A non-linear multiscale inversion approach for ambient noise tomography

2020 ◽  
Author(s):  
Iván Cabrera-Pérez ◽  
Luca D'Auria ◽  
Jean Soubestre ◽  
José Barrancos ◽  
Germán D Padilla ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Real Data ◽  
Progressive Increase ◽  
Industrial Applications ◽  
Small Scale ◽  
Ambient Noise Tomography ◽  
Linear Inversion ◽  
Non Linear ◽  
Regularization Techniques ◽  
Computational Resources

Summary Ambient noise tomography has been considerably used in the last decade in both academic and industrial research. In this work, we propose an innovative technique for ambient noise tomography based on non-linear multiscale inversions. Our method relies on a progressive increase in the model parametrization to reduce the non-linearity of the inverse problem. The developed method is compared with conventional inversion schemes (linear and non-linear), using different regularization techniques and two different network configurations. The inversion is tested on 22 different synthetic models including classical checkerboard tests. Furthermore, we performed the inversion using real data from a campaign in 2018 at Cumbre Vieja volcano (Canary Islands). The results obtained on both network configurations show an improvement compared to conventional linear and non-linear inversion schemes, especially when the ray path density is low. This technique does not require expensive computational resources, making it convenient for small scale industrial applications, especially in the framework of geothermal exploration.

Ambient noise tomography of Gran Canaria island (Canary Islands)

2021 ◽  
Author(s):  
Iván Cabrera Pérez ◽  
Jean Soubestre ◽  
Luca D'Auria ◽  
Germán Cervigón-Tomico ◽  
David Martínez van Dorth ◽  
...  
Keyword(s):  
Group Velocity ◽  
Canary Islands ◽  
Ambient Noise ◽  
Velocity Model ◽  
Dispersion Curves ◽  
Ambient Noise Tomography ◽  
Gran Canaria ◽  
Geothermal Reservoirs ◽  
Velocity Models ◽  
Non Linear

<p>The island of Gran Canaria is located in the Canarian Archipelago, with an area of 1560 km<sup>2 </sup>and a maximum altitude of 1956 m.a.s.l., being the third island of the archipelago in terms of extension and altitude. The island has two very well differentiated geological domains: the southwest domain or Paleo-Canarias, which is the geologically oldest part, and the northeast domain or Neo-Canarias, where are located the vents of the most recent Holocene eruptions. This volcanic island hosted Holocene eruptions. Therefore, apart from being affected by volcanic risk, it potentially hosts geothermal resources that could be exploited to increase the percentage of renewable energy in the Canary Islands.</p><p>The main objective of this work is to use Ambient Noise Tomography (ANT) for retrieving a high-resolution seismic velocity model of the first few kilometres of the crust, to improve local earthquake location and detect anomalies potentially related to active geothermal reservoirs. Currently, the 1-D velocity model of the island does not allow a correct determination of the hypocenters, being unable to take into account the substantial horizontal velocity contrasts correctly.</p><p>To realize the ANT, we deployed 28 temporary broadband seismic stations in two phases. Each campaign lasted at least one month. We also exploited data recorded by the permanent seismic network Red Sísmica Canaria (C7) operated by INVOLCAN. After applying standard data processing to retrieve Green’s functions from ambient noise cross-correlations, we retrieved the dispersion curves using the FTAN (Frequency Time ANalysis) technique. The inversion of dispersion curves to obtain group velocity maps was realized using a novel non-linear multiscale tomographic approach (MAnGOSTA, Multiscale Ambient NOiSe TomogrAphy). The forward modelling of surface waves traveltimes was implemented using a shortest-path algorithm that allows the topography to be taken into account. The MANgOSTA method consists of successive non-linear inversion steps on progressively finer grids. This technique allows retrieving 2-D group velocity models in the presence of substantial velocity contrasts with up to 100% of the relative variation. Then, we performed a depth inversion of the Rayleigh wave dispersion curves using a transdimensional Bayesian formulation. The final result is a 3-D model of P- and S-wave velocities of the island. The preliminary results show the presence of a low-velocity zone in the eastern part of the island that coincides spatially with anomalies observed in previous geophysical and geochemical studies and which could be related to actual or fossil geothermal reservoirs. Furthermore, the model shows the presence of high-velocity anomalies that are associated with the mafic core of the island.</p>

scholarly journals Crustal structures beneath the Eastern and Southern Alps from ambient noise tomography

Solid Earth ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 1947-1968 ◽  
Author(s):  
Ehsan Qorbani ◽  
Dimitri Zigone ◽  
Mark R. Handy ◽  
Götz Bokelmann ◽  
Keyword(s):  
Crustal Structure ◽  
Ambient Noise ◽  
Southern Alps ◽  
Small Scale ◽  
Ambient Noise Tomography ◽  
Tauern Window ◽  
Velocity Models ◽  
Austroalpine Nappes ◽  
Cross Correlations ◽  
Velocity Anomalies

Abstract. We study the crustal structure under the Eastern and Southern Alps using ambient noise tomography. We use cross-correlations of ambient seismic noise between pairs of 71 permanent stations and 19 stations of the Eastern Alpine Seismic Investigation (EASI) profile to derive new 3D shear velocity models for the crust. Continuous records from 2014 and 2015 are cross-correlated to estimate Green's functions of Rayleigh and Love waves propagating between the station pairs. Group velocities extracted from the cross-correlations are inverted to obtain isotropic 3D Rayleigh- and Love-wave shear-wave velocity models. Our models image several velocity anomalies and contrasts and reveal details of the crustal structure. Velocity variations at short periods correlate very closely with the lithologies of tectonic units at the surface and projected to depth. Low-velocity zones, associated with the Po and Molasse sedimentary basins, are imaged well to the south and north of the Alps, respectively. We find large high-velocity zones associated with the crystalline basement that forms the core of the Tauern Window. Small-scale velocity anomalies are also aligned with geological units of the Austroalpine nappes. Clear velocity contrasts in the Tauern Window along vertical cross sections of the velocity model show the depth extent of the tectonic units and their bounding faults. A mid-crustal velocity contrast is interpreted as a manifestation of intracrustal decoupling in the Eastern Alps that accommodated eastward escape of the Alcapa block.

Sensitivity enhancement of the ambient noise tomography and analysis of seasonal variations of noise sources to refine velocities in the lower crust in central Europe

2021 ◽  
Author(s):  
Jiri Kvapil ◽  
Jaroslava Plomerova ◽  
AlpArray Working Group
Keyword(s):  
Central Europe ◽  
Seasonal Variations ◽  
Lower Crust ◽  
Ambient Noise ◽  
Regional Scale ◽  
Dispersion Curves ◽  
Small Scale ◽  
Ambient Noise Tomography ◽  
Noise Sources

<p>The capability of the ambient noise tomography (ANT) to image subtle regional-scale velocity variations <span>in </span>the lower crust is limited by strong directionality of ambient noise sources in central Europe, which affects the quality of dispersion curves. Significant decrease of sensitivity kernels and sparse coverage of long interstation ray-pathes result in lower resolution at longer periods and thus <span>increase</span> uncertainty of the inversion solution <span>in</span> depth. <span>If</span> these well-known ANT <span>limitations</span> are properly addressed, the ANT is able to retrieve reliable high-resolution 3‑D shear velocities of the lower crust.</p><p>In this study we focus on seasonal variations of ambient noise sources in selected sites in different tectonic settings. We analyse ambient noise sources on continusly recorded wavefields from permanent observatories and temporary stations of AlpArray passive experiment with its complementary experiment and PACASE. These seismic networks with densely-spaced stations are well-suited for detailed analysis of period-dependent directionality of ambient noise sources and their effects on FTAN appearance and consequently on the quality of dispersion curves. In the second part of this study, we advocate a concept of layer-stripping during the stochastic inversion (enhanced ANT). It proved to be an efficient technique to explore the model space, particularly in the lower part of the crust. We discuss the sensitivity of the enhanced ANT to the imaged small-scale velocity features in the lower part of the crust, as well as the sensitivity to the sharp or gradational Moho in the models.</p>

Non-Linear Interaction of MHD Waves with Small-Scale Ionospheric Irregularities

2004 ◽  
Vol 61 (7-12) ◽  
pp. 1055-1071
Author(s):  
N. N. Gerasimova ◽  
V. G. Sinitsin ◽  
Yu. M. Yampolski
Keyword(s):  
Ionospheric Irregularities ◽  
Mhd Waves ◽  
Small Scale ◽  
Linear Interaction ◽  
Non Linear

Justifying the data analytical choice in single case research in relation to the expected data pattern

2019 ◽  
Author(s):  
Rumen Manolov
Keyword(s):  
Data Analysis ◽  
Visual Analysis ◽  
Multilevel Models ◽  
Single Case ◽  
Analytical Techniques ◽  
Real Data ◽  
Small Scale ◽  
Data User ◽  
Single Case Research ◽  
User Friendly

The lack of consensus regarding the most appropriate analytical techniques for single-case experimental designs data requires justifying the choice of any specific analytical option. The current text mentions some of the arguments, provided by methodologists and statisticians, in favor of several analytical techniques. Additionally, a small-scale literature review is performed in order to explore if and how applied researchers justify the analytical choices that they make. The review suggests that certain practices are not sufficiently explained. In order to improve the reporting regarding the data analytical decisions, it is proposed to choose and justify the data analytical approach prior to gathering the data. As a possible justification for data analysis plan, we propose using as a basis the expected the data pattern (specifically, the expectation about an improving baseline trend and about the immediate or progressive nature of the intervention effect). Although there are multiple alternatives for single-case data analysis, the current text focuses on visual analysis and multilevel models and illustrates an application of these analytical options with real data. User-friendly software is also developed.

Numerical Approaches for Modeling Gas–Solid Fluidized Bed Reactors: Comparison of Models and Application to Different Technical Problems

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Peter Ostermeier ◽  
Annelies Vandersickel ◽  
Stephan Gleis ◽  
Hartmut Spliethoff
Keyword(s):  
Calcium Carbonate ◽  
Size Distribution ◽  
Fluidized Bed ◽  
Fluid Model ◽  
Industrial Applications ◽  
Small Scale ◽  
Fluidized Bed Reactors ◽  
Discrete Phase Model ◽  
Technical Problems ◽  
Numerical Approaches

Gas–solid fluidized bed reactors play an important role in many industrial applications. Nevertheless, there is a lack of knowledge of the processes occurring inside the bed, which impedes proper design and upscaling. In this work, numerical approaches in the Eulerian and the Lagrangian framework are compared and applied in order to investigate internal fluidized bed phenomena. The considered system uses steam/air/nitrogen as fluidization gas, entering the three-dimensional geometry through a Tuyere nozzle distributor, and calcium oxide/corundum/calcium carbonate as solid bed material. In the two-fluid model (TFM) and the multifluid model (MFM), both gas and powder are modeled as Eulerian phases. The size distribution of the particles is approximated by one or more granular phases with corresponding mean diameters and a sphericity factor accounting for their nonspherical shape. The solid–solid and fluid–solid interactions are considered by incorporating the kinetic theory of granular flow (KTGF) and a drag model, which is modified by the aforementioned sphericity factor. The dense discrete phase model (DDPM) can be interpreted as a hybrid model, where the interactions are also modeled using the KTGF; however, the particles are clustered to parcels and tracked in a Lagrangian way, resulting in a more accurate and computational affordable resolution of the size distribution. In the computational fluid dynamics–discrete element method (CFD–DEM) approach, particle collisions are calculated using the DEM. Thereby, more detailed interparticulate phenomena (e.g., cohesion) can be assessed. The three approaches (TFM, DDPM, CFD–DEM) are evaluated in terms of grid- and time-independency as well as computational demand. The TFM and CFD–DEM models show qualitative accordance and are therefore applied for further investigations. The MFM (as a variation of the TFM) is applied in order to simulate hydrodynamics and heat transfer to immersed objects in a small-scale experimental test rig because the MFM can handle the required small computational cells. Corundum is used as a nearly monodisperse powder, being more suitable for Eulerian models, and air is used as fluidization gas. Simulation results are compared to experimental data in order to validate the approach. The CFD–DEM model is applied in order to predict mixing behavior and cohesion effects of a polydisperse calcium carbonate powder in a larger scale energy storage reactor.

scholarly journals Ambient Noise Tomography Images Accreted Terranes and Igneous Provinces in Hispaniola and Puerto Rico

2018 ◽  
Vol 45 (22) ◽  
pp. 12,293-12,301 ◽  
Author(s):  
D. A. Quiros ◽  
J. Pulliam ◽  
D. Barman ◽  
E. Polanco Rivera ◽  
V. Huerfano
Keyword(s):  
Puerto Rico ◽  
Ambient Noise ◽  
Ambient Noise Tomography ◽  
Igneous Provinces ◽  
Accreted Terranes
Sign in / Sign up

Export Citation Format

Share Document