58 research outputs found
The use of passive seismological imaging in speleogenetic studies: an example from Kanaan Cave, Lebanon
Among many parameters that control the evolution of caves stands the volume of unconsolidated clay sediments generally produced by the alteration of the calcareous rocks. Here we introduce the use of a passive seismological imaging technique to investigate the clay deposits and estimate its total volume in a cave. Applied for the first time for speleogenesis studies, the HVSR (Horizontal / Vertical Spectral Ration) is a geophysical technique that can help better interpret cave geomorphology. We apply seismological spectral techniques (H/V ratio) on ambient noise vibrations to derive the clay volume, as well as its shape. This technique applied on the clay volume reveals some internal details, such as fallen blocks prior to the deposit accumulation and helps to understand deposit evacuation dynamics. The study focuses on the Kanaan Cave, located in Metn District, Lebanon, and reveals new stages related to the cave speleogenesis. This technique could be applied on âparageneticâ caves where clay volume is frequently present in order to constrain the clay volume and reconstruct the buried floor shape of the cave, underneath the clay deposit
Searching for VHE gamma-ray emission associated with IceCube neutrino alerts using FACT, H.E.S.S., MAGIC, and VERITAS
The realtime follow-up of neutrino events is a promising approach to searchfor astrophysical neutrino sources. It has so far provided compelling evidencefor a neutrino point source: the flaring gamma-ray blazar TXS 0506+056 observedin coincidence with the high-energy neutrino IceCube-170922A detected byIceCube. The detection of very-high-energy gamma rays (VHE, ) from this source helped establish the coincidence andconstrained the modeling of the blazar emission at the time of the IceCubeevent. The four major imaging atmospheric Cherenkov telescope arrays (IACTs) -FACT, H.E.S.S., MAGIC, and VERITAS - operate an active follow-up program oftarget-of-opportunity observations of neutrino alerts sent by IceCube. Thisprogram has two main components. One are the observations of known gamma-raysources around which a cluster of candidate neutrino events has been identifiedby IceCube (Gamma-ray Follow-Up, GFU). Second one is the follow-up of singlehigh-energy neutrino candidate events of potential astrophysical origin such asIceCube-170922A. GFU has been recently upgraded by IceCube in collaborationwith the IACT groups. We present here recent results from the IACT follow-upprograms of IceCube neutrino alerts and a description of the upgraded IceCubeGFU system.<br
Update on the Combined Analysis of Muon Measurements from Nine Air Shower Experiments
Over the last two decades, various experiments have measured muon densities in extensive air showers over several orders of magnitude in primary energy. While some experiments observed differences in the muon densities between simulated and experimentally measured air showers, others reported no discrepancies. We will present an update of the meta-analysis of muon measurements from nine air shower experiments, covering shower energies between a few PeV and tens of EeV and muon threshold energies from a few 100 MeV to about 10GeV. In order to compare measurements from different experiments, their energy scale was cross-calibrated and the experimental data has been compared using a universal reference scale based on air shower simulations. Above 10 PeV, we find a muon excess with respect to simulations for all hadronic interaction models, which is increasing with shower energy. For EPOS-LHC and QGSJet-II.04 the significance of the slope of the increase is analyzed in detail under different assumptions of the individual experimental uncertainties
Search for Spatial Correlations of Neutrinos with Ultra-high-energy Cosmic Rays
For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above âŒ50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses have found a significant excess, and previously reported overfluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs
Modernisation de lâinstallation du site RĂ©sif-OGFO - Forage de Montbonnot (IsĂšre)
This image illustrates the modernization work carried out in 2015 on the OGFO site. This site is part of the RAP-RĂ©sif and consists of a set of three accelerometric sensors, one on the surface, one in a borehole at 40m and the third in a borehole at 580m in the bedrock under the alluvial/glacial layer that fills the GrĂ©sivaudan valley. This project to modernize the site's infrastructure was carried out with funding from OSUG's LABEX@2020. In the picture we see the construction company realizing the main protection slab of the installation with the installation of protection nozzles for the drilling heads. This site, operational since the 2000s, operated in total autonomy (solar power supply, 3G transmission), it was also the first metropolitan RĂ©sif site to benefit from 3G transmission (25/11/2009). Unfortunately since the year 2018, the borehole sensors have finally stopped working after more than 18 years in operation. An extraction operation was attempted but the sensors could not be brought to the surface (extraction rope and sensor cables broke). A study is currently underway to determine the depth of the boreholes that can still be exploited and to evaluate the possibilities of extracting the material remaining in the boreholes. We hope to be able to find a solution to fully re-instrument this site, which currently (2020) has only the surface sensor. THe site is a part of RĂ©sif, a research infrastructure dedicated to the observation and understanding of the internal Earth structure and dynamics. It is based on observation networks of high technological level, composed of seismological, geodetic and gravimetric instruments deployed densely throughout the French territory. The data collected allow to study with a high spatio-temporal resolution the ground deformation, the superficial and deep structures, the seismicity at the local and global scale and the natural hazards, especially seismic, on the French territory. RĂ©sif integrates with European (EPOS - European plate observatory system) and worldwide instruments to image the interior of the Earth as a whole and to study numerous natural phenomena.Cette image illustre les travaux de modernisation menĂ©s en 2015 sur le site OGFO. Ce site fait partie du RAP-RĂ©sif et se compose dâun ensemble de trois capteurs accĂ©lĂ©romĂ©triques, un en surface, un dans un forage Ă 40m et le troisiĂšme dans forage Ă 580m dans le bedrock sous la couche alluvionnaire/glaciĂšre qui remplit la vallĂ©e du GrĂ©sivaudan. Ce projet de modernisation de lâinfrastructure du site a Ă©tĂ© rĂ©alisĂ© grĂące Ă un financement du LABEX@2020 de lâOSUG. Sur lâimage nous voyons lâentreprise de BTP rĂ©aliser la dalle principale de protection de lâinstallation avec la mise en place de buse de protection des tĂȘtes de forage. Ce site opĂ©rationnel depuis les annĂ©es 2000 fonctionnait en totale autonomie (alimentation solaire, transmission 3G), ce fut dâailleurs le premier site RĂ©sif mĂ©tropolitain Ă bĂ©nĂ©ficier dâune transmission 3G (25/11/2009). Malheureusement depuis lâannĂ©e 2018, les capteurs en forage ont finalement cessĂ©s de fonctionner aprĂšs plus de 18 annĂ©es en opĂ©ration. Une opĂ©ration dâextraction a Ă©tĂ© tentĂ©e mais les capteurs nâont pas pu ĂȘtre remontĂ©s Ă la surface (cordage dâextraction et cĂąbles capteurs se sont rompus). Une Ă©tude est actuellement en cours pour dĂ©terminer la profondeur encore exploitable des forages et Ă©valuer les possibilitĂ©s dâextraction du matĂ©riel restant dans les forages. Nous espĂ©rons pouvoir trouver une solution permettant de rĂ©-instrumenter pleinement ce site, qui actuellement (2020) ne comporte plus que le capteur de surface. Le site fait partie de RĂ©sif, une infrastructure de recherche dĂ©diĂ©e Ă lâobservation et la comprĂ©hension de la structure et de la dynamique Terre interne. Il se base sur des rĂ©seaux dâobservation de haut niveau technologique, composĂ©s dâinstruments sismologiques, gĂ©odĂ©siques et gravimĂ©triques dĂ©ployĂ©s de maniĂšre dense sur tout le territoire français. Les donnĂ©es recueillies permettent dâĂ©tudier avec une haute rĂ©solution spatio-temporelle la dĂ©formation du sol, les structures superficielles et profondes, la sismicitĂ© Ă lâĂ©chelle locale et globale et les alĂ©as naturels, et plus particuliĂšrement sismiques, sur le territoire français. RĂ©sif sâintĂšgre aux dispositifs europĂ©ens (EPOS - European plate observatory system) et mondiaux dâinstruments permettant dâimager lâintĂ©rieur de la Terre dans sa globalitĂ© et dâĂ©tudier de nombreux phĂ©nomĂšnes naturels
Le monitoring Ă©nergĂ©tique pour les systĂšmes dâacquisition en milieu naturel difficile
Acquisitions systems are regularly used in difficult natural environment. To complete the scientific acquisition, it is customary to memorise the battery voltage in order to follow the battery state on a daily basis. It is a minimal energetic monitoring, but is it sufficient ? Are these measures sufficient to detect and understand an anomaly of the system ? Would it not be interesting to measure the battery voltage and the charge current of these batteries or the consumption current of systems more often ? To answer this question, between 2011 and 2014, an energetic monitoring has been implemented on instrumented sites of high and medium-sized mountains within the framework of several projects of landscape monitoring of ISTerre laboratory.Des systĂšmes dâacquisition autonomes sont rĂ©guliĂšrement utilisĂ©s en milieu naturel difficile. En complĂ©ment Ă lâacquisition scientifique, il est courant dâenregistrer la tension de la batterie pour suivre quotidiennement lâĂ©tat de celle-ci. Il sâagit dâun monitoring Ă©nergĂ©tique minimal, mais est-ce suffisant ? Est-ce que ces mesures quotidiennes suffisent Ă dĂ©tecter et Ă comprendre une quelconque anomalie du systĂšme ? Ne serait-il pas intĂ©ressant de mesurer plus frĂ©quemment les tensions et Ă©galement les courants de charge des batteries ou de consommation des systĂšmes ? Pour rĂ©pondre Ă cette question, entre 2011 et 2014, un monitoring Ă©nergĂ©tique a Ă©tĂ© mis en place sur des sites de haute et moyenne montagne dans le cadre de divers projets de suivi de mouvements de terrain du laboratoire ISTerre.Darras Lionel, MARISCAL Armand. Le monitoring Ă©nergĂ©tique pour les systĂšmes dâacquisition en milieu naturel difficile. In: Collection EDYTEM. Cahiers de gĂ©ographie, numĂ©ro 19, 2017. Monitoring en milieux naturels. Retours dâexpĂ©riences en terrains difficiles. pp. 19-24
LE MONITORING ĂNERGETIQUE POUR LES SYSTĂMES D'ACQUISITION EN MILIEU NATUREL DIFFICILE
National audienceAcquisitions systems are regularly used in difficult natural environment. To complete the scientific acquisition, it is customary to memorise the battery voltage in order to follow the battery state on a daily basis. It is a minimal energetic monitoring, but is it sufficient? Are these measures sufficient to detect and understand an anomaly of the system? Would it not be interesting to measure the battery voltage and the charge current of these batteries or the consumption current of systems more often? To answer this question, between 2011 and 2014, an energetic monitoring has been implemented on instrumented sites of high and medium-sized mountains within the framework of several projects of landscape monitoring of ISTerre laboratory.Des systÚmes d'acquisition autonomes sont réguliÚrement utilisés en milieu naturel difficile. En complément à l'acquisition scientifique, il est courant d'enregistrer la tension de la batterie pour suivre quotidiennement l'état de celle-ci. Il s'agit d'un monitoring énergétique minimal, mais est-ce suffisant ? Est-ce que ces mesures quotidiennes suffisent à détecter et à com-prendre une quelconque anomalie du systÚme ? Ne serait-il pas intéressant de mesurer plus fréquemment les tensions et éga-lement les courants de charge des batteries ou de consommation des systÚmes ? Pour répondre à cette question, entre 2011 et 2014, un monitoring énergétique a été mis en place sur des sites de haute et moyenne montagne dans le cadre de divers projets de suivi de mouvements de terrain du laboratoire ISTerre
Utilisation d'une pile à combustible au méthanol en complément de l'énergie solaire pour les systÚmes d'acquisition en milieu naturel
En milieu isolĂ©, des stations d'acquisition autonomes sont rĂ©guliĂšrement utilisĂ©es Ă des fins scientifiques. Elles sont gĂ©nĂ©ralement alimentĂ©es par des batteries au plomb couplĂ©es Ă des panneaux solaires. La localisation de ces stations est souvent imposĂ©e par le type de mesures souhaitĂ©es. Il arrive que l'Ă©nergie rĂ©cupĂ©rĂ©e par les panneaux solaires soit insuffisante. Cette alimentation solaire pourrait ĂȘtre complĂ©tĂ©e par une autre Ă©nergie naturelle comme l'Ă©olien mais ce n'est pas toujours possible. Il est intĂ©ressant d'Ă©tudier une autre solution. Une pile Ă combustible au mĂ©thanol est souvent utilisĂ©e sur les bateaux et les camping-cars en complĂ©ment de panneaux solaires mais une telle solution est-elle concevable et suffisamment fiable en sites isolĂ© avec un fonctionnement autonome ? Pendant 3 annĂ©es (de 2011 Ă 2014), sur 3 sites de suivi de glissement de terrain, une pile Ă combustible au mĂ©thanol a Ă©tĂ© utilisĂ©e en complĂ©ment de l'Ă©nergie solaire. Les donnĂ©es Ă©nergĂ©tiques issues de la pile ainsi que les tempĂ©ratures ont Ă©tĂ© acquises en continu. A partir du traitement de ces donnĂ©es, cet article prĂ©sente le retour de ces expĂ©riences avec les Ă©vĂ©nements observĂ©s, les difficultĂ©s rencontrĂ©es ainsi que les solutions trouvĂ©es
Utilisation d'une pile à combustible au méthanol en complément de l'énergie solaire pour les systÚmes d'acquisition en milieu naturel
En milieu isolĂ©, des stations d'acquisition autonomes sont rĂ©guliĂšrement utilisĂ©es Ă des fins scientifiques. Elles sont gĂ©nĂ©ralement alimentĂ©es par des batteries au plomb couplĂ©es Ă des panneaux solaires. La localisation de ces stations est souvent imposĂ©e par le type de mesures souhaitĂ©es. Il arrive que l'Ă©nergie rĂ©cupĂ©rĂ©e par les panneaux solaires soit insuffisante. Cette alimentation solaire pourrait ĂȘtre complĂ©tĂ©e par une autre Ă©nergie naturelle comme l'Ă©olien mais ce n'est pas toujours possible. Il est intĂ©ressant d'Ă©tudier une autre solution. Une pile Ă combustible au mĂ©thanol est souvent utilisĂ©e sur les bateaux et les camping-cars en complĂ©ment de panneaux solaires mais une telle solution est-elle concevable et suffisamment fiable en sites isolĂ© avec un fonctionnement autonome ? Pendant 3 annĂ©es (de 2011 Ă 2014), sur 3 sites de suivi de glissement de terrain, une pile Ă combustible au mĂ©thanol a Ă©tĂ© utilisĂ©e en complĂ©ment de l'Ă©nergie solaire. Les donnĂ©es Ă©nergĂ©tiques issues de la pile ainsi que les tempĂ©ratures ont Ă©tĂ© acquises en continu. A partir du traitement de ces donnĂ©es, cet article prĂ©sente le retour de ces expĂ©riences avec les Ă©vĂ©nements observĂ©s, les difficultĂ©s rencontrĂ©es ainsi que les solutions trouvĂ©es
Can we trust high-frequency content in strong-motion database signals ? Impact of housing, coupling, and installation depth of seismic sensors
Seismic hazard studies provide indicators of seismic motion that are expressed for "free-field," that is, representative of the ground motion exactly at the free surface, without disturbances due to interactions between soil and buildings or other structures. Most of these studies are based on ground-motion prediction equations, which are, themselves, formulated to predict free-field motion, as they are derived from similarly free data. However, is this really the case? In this study, we use several examples to illustrate how small structures hosting permanent strong-motion stations (often anchored on small concrete slabs) generate soilstructure interaction effects that can amplify the high-frequency part of the earthquake signal (10 Hz) by up to a factor of 2-3 for stations on soils. We also show that the installation depth of a station, even if very shallow (i.e., a few meters), can change the recorded response, mainly by deamplifying the signal in high frequencies (> 10 Hz) by a factor up to 0.3. Such effects imply that there are actual differences between recorded and true free-field signals. Depending on the housing conditions, these effects can have significant impact on response spectra at high frequencies, and on measurements of the kappa parameter. It is, thus, becoming clear that such effects should be taken into account in studies involving high-frequency seismic motion. To do so, scientists need a detailed description of the conditions of installation and housing of seismological and accelerometric stations, which often lacks from the metadata distributed through the various, commonly used web services. Increasing such information and facilitating the access to it would allow the identification of stations that are problematic and of those that are truly close to free-field recording conditions. In a subsequent step, it would be important to quantify the modification curve of the response of stations that experience such effects
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