Estimating crustal thickness in Belgium using Moho-reflected waves

We present the results of the determination of the Moho depth underneath Belgium using reflected P and S-waves (PmP- and SmS-waves). Previous studies suggest differences of the Moho depth in the different parts of the region. In the lower Rhine Embayment in the northeast, the Moho depth is considered to be shallow (25 km). In the Brabant Massif in the west the crustal thickness is supposed to be larger (up to 38 km). The southeast of Belgium is characterised by the Variscan allochtone, where the Moho depth is around 30 km. In this study, PmP/SmS-waves of ~150 well-located local earthquakes and explosions in the North Sea registered by 37 stations of the permanent seismic network and by mobile stations installed by the Royal Observatory of Belgium were used. More than 750 PmP/SmS-waves were modelled to determine the Moho depth with the following procedure. PmP-arrivals are picked and the locations of the PmP-bounce points are determined and mapped. Over this map a 20 x 20 km grid is placed and for each grid cell an iteration is performed to determine the Moho depth. The thickness of the crust varies between 25 and 36 km and is slightly shallower in the northeast of Belgium (28–30–32 km) than to the southwest (33-34 km). Underneath the Brabant massif however Moho depths of 31 km are found, which is in contradiction with previous results

Subradiant states of quantum bits coupled to a one-dimensional waveguide

The properties of coupled emitters can differ dramatically from those of their individual constituents. Canonical examples include sub- and super-radiance, wherein the decay rate of a collective excitation is reduced or enhanced due to correlated interactions with the environment. Here, we systematically study the properties of collective excitations for regularly spaced arrays of quantum emitters coupled to a one-dimensional (1D) waveguide. We find that, for low excitation numbers, the modal properties are well-characterized by spin waves with a definite wavevector. Moreover, the decay rate of the most subradiant modes obeys a universal scaling with a cubic suppression in the number of emitters. Multi-excitation subradiant eigenstates can be built from fermionic combinations of single excitation eigenstates; such "fermionization" results in multiple excitations that spatially repel one another. We put forward a method to efficiently create and measure such subradiant states, which can be realized with superconducting qubits. These measurement protocols probe both real-space correlations (using on-site dispersive readout) and temporal correlations in the emitted field (using photon correlation techniques).Comment: 21 pages, 9 figure

Integrated geophysical and petrological study of fluid expulsion features along the Moroccan Atlantic margin

In this study we integrate a geophysical – carbonate petrological data set, collected during the TTR-14 cruise (summer 2004) along the Moroccan Atlantic margin in Gulf of Cadiz (Southern area, 400m – 1000m and El Arraiche mud volcano field). This allows us to investigate the deeper structure and its control on fluid venting, to address the nature of seafloor topographical features, fluid geochemistry and venting processes. The deeper structure of the Southern area is dominated by two NW trending anticlinal acoustic basement ridges. Their northern flank and top is cut by major present-day active, normal faults, along which four dome structures and the Meknes mud volcano (mv), are concentrated. These ridges correspond to rotated, faultbounded blocks breaking up the top of the accretionary wedge. This indicates the southward prolongation of extensional tectonics and its structural control on mud volcanism, south of the El Arraiche field, which is also evidenced by the typical sandstone mud breccias recovered at the Meknes mv. Carbonate cemented mud breccia from the Meknes (type M) and the Kidd (type K) mv, and cemented sediment portions from Pen Duick Escarpment (type PD), all possess similar carbon isotopic (-19 to -29%¸ VPDB) and carbonate geochemical signatures, indicating seepage of a geochemical similar thermogenic hydrocarbon-bearing fluid source. Slightly elevated d18O values of HMC-cemented type M crusts suggest the former presence and dissociation of gas hydrates. The brecciated fabric, intraclasts and aragonite cement morphology, typical of type K crusts testify of a relative vigorous fluid ascent. HMC-calcian dolomite cemented PD crusts were likely formed under conditions of slower fluid ascent. Their actual near-seafloor occurrence, well above the base of the SRZ, is hypothesized to relate to erosion and migration of the SRZ by variations in upward hydrocarbon fluxes

Local seismic tomography in Belgium: implications for the geological structure

We present the results of a local seismic tomography in Belgium using well-located local earthquakes registered by 37 stations of the permanent seismic network and by mobile stations installed by the Royal Observatory of Belgium. Previous studies did not offer a lot of information on the middle and lower crust. The seismic profiles shot in the region (Belcorp, Decorp, Ecors, . . . ) all show an unreflective middle and lower crust. The gravimetric and magnetic data show the presence of a sharp transition between the Brabant Massive and the Ardennes allochtone, furthermore, a broad positive gravimetric anomaly, is interpreted as a Moho uplift underneath the Campine region. Our results confirm the sharp transition between the Brabant Massif (higher than expected velocities) and the Ardennes allochtone (lower than expected velocities). At 27 km of depth lower crust – upper mantle velocities (7.50 km/s) are found underneath the Campine region and the Eifelplume region, confirming the Moho uplifts to 28 km underneath these regions. At 13 km similar velocities (7.50 km/s) are seen underneath the Eifelplume, they correspond to a lower crust-upper mantle that trusted in the crust during the Variscan orogeny

Submeter mapping of methane seeps by ROV observations and measurements at the Hikurangi Margin, New Zeeland

During R.V. Sonne cruise SO191-3, part of the "New (Zealand Cold) Vents" expedition, RCMG deployed their CHEROKEE ROV "Genesis" on the Hikurangi Margin. This accretionary margin, on the east coast of New Zealand, is related to the subduction of the Pacific Plate under the Australian Plate. Several cold seep locations as well as an extensive BSR, indicating the presence of gas hydrates, have been found at this margin. The aim of the ROV-work were to precisely localize active methane seeps, to conduct detailed visual observations of the seep structures and activity, and to perform measurements of physical properties and collect samples at and around the seep locations. The ROV allowed first ever visual observations of bubble-releasing seeps at the Hikurangi Margin. Seeps were observed at Faure Site and LM-3 in the Rock Garden area, at a flat to moderately undulating sea floor where soft sediments alternate with carbonate platforms. Bubble-releasing activity was very variable in time, with periods of almost non-activity (5 bubbles/second) alternating with periods of violent outbursts (190 bubbles/second). Bubbles sizes ranged from less than 5 mm to more than 20 mm. At Faure Site, bubble release was monitored over a period of 20 minutes, resulting in the observation of 6 outbursts, each lasting 1 minute at a 3 minute interval. These violent outbursts were accompanied by the displacement and resuspension of sediment grains and the formation of small depressions showing what is possibly an initial stage of pockmark formation. At the LM-3 site only some small bubble seeps were observed near a large carbonate platform covered by Bathymodiolus mussels, Calyptogena shells and tube worms. Sediment-temperature measurements, in both areas, were largely comparable with the bottom-water temperature except at LM-3, at a site densely populated by polychaetes, where anomalous low sediment-temperature was measured. Overall, both seep areas are very confined in space and bottom-water sampling revealed that the released methane has a microbial signature

Boolean delay equations on networks: An application to economic damage propagation

We introduce economic models based on Boolean Delay Equations: this formalism makes easier to take into account the complexity of the interactions between firms and is particularly appropriate for studying the propagation of an initial damage due to a catastrophe. Here we concentrate on simple cases, which allow to understand the effects of multiple concurrent production paths as well as the presence of stochasticity in the path time lengths or in the network structure. In absence of flexibility, the shortening of production of a single firm in an isolated network with multiple connections usually ends up by attaining a finite fraction of the firms or the whole economy, whereas the interactions with the outside allow a partial recovering of the activity, giving rise to periodic solutions with waves of damage which propagate across the structure. The damage propagation speed is strongly dependent upon the topology. The existence of multiple concurrent production paths does not necessarily imply a slowing down of the propagation, which can be as fast as the shortest path.Comment: Latex, 52 pages with 22 eps figure

COCARDE: A research platform for a new look to ancient mounds

Carbonate mounds are important contributors of life in different settings, from warm-water to cold-water environments, and throughout geological history. Research on modern carbonate mounds over the last years made a major contribution to our overall understanding of these particular sedimentary systems. By looking to the modern carbonate mound community, some fundamental questions could be addressed, until now not yet explored in fossil mound settings.The international network COCARDE (Cold-Water Carbonate Reservoir Systems in Deep Environment) is a platform for exploring new insights in cold- and warm-water carbonate mound research of recent and ancient mound systems (http://www.cocarde.eu). One aim of the COCARDE network is to bring scientific communities together, to study recent carbonate mounds in midslope environments in the present ocean, and to investigate fossil mounds spanning the whole Phanerozoic time.Scientific challenges on modern and ancient carbonate mound systems got already well defined during two dedicated workshops of the COCARDE network: 1) the ESF Magellan COCARDEWorkshop in Fribourg, Switzerland, January 21-24, 2009, and 2) the ESF MiCROSYSTEMS – FWO COCARDE Flanders – ESF CHECREEF Workshop and Field Seminar, Oviedo, Spain, September 16–20, 2009.The wide spectrum of disciplines in geosciences and biology are summarized in the following five topics for the carbonate mound research: i) Palaeoenvironment; ii) The Microbial Filter; iii) Petrophysical Characterization; iv) Connectivity and Compartmentalization – the Fluid System; v) Advancing our Insight in Phanerozoic Reef Systems– the Slope Niche. One of the most important outcomes of these meetings was the identification of the need for combined research efforts on fossil and modern carbonate settings to provide the baseline reference standard for a better understanding of these exceptional systems and their potential as hydrocarbon reservoirs