Helicopter Location and Tracking using Seismometer Recordings

We use frequency domain methods usually applied to volcanic tremor to analyse ground based seismic recordings of a helicopter. We preclude misinterpretations of tremor sources and show alternative applications of our seismological methods. On a volcano, the seismic source can consist of repeating, closely spaced, small earthquakes. Interestingly, similar signals are generated by helicopters, due to repeating pressure pulses from the rotor blades. In both cases the seismic signals are continuous and referred to as tremor. As frequency gliding is in this case merely caused by the Doppler effect, not a change in the source, we can use its shape to deduce properties of the helicopter and its flight path. We show in this analysis that the number of rotor blades, rotor revolutions per minute (RPM), helicopter speed, flight direction, altitude and location can be deduced from seismometer recordings. Access to GPS determined flight path data from the helicopter offers us a robust way to test our location method

Precision radial velocities with CSHELL

Radial velocity identification of extrasolar planets has historically been dominated by optical surveys. Interest in expanding exoplanet searches to M dwarfs and young stars, however, has motivated a push to improve the precision of near infrared radial velocity techniques. We present our methodology for achieving 58 m/s precision in the K band on the M0 dwarf GJ 281 using the CSHELL spectrograph at the 3-meter NASA IRTF. We also demonstrate our ability to recover the known 4 Mjup exoplanet Gl 86 b and discuss the implications for success in detecting planets around 1-3 Myr old T Tauri stars.Comment: 31 pages, 3 figures, 2 tables, accepted for publication in Ap

A multibranch, multitarget neural network for rapid point-source inversion in a microseismic environment: examples from the Hengill Geothermal Field, Iceland

Despite advanced seismological techniques, automatic source characterization for microseismic earthquakes remains difficult and challenging since current inversion and modelling of high-frequency signals are complex and time consuming. For real-time applications such as induced seismicity monitoring, the application of standard methods is often not fast enough for true complete real-time information on seismic sources. In this paper, we present an alternative approach based on recent advances in deep learning for rapid source-parameter estimation of microseismic earthquakes. The seismic inversion is represented in compact form by two convolutional neural networks, with individual feature extraction, and a fully connected neural network, for feature aggregation, to simultaneously obtain full moment tensor and spatial location of microseismic sources. Specifically, a multibranch neural network algorithm is trained to encapsulate the information about the relationship between seismic waveforms and underlying point-source mechanisms and locations. The learning-based model allows rapid inversion (within a fraction of second) once input data are available. A key advantage of the algorithm is that it can be trained using synthetic seismic data only, so it is directly applicable to scenarios where there are insufficient real data for training. Moreover, we find that the method is robust with respect to perturbations such as observational noise and data incompleteness (missing stations). We apply the new approach on synthesized and example recorded small magnitude (M <= 1.6) earthquakes at the Hellisheioi geothermal field in the Hengill area, Iceland. For the examined events, the model achieves excellent performance and shows very good agreement with the inverted solutions determined through standard methodology. In this study, we seek to demonstrate that this approach is viable for microseismicity real-time estimation of source parameters and can be integrated into advanced decision-support tools for controlling induced seismicity

Seismic tremor reveals slow fracture propagation prior to the 2018 eruption at Sierra Negra volcano, Galápagos

Seismic tremor observed near active volcanoes is an important tool for volcano monitoring as it often appears shortly before eruptions. Although tremor can be generated by a variety of physical processes it is usually interpreted as direct evidence for flowing magma in the sub-surface. These interpretations typically feed into risk assessments for potential eruptions. Using the temporal evolution of tremor amplitude and spectral data from a distributed seismic network that captured the 2018 eruption at Sierra Negra in Galapagos, we determine that tremor is not directly related to sub-surface fluid movement. Instead at Sierra Negra tremor likely indicates a slowly propagating fracture, which is later exploited as a pathway for silent magma flow. Distinct differences in the source migration and the spectral character of pre-eruptive and co-eruptive tremor allow both a location estimate of the future eruption site and a precise timing of the eruption onset

Micrometre-scale deformation observations reveal fundamental controls on geological rifting

Many of the world’s largest volcanic eruptions are associated with geological rifting where major fractures open at the Earth’s surface, yet fundamental controls on the near-surface response to the rifting process are lacking. New high resolution observations gleaned from seismometer data during the 2014 Bárðarbunga basaltic dyke intrusion in Iceland allow us unprecedented access to the associated graben formation process on both sub-second and micrometre scales. We find that what appears as quasi steady-state near-surface rifting on lower resolution GPS observation comprises discrete staccatolike deformation steps as the upper crust unzips through repetitive low magnitude (MW < 0) failures on fracture patches estimated between 300 m2 and 1200 m2 in size. Stress drops for these events are one to two orders of magnitude smaller than expected for tectonic earthquakes, demonstrating that the uppermost crust in the rift zone is exceptionally weak

Source geometry from exceptionally high resolution long period event observations at Mt Etna during the 2008 eruption

During the second half of June, 2008, 50 broadband seismic stations were deployed on Mt Etna volcano in close proximity to the summit, allowing us to observe seismic activity with exceptionally high resolution. 129 long period events (LP) with dominant frequencies ranging between 0.3 and 1.2 Hz, were extracted from this dataset. These events form two families of similar waveforms with different temporal distributions. Event locations are performed by cross-correlating signals for all pairs of stations in a two-step scheme. In the first step, the absolute location of the centre of the clusters was found. In the second step, all events are located using this position. The hypocentres are found at shallow depths (20 to 700 m deep) below the summit craters. The very high location resolution allows us to detect the temporal migration of the events along a dike-like structure and 2 pipe shaped bodies, yielding an unprecedented view of some elements of the shallow plumbing system at Mount Etna. These events do not seem to be a direct indicator of the ongoing lava flow or magma upwelling

Dynamic earthquake triggering response tracks evolving unrest at Sierra Negra volcano, Galápagos Islands

The propensity for dynamic earthquake triggering is thought to depend on the local stress state and amplitude of the stress perturbation. However, the nature of this dependency has not been confirmed within a single crustal volume. Here, we show that at Sierra Negra volcano, Galápagos Islands, the intensity of dynamically triggered earthquakes increased as inflation of a magma reservoir elevated the stress state. The perturbation of short-term seismicity within teleseismic surface waves also increased with peak dynamic strain. Following rapid coeruptive subsidence and reduction in stress and background seismicity rates, equivalent dynamic strains no longer triggered detectable seismicity. These findings offer direct constraints on the primary controls on dynamic triggering and suggest that the response to dynamic stresses may help constrain the evolution of volcanic unrest

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at s√=7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pTpT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HTHT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb−1. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pTpT distributions of the leading jets at high pTpT values, the distributions of the HTHT at high-HTHT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.Funded by SCOAP

Parvovirus B19 infection in sickle cell disease: An analysis from the Centers for Disease Control haemoglobinopathy blood surveillance project

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155921/1/tme12671_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155921/2/tme12671.pd