Multiscale characterisation of chimneys/pipes: Fluid escape structures within sedimentary basins

Evaluation of seismic reflection data has identified the presence of fluid escape structures cross-cutting overburden stratigraphy within sedimentary basins globally. Seismically-imaged chimneys/pipes are considered to be possible pathways for fluid flow, which may hydraulically connect deeper strata to the seabed. The properties of fluid migration pathways through the overburden must be constrained to enable secure, long-term subsurface carbon dioxide (CO2) storage. We have investigated a site of natural active fluid escape in the North Sea, the Scanner pockmark complex, to determine the physical characteristics of focused fluid conduits, and how they control fluid flow. Here we show that a multi-scale, multi-disciplinary experimental approach is required for complete characterisation of fluid escape structures. Geophysical techniques are necessary to resolve fracture geometry and subsurface structure (e.g., multi-frequency seismics) and physical parameters of sediments (e.g., controlled source electromagnetics) across a wide range of length scales (m to km). At smaller (mm to cm) scales, sediment cores were sampled directly and their physical and chemical properties assessed using laboratory-based methods. Numerical modelling approaches bridge the resolution gap, though their validity is dependent on calibration and constraint from field and laboratory experimental data. Further, time-lapse seismic and acoustic methods capable of resolving temporal changes are key for determining fluid flux. Future optimisation of experiment resource use may be facilitated by the installation of permanent seabed infrastructure, and replacement of manual data processing with automated workflows. This study can be used to inform measurement, monitoring and verification workflows that will assist policymaking, regulation, and best practice for CO2 subsurface storage operations

Large-scale mass wasting in the western Indian Ocean constrains onset of East African rifting

Faulting and earthquakes occur extensively along the flanks of the East African Rift System, including an offshore branch in the western Indian Ocean, resulting in remobilization of sediment in the form of landslides. To date, constraints on the occurrence of submarine landslides at margin scale are lacking, leaving unanswered a link between rifting and slope instability. Here, we show the first overview of landslide deposits in the post-Eocene stratigraphy of the Tanzania margin and we present the discovery of one of the biggest landslides on Earth: the Mafia mega-slide. The emplacement of multiple landslides, including the Mafia mega-slide, during the early-mid Miocene is coeval with cratonic rifting in Tanzania, indicating that plateau uplift and rifting in East Africa triggered large and potentially tsunamigenic landslides likely through earthquake activity and enhanced sediment supply. This study is a first step to evaluate the risk associated with submarine landslides in the region

A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS4_4 measured from stellar occultations

This work aims at constraining the size, shape, and geometric albedo of the dwarf planet candidate 2002 MS4 through the analysis of nine stellar occultation events. Using multichord detection, we also studied the object's topography by analyzing the obtained limb and the residuals between observed chords and the best-fitted ellipse. We predicted and organized the observational campaigns of nine stellar occultations by 2002 MS4 between 2019 and 2022, resulting in two single-chord events, four double-chord detections, and three events with three to up to sixty-one positive chords. Using 13 selected chords from the 8 August 2020 event, we determined the global elliptical limb of 2002 MS4. The best-fitted ellipse, combined with the object's rotational information from the literature, constrains the object's size, shape, and albedo. Additionally, we developed a new method to characterize topography features on the object's limb. The global limb has a semi-major axis of 412 $\pm$ 10 km, a semi-minor axis of 385 $\pm$ 17 km, and the position angle of the minor axis is 121 $^\circ$ $\pm$ 16$^\circ$. From this instantaneous limb, we obtained 2002 MS4's geometric albedo and the projected area-equivalent diameter. Significant deviations from the fitted ellipse in the northernmost limb are detected from multiple sites highlighting three distinct topographic features: one 11 km depth depression followed by a 25$^{+4}_{-5}$ km height elevation next to a crater-like depression with an extension of 322 $\pm$ 39 km and 45.1 $\pm$ 1.5 km deep. Our results present an object that is $\approx$138 km smaller in diameter than derived from thermal data, possibly indicating the presence of a so-far unknown satellite. However, within the error bars, the geometric albedo in the V-band agrees with the results published in the literature, even with the radiometric-derived albedo

Pluto's lower atmosphere and pressure evolution from ground-based stellar occultations, 1988-2016

Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft. Aims. The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015. Methods. Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 μbar to 10 nbar). Results. (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4–7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere

Incident pressure measurement in air blast using wireless sensors

International audienceThis paper presents the wireless measurement of the incident pressure inside the fire ball of an air blast shock wave. The wireless sensor setup and the experimental configuration are described. The wired and wireless experimental results are compared and analyszd. To our best knowledge, it is the first time that a wireless device takes place inside the fireball of an explosion for the measurement of the incident pressure in such harsh environment

Transient response of miniaturized piezoresistive sensors for side-on pressure shockwave

International audienceTransient response of a miniaturized silicon piezoresistive sensor is simulated here for the first time when a pressure shock wave propagates along the sensor's surface, or equivalently, for side-on pressure shock wave in air. These mechanical simulations show that it is possible to reduce the sensor's reaction time by a factor about 10 from carefully adjusting the membrane dimensions

Dynamic Mechanical Simulation of Miniature Silicon Membrane during Air Blast for Pressure Measurement †

International audienceThe development of new ultra-fast sensors for pressure air blast monitoring requires taking into account the very short rise time of pressure occurring during explosion. Simulations show here that the dynamic mechanical behavior of membrane-based sensors depends significantly on this rise time when the fundamental mechanical resonant frequency of the membrane is higher than 10 MHz

Design, Fabrication and Characterization of a Novel Piezoresistive Pressure Sensor for Blast Waves Monitoring

International audienceIn several side-on configurations, the monitoring of blast wave requires sensor with very low response time (< 1 µs). The sensing area of commercial sensors are too high to fulfill this specification. New transducers are focused on miniature membrane (diameter < 100 µm), but with optical transduction which suffers from low integration capabilities for multiple transducers. In this communication, a miniature piezoresistive pressure transducer based on silicon membrane and silicon gauges is designed and fabricated. Shock tube characterizations of the sensor have shown promising dynamic behavior, with a rise time of 30 ns and a response time lower than 1 µs thanks to the membrane fundamental resonant frequency of 20 MHz. Undesirable mechanical effects leading to the response drift after 1 µs are discussed and interpreted as the result of the holder deformation

Design, Fabrication and Characterization of a Novel Piezoresistive Pressure Sensor for Blast Waves Monitoring

International audienceIn several side-on configurations, the monitoring of blast wave requires sensor with very low response time (< 1 µs). The sensing area of commercial sensors are too high to fulfill this specification. New transducers are focused on miniature membrane (diameter < 100 µm), but with optical transduction which suffers from low integration capabilities for multiple transducers. In this communication, a miniature piezoresistive pressure transducer based on silicon membrane and silicon gauges is designed and fabricated. Shock tube characterizations of the sensor have shown promising dynamic behavior, with a rise time of 30 ns and a response time lower than 1 µs thanks to the membrane fundamental resonant frequency of 20 MHz. Undesirable mechanical effects leading to the response drift after 1 µs are discussed and interpreted as the result of the holder deformation

Design, Fabrication and Characterization of a Novel Piezoresistive Pressure Sensor for Blast Waves Monitoring

International audienceIn several side-on configurations, the monitoring of blast wave requires sensor with very low response time (< 1 µs). The sensing area of commercial sensors are too high to fulfill this specification. New transducers are focused on miniature membrane (diameter < 100 µm), but with optical transduction which suffers from low integration capabilities for multiple transducers. In this communication, a miniature piezoresistive pressure transducer based on silicon membrane and silicon gauges is designed and fabricated. Shock tube characterizations of the sensor have shown promising dynamic behavior, with a rise time of 30 ns and a response time lower than 1 µs thanks to the membrane fundamental resonant frequency of 20 MHz. Undesirable mechanical effects leading to the response drift after 1 µs are discussed and interpreted as the result of the holder deformation