According to the International Data Centre (IDC), the Sea of Okhotsk earthquake occurred at 05:44:49.7 on May 24, 2013, had coordinates 54.89°N,153.31°E, mb=6.27, and depth of 604 km. The USGS moment magnitude is 8.3. The previous event detected by the IDC in the surrounding volume 53°N-57°N, 151°E-155°E, depth from 400 to 700 km occurred on February 6, 2012. Using the same seismic data from the stations of the International Monitoring System together with detection and phase association methods based on waveform cross correlation, a series of low-magnitude earthquakes was recovered immediately before this major earthquake. More than 200 events obeying the Event Definition Criteria adapted by the IDC were found between May 13 and the mainshock, with a sudden increase in their occurrence rate starting on the afternoon May 19. The evolution of the numbers of these low-magnitude earthquakes in various ranges of statistical significance within the source volume demonstrates some features, which can be related to the approaching initiation of the Sea of Okhotsk earthquake.
During the era of NASA's Apollo missions, Keith S. Runcorn proposed an explanation of discrepancy between the Moon's negligible global magnetic field and magnetized samples of lunar regolith, based on identical vanishing of external magnetic field of a spherical shell, magnetized by an internal source which is no longer present. We revisit and generalize the Runcorn's result, showing that it is a consequence of a (weighted) orthogonality of gradients of harmonic functions on a spherical shell in arbitrary number of dimensions. Furthermore, we explore bounds on external magnetic field in the case when the idealized spherical shell is replaced with a more realistic geometric shape and when the thermoremanent magnetization susceptibility deviates from the spherical symmetry. Finally, we analyse a model of thermoremanent magnetization acquired by crustal inward cooling of a spherical astrophysical body and put some general bounds on the associated magnetic field.
Abstract The colony-forming cyanobacteria Trichodesmium spp. are considered one of the most important nitrogen-fixing genera in the warm, low nutrient ocean. Despite this central biogeochemical role, many questions about their evolution, physiology, and trophic interactions remain unanswered. To address these questions, we describe Trichodesmium pangenomic potential via significantly improved genomic assemblies from two isolates and 15 new >50% complete Trichodesmium metagenome-assembled genomes from hand-picked, Trichodesmium colonies spanning the Atlantic Ocean. Phylogenomics identified ~four N2 fixing clades of Trichodesmium across the transect, with T. thiebautii dominating the colony-specific reads. Pangenomic analyses showed that all T. thiebautii MAGs are enriched in COG defense mechanisms and encode a vertically inherited Type III-B Clustered Regularly Interspaced Short Palindromic Repeats and associated protein-based immunity system (CRISPR-Cas). Surprisingly, this CRISPR-Cas system was absent in all T. erythraeum genomes, vertically inherited by T. thiebautii, and correlated with increased signatures of horizontal gene transfer. Additionally, the system was expressed in metaproteomic and transcriptomic datasets and CRISPR spacer sequences with 100% identical hits to field-assembled, putative phage genome fragments were identified. While the currently CO2-limited T. erythraeum is expected to be a ‘winner’ of anthropogenic climate change, their genomic dearth of known phage resistance mechanisms, compared to T. thiebautii, could put this outcome in question. Thus, the clear demarcation of T. thiebautii maintaining CRISPR-Cas systems, while T. erythraeum does not, identifies Trichodesmium as an ecologically important CRISPR-Cas model system, and highlights the need for more research on phage-Trichodesmium interactions.
Elsa Giraudat, Arnaud Burtin, Arthur Le Ber
et al.
In geophysics, volcanoes are particularly difficult to image because of the multi-scale heterogeneities of fluids and rocks that compose them and their complex non-linear dynamics. By exploiting seismic noise recorded by a sparse array of geophones, we are able to reveal the magmatic and hydrothermal plumbing system of La Soufrière volcano in Guadeloupe. Spatio-temporal cross-correlation of seismic noise actually provides the impulse responses between virtual geophones located inside the volcano. The resulting reflection matrix can be exploited to numerically perform an auto-focus of seismic waves on any reflector of the underground. An unprecedented view on the volcano's inner structure is obtained at a half-wavelength resolution. This innovative observable provides fundamental information for the conceptual modeling and high-resolution monitoring of volcanoes.
J. Peña-Rodríguez, J. Jaimes-Teherán, K. Dlaikan-Castillo
et al.
Muography is an imaging technique based on attenuation of the directional muon flux traversing geological or anthropic structures. Several simulation frameworks help to perform muography studies by combining specialised codes from the muon generation (CORSIKA and CRY) and the muon transport (GEANT4, PUMAS, and MUSIC) to the detector performance (GEANT4). This methodology is very precise but consumes significant computational resources and time. In this work, we present the end-to-end python-based MUographY Simulation Code. MUYSC implements a muography simulation framework capable of rapidly estimating rough muograms of any geological structure worldwide. MUYSC generates the muon flux at the observation place, transports the muons along the geological target, and determines the integrated muon flux detected by the telescope. Additionally, MUYSC computes the muon detector parameters (acceptance, solid angle, and angular resolution) and reconstructs the 3-dimensional density distribution of the target. We evaluated its performance by comparing it with previous results of several simulation frameworks.
Joshua D. White, Anantha Aiyyer, James O. H. Russell
We examined the sensitivity of African easterly waves (AEWs) to elevated terrain over North Africa using a numerical weather prediction model. We formed five ensembles of simulated AEW activity with orographic features independently reduced in four key regions. The ensemble members consisted of 10 consecutive AEW seasons simulated separately. From the ensembles, the southern AEW stormtrack was most sensitive to the reduction of the Ethiopian highlands. Energy budgets showed that diminished diabatic heating associated with precipitating convection was the likely driver of the weaker AEWs. Baroclinic overturning was the dominant pathway for this response. The northern AEW stormtrack was most sensitive to the reduction of the Hoggar and Tibesti mountains. In this case, a reduction in the vertical shear and diminished baroclinic energy conversions from the background state was associated with weaker AEWs. Through terrain reduction, our results provide a view of thermodynamic and dynamic feedback in AEWs that is complementary to what has been shown in past studies.
The study of planets outside our solar system may lead to major advances in our understanding of the Earth, and provide insight into the universal set of rules by which planets form and evolve. To achieve these goals requires applying geoscience's wealth of Earth observations to fill in the blanks left by the necessarily minimalist exoplanetary observations. In turn, Earth's many one-offs, e.g., plate tectonics, surface liquid water, a large moon, and life - which have long presented chicken and egg type conundrums for geoscientists - may find resolution in the study of exoplanets possessing only a subset of these phenomena.
Marcus Bursik, Qingyuan Yang, Adele Bear-Crozier
et al.
Volcanic ash clouds often become multilayered and thin with distance from the vent. We explore one mechanism for development of this layered structure. We review data on the characteristics of turbulence layering in the free atmosphere, as well as examples of observations of layered clouds both near-vent and distally. We then explore and contrast the output of volcanic ash transport and dispersal models with models that explicitly use the observed layered structure of atmospheric turbulence. The results suggest that the alternation of turbulent and quiescent atmospheric layers provides one mechanism for development of multilayered ash clouds by modulating the manner in which settling occurs.