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Your search keyword '"Limberger, Fabian"' showing total 11 results
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11 results on '"Limberger, Fabian"'

1. When linear inversion fails: neural-network optimization for sparse-ray travel-time tomography of a volcanic edifice

Author

Komeazi, Abolfazl, Rümpker, Georg, Faber, Johannes, Limberger, Fabian, and Srivastava, Nishtha

Subjects
Physics - Geophysics
Abstract

In this study, we present an artificial neural network (ANN)-based approach for travel-time tomography of a volcanic edifice. We employ ray tracing to simulate the propagation of seismic waves through the heterogeneous medium of a volcanic edifice, and an inverse modeling algorithm that uses an ANN to estimate the velocity structure from the observed travel-time data. The performance of the approach is evaluated through a 2-dimensional numerical study that simulates i) an active source seismic experiment with few (explosive) sources placed on one side of the edifice and a dense line of receivers placed on the other side, and ii) earthquakes located inside the edifice and receivers placed on both sides of the edifice. The results are compared with those obtained from conventional damped linear inversion, demonstrating that the ANN-based approach outperforms the classical approach, particularly in situations with sparse ray coverage. Our study emphasizes the advantages of employing a relatively simple ANN architecture in conjunction with second-order optimizers to minimize the loss function. The ANN-based approach is computationally efficient and capable of providing high-resolution velocity images of anomalous structures within the edifice, making it a potentially valuable tool for the detection of low velocity anomalies related to magmatic intrusions or mush., Comment: 26 pages, 9 figures in the main text, 6 figures in supplementary material, 1 table in the main text, 1 table in supplementary material

Published
2023

7. The impact of seismic noise produced by wind turbines on seismic borehole measurements.

Author

Limberger, Fabian, Rümpker, Georg, Lindenfeld, Michael, and Deckert, Hagen

Subjects
MICROSEISMS, WIND turbines, SEISMIC wave velocity, AERODYNAMIC noise, SEISMOMETERS
Abstract

Seismic signals produced by wind turbines can have an adverse effect on seismological measurements up to distances of several kilometres. Based on numerical simulations of the emitted seismic wavefield, we study the effectivity of seismic borehole installations as a way to reduce the incoming noise. We analyse the signal amplitude as a function of sensor depth and investigate effects of seismic velocities, damping parameters and geological layerings in the subsurface. Our numerical approach is validated by real data from borehole installations affected by wind turbines. We demonstrate that a seismic borehole installation with an adequate depth can effectively reduce the impact of seismic noise from wind turbines in comparison to surface installations. Therefore, placing the seismometer at greater depth represents a potentially effective measure to improve or retain the quality of the recordings at a seismic station. However, the advantages of the borehole decrease significantly with increasing signal wavelength. [ABSTRACT FROM AUTHOR]

Published
2023
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8. Seismic radiation from wind turbines: observations and analytical modeling of frequency-dependent amplitude decays

Author

Limberger, Fabian, Lindenfeld, Michael, Deckert, Hagen, and Rümpker, Georg

Subjects
ddc:550
Abstract

In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen, Germany. Average power spectral densities (PSDs) are calculated from 10 min time segments extracted from (up to) 6 months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify seven distinct PSD peaks in the frequency range between 1 and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b values exhibit a linear frequency dependence and range from b=0.39 at 1.14 Hz to b=3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach that approximates the surface wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase shift elimination method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the seven prominent frequencies shows very good agreement and allows the constraint of shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.

Published
2021

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