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Decoupled joint inversion with variable splitting: example scheme for magnetotelluric, seismic and gravity data
Full text linkWe present a general framework for multiphysics joint inversion of any number of geophysical data sets. Its main feature is the use of the variable splitting approach: an auxiliary multiparameter model space is introduced in which minimization of the coupling and stabilizing functionals is carried out. The use of rediscretization and interpolation to map between this auxiliary space and the model spaces allows the coupled models to have completely different parametrizations. Joint inversion is decoupled into the individual inversion and the coupling-regularization subproblems, each of which can be solved by a different optimization algorithm. For each subproblem, the linking term controlling the distance between the model and the corresponding auxiliary variable takes the form of a quadratic regularization with a reference model. As a result, any existing inversion code supporting such regularization can be integrated without modifications into the developed framework. As a concrete example scheme, we consider an application of the framework to 3-D joint inversion of magnetotelluric, seismic refraction and gravity data. We discuss different coupling functionals, mainly those corresponding to the more universal structural constraints: joint total variation, joint minimum support, cross-gradient, one-way cross-gradient and their combinations for a general multimodel case. The use of coupling based on explicit ‘petrophysical’ relationship between the properties is also considered. Performance of the developed framework is studied on three synthetic cases: a time-lapse joint inversion of full-tensor gravity gradiometry and seismic data, a joint inversion of magnetotelluric, seismic and gravity data and a joint inversion for electrical resistivity tomography and audio-magnetotellurics
Monitoring Northeast Atlantic Ocean Wave Heights Using Terrestrially Recorded Seismic Signals
No full textThe monitoring of ocean Significant Wave Heights (SWH) utilizes a variety of techniques, including insitu buoys, numerical ocean wave modeling, and satellite altimetry. Each method has its own strengths and weaknesses in terms of spatial and temporal resolution.
This study conducts a comparative analysis between estimated wave heights from Numerical Wave Modeling (HINDCAST) and measured buoy data. Subsequently, both datasets are utilized as inputs for a new approach to estimate Significant Wave Heights (SWH) using an Artificial Neural Network (ANN) applied to terrestrial seismic data (microseisms). This approach combines the spatial and temporal resolutions of buoy and HINDCAST data, enabling the potential for quasi-real time monitoring under specific conditions. The ANN is trained using both seismic amplitude data from the Irish National Seismic Network (INSN), buoy measurements and HINDCAST data, to estimate SWH at specific locations, offshore in the Northeast Atlantic.
Preliminary comparisons between the Artificial Neural Network (ANN) results and Buoy/HINDCAST data indicate a strong correlation between secondary microseism amplitudes recorded on land and ocean significant wave height (SWH). Notably, for small and moderate measured wave heights, the ocean wave heights derived from terrestrial seismic measurements show minimal discrepancies between the ANN and actual Buoy data, as well as between the ANN and HINDCAST data. This promising result highlights the potential for the continuous estimation of offshore ocean wave heights from dependable land based seismic observations
Lithospheric Structure Beneath the Sierra Nevada de Santa Marta, Colombia, Observed from Receiver Function Profiles and Relocated Seismicity
No full textIn the north-western region of South America takes place the subduction of two tectonic plates, the Nazca and Caribbean plates, and the convergence with the Panama-Choco arc. To the north of Colombia, the Sierra Nevada de Santa Marta (SNSM) is a tetrahedron-shaped mountain, located above the Caribbean slab, and at the intersection of important fault structures such as the Santa Marta-Bucaramanga Fault and the Oca Fault.
Some features of the SNSM are puzzling, including its coastal location and high elevation of more than 5.7 km, and its significant positive Bouguer anomaly (>130 mGal). These observations and previous receiver function studies suggest that the SNSM isn’t supported by a crustal root. The loss of this crustal root could have resulted from its eclogitization followed by its removal due to gravitational instabilities.
In the present study, we investigate the lithospheric structure beneath the SNSM using receiver functions and seismicity distribution. Receiver functions are calculated for the period 2014 to 2024 using stations from the Colombian national network and the Caribbean-Mérida Andes Seismic arrays, surrounding the SNSM. The seismicity include approximately 9000 events from 2016 to 2022, observed by the same seismological networks, and relocated using a recent 3D velocity model. The updated Moho topography for this area shows a significant relief below the SNSM and relatively shallow values. Using receiver function profiles and the relocated seismicity, we also investigate the lithospheric structure of the South American plate and the Caribbean subducting slabs, as well as the seismic anisotropy in this region
Magnetotelluric evidence for the deep causes of different eruptive styles of Changbaishan Tianchi and Longgang volcanoes
Full text linkLonggang Volcano (LGV) and Changbaishan Tianchi Volcano (CTV) share a common magmatic source at
mantle depths. However, the two volcanoes have produced completely different types of eruptions. By
performing 3D inversion of an MT dataset that completely covers the LGV and CTV, we have obtained
high-resolution electrical resistivity images. The results reveal that the two volcanoes have distinct
magmatic plumbing systems, and this is likely the reason for their different eruptive styles. Results
from 3D modeling do not show a magma chamber in the shallow crust beneath LGV, interpreted as the
rapid rise of the magma from the mantle is responsible for producing a series of densely distributed
volcanic cones in the LGV field. In contrast, there is a magma chamber in the upper crust beneath the
CTV, where the fractional crystallization and mixing of magma has occurred. This magma chamber
has facilitated multiple centralized eruptions, and thereby has led to the formation of the large CTV
volcanic cone. These results indicate that differences in their crustal structures may have controlled the
different eruptive activities of the LGV and CTV in CVS, Northeast China
Textual Structure, Dialogue and the Layout of the Manuscripts of Acallam na Senórach
Full text linkIn the medieval Irish frame narrative Acallam na Senórach ‘The Colloquy of the Ancients’, the ancient Irish warriors Caílte and Oisín meet Saint Patrick and take him on a tour of Ireland, telling him hundreds of stories about the late Finn mac Cumaill. The nature of the text has led scholars to see Acallam na Senórach as episodic; yet, no research has been done into the manuscript evidence relating to how scribes and medieval readers may have conceived of the narrative as containing different parts, such as how the text is displayed on the page and which initials are coloured or indented in the margins. This article draws on the concepts of ‘grammar of legibility’ (Parkes 1992: 23) and ‘lisibilité du texte’ ‘legibility of the text’ (Bergeron & Ornato 1990: 151–152) to address this desideratum. The present study focusses on the five manuscripts (s. xv–xvii) in which Acallam na Senórach survives, and demonstrates that layout, colours, litterae notabiliores and paragraphs are used as a way to mark dialogue and the textual structure of the narrative
Connecting stellar and galactic scales: Energetic feedback from stellar wind bubbles to supernova remnants
No full textContext. Energy and momentum feedback from stars is a key element in models of galaxy formation and interstellar medium (ISM) dynamics, but resolving the relevant length scales in order to directly include this feedback remains beyond the reach of current-generation simulations.
Aims. We aim to constrain the energy feedback of winds, photoionisation, and supernovae (SNe) from massive stars.
Methods. We measure the thermal and kinetic energy imparted to the ISM on various length scales, which we calculate from high-resolution 1D radiation-hydrodynamics simulations. Our grid of simulations covers a broad range of densities, metallicities, and state-of-the-art evolutionary models of single and binary stars.
Results. A single star or binary system can carve a cavity of tens of parsecs (pc) in size into the surrounding medium. During the pre-SN phase, post-main sequence stellar winds and photoionisation dominate. While SN explosions dominate the total energy budget, the pre-SN feedback is of great importance by reducing the circumstellar gas density and delaying the onset of radiative losses in the SN remnant. Contrary to expectations, the metallicity dependence of the stellar wind has little effect on the cumulative energy imparted by feedback to the ISM; the only requirement is the existence of a sufficient level of pre-SN radiative and mechanical feedback. The ambient medium density determines how much and when feedback energy reaches distances of ≳10–20 pc and affects the division between kinetic and thermal feedback.
Conclusions. Our results can be used as a subgrid model for feedback in large-scale simulations of galaxies. The results reinforce that the uncertain mapping of stellar evolution sequences to SN explosion energy is very important for determining the overall feedback energy from a stellar population
Review of Smyth, Marina: The 'Liber de ordine creaturarum'. Turnhout: Brepols. Brepols Library of Christian Sources 5. 2023. 191 pp. ISBN: 978-2-503-59678-5.
No full textLiber de ordine creaturarum (DOC) is an anonymous Hiberno-Latin work of theological cosmology that was composed in the second half of the seventh century. The review begins with an assessment of DOC's philosophical and theological significance. The volume itself is largely a composite of two earlier publications: Díaz y Díaz (1972: edition and notes), and Smyth (2011: translation and introduction)
Stacking of Distributed Dynamic Strain Reveals Link Between Seismic Velocity Changes and the 2020 Unrest in Reykjanes
Full text linkIn this study, we measure seismic velocity variations during two cycles of crustal inflation and deflation in 2020 on the Reykjanes peninsula (SW Iceland) by applying coda wave interferometry to ambient noise recorded by distributed dynamic strain sensing (also called DAS). We present a new workflow based on spatial stacking of raw data prior to cross-correlation which substantially improves the spatial coherency and the time resolution of measurements. Using this approach, a strong correlation between velocity changes and ground deformation (in the vertical and horizontal direction) is revealed. Our findings may be related to the infiltration of volcanic fluids at shallow depths, even though the concurrent presence of various processes complicates the reliable attribution of observations to specific geological phenomena. Our work demonstrates how the spatial resolution of DAS can be exploited to enhance existing methodologies and overcome limitations inherent in conventional seismological data sets
Machine Learning Approaches to Seismic Velocity Model and Seismogram Prediction in Earth’s Shallow Crust
Full text linkRecent advances in machine learning present new ways for geoscientists to predict geological subsurface properties. Fourier Neural Operators (FNOs) are increasingly being used as an alternative to conventional seismic imaging approaches. FNOs have been shown to predict accurate simulations of seismic waves several hundred times faster than physics-based solvers post-training. In synthetic volcanic settings, FNOs have been applied successfully to both the forward and inverse problem, capturing fine-scale velocity structure in heterogeneous models and seismograms. However, transferring the successful performance of simulation-trained FNOs to field-gathered seismic data is yet to be attained. To achieve this, training models must contain representative small-scale velocity heterogeneities and topography to produce highly scattered codas in synthetic seismograms. This research presents work in progress on simulation-to-real FNO
applications using field-gathered seismic data from offshore sedimentary basin settings as a testbed environment. Historical seismic survey datasets from Atlantic sedimentary basins are often accompanied by additional site-specific
geological constraints. This makes the creation of synthetic velocity models and seismograms with field-derived properties possible, centering the collation of data for real-world machine learning applications in the numerical domain. The longterm research goal is to bring insights gained from training FNOs on a better understood seismic environment to volcanic and other complex environments in future work