Evidence of episodic long-lived eruptions in the Yuma,Ginsburg, Jesús Baraza and Tasyo mud volcanoes,Gulf of Cádiz

High-resolution single channel and multichannel seismic reflection profiles and multibeam bathymetric and backscatter data collected during several cruises over the period 1999 to 2007 have enabled characterising not only the seabed morphology but also the subsurface structural elements of the Yuma, Ginsburg, Jesús Baraza and Tasyo mud volcanoes (MVs) in the Gulf of Cádiz at 1,050–1,250 m water depth. These MVs vary strongly in morphology and size. The data reveal elongated cone-shaped edifices, rimmed depressions, and scarps interpreted as flank failures developed by collapse, faulting, compaction and gravitational processes. MV architecture is characterised by both extrusive and intrusive complexes, comprising stacked edifices (including seabed cones and up to four buried bicones) underlain by chaotic vertical zones and downward-tapering cones suggesting feeder systems. These intrusive structures represent the upper layer of the feeder system linking the fluid mud sources with the constructional edifices. The overall architecture is interpreted to be the result of successive events of mud extrusion and outbuilding alternating with periods of dormancy. Each mud extrusion phase is connected with the development of an edifice, represented by a seabed cone or a buried bicone. In all four MVs, the stacked edifices and the intrusive complexes penetrate Late Miocene–Quaternary units and are rooted in the Gulf of Cádiz wedge emplaced during the late Tortonian. Major phases of mud extrusion and outbuilding took place since the Late Pliocene, even though in the Yuma and Jesús Baraza MVs mud volcanism started in the Late Miocene shortly after the emplacement of the Gulf of Cádiz wedge. This study shows that fluid venting in the eastern sector of the Gulf of Cádiz promoted the outbuilding of large long-lived mud volcanoes active since the Late Miocene, and which have been reactivated repeatedly until recent times.     

Asteroids (65) Cybele, (107) Camilla and (121) Hermione: Infrared spectral diversity among the Cybeles

We find a clear diversity in the 3 μm and 10 μm features of three Cybele asteroids: (107) Camilla, (121) Hermione, and (65) Cybele. (121) Hermione exhibits a “check-like” 3 μm feature, which may be attributed to OH-dominated minerals and (107) Camilla shows a rounded “bowl” like feature closer to that of (65) Cybele, which may be attributed to H₂O-dominated minerals. The 10 μm features of these three asteroids are also different from each other.     

Distribution and thickness of sedimentary facies in the coastal dune, beach and nearshore sedimentary system at Maspalomas, Canary Islands

Numerous studies have shown that most beaches and coastal dune systems of the world are currently eroding but very few have investigated the combined sediment budgets of subaerial and nearshore submarine systems. In the case of the dune field of the Maspalomas Natural Special Reserve (in the south of Gran Canaria), the adjacent Maspalomas and El Inglés beaches and the adjacent submarine platform, the sediment budgets have been severely affected by erosion over the past few decades. The objectives of this study were to investigate the availability of sand within the modern sedimentary system, including the coastal dunes, the beaches and the submerged shelf, but also to assess local sediment sinks. An isopach map generated on the basis of topo-bathymetric data and seismic-reflection profiles revealed that sediment thickness varies from 0–22 m in the study area. Expanses of relatively low sediment thickness were identified in the south-western sector of the coastal dune field along Maspalomas beach, and in the nearshore region to the south of this beach. These localized sediment-deficit areas earmark Maspalomas beach as the most vulnerable shore strip threatened by erosion. The shallow seismic data also revealed that the submarine platform south of Maspalomas represents a marine terrace cut into an ancient alluvial fan, thus documenting an influence of the geomorphological heritage on the present-day morphodynamics. A side-scan sonar mosaic of this nearshore platform enabled the delimitation of areas covered by rock, boulders and gravel, vegetated sand patches and a mobile sand facies, the latter including ripple and megaripple fields. The megaripple field in a valley close to the talus of the marine terrace has been identified as a major sediment sink of the Maspalomas sedimentary system. It is fed by south-westerly storm-wave events. The sediment deficit in the coastal dune field and along Maspalomas beach can therefore only be explained by a currently faster loss of sediment to an offshore sink than can be compensated by the supply of sand from outside the system.     

Heat flow and depth to a possible internal ocean on Triton

The Raz Fossae, a pair of ≈15-km wide trough en echelon interpreted as grabens, can be used to propose an estimation of the depth to the brittle-ductile transition on Triton. This estimation may in turn give an idea of the thermal state of Triton's icy lithosphere when these features formed. Given the young age of its surface, the conclusions obtained could be roughly applicable to the present state of this satellite of Neptune. Considering water or ammonia dihydrate as possible components of the lithosphere and a feasible range of strain rates, it was estimated that surface heat flow is greater than that inferred from radiogenic heating, especially for a lithosphere dominated by water. Also, an internal ocean could lie at a depth of only ∼20 km beneath the surface. The presence over the surface of an insulating layer of ice of low thermal conductivity (e.g., nitrogen) or of regolith would only substantially alter these estimates if the effective surface temperature were considerably higher than the observed value of 38 K.     

A model of characteristic earthquakes and its implications for regional seismicity

Regional seismicity (i.e. that averaged over large enough areas over long enough periods of time) has a size–frequency relationship, the Gutenberg–Richter law, which differs from that found for some seismic faults, the Characteristic Earthquake relationship. But all seismicity comes in the end from active faults, so the question arises of how one seismicity pattern could emerge from the other. The recently introduced Minimalist Model of Vázquez‐Prada et al. of characteristic earthquakes provides a simple representation of the seismicity originating from a single fault. Here, we show that a Characteristic Earthquake relationship together with a fractal distribution of fault lengths can accurately describe the total seismicity produced in a region. The resulting earthquake catalogue accounts for the addition of both all the characteristic and all the non‐characteristic events triggered in the faults. The global accumulated size–frequency relationship strongly depends on the fault length fractal exponent and, for fractal exponents close to 2, correctly describes a Gutenberg–Richter distribution with a b exponent compatible with real seismicity.     

Scientific program construction principles and time allocation scheme for the World Space Observatory—Ultraviolet mission

We present scientific program construction principles and a time allocation scheme developed for the World Space Observatory—Ultraviolet (WSO-UV) mission, which is an international space observatory for observation in UV spectral range 100–300 nm. The WSO-UV consists of a 1.7 m aperture telescope with instrumentation designed to carry out high resolution spectroscopy, long-slit low resolution spectroscopy and direct sky imaging. The WSO-UV Ground Segment is under development by Spain and Russia. They will coordinate the Mission and Science Operations and provide the satellite tracking stations for the project.     

Analysing the positional accuracy of GNSS multi-tracks obtained from VGI sources to generate improved 3D mean axes

ABSTRACT

The sharing of Global Navigation Satellite System (GNSS) tracks on the Internet is increasing enormously. Every day a great number of users capture routes using different devices and share these data. Individually these tracks present a poor positional accuracy because these devices obtain positions with accuracy of about 5-10 metres. In addition, they are usually captured for navigation and not for surveying. However, we can take advantage of the great quantity of tracks of the same linear element in order to obtain a more accurate solution. This study analyses this possibility using a wide set of tracks obtained in known conditions. We emulated those tracks obtained by Volunteered Geographic Information (VGI) users and we compared the mean axis obtained using all tracks with others obtained from a more accurate source. Additionally, we analyse the displacement of other axes obtained by varying several parameters such as the number of tracks and their length or by dividing the route into sections in function of sinuosity, etc. The results have shown an improved 3D mean axis and the viability of the method proposed in this study in order to use axes obtained from several tracks in maps at certain scales.