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The devastating Wenchuan earthquake in 2008 struck along a fault zone that displayed low rates of deformation. Analysis of GPS and InSAR data suggests that as structural barriers failed during a single earthquake, the rupture cascaded across multiple fault segments, which may explain the high magnitude of the event. The image was produced by Jianbao Sun, and it shows the surface deformation associated with the 2008 Wenchuan earthquake as inferred from Interferometric Synthetic Aperture Radar (InSAR).Article p718; Backstory p732
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During an earthquake, friction is a key control on the initiation, propagation and termination of fault motion. Laboratory experiments that use variable slip rates suggest that friction evolves in a more complex fashion than generally assumed.
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Now that stratospheric ozone depletion has been controlled by the Montreal Protocol, interest has turned to the effects of climate change on the ozone layer. An atmospheric chemistry model suggests that climate change will increase the stratosphere-to-troposphere ozone flux by 23% globally between 1965 and 2095, altering the amount of ultraviolet radiation reaching Earth’s surface.
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Earthquakes often occur in areas that lack an array of seismometers, resulting in a scarcity of local measurements from some regions of great geological interest. In such regions, some earthquakes themselves may be turned into virtual seismometers that are capable of measuring strain caused by passing waves from other earthquakes.
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Rocks near the San Andreas fault are pervasively crushed at distances of up to 400 m from its core. Laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates (>150 s−1) associated with a supershear rupture—a rupture propagating at a velocity equal to greater than that of seismic shear waves.
1.1-billion-year-old volcanic rocks in North America are thought to record asymmetric geomagnetic reversals, indicating non-axial dipolar behaviour of the magnetic field. High-resolution data from Ontario suggest that the reversals were instead symmetric, and that the apparent reversal asymmetry is an aliasing effect of the low resolution of earlier samples combined with the rapid motion of North America.
The devastating Wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation. Analysis of GPS and InSAR data suggests that, as structural barriers failed during a single earthquake, the rupture cascaded across multiple fault segments, which may explain the high magnitude of the event.
The initial production of oxygen in early Earth’s oceans altered the redox chemistry and cycling of nitrogen. A record of nitrogen isotopes from preserved organic matter indicates nitrogen cycling in the presence of free oxygen 2.67 billion years ago, about 200 million years before the first geochemical evidence for atmospheric free oxygen.