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In this study, 3-D models of P-wave velocity (Vp) and P- and S-wave ratio (Vp/Vs) of the crust and upper mantle in the Eastern and eastern Southern Alps (northern Italy and southern Austria) were calculated using local earthquake tomography (LET). The dataset includes high-quality arrival-times from well-constrained hypocenters observed by the dense, temporary seismic networks of the AlpArray AASN and SWATH-D. The resolution of the LET was checked by synthetic tests and analysis of the Model Resolution Matrix. The small inter-station spacing (average of ∼15 km within the SWATH-D network) allowed us to image crustal structure at unprecedented resolution across a key part of the Alps. The derived P velocity model revealed a highly heterogeneous crustal structure in the target area. One of the main findings is that the lower crust is thickened, forming a bulge at 30-50 km depth just south of and beneath the Periadriatic Fault and the Tauern Window. This indicates that the lower crust decoupled both from its mantle substratum as well as from its upper crust. The Moho, taken to be the iso-velocity contour of Vp=7.25 km/s, agrees with the Moho depth from previous studies in the European and Adriatic forelands. It is shallower on the Adriatic side than on the European side. This is interpreted to indicate that the European Plate subducted beneath the Adriatic Plate in the Eastern and eastern Southern Alps.

E. coli type 1A topoisomerases (topos), topo I (topA) and topo III (topB) have both relaxation and decatenation activities. B. subtilis and E. coli topA topB null cells can survive owing to DNA amplifications allowing overproduction of topo IV, the main cellular decatenase that can also relax supercoiling. We show that overproducing human topo IB, a relaxase but not a decatenase, can substitute for topo IV in allowing E. coli topA null but not topA topB null cells to survive. Deleting topB exacerbates phenotypes of topA null mutants including hypernegative supercoiling, R-loop formation, and RNase HI-sensitive replication, phenotypes that are not corrected by topo IV overproduction. These phenotypes lead to Ter DNA amplification causing a chromosome segregation defect that is corrected by topo IV overproduction. Furthermore, topA topB null mutants not overproducing topo IV acquire uvrB or uvrC mutations, revealing a nucleotide excision repair (NER)-dependent problem with replication fork progression. Thus, type IA topos maintain the stability of the genome by providing essential relaxase and decatenase activities to prevent and solve topological stress related to R-loops and NER. Moreover, excess R-loop formation is well tolerated in cells that have enough topoisomerase activity to support the subsequent replication-related topological stress.

In this study, we analyzed a large seismological dataset from temporary and permanent networks in the southern and eastern Alps to establish high-precision hypocenters and 1-D VP and VP/VS models. The waveform data of a subset of local earthquakes with magnitudes in the range of 1–4.2 ML were recorded by the dense, temporary SWATH-D network and selected stations of the AlpArray network between September 2017 and the end of 2018. The first arrival times of P and S waves of earthquakes are determined by a semi-automatic procedure. We applied a Markov chain Monte Carlo inversion method to simultaneously calculate robust hypocenters, a 1-D velocity model, and station corrections without prior assumptions, such as initial velocity models or earthquake locations. A further advantage of this method is the derivation of the model parameter uncertainties and noise levels of the data. The precision estimates of the localization procedure is checked by inverting a synthetic travel time dataset from a complex 3-D velocity model and by using the real stations and earthquakes geometry. The location accuracy is further investigated by a quarry blast test. The average uncertainties of the locations of the earthquakes are below 500 m in their epicenter and ∼ 1.7 km in depth. The earthquake distribution reveals seismicity in the upper crust (0–20 km), which is characterized by pronounced clusters along the Alpine frontal thrust, e.g., the Friuli-Venetia (FV) region, the Giudicarie–Lessini (GL) and Schio-Vicenza domains, the Austroalpine nappes, and the Inntal area. Some seismicity also occurs along the Periadriatic Fault. The general pattern of seismicity reflects head-on convergence of the Adriatic indenter with the Alpine orogenic crust. The seismicity in the FV and GL regions is deeper than the modeled frontal thrusts, which we interpret as indication for southward propagation of the southern Alpine deformation front (blind thrusts).

International audience

La generalisation du ravinement et la baisse de la productivite des terres sont quelques-unes des principales contraintes qui assaillent l’utilisation des sols au Sahel. Pour gerer efficacement ces sols, une evaluation des processus hydro-erosifs est necessaire. Ce travail a ainsi pour objectif d’analyser la dynamique hydro-erosive sur un site experimental installe depuis 2004 dans la region de Niamey (Niger). Sur ce site, le dispositif de mesure est compose de huit parcelles de mesures de ruissellement et d’erosion, des stations hydrometriques a l’exutoire des deux bassins versants endoreiques et de plusieurs piquets destines aux suivis morpho-dynamiques des ravines. Apres une decennie d’observation, les ruissellements mesures sur les parcelles se caracterisent par une dynamique saisonniere croissante sur les surfaces encroutees (croutes biologique et d’erosion) et decroissante sur les surfaces cultivees. Le coefficient de ruissellement varie de 5 % sur la surface cultivee a 58 % sur la croute d’erosion. Au cours des 10 annees de mesure, ce coefficient a connu une forte croissance en particulier sur la jachere (+ 80 %) et sur la surface cultivee (+ 300 %), traduisant ainsi la degradation des sols. A l’echelle des bassins versants, l’augmentation du coefficient de ruissellement s’accompagne d’une erosion areolaire qui decape le sol a une vitesse moyenne de 5 mm/an et d’une erosion lineaire active, de l’ordre de 4 m3/an au niveau des ravines suivies. Les transferts sedimentaires qui en resultent agissent sur le fonctionnement morpho-sedimentaire des cours d’eau. Des amenagements antierosifs sont necessaires pour dissiper les processus hydro-erosifs et preserver les services ecosystemiques des sols des bassins. Widespread gullying and the declining land productivity are some of the main constraints plaguing land use in the Sahel. In order to effectively manage these soils, it has become necessary to assess the hydro-erosive processes. The current study, thus, aims at analyzing the hydro-erosion dynamics on an experimental site installed since 2004 in the Niamey region (Niger Republic). On this site, the measurement device is made up of eight runoff and erosion measurement plots, hydrometric stations at the outlet of the two endorheic watersheds and several stakes intended for morpho-dynamic monitoring of the gullies. After a decade of observation, the runoff measured on the plots is characterized by an increasing seasonal dynamic on encrusted surfaces (biological and erosion crusts) and a decreasing one on cultivated surfaces. The runoff coefficient varies from 5% on the cultivated area to 58% on the erosion crust. Over the 10 years of measurement, this coefficient has greatly increased, especially on the fallow (+ 80%) and on cultivated area (+ 300%); this increase consequently reflects soil degradation. At the watershed scale, the increase in the runoff coefficient is accompanied by area erosion (or the erosion of the area out of the basin) which strikes the soil at an average speed of 5 mm/year and active linear erosion measuring 4 m3/year as observed at the monitored (the ongoing investigated) gullies. The resulting sediment transfers act on the morpho-sedimentary functioning of rivers. Anti-erosion facilities are necessary to dissipate the hydro-erosive processes and preserve the ecosystem services of the soil in the basins

Using a regional geological and geophysical dataset, we reconstructed the stratigraphic evolution of the Lower Magdalena Valley Basin and San Jacinto fold belt of northwestern Colombia. Detailed interpretations of reflection seismic data and new geochronology analyses reveal that the basement of the Lower Magdalena Basin is the northward continuation of the basement terranes of the northern Central Cordillera and consists of Permian – Triassic metasedimentary rocks intruded by Upper Cretaceous granitoids. Structural analyses suggest that the NE–SW strike of faults in basement rocks underlying the northeastern Lower Magdalena is inherited from a Jurassic rifting event, while the ESE–WNW—striking faults in the western part originated from a Late Cretaceous to Eocene strike–slip and extensional episode. The Upper Cretaceous to lower Eocene sedimentary rocks preserved in the present–day San Jacinto fold belt were deposited in a submarine, forearc basin formed during the coeval oblique convergence between the Caribbean and South American Plates. A lower to middle Eocene angular unconformity at the top of the upper Paleocene to lower Eocene San Cayetano sequence, the termination of the activity of the Romeral Fault System, and the cessation of arc magmatism are all interpreted to indicate the onset of low–angle orthogonal subduction of the Caribbean Plateau beneath South America between 56 and 43 Ma. Flat subduction of the plateau has continued to the present and would be the main cause of amagmatic post–Eocene deposition and formation of the Lower Magdalena Valley Forearc Basin. Extensional reactivation of inherited, pre–Oligocene basement faults was crucial for the tectonic segmentation of the basin and the formation of its two depocenters (Plato and San Jorge). Late Oligocene to early Miocene fault–controlled subsidence allowed initial infill of the Lower Magdalena, while uplift of Andean terranes made possible the connection of the Lower and Middle Magdalena Valleys, and the formation of the largest Colombian drainage system (Magdalena River system). This drainage system started delivering enormous amounts of sediments in middle Miocene times, as fault–controlled subsidence was gradually replaced by sedimentary loading. Such dramatic increase in sedimentation and the huge volume of sediment being delivered to the trench caused the formation of forearc highs in San Jacinto and of an accretionary prism farther to the west. Our results highlight the fundamental role of plate kinematics, inherited basement structure and sediment flux on the evolution of forearc basins such as the Lower Magdalena and San Jacinto.

We are providing the geophysical data used to develop a gravity validated 3D lithospheric configuration of the Caribbean and north South American plates. The sources of these data are described in Section 4 of this README. Republication of subsets of these data are with permission of the authors or allowed by the licences of the input data. This data repository contains the lithospheric layers of the gravity validated 3D structural and density model of the Caribbean and north South American plates. In this model, the integration of different publicly available geophysical datasets was made, after an interpolation to a homogeneous spatial resolution of 25 km was performed. The data repository also contains the average density of the crystalline crust obtained after forward modelling the gravity anomalies. Additionally, the rotation files of the GPlates reconstructions of the Caribbean Large Igneous Plateau (CLIP) back to 90 Ma are included. This kinematic analysis was based on different reconstructions previously published by other authors. Further information and citations are given on the README file associated to this data repository.

International audience

The Alps formed during the African-European collision. Although the Alps are in the focus of geoscientific research over decades, its crustal and upper-mantle structure are still not completely known. The Periadriatic Lineament, a late orogonic fault active in Oligo-Miocene time, is sinistrally offset by the Guidicarie Fault. It is controversially discussed whether or not a switch in the subduction polarity on either side of the Guidicarie Fault can be observed. Our aim is to reveal the 3-D crustal structure of this section of the Alps at high-resolution by local earthquake tomography (LET). We use data of a temporary seismic network in the Southern and Eastern Alps (SWATH-D) which consists of 150 stations with an inter-station spacing of 15 km. The data from selected AlpArray (AASN) stations was included too. The first results of the inversion for hypocenters, velocity model, and station corrections are in a good agreement with the previous local and regional studies. However, our 1-D velocity model for this particular part of the Alps indicates upper-crustal velocities that are higher than the Alpine average. The seismicity pattern comprises diffuse clusters of earthquakes within the upper 25 km of the crust in the Friuli, Lake-Garda, Trentino and Brenner regions. The centre of the study region shows anomalously low seismic activity. This seismicity pattern indicates where ongoing Adria-Europe convergence is currently accommodated. A preliminary 3-D inversion shows satisfactory resolution and reveals the structure of the crust and uppermost mantle down to 50 km in most of the target area.

Collision with and subduction of an oceanic plateau is a rare and transient process that usually leaves an indirect imprint only. Through a tectonostratigraphic analysis of pre-Oligocene sequences in the San Jacinto fold belt of northern Colombia, we show the Late Cretaceous to Eocene tectonic evolution of northwestern South America upon collision and ongoing subduction with the Caribbean Plate. We linked the deposition of four fore-arc basin sequences to specific collision/subduction stages and related their bounding unconformities to major tectonic episodes. The Upper Cretaceous Cansona sequence was deposited in a marine fore-arc setting in which the Caribbean Plate was being subducted beneath northwestern South America, producing contemporaneous magmatism in the present-day Lower Magdalena Valley basin. Coeval strike-slip faulting by the Romeral wrench fault system accommodated right-lateral displacement due to oblique convergence. In latest Cretaceous times, the Caribbean Plateau collided with South America marking a change to more terrestrially influenced marine environments characteristic of the upper Paleocene to lower Eocene San Cayetano sequence, also deposited in a fore-arc setting with an active volcanic arc. A lower to middle Eocene angular unconformity at the top of the San Cayetano sequence, the termination of the activity of the Romeral Fault System, and the cessation of arc magmatism are interpreted to indicate the onset of low-angle subduction of the thick and buoyant Caribbean Plateau beneath South America, which occurred between 56 and 43Â Ma. Flat subduction of the plateau has continued to the present and would be the main cause of amagmatic post-Eocene deposition.