Institut De Physique Research Articles

GEOSCOPE Network: 40 Yr of Global Broadband Seismic Data

Abstract The GEOSCOPE observatory (Institut de physique du globe de Paris [IPGP] and École et Observatoire des Sciences de la Terre de Strasbourg, 1982) provides more than four decades of high-quality continuous broadband data to the scientific community. Started in 1982 with only two stations, the network has grown over the years thanks to numerous international partnerships. At present, 34 stations operate in 18 countries across all continents and on islands throughout the oceans, filling important gaps in global Earth coverage. Most of the first installed stations are still running today, allowing for long-term observations, and new sites are being prospected to further improve global coverage. Over the years, GEOSCOPE has contributed to defining today’s global seismology standards (data format, data quality level, instrumentation requirements), being the French contribution to the international effort for global seismic observations. The stations are instrumented with the best quality seismometers (from the very first STS-1 in the early 80s to the last STS-6A and Trillium T360 today) and digitizers (Q330HR and Centaur) to record with high fidelity the ground motions generated by all types of seismic sources. Real-time data are sent to the tsunami warning centers and both validated and real-time data are available at the IPGP, Epos-France and Earthscope data centers. The quality of GEOSCOPE data and metadata is ensured by daily and yearly validation that enables issue detection and mitigation. GEOSCOPE, in collaboration with the other global networks, has played and continues to play a crucial role in the study of Earth’s structure and global dynamics and the characterization of all types of seismic sources.

The 4th Southeast Asian Conference on Geophysics (SEACG) 2022: Great Challenges and Opportunities of Geophysics Today and Future

The Southeast Asian Conference on Geophysics (SEACG) is a biannual event held by the Geophysical Engineering Department, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung (ITB), Indonesia. The SEACG has been successfully conducted since 2016, and several selected papers have been published in the IOP Conference Series: Earth and Environmental Science. The first (2016) and second (2018) conferences were held offline in Bali, Indonesia, while the third conference (2020) was held virtually due to the Covid19 pandemic. Along with the end of the Covid19 pandemic, the current event (2022) is being run as a hybrid conference (physical and virtual), live from Bandung, Indonesia.The conference theme of the SEACG 2022 is “Great Challenges and Opportunities of Geophysics Today and Future.” The program lasts two days, from August 9, 2022, to August 10, 2022, and is sponsored by the Institute of Research and Community Services, ITB. There are 11 invited international speakers (30-minute duration) and 88 contributed speakers (20 min duration) who presented their ideas. With five panel rooms, 35 contributed speakers delivered offline presentations and 53 virtually via Zoom. The speakers, both invited and contributed, presented and introduced new geophysical insights and techniques.The panel discussion featured intriguing topics and invited speakers from various institutions, such as Institut Teknologi Bandung – Indonesia (Dr.rer.nat. R. Mohammad Rachmat Sule, Dr. Tedi Yudistira, Prof. Sri Widiyantoro, Prof. Wahyu Srigutomo, and Prof. Wawan Gunawan Abdul Kadir), CSIRO – Australia (Dr. Erdinc Saygin), Australian National University – Australia (Prof. Phil Cummins), University of Tokyo – Japan (Prof. Takeshi Tsuji), JGI, Inc. – Japan (Moeto Fujisawa, M.Sc.), Ocean University of China – China (Dr. Zhijun Du), and Institut de Physique du Globe de Paris – France (Dr. Jean-Philippe Metaxian). The event was opened by Dr. Fatkhan (the Head of the Geophysical Engineering Master and Doctorate Degree Program, ITB) and closed by Dr. Warsa (the Head of the Geophysical Engineering Bachelor Degree Program, ITB).The SEACG 2022 provided a platform for academics, professionals, and students to discuss and promote scientific results related to recent advancements in geophysical methods and related sciences. The conference covered various session topics, such as Fault and Deformation Study, Passive Seismic, Environmental Geophysics, Geophysical Approaches in Hydrocarbon, Geophysical Approaches in Geothermal, Advance Geophysics, Vulcanology, Tomography, Seismic Hazards, Geomagnetic, and Seismology.We would thank the organization’s team members, the reviewers, and the faculty staff. They have worked very hard to make this event possible. We wish all attendees of SEACG 2022 have an exciting experience and enjoy the moment in this scientific forum.List of Organizing Committee, Documentation are available in this pdf.

Building a Natural-Hazard-Resilient High-Quality Seismic Network: How WI Network Sustained Hurricanes Maria and Irma

Abstract Between 2008 and 2014, the Institut de Physique du Globe de Paris (IPGP) and the University of the West Indies, Seismic Research Centre (UWI-SRC) designed and built a regional seismic network across the Lesser Antilles. One of the goals of the network is to provide real-time seismic data to the tsunami warning centers in the framework of the Intergovernmental Coordination Group working toward the establishment of a tsunami and other coastal hazards early warning system (ICG-CARIBE-EWS) for the Caribbean and adjacent regions (McNamara et al., 2016). In an area prone to hurricanes, earthquakes, tsunamis, and volcanic eruptions, we chose different techniques and technologies to ensure that our cooperated network could survive and keep providing data in case of major natural hazards. The Nanometrics very small aperture terminal (VSAT) technology is at the heart of the system. It allows for duplicated data collection at the three observatories (Trinidad, Martinique, and Guadeloupe; Anglade et al., 2015). In 2017, the network design and implementation were put to the test with Saffir–Simpson category 5 hurricanes Irma and Maria that went, respectively, through the north and central portion of the Lesser Antilles, mainly impacting the sites operated by volcanological and seismological observatories of IPGP in Martinique (Observatoire Volcanologique et Sismologique de Martinique [OVSM]) and in Guadeloupe (Observatoire Volcanologique et Sismologique de Guadeloupe [OVSG]). Our concepts proved to be valid with a major data shortage of less than 12 hr and only two stations having sustained heavy damage. In this article, we review the strengths and weaknesses of the initial design and discuss various steps that can be taken to enhance the ability of our cooperated network to provide timely real-time seismic data to tsunami warning centers under any circumstances.

GIUSEPPE FOLGHERAITER: THE ITALIAN PIONEER OF ARCHAEOMAGNETISM

ABSTRACT The history of the science of archaeomagnetism conventionally starts in 1600 with the publication of William Gilbert's monumental work De Magnete, but the theoretical basis of this scientific field has to be positioned at the end of the nineteenth century. In Italy at that time, a number of scientists such as Giambattista Beccaria, Macedonio Melloni and Silvestro Gherardi, were working on magnetic field characteristics and their work variously contributed to the early study of Earth and rock magnetism. A major contribution to the birth of paleomagnetism as a science, and archaeomagnetism as a dating technique, was produced by Giuseppe Folgheraiter (1856–1913) by means of his research on the magnetic properties of volcanic deposits and his attempts to date ancient pottery of different epochs based on the magnetic properties of clay materials. Initially, Folgheraiter studied the rock magnetism of the volcanic rocks of Latium where he replicated the findings of Macedonio Melloni, who had studied Vesuvius lavas, and found that volcanic rocks are affected by a permanent magnetization. In addition, Folgheraiter verified the discovery by Filippo Keller of the Punti distinti. Folgheraiter also made the innovative proposal that lightning strongly influences the magnetic properties of lavas resulting in magnetic disorder. The main analytical effort of Folgheraiter at the end of the nineteenth century was dedicated to the study of the variations of magnetic inclination in different epochs as registered in archaeological pottery. He produced archaeomagnetic sets of analyses on 191 samples grouped into 10 epochs, that resulted in the first reconstruction of a geomagnetic secular variation curve (SVC). Even if nowadays the Folgheraiter analytical results have been replaced by more precise measurements, a great portion of the development of modern archaeomagnetic techniques originated with Folgheraiter’s experiments and intuitions. Many of those advances were improved upon only during the first half of the twentieth century by Emile Thellier (1904–1987). Actually, the well-known work by Thellier, resulting in the birth of the Saint Maur archaeomagnetic laboratory at the Institut de Physique du Globe de Paris, had as a starting point the theories and suggestions developed by Giuseppe Folgheraiter. Based on the studies by Thellier, the well-known secular variation curve for France was derived, later to be perfected by Ileana Bucur in 1994.

Volcano Crisis Management at Piton de la Fournaise (La Réunion) during the COVID-19 Lockdown

Abstract In March 2020, the coronavirus disease 2019 outbreak was declared a pandemic by the World Health Organization and became a global health crisis. Authorities worldwide implemented lockdowns to restrict travel and social exchanges in a global effort to counter the pandemic. In France, and in French overseas departments, the lockdown was effective from 17 March to 11 May 2020. It was in this context that the 2–6 April 2020 eruption of Piton de la Fournaise (La Réunion Island, Indian Ocean) took place. Upon the announcement of the lockdown in France, a reduced activity plan was set up by the Institut de Physique du Globe de Paris, which manages the Observatoire Volcanologique du Piton de la Fournaise (OVPF). The aim was to (1) maintain remote monitoring operations by teleworking and (2) authorize fieldwork only for critical reasons, such as serious breakdowns of stations or transmission relays. This eruption provided an opportunity for the observatory to validate its capacity to manage a volcanic crisis with 100% remotely operated monitoring networks. We thus present the long- and short-term precursors to the eruption, and the evolution of the eruption recorded using the real-time monitoring data as communicated to the stakeholders. The data were from both continuously recording and transmitting field instruments as well as satellites. The volcano observatory staff remotely managed the volcano crisis with the various stakeholders based only on these remotely functioning networks. Monitoring duties were also assured in the absence of ad hoc field investigation of the eruption by observatory staff or face-to-face communications. The density and reliability of the OVPF networks, combined with satellite observations, allowed for trustworthy instrument-based monitoring of the eruption and continuity of the OVPF duties in issuing regular updates of volcanic activity in the context of a double crisis: volcanic and health.

First Optical Seismometer at the Top of La Soufrière Volcano, Guadeloupe

Abstract Accurate monitoring of volcanic activity demands expertise in fields including geophysics, geology, and geochemistry. Data obtained from the most recent technical advances are particularly vital in pre-eruptive phases. In particular, seismic monitoring in near real time is essential to locating and discriminating early signs among different sources of seismic waves, especially those related to movement and overpressure in underground fluids. Among the major indicators of volcanic restlessness are fumaroles, or gas and steam vents, often located near a volcanic summit. Their activity could be monitored by seismometers in their vicinity, but today’s standard instruments cannot last very long when exposed to the high temperatures and the billowing, sulfurous, acidic gases near a fumarole. Conventional gear may also not be accessible for emergency deployment, or repair, even in pre-eruptive phases. La Soufrière de Guadeloupe Volcano in the Caribbean typifies such challenges. Its last significant event was a phreatic (gas and steam) eruption in 1976 that prompted evacuation of the archipelago’s nearby capital. Since early 2018, the 1467-meter-high stratovolcano has shown signs of increased activity. To provide a hardy, high-resolution monitoring system, we installed a recently developed type of seismometer just 10 m from a vigorous summit fumarole. The sensor is a purely opto-mechanical geophone that is interrogated through a 1.5 km fiber-optic cable by a remote, and thus it is a much safer optic-electronic system down the volcano’s flank. The ESEO Group and the Institut de Physique du Globe de Paris (IPGP) started development of this novel seismometer in 2008. The 2019 Guadeloupe installation is part of the HIgh PERformance SeISmometer (HIPERSIS) project (French Agence Nationale de la Recherche [ANR]). It is, to our knowledge, the first high-resolution optical seismometer ever installed on an active volcano or other active, hazardous zone. We report here the details of this installation, the means we are using for measurements, and our implementation strategy, and we share some of the first results. Such an optical seismometer, as well as a variety of other geophysical sensors built on the same principle, can be installed in a wide variety of sites with fibers up to 50 km long.

Using γ rays to disentangle fusion-fission and quasifission near the Coulomb barrier: A test of principle in the fusion-fission and quasielastic channels

The overlap in the mass symmetric region of the reaction products from fusion-fission and quasifission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The approach proposed here relies on the fact that fusion-fission and quasifission are characterized by different timescales. Within this framework, we performed a detailed study to find out how timescales can be probed via angular momentum transfer as measured via γ-ray multiplicities. The proof of principle was carried out by measuring the γ rays in coincidence with fusion-fission and quasielastic binary fragments in the reaction S32 + Au197 at beam energy near the Coulomb barrier. The experiment was performed at the Accelerateur Lineaire Tandem a Orsay (ALTO) facility at the Institut De Physique Nucleaire (IPN) in Orsay (France) using a detection setup consisting of ORGAM (ORsay GAMma) and PARIS (Photon Array Radioactive Ion Stable beams) γ-detectors arrays coupled with the CORSET (CORrelation SETup) time-of-flight spectrometer. Results of the sensitivity of this method to distinguish reaction channels with different dynamics are discussed.

Preface

R. M. Rachmat Sule1, Zulfakriza1*, David P. Sahara1, Fernando Lawrens H2, Rexha Verdhora Ry3Department of Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Indonesia2Kyushu University, Japan, 3Australian National University, Australiaemail: seacg2018@gmail.comThis issue of Journal IOP Conference Series: Earth and Environmental Science contains the outstanding papers presented at Southeast Asian Conference on Geophysics (SEACG) 2018. The SEACG is the second event which was organized by Department of Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung (ITB). It was held for 3 days between 7 and 9 August, 2018 in Bali – a small beautiful island and a part of Indonesia archipelago.This conference provided a venue for collaboration, sharing and developing new ideas and technologies. The SEACG created an opportunity for academics, professionals, and students to promote and discuss the scientific results related to recent development in geophysical methods and related science. Topics to be during the conference including: (1) applied geophysics, (2) earthquake seismology and volcanology (3) environmental geophysics, (4) geophysical exploration for oil and gas, (5) applied geophysics for geothermal exploration, (6) seismic method for geothermal exploration, (7) gravity method, (8) rock physics, and (9) near surface geophysics.The main objective of this conference is to lead to develop new ideas and technologies in geophysical methods and related science. This year, our theme was “Geophysics: From Energy Sustainability to Geohazard and Infrastructure”, presented by the invited speakers. The invited speakers are Prof. Djoko Santoso (ITB), Prof. Sigit Sukmono (ITB), Prof. Phil Cummins (Australian National University), Prof. François Beauducel (Institut de Physique du Globe de Paris), and Prof. Nanang T. Puspito (ITB).List of Photographs and Committees are available in this PDF.

Escape-suppression shield detector for the MINIBALL $ \gamma$γ-ray spectrometer

A bismuth-germanate (BGO) escape-suppression shield for the high-purity germanium triple-cluster detector of the MINIBALL \( \gamma\)-ray spectrometer was designed and built. Monte Carlo simulations with the simulation code GEANT4 were performed to guide the construction and to determine the detector geometry of the new BGO shield. After the first measurements concerning mechanical properties of the BGO housing and the performance of the photomultiplier tubes at the Institut de Physique Nucleaire, Orsay, the prototype BGO escape-suppression shield was combined with a MINIBALL triple-cluster detector at the Institut fur Kernphysik, Cologne. A dedicated electronics and digital data-acquisition system was put into operation in order to determine timing properties of the combined coincidence measurement and to measure values for the energy resolution of the BGO detectors, for the BGO low-energy threshold, and for the crucial peak-to-total ratio (P/T). The measured P/T value for a standard 60Co \( \gamma\)-ray source compares well with expectations and will allow to proceed with the amendment of the MINIBALL triple-cluster detectors with an escape-suppression shield for improved in-beam \( \gamma\)-ray spectroscopy especially at the new HIE-ISOLDE accelerator for radioactive ion beams at CERN.

The STELLA apparatus for particle-Gamma coincidence fusion measurements with nanosecond timing

The STELLA (STELlar LAboratory) experimental station for the measurement of deep sub-barrier light heavy-ion fusion cross sections has been installed at the Andromède accelerator at the Institut de Physique Nucléaire, Orsay (France). The setup is designed for the direct experimental determination of heavy-ion fusion cross sections as low as tens of picobarn. The detection concept is based on the coincident measurement of emitted gamma rays with the UK FATIMA (FAst TIMing Array) and evaporated charged particles using a silicon detector array. Key developments relevant to reaching the extreme sub-barrier fusion region are a rotating target mechanism to sustain beam intensities above 10μA, an ultra-high vacuum of 10−8 mbar to prevent carbon built-up and gamma charged-particle timing in the order of nanoseconds sufficient to separate proton and alpha particles.

Measurement of the liquid argon energy response to nuclear and electronic recoils

A liquid argon time projection chamber, constructed for the Argon Response to Ionization and Scintillation (ARIS) experiment, has been exposed to the highly collimated and quasi-monoenergetic LICORNE neutron beam at the Institute de Physique Nuclaire Orsay in order to study the scintillation response to nuclear and electronic recoils. An array of liquid scintillator detectors, arranged around the apparatus, tag scattered neutrons and select nuclear recoil energies in the [7, 120] keV energy range. The relative scintillation efficiency of nuclear recoils was measured to high precision at null field, and the ion-electron recombination probability was extracted for a range of applied electric fields. Single Compton scattered electrons, produced by gammas emitted from the de-excitation of $^7$Li* in coincidence with the beam pulse, along with calibration gamma sources, are used to extract the recombination probability as a function of energy and electron drift field. The ARIS results have been compared with three recombination probability parameterizations (Thomas-Imel, Doke-Birks, and PARIS), allowing for the definition of a fully comprehensive model of the liquid argon response to nuclear and electronic recoils down to a few keV range. The constraints provided by ARIS to the liquid argon response at low energy allow the reduction of systematics affecting the sensitivity of dark matter search experiments based on liquid argon

The equatorial electrojet (EEJ) current deduced from CHAMP satellite and ground magnetic measurements in West Africa

The equatorial electrojet (EEJ) is an intense daytime ionospheric current that circulates eastward along the geomagnetic dip equator. In this work, the EEJ current intensity was studied from ground-based magnetic data and CHAllenging Minisatellite Playoad (CHAMP) satellite observations. The ground-based magnetic data were recorded along a meridian chain of three stations across the dip equator in West Africa. These stations were operated by the Institut de Physique du Globe de Paris (IPGP). For the CHAMP satellite data, vector magnetometer records during geomagnetically quiet periods with Kp ≤ 2 were used. To estimate the EEJ current intensity, we have first isolated its magnetic effect from CHAMP satellite observations for 10 years (from July 2000 to September 2010). The results were used to analyze the EEJ seasonal variability and the local time and longitude dependence. In addition, a comparison between ground-based and satellite observations of the EEJ current intensity was made. A good correlation was found between satellite and ground-based EEJ current intensity, with an average correlation coefficient of r 2 ~0.93. This performed correlation show that the technique used in this study can be extended to all ground magnetic stations for modeling the EEJ phenomena.

Shielding design and radioprotection for Andromede and ThomX accelerators

The Institut de physique nucleaire – Institute of Nuclear Physics (IPN) and the Laboratoire de l’accelerateur lineaire – Laboratory of the linear accelerator (LAL) are about to build two accelerators at the University Paris-Sud, Orsay. Andromede is a new imaging mass spectrometry instrument for surface analysis: the electron positron emission microscope (EPEM) will analyse impacts on a surface made by nano-particles (Au404) in the keV to MeV range to study ion-surface interactions. ThomX is a compact X-ray source (energy up to 90 keV – flux up to 10 13 photons.s -1 ) that will produce X-rays using Compton backscattering effect between an electron beam and a laser. In order to use these machines in the same area, hutches are designed to comply with French regulations for radiation protection. This paper presents the methods used to design the hutches, complying with safety objectives, technical issues and budget.

Fluxgate vector magnetometers: A multisensor device for ground, UAV, and airborne magnetic surveys

Fluxgate magnetometers are quite uncommon in geophysics. Recent advances in calibration of the devices and their magnetic compensation ability led Institut de Physique du Globe de Strasbourg to develop instruments for magnetic measurements at different scales for a wide range of applications — from submetric measurements on the ground to aircraft-conducted acquisition by unmanned aerial vehicles (UAVs). A case study on the aerial military base BA112 shows the usefulness of the instruments for the detection of underground pipes, unexploded ordnance, and archaeological remains.

W phase source inversion using high‐rate regional GPS data for large earthquakes

AbstractW phase moment tensor inversion has proven to be a reliable method for rapid characterization of large earthquakes. For global purposes it is used at the United States Geological Survey, Pacific Tsunami Warning Center, and Institut de Physique du Globe de Strasbourg. These implementations provide moment tensors within 30–60 min after the origin time of moderate and large worldwide earthquakes. Currently, the method relies on broadband seismometers, which clip in the near field. To ameliorate this, we extend the algorithm to regional records from high‐rate GPS data and retrospectively apply it to six large earthquakes that occurred in the past 5 years in areas with relatively dense station coverage. These events show that the solutions could potentially be available 4–5 min from origin time. Continuously improving GPS station availability and real‐time positioning solutions will provide significant enhancements to the algorithm.

Global analysis of the high temperature infrared emission spectrum of (12)CH4 in the dyad (ν2/ν4) region.

We report new assignments of vibration-rotation line positions of methane ((12)CH4) in the so-called dyad (ν2/ν4) region (1100-1500 cm(-1)), and the resulting update of the vibration-rotation effective model of methane, previously reported by Nikitin et al. [Phys. Chem. Chem. Phys. 15, 10071 (2013)], up to and including the tetradecad. High resolution (0.01 cm(-1)) emission spectra of methane have been recorded up to about 1400 K using the high-enthalpy source developed at Institut de Physique de Rennes associated with the Fourier transform spectrometer of the SOLEIL synchrotron facility (AILES beamline). Analysis of these spectra allowed extending rotational assignments in the well-known cold band (dyad-ground state (GS)) and related hot bands in the pentad-dyad system (3000 cm(-1)) up to Jmax = 30 and 29, respectively. In addition, 8512 new transitions belonging to the octad-pentad (up to J = 28) and tetradecad-octad (up to J = 21) hot band systems were successfully identified. As a result, the MeCaSDa database of methane was significantly improved. The line positions assigned in this work, together with the information available in the literature, were fitted using 1096 effective parameters with a dimensionless standard deviation σ = 2.09. The root mean square deviations dRMS are 3.60 × 10(-3) cm(-1) for dyad-GS cold band, 4.47 ×10(-3) cm(-1) for the pentad-dyad, 5.43 × 10(-3) cm(-1) for the octad-pentad, and 4.70 × 10(-3) cm(-1) for the tetradecad-octad hot bands. The resulting new line list will contribute to improve opacity and radiative transfer models for hot atmospheres, such as those of hot-Jupiter type exoplanets.

Characterization of uranium carbide target materials to produce neutron-rich radioactive beams

In the framework of a R&D program aiming to develop uranium carbide (UCx) targets for radioactive nuclear beams, the Institut de Physique Nucléaire d’Orsay (IPNO) has developed an experimental setup to characterize the release of various fission fragments from UCx samples at high temperature. The results obtained in a previous study have demonstrated the feasibility of the method and started to correlate the structural properties of the samples and their behavior in terms of nuclear reaction product release. In the present study, seven UCx samples have been systematically characterized in order to better understand the correlation between their physicochemical characteristics and release properties. Two very different samples, the first one composed of dense UC and the second one of highly porous UCx made of multi-wall carbon nanotubes, were provided by the ActILab (ENSAR) collaboration. The others were synthesized at IPNO. The systems for irradiation and heating necessary for the release studies have been improved with respect to those used in previous studies. The results show that the open porosity is hardly the limiting factor for the fission product release. The homogeneity of the microstructure and the pore size distribution contributes significantly to the increase of the release. The use of carbon nanotubes in place of traditional micrometric graphite particles appears to be promising, even if the homogeneity of the microstructure can still be enhanced.

Water, oceanic fracture zones and the lubrication of subducting plate boundaries—insights from seismicity

We investigate the relationship between subduction processes and related seismicity for the Lesser Antilles Arc using the Gutenberg–Richter law. This power law describes the earthquake-magnitude distribution, with the gradient of the cumulative magnitude distribution being commonly known as the b-value. The Lesser Antilles Arc was chosen because of its along-strike variability in sediment subduction and the transition from subduction to strike-slip movement towards its northern and southern ends. The data are derived from the seismicity catalogues from the Seismic Research Centre of The University of the West Indies and the Observatoires Volcanologiques et Sismologiques of the Institut de Physique du Globe de Paris and consist of subcrustal events primarily from the slab interface. The b-value is found using a Kolmogorov–Smirnov test for a maximum-likelihood straight line-fitting routine. We investigate spatial variations in b-values using a grid-search with circular cells as well as an along-arc projection. Tests with different algorithms and the two independent earthquake cataloges provide confidence in the robustness of our results. We observe a strong spatial variability of the b-value that cannot be explained by the uncertainties. Rather than obtaining a simple north–south b-value distribution suggestive of the dominant control on earthquake triggering being water released from the sedimentary cover on the incoming American Plates, or a b-value distribution that correlates with on the obliquity of subduction, we obtain a series of discrete, high b-value ‘bull's-eyes’ along strike. These bull's-eyes, which indicate stress release through a higher fraction of small earthquakes, coincide with the locations of known incoming oceanic fracture zones on the American Plates. We interpret the results in terms of water being delivered to the Lesser Antilles subduction zone in the vicinity of fracture zones providing lubrication and thus changing the character of the related seismicity. Our results suggest serpentinization around mid-ocean ridge transform faults, which go on to become fracture zones on the incoming plate, plays a significant role in the delivery of water into the mantle at subduction zones.

Preliminary investigation of scintillator materials properties: SrI2:Eu, CeBr3 and GYGAG:Ce for gamma rays up to 9 MeV

In this work we measured the performance of a 2ʺ×2ʺ cylindrical tapered crystal of SrI2:Eu, a 2ʺ×3ʺ cylindrical sample of CeBr3 and a 2ʺ×0.3ʺ cylindrical sample of GYGAG:Ce. These scintillators are prototypes in volume or material and were provided by the Lawrence Livermore National Laboratory and by the Institut de Physique Nucléaire d׳Orsay. The gamma-ray energy resolution was measured in the energy range of 0.1–9MeV using different sources. Each scintillator was scanned along x, y and z axes, using a 400MBq collimated 137Cs source. Owing to the GYGAG:Ce thickness, it was not possible to obtain the value of the energy resolution at 9MeV and to scan the crystal along the z axis. The 662keV full energy peak position and its FWHM were measured relative to the full energy peaks positions produced by a non-collimated 88Y source. The signals of the detectors were additionally digitized and compared, up to 9MeV, using a 12bit LeCroy 600MHz oscilloscope.

Low-lying intruder and tensor-driven structures inAs82revealed byβdecay at a new movable-tape-based experimental setup

The $\ensuremath{\beta}$ decay of $^{82}\mathrm{Ge}$ was re-investigated using the newly commissioned tape station BEDO at the electron-driven ISOL (isotope separation on line) facility ALTO operated by the Institut de Physique Nucl\'eaire, Orsay. The original motivation of this work was focused on the sudden occurrence in the light $N=49$ odd-odd isotonic chain of a large number of $J\ensuremath{\le}1$ states (positive or negative parity) in $^{80}\mathrm{Ga}$ by providing a reliable intermediate example, viz., $^{82}\mathrm{As}$. The extension of the $^{82}\mathrm{As}$ level scheme towards higher energies from the present work has revealed three potential ${1}^{+}$ states above the already known one at 1092 keV. In addition our data allow ruling out the hypothesis that the 843 keV level could be a ${1}^{+}$ state. A detailed analysis of the level scheme using both an empirical core-particle coupling model and a fully microscopic treatment within a Skyrme-QRPA (quasiparticle random-phase approximation) approach using the finite-rank separable approximation was performed. From this analysis two conclusions can be drawn: (i) the presence of a large number of low-lying low-spin negative parity states is due to intruder states stemming from above the $N=50$ shell closure, and (ii) the sudden increase, from $^{82}\mathrm{As}$ to $^{80}\mathrm{Ga}$, of the number of low-lying ${1}^{+}$ states and the corresponding Gamow-Teller fragmentation are naturally reproduced by the inclusion of tensor correlations and couplings to 2p-2h excitations.