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Highlights: [•] The classical Mid-Cretaceous tectonic űcrisisƇ of Tunisia is actually mainly of Albian age. [•] Synsedimentary deformations increased throughout the Early to Middle Albian. [•] Extensional deformation preceded and triggered halokinetic movements. [•] This Albian tectonics was related to the opening of the equatorial Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Magnetic anomaly data are presented from a new helicopter-borne high-resolution aeromagnetic survey in southern McMurdo Sound. Anomaly data have been acquired at a common 305 m elevation above the McMurdo and southern McMurdo ice shelves and draped over the volcanic islands that pin them. The resulting anomaly patterns provide a significant advance in the understanding of the rift related geology beneath the floating ice shelves. More extensive Erebus Volcanic Province (McMurdo Volcanic Group) rocks are indicated along with a significant blanket of glaci-volcaniclastic sediment on the seafloor between the volcanic islands in southern McMurdo Sound. These glaci-volcaniclastic sediments are inferred to originate from former grounding of the southern McMurdo Ice Shelf as a marine ice sheet. A strong N–S fabric is also observed in the anomaly data suggesting that the rift structure observed in the Victoria Land basin persists to the south beneath the McMurdo and southern McMurdo ice shelves. W–N–W transfer faults identified within the Transantarctic Mountain rift flank to the west are not obvious in the aeromagnetic data set, implying that the ‘Discovery Accommodation Zone’ may be restricted to the region between a southward extension of the range bounding fault that marks the limit of the Victoria Land Basin and the right lateral offset in the Transantarctic Mountain front in southern Victoria Land. [ABSTRACT FROM AUTHOR]

We present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of France. This experiment was set-up at the boundary between the Ligurian basin and the southern subalpine thrust belt (the Nice arc), which is a complex tectonic region that undergoes low to moderate seismicity. We recorded more than 500 microearthquakes, among which 348 occurred exactly in the centre of the network during a very active seismic sequence that lasted mainly over 2 months. We performed an absolute location of all of the events and calculated the magnitudes. Then we applied a cross-correlation technique to gather similar events and to relocate relatively few of them. This method revealed a very clear alignment of 19 events in a direction N120° oblique to the N20° general trend of seismicity. Focal mechanisms were determined for the four largest events and composite solutions for 32 smaller ones. Both the alignments of the earthquakes and the focal solutions revealed that two oblique segments of the fault were activated during the crisis. The main segment (8 km long) that was oriented NNE with a left-lateral strike slip movement is called the Blausasc fault. Taking into account the tectonic evolution and the relationships between surface structures and the distribution of earthquakes, and through a paleaoreconstruction of the tectonic evolution, we propose that the Blausasc fault is the hidden root of the Peille-Laghet fault, which has a mapped length of at least 15 km. The smaller segment (0.6 km long) that was activated during the crisis could be interpreted as an antithetic Riedel fracture. The active Blausasc fault is located in a densely populated zone, at only 10 km from the crowded cities of Monaco and Nice. It is thus particularly interesting to analyse it for hazard assessment. In the last section, we present a simulation that is aimed at predicting what the ground motion in the city of Nice would be like if an earthquake of magnitude 5.7 occurs on this fault. For this, we used the recordings of the largest event of the seismic sequence ( Ml= 3.2) and an empirical Green's function summation scheme to simulate the ground motion at two stations situated in urban environments. The values obtained show that especially on soft soil sites, the effects of such an earthquake would be considerable in the city of Nice. [ABSTRACT FROM AUTHOR]

The misfit angles between observed and theoretical slip directions are important in evaluating the reliability of the solution to a stress tensor inversion. The distance between stress tensors is also essential for evaluating the resolution of a method of separating stresses from heterogeneous fault-slip data. Here, we define ‘angular stress distance’ for this purpose. This new method has the attribute of improved distance measurements compared with existing methods. The value of angular stress distance is equivalent to a number of important properties. First, the distance between the correct and optimal stresses for a data set approximates the mean misfit angle. Secondly, when we evaluate the dispersion of reduced stress tensors obtained via a bootstrap or other resampling technique, the value of the dispersion evaluated with the mean distance of the tensors from the optimal solution is approximately equal to the noise level of the data. Thirdly, the distance is equal to the Lode angle difference of the stresses if they have common principal orientations. We demonstrate that stresses cannot share common principal axes if their distance is greater than a certain threshold value. The relationships among the distances that have been proposed for reduced stress tensors are also discussed. [ABSTRACT FROM AUTHOR]

In order to estimate the averaged fault zone structure, i.e. the width, shear wave velocity andQs of the Mozumi-Sukenobu fault, central Japan, we analysed the Love-wave-type fault zone trapped waves recorded by a seismic array deployed in a subsurface survey gallery. We selected the typical Love-wave-type trapped waves based on the characteristics of dispersion, amplitude, apparent velocity and the polarization of wave trains following the direct shear wave. We selected nine events showing typical Love-wave-type trapped waves from 154 earthquakes. Epicentres of the events were located along the surface trace of the Mozumi-Sukenobu fault. The nine events showing trapped waves were found to be located in a plane dipping to the south at an angle of approximately 75° to 85°. The duration of the fault zone trapped waves increase non-linearly with the increase of hypocentral distance. This result implies an increase in shear wave velocity of the fault zone with depth and/or horizontal distance from the array. In order to obtain averaged fault zone structure from hypocentre to receiver, we assumed fault zone structure to be a 2-D uniform low-velocity waveguide, and modelled the dispersion curve and the waveform of trapped waves using an analytical solution. The width, shear wave velocity andQs of the fault zone were estimated to be 160 to 400 m, 2.9 to 3.1 km s−1 and 60 to 90, respectively. The width of the fault zone estimated in this analysis is consistent with the width of the extent of fault zone at the survey gallery. We also conducted 3-D finite difference simulation (3-D FDM) on fault zone trapped waves using depth-dependent structure models referred to the 2-D averaged structure, indicating the possible depth-dependent structures. The 2-D modelling is useful as an initial guide to the 3-D imaging of a fault zone. [ABSTRACT FROM AUTHOR]