |

    On 29 September 2009, a tsunami devastated the Samoan and northern Tongan islands. It is shown here that an unusual earthquake sequence preceded this tsunami. A magnitude-8 earthquake in the outer-rise intraplate region occurred almost simultaneously with rupture of the shallow subduction interplate interface, equivalent to a magnitude-8 earthquake. The findings provide information on strain release mechanisms at subduction zones, and a possible mechanism for the occasional large tsunamis generated at the Tonga subduction zone.

    • J. Beavan
    • , X. Wang
    •  & R. Kautoke

  • News & Views |

    A puzzling case is presented by the occurrence of two large but dissimilar earthquakes at almost the same time and place. One must have acted as the trigger, but which one and how did it do so?

    • Kenji Satake

  • Letter |

    High 3He/4He ratios in some basalts have been interpreted as evidence for ancient reservoirs preserved in the Earth’s mantle; however, such rocks have never been observed to host the primitive lead-isotopic compositions required for an early formation age. These authors show that Baffin Island and West Greenland lavas exhibit primitive lead-isotope ratios consistent with a mantle source age of 4.55–4.45 billion years, and that their source may be the most ancient accessible reservoir in the mantle.

    • Matthew G. Jackson
    • , Richard W. Carlson
    •  & Jerzy Blusztajn

  • Letter |

    These authors show that simultaneous crystallization and melting at the surface of the Earth's inner core can result in a translational mode of thermal convection within the inner core, producing the observed stratified layer of reduced seismic velocity at the base of the outer core. The dynamical model they propose also introduces an asymmetry between hemispheres that may explain the enigmatic East–West asymmetry in seismic properties of the inner core.

    • Thierry Alboussière
    • , Renaud Deguen
    •  & Mickaël Melzani

  • Letter |

    These authors report the concentrations of hydrogen, chlorine and sulphur in the mineral apatite from a lunar basalt, and show that the concentrations are indistinguishable from apatites in common terrestrial igneous rocks. They conclude that both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable materials within the Earth.

    • Jeremy W. Boyce
    • , Yang Liu
    •  & Lawrence A. Taylor

  • Letter |

    Diamonds are formed under high pressure more than 150 kilometres deep in the Earth's mantle, and are brought to the surface mainly by volcanic rocks called kimberlites. Here, plate reconstructions and tomographic images have been used to show that the edges of the largest heterogeneities in the deepest mantle, stable for at least 200 million years and possibly for 540 million years, seem to have controlled the eruption of most Phanerozoic kimberlites. This has implications for future exploration for kimberlites.

    • Trond H. Torsvik
    • , Kevin Burke
    •  & Lewis D. Ashwal

  • News Feature |

    An imminent swarm of tiny quakes beneath western North America could help seismologists prepare for a big one — but only if they can learn to interpret the tremors, finds Naomi Lubick.

    • Naomi Lubick

  • Letter |

    Here, global mantle flow is computed on the basis of recent, high-resolution seismic tomography, to investigate the role of buoyancy-driven and plate-motion-induced mantle circulation in the Mediterranean region. The findings show that mantle flow explains much of the observed dynamic topography and microplate motion in the region. Small-scale convection in the uppermost mantle may also hold the key to understanding complex mobile belts elsewhere.

    • Claudio Faccenna
    •  & Thorsten W. Becker

  • News & Views |

    Density variations within Earth's mantle may be a significant driver of both horizontal and vertical surface movements. The fingerprints of such mantle processes have been found in the Mediterranean region.

    • Rinus Wortel
    •  & Rob Govers

  • Letter |

    Here, first-principles methods have been applied to calculate diffusion rates in the mineral post-perovskite under the conditions found in the Earth's lower mantle. The results show that the diffusion of Mg2+ and Si4+ in post-perovskite is extremely anisotropic. This could render post-perovskite up to four orders of magnitude weaker than perovskite, and might reconcile seismic observations of a D” reflector with recent experiments showing that the perovskite to post-perovskite transition is too wide to cause sharp reflectors.

    • M. W. Ammann
    • , J. P. Brodholt
    •  & D. P. Dobson

  • News & Views |

    The influence of the region where the lower mantle meets the core extends to Earth's surface. A computational study of mineral properties shows one way forward in understanding this enigmatic zone.

    • James A. Van Orman

  • Letter |

    The direction of tectonic plate motion at the Earth's surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally, implying large-scale coupling between the mantle and surface plates. But the fit is poor at subduction zones. Here, three-dimensional numerical models of buoyancy-driven deformation for the Alaska subduction–transform system are used to find the origin of the regional decoupling of flow. The results imply local rapid transport of geochemical signatures through subduction zones.

    • Margarete A. Jadamec
    •  & Magali I. Billen

  • News & Views |

    Increased erosion associated with the rise of the world's great mountain ranges has been held to be the cause of a prolonged episode of past climate cooling. That connection is now brought into doubt.

    • Yves Goddéris

  • Letter |

    The magnetic field inside the Earth's outer core cannot be directly probed. The intensity of the magnetic field at the core–mantle boundary is estimated to be 0.3 mT, and geodynamo models predict a value about ten times larger (3 mT) for the core's interior. Other data, however, indicate an internal field of only around 0.2 mT. This discrepancy has now been resolved: an ensemble inversion of core flow models finds a torsional wave recurring every 6 years, leading to an estimated field strength of around 4 mT inside the core.

    • Nicolas Gillet
    • , Dominique Jault
    •  & Alexandre Fournier

  • Letter |

    Zonal jets are common in nature and are spontaneously generated in turbulent systems. Because the Earth's outer core is believed to be in a turbulent state, it is possible that there is zonal flow in the liquid iron of the outer core. By investigating numerical simulations of the geodynamo with lower viscosities than most previous simulations have been able to use, a convection regime of the outer core is now found that has a dual structure comprising inner, sheet-like radial plumes and an outer, westward cylindrical zonal flow.

    • Takehiro Miyagoshi
    • , Akira Kageyama
    •  & Tetsuya Sato

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