Fundamental and higher two-dimensional resonance modes of an Alpine valley

We investigated the sequence of 2-D resonance modes of the sediment fill of Rhône Valley, Southern Swiss Alps, a strongly overdeepened, glacially carved basin with a sediment fill reaching a thickness of up to 900 m. From synchronous array recordings of ambient vibrations at six locations between Martigny and Sion we were able to identify several resonance modes, in particular, previously unmeasured higher modes. Data processing was performed with frequency domain decomposition of the cross-spectral density matrices of the recordings and with time-frequency dependent polarization analysis. 2-D finite element modal analysis was performed to support the interpretation of processing results and to investigate mode shapes at depth. In addition, several models of realistic bedrock geometries and velocity structures could be used to qualitatively assess the sensitivity of mode shape and particle motion dip angle to subsurface properties. The variability of modal characteristics due to subsurface properties makes an interpretation of the modes purely from surface observations challenging. We conclude that while a wealth of information on subsurface structure is contained in the modal characteristics, a careful strategy for their interpretation is needed to retrieve this informatio

Extracellular traps are associated with human and mouse neutrophil and macrophage mediated killing of larval Strongyloides stercoralis.

Neutrophils are multifaceted cells that are often the immune system\u27s first line of defense. Human and murine cells release extracellular DNA traps (ETs) in response to several pathogens and diseases. Neutrophil extracellular trap (NET) formation is crucial to trapping and killing extracellular pathogens. Aside from neutrophils, macrophages and eosinophils also release ETs. We hypothesized that ETs serve as a mechanism of ensnaring the large and highly motile helminth parasite Strongyloides stercoralis thereby providing a static target for the immune response. We demonstrated that S. stercoralis larvae trigger the release of ETs by human neutrophils and macrophages. Analysis of NETs revealed that NETs trapped but did not kill larvae. Induction of NETs was essential for larval killing by human but not murine neutrophils and macrophages in vitro. In mice, extracellular traps were induced following infection with S. stercoralis larvae and were present in the microenvironment of worms being killed in vivo. These findings demonstrate that NETs ensnare the parasite facilitating larval killing by cells of the immune system

Ambient seismic source inversion

Ocean waves and other phenomena occurring at the Earth’s surface interact with the Earth’s crust and cause faint seismic signals that can be measured at great distance. The sources of these ambient vibrations are of long-standing interest in seismology, both in their own right, as they carry information about environmental processes and conditions, and because they persistently probe the Earth’s interior, providing signals for nearly continuous imaging and monitoring of subsurface structure even in areas of low seismicity. Here, we present the first application of an iterative inversion method for the sources of ambient seismic noise with a three-dimensional Earth model. In a step leading up to inversion, we investigate how robust information about noise source properties can be derived from cross-correlations of continuously recorded ambient noise. Signal energy ratios of ambient signals traveling in opposite directions can be used to rapidly elaborate first-order estimates of ambient noise source distribution at a regional and global scale. At the regional scale, windowed signal energy measurements taken on the cross-correlation reflect the rapidly changing ambient noise field excited by passing storms. Based on a Green’s function database approach, we numerically model cross-correlations of the ambient seismic noise in a three-dimensional Earth model with laterally varying seismic structure. This allows us to construct a gradient-based, non-linear iterative inversion for the time-, location- and frequency dependent source power spectral density of ambient noise that honours the three-dimensional structure of the Earth’s interior. We apply this inversion to ten-year averaged observations of vertical-component ambient noise recorded in North and South hemisphere winter, in order to image the sources of the Earth’s hum, which is the long-periodic background seismic signal. The results reveal seasonally varying, narrowly delineated areas of high hum excitation, predominantly located at Pacific shelves or coasts during North Hemisphere winter, and at Southern Ocean locations of shallow bathymetry, as well as South Pacific shelves or coasts during austral winter. The investigated inversion method contributes to the development of full-waveform inversion with ambient noise cross-correlations. Future extension to horizontal- and mixed-component cross-correlations, as well as applications to ambient noise at the regional scale, may help advance our understanding of ambient noise excitation processes

Optimal processing for seismic noise correlations

ISSN:0956-540XISSN:1365-246

Efficient cross-correlation modelling for noise source inversion

ISSN:1029-7006ISSN:1607-796

Rapid finite-frequency microseismic noise source inversion at regional to global scales

Ambient noise cross-correlations can be used as self-consistent observables, opening novel possibilities for investigating ambient noise sources. To optimise the forward-modelling of global ambient noise cross-correlations for any given distribution of noise sources in the microseismic frequency range up to 0.2 Hz, we implement (i) pre-computed wavefields and (ii) spatially variable grids. This enables rapid inversions for microseismic noise sources based on finite-frequency source sensitivity kernels. We use this advancement to perform regional and global gradient-based iterative inversions of the logarithmic energy ratio in the causal and acausal branches of micro-seismic noise cross-correlations. Synthetic inversions show promising results, with good recovery of the main dominant noise sources of the target model. Data inversions for several consecutive days at the beginning of October 2019 demonstrate the capability of inverting for the spatio-temporal variations of the sources of secondary microseisms in the ocean. This paves the way for daily ambient noise source inversions which could help improve full-waveform ambient noise tomography and subsurface monitoring methods.ISSN:0956-540XISSN:1365-246

Generalized interferometry – I: theory for interstation correlations

We develop a general theory for interferometry by correlation that (i) properly accounts for heterogeneously distributed sources of continuous or transient nature, (ii) fully incorporates any type of linear and nonlinear processing, such as one-bit normalization, spectral whitening and phase-weighted stacking, (iii) operates for any type of medium, including 3-D elastic, heterogeneous and attenuating media, (iv) enables the exploitation of complete correlation waveforms, including seemingly unphysical arrivals, and (v) unifies the earthquake-based two-station method and ambient noise correlations. Our central theme is not to equate interferometry with Green function retrieval, and to extract information directly from processed interstation correlations, regardless of their relation to the Green function. We demonstrate that processing transforms the actual wavefield sources and actual wave propagation physics into effective sources and effective wave propagation. This transformation is uniquely determined by the processing applied to the observed data, and can be easily computed. The effective forward model, that links effective sources and propagation to synthetic interstation correlations, may not be perfect. A forward modelling error, induced by processing, describes the extent to which processed correlations can actually be interpreted as proper correlations, that is, as resulting from some effective source and some effective wave propagation. The magnitude of the forward modelling error is controlled by the processing scheme and the temporal variability of the sources. Applying adjoint techniques to the effective forward model, we derive finite-frequency Fréchet kernels for the sources of the wavefield and Earth structure, that should be inverted jointly. The structure kernels depend on the sources of the wavefield and the processing scheme applied to the raw data. Therefore, both must be taken into account correctly in order to make accurate inferences on Earth structure. Not making any restrictive assumptions on the nature of the wavefield sources, our theory can be applied to earthquake and ambient noise data, either separately or combined. This allows us (i) to locate earthquakes using interstation correlations and without knowledge of the origin time, (ii) to unify the earthquake-based two-station method and noise correlations without the need to exclude either of the two data types, and (iii) to eliminate the requirement to remove earthquake signals from noise recordings prior to the computation of correlation functions. In addition to the basic theory for acoustic wavefields, we present numerical examples for 2-D media, an extension to the most general viscoelastic case, and a method for the design of optimal processing schemes that eliminate the forward modelling error completely. This work is intended to provide a comprehensive theoretical foundation of full-waveform interferometry by correlation, and to suggest improvements to current passive monitoring methods.ISSN:0956-540XISSN:1365-246

Quantifying gender gaps in seismology authorship

According to 2018 demographic data of the American Geophysical Union Fall Meeting, seismology is among the geoscience ?elds with the lowest representation of women. To understand whether this reflects seismology more generally, we investigate women's authorship of peer-reviewed publications, a key factor in career advancement. Building upon open-source tools for web-scraping, we create a database of bibliographic information for seismological articles published in 14 international journals from 2010 to 2020. We use the probabilities of author names being either male- or female-gendered to analyse the representation of women authors in terms of author position and subsequently per journal, year, and publication productivity. The results indicate that (1) the overall probability of the first (last) author being female is 0.28 (0.19); (2) with the calculated rate of increase from 2010 to 2020, equal probabilities of female and male authorship would be reached towards the end of the century; (3) compared to the overall probability of male authorship (0.76), single-authored papers in our database are disproportionately published by male authors (with a probability of 0.83); (4) female representation decreases among highly productive authors; and (5) rather than being random, the composition of authorship appears to be influenced by gender - firstly, all-male author teams are more common than what would be expected if teams were composed randomly; secondly, the probability that first or co-authors are female increases when the last author is female, but first female authors have a low probability of working with female co-authors.ISSN:1869-9510ISSN:1869-952

Towards full waveform ambient noise inversion

ISSN:0956-540XISSN:1365-246