Laboratory experiments have established that many of the materials comprising the Earth are strongly anisotropic in terms of seismic-wave speeds. Observations of azimuthal and radial anisotropy in ...the upper mantle are attributed to the lattice-preferred orientation of olivine caused by the shear strains associated with deformation, and provide some of the most direct evidence for deformation and flow within the Earth's interior. Although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes, large-scale observations have been limited to regions of particularly thick crust. Here we show that observations from ambient noise tomography in the western United States reveal strong deep (middle to lower)-crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the Cenozoic Era (since ∼65 Myr ago). The coincidence of crustal radial anisotropy with the extensional provinces of the western United States suggests that the radial anisotropy results from the lattice-preferred orientation of anisotropic crustal minerals caused by extensional deformation. These observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension.
Ambient noise tomography is a rapidly emerging field of seismological research. This paper presents the current status of ambient noise data processing as it has developed over the past several years ...and is intended to explain and justify this development through salient examples. The ambient noise data processing procedure divides into four principal phases: (1) single station data preparation, (2) cross-correlation and temporal stacking, (3) measurement of dispersion curves (performed with frequency—time analysis for both group and phase speeds) and (4) quality control, including error analysis and selection of the acceptable measurements. The procedures that are described herein have been designed not only to deliver reliable measurements, but to be flexible, applicable to a wide variety of observational settings, as well as being fully automated. For an automated data processing procedure, data quality control measures are particularly important to identify and reject bad measurements and compute quality assurance statistics for the accepted measurements. The principal metric on which to base a judgment of quality is stability, the robustness of the measurement to perturbations in the conditions under which it is obtained. Temporal repeatability, in particular, is a significant indicator of reliability and is elevated to a high position in our assessment, as we equate seasonal repeatability with measurement uncertainty. Proxy curves relating observed signal-to-noise ratios to average measurement uncertainties show promise to provide useful expected measurement error estimates in the absence of the long time-series needed for temporal subsetting.
Surface wave dispersion measurements from ambient seismic noise and array‐based measurements from teleseismic earthquakes observed with the EarthScope/USArray Transportable Array (TA) are inverted ...using a Monte Carlo method for a 3‐D VS model of the crust and uppermost mantle beneath the western United States. The combination of data from these methods produces exceptionally broadband dispersion information from 6 to 100 s period, which constrains shear wave velocity structures in the crust and uppermost mantle to a depth of more than 100 km. The high lateral resolution produced by the TA network and the broadbandedness of the dispersion information motivate the question of the appropriate parameterization for a 3‐D model, particularly for the crustal part of the model. We show that a relatively simple model in which VS increases monotonically with depth in the crust can fit the data well across more than 90% of the study region, except in eight discrete areas where greater crustal complexity apparently exists. The regions of greater crustal complexity are the Olympic Peninsula, the MendocinoTriple Junction, the Yakima Fold Belt, the southern Cascadia back arc, the Great Central Valley of California, the Salton Trough, the Snake River Plain, and the Wasatch Mountains. We also show that a strong Rayleigh‐Love discrepancy exists across much of the western United States, which can be resolved by introducing radial anisotropy in both the mantle and notably the crust. We focus our analysis on demonstrating the existence of crustal radial anisotropy and primarily discuss the crustal part of the isotropic model that results from the radially anisotropic model by Voigt averaging. Model uncertainties from the Monte Carlo inversion are used to identify robust isotropic features in the model. The uppermost mantle beneath the western United States is principally composed of four large‐scale shear wave velocity features, but lower crustal velocity structure exhibits far greater heterogeneity. We argue that these lower crustal structures are predominantly caused by interactions with the uppermost mantle, including the intrusion and underplating of mafic mantle materials and the thermal depression of wave speeds caused by conductive heating from the mantle. Upper and middle crustal wave speeds are generally correlated, and notable anomalies are inferred to result from terrane accretion at the continental margin and volcanic intrusions.
Aims.
We report on ESPRESSO high-resolution transmission spectroscopic observations of two primary transits of the highly irradiated, ultra-hot Jupiter-sized planet, WASP-76b. We investigated the ...presence of several key atomic and molecular features of interest that may reveal the atmospheric properties of the planet.
Methods.
We extracted two transmission spectra of WASP-76b with
R
≈ 140 000 using a procedure that allowed us to process the full ESPRESSO wavelength range (3800–7880 Å) simultaneously. We observed that at a high signal-to-noise ratio, the continuum of ESPRESSO spectra shows ‘wiggles’, which are likely caused by an interference pattern outside the spectrograph. To search for the planetary features, we visually analysed the extracted transmission spectra and cross-correlated the observations against theoretical spectra of different atomic and molecular species.
Results.
The following atomic features are detected: Li
I
, Na
I
, Mg
I
, Ca
II
, Mn
I
, K
I
, and Fe
I
. All are detected with a confidence level between 9.2
σ
(Na
I
) and 2.8
σ
(Mg
I
). We did not detect the following species: Ti
I
, Cr
I
, Ni
I
, TiO, VO, and ZrO. We impose the following 1
σ
upper limits on their detectability: 60, 77, 122, 6, 8, and 8 ppm, respectively.
Conclusions.
We report the detection of Li
I
on WASP-76b for the first time. In addition, we confirm the presence of Na
I
and Fe
I
as previously reported in the literature. We show that the procedure employed in this work can detect features down to the level of ~0.1% in the transmission spectrum and ~10 ppm by means of a cross-correlation method. We discuss the presence of neutral and singly ionised features in the atmosphere of WASP-76b.
We have applied ambient noise surface wave tomography to data that have emerged continuously from the EarthScope USArray Transportable Array (TA) between October 2004 and January 2007. Estimated ...Green's functions result by cross‐correlating noise records between every station‐pair in the network. The 340 stations yield a total of more than 55,000 interstation paths. Within the 5‐ to 50‐s period band, we measure the dispersion characteristics of Rayleigh waves using frequency‐time analysis. High‐resolution group velocity maps at 8‐, 16‐, 24‐, 30‐, and 40‐s periods are presented for the western United States. The footprint of the TA encloses a region with a resolution of about the average interstation spacing (∼70 km). Velocity anomalies in the group velocity maps correlate well with the dominant geological features of the western United States. Coherent velocity anomalies are associated with the Sierra Nevada, Peninsular, and Cascade Ranges, Great Valley, Salton Trough, and Columbia basins, the Columbia River flood basalts, the Snake River Plain and Yellowstone, and mantle wedge features associated with the subducting Juan de Fuca plate.
Ambient noise tomography and multiple plane wave earthquake tomography are new methods of surface wave analysis that yield much more highly refined information about the crust and uppermost mantle ...than traditional surface wave techniques. Applied together to data observed at more than 300 broadband seismic stations from the Transportable Array component of the EarthScope USArray, these methods yield surface wave dispersion curves from 8 to 100 s period across the entire western United States with unprecedented resolution. We use the local Rayleigh wave phase speed curves to construct a unified isotropic 3‐D Vs model to a depth of about 150 km. Crustal and uppermost mantle features that underlie the western United States are revealed in striking relief. As the USArray continues to sweep eastward across the United States, the substructure of the entire country will be unveiled.
Context.
The bright star
π
Men was chosen as the first target for a radial velocity follow-up to test the performance of ESPRESSO, the new high-resolution spectrograph at the European Southern ...Observatory’s Very Large Telescope. The star hosts a multi-planet system (a transiting 4
M
⊕
planet at ~0.07 au and a sub-stellar companion on a ~2100-day eccentric orbit), which is particularly suitable for a precise multi-technique characterization.
Aims.
With the new ESPRESSO observations, which cover a time span of 200 days, we aim to improve the precision and accuracy of the planet parameters and search for additional low-mass companions. We also take advantage of the new photometric transits of
π
Men c observed by TESS over a time span that overlaps with that of the ESPRESSO follow-up campaign.
Methods.
We analysed the enlarged spectroscopic and photometric datasets and compared the results to those in the literature. We further characterized the system by means of absolute astrometry with H
IPPARCOS
and
Gaia
. We used the high-resolution spectra of ESPRESSO for an independent determination of the stellar fundamental parameters.
Results.
We present a precise characterization of the planetary system around
π
Men. The ESPRESSO radial velocities alone (37 nightly binned data with typical uncertainty of 10 cm s
−1
) allow for a precise retrieval of the Doppler signal induced by
π
Men c. The residuals show a root mean square of 1.2 m s
−1
, which is half that of the HARPS data; based on the residuals, we put limits on the presence of additional low-mass planets (e.g. we can exclude companions with a minimum mass less than ~2
M
⊕
within the orbit of
π
Men c). We improve the ephemeris of
π
Men c using 18 additional TESS transits, and, in combination with the astrometric measurements, we determine the inclination of the orbital plane of
π
Men b with high precision (
i
b
=45.8
−1.1
+1.4
deg). This leads to the precise measurement of its absolute mass
m
b
=14.1
−0.4
+0.5
M
Jup
, indicating that
π
Men b can be classified as a brown dwarf.
Conclusions.
The
π
Men system represents a nice example of the extreme precision radial velocities that can be obtained with ESPRESSO for bright targets. Our determination of the 3D architecture of the
π
Men planetary system and the high relative misalignment of the planetary orbital planes put constraints on and challenge the theories of the formation and dynamical evolution of planetary systems. The accurate measurement of the mass of
π
Men b contributes to make the brown dwarf desert a bit greener.
While much literature has been produced on globalization, privatization, and the State individually, it has not been common to treat them together, at least not in the field of comparative and ...international education. There is excellent work that has documented the ways in which globalization and privatization have influenced education reform, but extant scholarship typically has not engaged with theories of the State. In this paper, through the case of Honduras, we explore the aforementioned issues. First, we draw on the approach of Critical International Political Economy (CIPE) to understand the ways that (political-economic) globalization and privatization have affected and manifested in both policymaking and the provision of education. The second half of the paper then turns the gaze back on the Honduran State and draws on State theory literature to consider why globalization and privatization have been able to be so influential in the first place.
Likelihood testing of induced earthquakes in Oklahoma and Kansas has identified the parameters that optimize the forecasting ability of smoothed seismicity models and quantified the recent temporal ...stability of the spatial seismicity patterns. Use of the most recent 1 year period of earthquake data and use of 10–20 km smoothing distances produced the greatest likelihood. The likelihood that the locations of January–June 2015 earthquakes were consistent with optimized forecasts decayed with increasing elapsed time between the catalogs used for model development and testing. Likelihood tests with two additional sets of earthquakes from 2014 exhibit a strong sensitivity of the rate of decay to the smoothing distance. Marked reductions in likelihood are caused by the nonstationarity of the induced earthquake locations. Our results indicate a multiple‐fold benefit from smoothed seismicity models in developing short‐term earthquake rate forecasts for induced earthquakes in Oklahoma and Kansas, relative to the use of seismic source zones.
Key Points
Optimized spatial distribution forecasts use epicenter locations from the previous year and kernel smoothing distances of 10–20 km
Probability gains achieved from the forecasts of induced earthquake locations decay over the course of about 6–12 months
This work was motivated by the development of a short‐term seismic hazard model that includes the effects of induced earthquakes
In order to investigate the seasonal variations of antimicrobial properties and chemical composition of essential oils (EOs), three different cultivars of Citrus limon L. Burm. spp. (Femminello Santa ...Teresa, Monachello and Femminello Continella) were collected at 6-week intervals, from December 2012 to April 2013, for a total of four harvests. The EOs were extracted from lemon peel by hydro-distillation. The antimicrobial activity, tested by paper disc diffusion method, was evaluated against common food-related pathogenic bacteria (Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica and Enterobacter spp.). EOs were more effective against Gram-positive than Gram-negative bacteria at each collection time, but a strong strain dependence was evidenced. Monachello EOs showed the highest inhibition power. The chemical characterisation of the EOs performed by gas chromatography/mass spectrometry identified from 36 to 42 molecules. The chemical difference registered among samples and seasons may explain the different antimicrobial efficacies recorded.
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