Rupture propagation of an earthquake strongly influences potentially destructive ground shaking. Variable rupture behaviour is often caused by complex fault geometries, masking information on fundamental frictional properties. Geometrically smoother ocean transform fault (OTF) plate boundaries offer a favourable environment to study fault zone dynamics because strain is accommodated along a single, wide zone (up to 20 km width) offsetting homogeneous geology comprising altered mafic or ultramafic rocks. However, fault friction during OTF ruptures is unknown: no large (Mw>7.0) ruptures had been captured and imaged in detail. In 2016, we recorded an Mw 7.1 earthquake on the Romanche OTF in the equatorial Atlantic on nearby seafloor seismometers. We show that this rupture had two phases: (1) up and eastwards propagation towards the weaker ridge-transform intersection (RTI), then (2) unusually, back-propagation westwards at super-shear speed toward the fault's centre. Deep slip into weak fault segments facilitated larger moment release on shallow locked zones, highlighting that even ruptures along a single distinct fault zone can be highly dynamic. The possibility of reversing ruptures is absent in rupture simulations and unaccounted for in hazard assessments.

Abstract:With the upcoming availability of the next generation of high quality orbiting hyperspectral sensors, a major step toward improved regional soil mapping and monitoring and delivery of quantitative soil maps is expected. This study focuses on the determination of the prediction accuracy of spectral models for the mapping of common soil properties based on upcoming EnMAP (Environmental Mapping and Analysis Program) satellite data using semi-operational soil models. Iron oxide (Fe d ), clay, and soil organic carbon (SOC) content are predicted in test areas in Spain and Luxembourg based on a semi-automatic Partial-Least-Square (PLS) regression approach using airborne hyperspectral, simulated EnMAP, and soil chemical datasets. A variance contribution analysis, accounting for errors in the dependent variables, is used alongside classical error measurements. Results show that EnMAP allows predicting iron oxide, clay, and SOC with an R 2 between 0.53 and 0.67 compared to Hyperspectral Mapper (HyMap)/Airborne Hyperspectral System (AHS) imagery with an R 2 between 0.64 and 0.74. Although a slight decrease in soil prediction accuracy is observed at the spaceborne scale compared to the airborne scale, the decrease in accuracy is still reasonable. Furthermore, spatial distribution is coherent between the HyMap/AHS mapping and simulated EnMAP mapping as shown with a spatial structure analysis with a systematically lower semivariance at the EnMAP scale.

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Understanding the mechanisms by which earthquake cycles produce folding and accommodate shortening is essential to quantify the seismic potential of active faults and integrate aseismic slip within our understanding of the physical mechanisms of the long-term deformation. However, measuring such small deformation signals in mountainous areas is challenging with current space-geodesy techniques, due to the low rates of motion relative to the amplitude of the noise. Here we successfully carry out a multitemporal Interferometric Synthetic Aperture Radar analysis over the North Qaidam fold-thrust system in NE Tibet, where eight M w > 5.2 earthquakes occurred between 2003 and 2009. We report various cases of aseismic slip uplifting the thickened crust at short wavelengths. We provide a rare example of a steep, shallow, 13-km-long and 6-km-wide afterslip signal that coincides spatially with an anticline and that continues into 2011 in response to a M w 6.3 event in 2003. We suggest that a buried seismic slip during the 2003 earthquake has triggered both plastic an-elastic folding and aseismic slip on the shallow thrusts. We produce a first-order two-dimensional model of the postseismic surface displacements due to the 2003 earthquake and highlight a segmented slip on three fault patches that steepen approaching the surface. This study emphasizes the fundamental role of shallow aseismic slip in the long-term and permanent deformation of thrusts and folds and the potential of Interferometric Synthetic Aperture Radar for detecting and characterizing the spatiotemporal behavior of aseismic slip over large mountainous regions.