Miroslav Halló


Last Name

Halló

First Name

Miroslav

ORCID

0000-0001-5865-7767

Organisational unit

Filters

2020 - 202521
Reset filters

Search Results

Publications 1 - 10 of 21
  • Investigating the effects of random data errors on the waveform-based moment tensor inversion
    Item type: Journal Article
    Moghtased-Azar, Khosro; Zeynal-Kheiri, H.; Halló, Miroslav (2022)
    Geophysical Journal International
    The linear Gauss-Markov model for waveform-based moment tensor inversion often relies on the overdetermined least-squares method. It needs a proper stochastic model of the observables for accurate and precise estimates of the unknown parameters. Furthermore, estimating the level and distribution of random errors in the observed waveforms is challenging due to assessing the minimum-variance unbiased estimator (MVUE). Hence, according to the considerable effects of random data errors in assessing the uncertainty of the moment tensor components, this paper aims to describe an MVUE of the data covariance matrix and its application on uncertainty quantification of the moment tensor. The used mathematical prescription allows us to use the covariance matrix for the three-component noise records at every station and all possible cross-correlations among the recorded noise wavefield. To illustrate the proposed method's performance, we conducted tests with synthetic data using configuration of the 2018 M-w 6.8 Zakynthos (Ionian Sea, Greece) earthquake. Both uncorrelated and correlated random noise traces were added to the synthetic waveform data in amounts between 5 and 20 per cent of the maximum amplitude. In order to test the efficiency of the method, we considered three different structures of covariance matrix: (i) diagonal matrix (contains a variance of individual measurements at seismic stations), (ii) block-diagonal matrix (considering cross-covariance among three components at each station), and (iii) full covariance matrix. Test results are presented by comparison of the moment tensor inversion outcomes with known noise levels of generated synthetic data and with synthetic focal mechanisms, the ability of the estimated full covariance matrix in illustrating the minimum variance of parameters (namely, minimum posterior uncertainties), unbiased of the parameters, and values of the cross-correlations between the components of each station and also among stations. Finally, we applied the method to the real waveforms of the Zakynthos earthquake having inferred focal mechanism of strike/dip/rake angles 13/40/171 (deg) with 33 per cent double couple (DC) and -61 per cent compensated linear vector dipole component (CLVD). The focal mechanism solution has strike/dip/rake angles 19/34/177 (deg) with 69 per cent DC and -23 per cent CLVD when using our estimated full covariance matrix.
  • Empirical H/V spectral ratios at the InSight landing site and implications for the martian subsurface structure
    Item type: Journal Article
    Carrasco, Sebastián; Knapmeyer-Endrun, Brigitte; Margerin, Ludovic; et al. (2023)
    Geophysical Journal International
    The horizontal-to-vertical (H/V) spectral ratio inversion is a traditional technique for deriving the local subsurface structure on Earth. We calculated the H/V from the ambient vibrations at different wind levels at the InSight landing site, on Mars, and also computed the H/V from the S-wave coda of the martian seismic events (marsquakes). Different H/V curves were obtained for different wind periods and from the marsquakes. From the ambient vibrations, the recordings during low-wind periods are close to the instrument self-noise level. During high-wind periods, the seismic recordings are highly contaminated by the interaction of the lander with the wind and the martian ground. Therefore, these recordings are less favourable for traditional H/V analysis. Instead, the recordings of the S-wave coda of marsquakes were preferred to derive the characteristic H/V curve of this site between 0.4 and 10 Hz. The final H/V curve presents a characteristic trough at 2.4 Hz and a strong peak at 8 Hz. Using a full diffuse wavefield approach as the forward computation and the Neighbourhood Algorithm as the sampling technique, we invert for the 1-D shear wave velocity structure at the InSight landing site. Based on our inversion results, we propose a strong site effect at the InSight site to be due to the presence of a shallow high-velocity layer (SHVL) over low-velocity units. The SHVL is likely placed below a layer of coarse blocky ejecta and can be associated with Early Amazonian basaltic lava flows. The units below the SHVL have lower velocities, possibly related to a Late Hesperian or Early Amazonian epoch with a different magmatic regime and/or a greater impact rate and more extensive weathering. An extremely weak buried low velocity layer (bLVL) between these lava flows explains the data around the 2.4 Hz trough, whereas a more competent bLVL would not generate this latter feature. These subsurface models are in good agreement with results from hammering experiment and compliance measurements at the InSight landing site. Finally, this site effect is revealed only by seismic events data and explains the larger horizontal than vertical ground motion recorded for certain type of marsquakes.
  • Full-waveform prediction of high-frequency ground motion at depth from surface recordings in Japan
    Item type: Conference Paper
    Halló, Miroslav; Bergamo, Paolo; Fäh, Donat (2022)
    Proceedings of the Third European Conference on Earthquake Engineering and Seismology – 3ECEES
    The earthquake shaking observed on the ground surface differs from the shaking at depth beneath. This applies to observed temporal waveforms and intensity measure types such as PGA, and PGV. Such phenomenon is caused by the near-surface layers of soft rocks and soils that cause amplification and attenuation of seismic waves. The prediction of a possible ground motion at a site of interest is important for earthquake resistance design. Advancements in the prediction of the ground motion at depth are especially important for the design of deep geological disposals, buildings with deep foundations, or for studies of soil-structure interaction. In this contribution, we demonstrate our recently developed method to predict high-frequency ground motion at depth from surface recordings. We make use of a stochastic model formulated in the Fourier domain, which is based on a response of a layered 1D medium to incident body waves. We apply the method to predict borehole waveforms from surface recordings of the 2018 northern Osaka and 2013 Awaji Island earthquakes (Japan). Comparison of predicted and observed acceleration waveforms at four borehole sites show a high level of similarity in the broadband frequency range and well-predicted values of PGA and PGV at depth.
  • Multipath Transfer-Function Correction Method to Predict Site-Specific Amplification at City Scale
    Item type: Journal Article
    Halló, Miroslav; Bergamo, Paolo; Fäh, Donat (2024)
    Seismological Research Letters
    The site-specific amplification of seismic waves is an essential component of local seismic hazard assessment. It can be evaluated from empirical data, but measurements are feasible just in a limited number of locations. Hence, at the city scale, there is a need for the theoretical prediction and interpolation of the amplification. In this article, we introduce a physics-based method to predict the site-specific amplification and duration in a broad frequency range. The method is based on a novel energy-based concept of the multipath propagation of waves in viscoelastic media with random heterogeneities. The amplification is expressed by the surface-outcrop transfer function of the multipath wave propagation, which is defined by expected values of the energy spectral ratio. The method is applied to the near-surface 2D velocity model in the city of Zürich in Switzerland. The predicted amplification is validated by empirical data at a nearby seismic station, and it is compared with the soil class and other site-condition proxies. Finally, the method performance is demonstrated by the prediction of site-specific seismic waveforms and response spectra for the 2022 ML 4.7 Mulhouse earthquake.
  • Joint probabilistic multi-zonal trans-dimensional inversion on properties of near-surface layers from dispersion and ellipticity curves
    Item type: Conference Paper
    Halló, Miroslav; Imperatori, Walter; Panzera, Francesco; et al. (2021)
    6th IASPEI / IAEE International Symposium: Effects of Surface Geology on Seismic Motion - ESG6 Extended Abstracts
    This research focuses on the validation and application of a novel Bayesian approach to infer near-surface layered velocity models from dispersion and ellipticity curves. The inversion method relies on a varying number of layers, and it is formulated in the trans-dimensional Bayesian framework. The number of layers is treated as the model complexity governed by the law of parsimony. The model space is explored by a Markov chain Monte Carlo algorithm producing an ensemble of models drawn from the posterior probability of model parameters. The inversion method introduces also a multi-zonal formulation of the prior, allowing to include additional information to the inversion (e.g., from well logs). In this contribution, we focus on a validation of the inversion method using a synthetic test with a velocity gradient. We apply the approach to a Swiss site and show a comparison of the predicted theoretical and empirical amplification functions.
  • Investigating the subsurface in a shallow water environment using array and single-station ambient vibration techniques
    Item type: Journal Article
    Shynkarenko, Anastasiia; Lontsi, Agostiny Marrios; Kremer, Katrina; et al. (2021)
    Geophysical Journal International
    Single-station and array ambient vibration techniques are widely used in onshore environments, in particular to retrieve the subsurface structure and shear-wave velocity profiles. We apply these techniques offshore in Lake Lucerne (Switzerland) using single-station and array Ocean Bottom Seismometer (OBS) data. This lake has experienced tsunamigenic subaquatic slope failures in the past and still has sediment-charged slopes that might fail in the presence of a seismic or aseismic trigger. The application of traditional onshore methods offshore brings additional challenges related to the processing of recorded data. To overcome these challenges, we perform multibeam bathymetry surveys to precisely locate the OBS on the lake floor and airgun shootings to determine the orientation of the horizontal components of the seismometer and to correct the time drift of the recorder. Then we obtain surface-wave phase velocity dispersion curves of Scholte and Love waves, and Scholte wave ellipticity curves at six subaquatic slopes. After the estimation of the dispersion curves, we deal with their modal identification using mode attribution analysis. The shear-wave velocity and thickness of the sedimentary layers at the investigated slopes are inferred using a transdimensional Bayesian inversion algorithm. The resolved velocity profiles show very low shear-wave velocities in shallow lake sediments and allow us to improve the understanding of the local stratigraphy. This research contributes to the assessment of stability and tsunamigenic potential of subaquatic slopes in Lake Lucerne.
  • Erneuerung des Starkbebennetzwerks in der Schweiz (2009‐2023) - Abschlussbericht
    Item type: Report
    Fäh, Donat; Duvernay, Blaise; Michel, Clotaire; et al. (2024)
    Mit seinem Beschluss vom 18. Februar 2009 hat der Bundesrat den Antrag für die Erneuerung des Starkbebennetzes der Schweiz (Phase 1) gutgeheissen und deren Realisierung in Auftrag gegeben. Das Projekt umfasst in dieser ersten Phase (2009‐2013) die Installation und Inbetriebnahme von 30 modernen Erdbebenstationen. Diese sollen in erster Linie bestehende Lücken in der nationalen Überwachung schliessen. Dabei wurden alte Stationen teilweise ersetzt, aber auch neue Standorte realisiert. Im Rahmen des Projektes wurden neue Standards für die Installation von Starkbebenstationen definiert. Aufgrund der erfolgreichen ersten Phase hat der Bundesrat mit seinem Beschluss vom 30. Januar 2013 der Realisierung der zweiten Phase der Erneuerung des Starkbebenmessnetzes (2013‐2023) zugestimmt. In dieser zweiten Phase werden 70 Starkbebenmessstationen gebaut, davon vier Bohrlochinstallationen. Abbildung 1 gibt einen Überblick über die 100 Starkbebenstationen, die in den Phasen 1 und 2 installiert wurden. Beide Projektphasen wurden von einer Steuerungsgruppe unter der Leitung des Bundesamts für Umwelt (BAFU) begleitet. Für alle installierten Stationen wurde eine Standortcharakterisierung durchgeführt. Dabei kamen Ein‐Stations‐Methoden der seismischen Bodenunruhe, passive Arraymessungen und aktive seismische Messungen zum Einsatz. An Standorten mit besonderen Bodeneigenschaften, die bei Erdbeben zu nichtlinearem Materialverhalten oder Bodenverflüssigung neigen, wurden CPT‐ Messungen durchgeführt. Die Standortcharakterisierung wurde für jeden Standort in einem Bericht zusammengefasst. Die Messdaten und Auswertungen wurden in einer Datenbank gespeichert. Eine Beschreibung der Standorte und die Berichte zur Standortcharakterisierung sowie die Erdbebenaufzeichnungen der Starkbebenstationen sind auf den Webseiten des Schweizerischen Erdbebendienstes zugänglich.
  • Novel Bayesian inversion of dispersion and ellipticitycurves intended for subsurface characterization
    Item type: Other Conference Item
    Halló, Miroslav; Imperatori, Walter; Panzera, Francesco; et al. (2021)
    Properties of subsurface structure determine principal effects of local ground motion. Attributes of primary importance, i.e. S- and P-wave velocity profiles, can be inferred from Rayleigh and Love wave dispersion and ellipticity curves as retrieved from the single-station and array measurements. However, the measured data are subject to uncertainty and the solution exhibits significant inherent non-uniqueness as different velocity models provide a similar fit to observed data. This highlights the importance of rigorous treatment of uncertainty. Standard non-linear optimization inversion techniques chasing velocity models that provide a minimal data misfit; then a set of tested models might not be representative in terms of solution uncertainty. This can be overcome by an inversion formulation in the Bayesian (probabilistic) framework, where the uncertainty of the measured data is rigorously propagated to results. This research is focused on the development and application of a novel Bayesian inversion method intended for local subsurface characterization. Our inversion method is formulated in the transdimensional Bayesian parameter space, where 1-D velocity models may have a varying number of layers. The number of layers is treated as the model complexity that is governed by the data-driven law of parsimony. This parameter space is explored by a reversible-jump Markov chain Monte Carlo algorithm that produces an ensemble of models representative in terms of solution uncertainty. To suppress a possible dependency on an initial model, we use multiple parallel Markov chains with independent and random initial models (parallel tempering technique). We introduce also a multizonal formulation of the prior, allowing to include additional information to the inversion (from geological profiles, etc.). In this contribution, we present a validation of the inversion method using a synthetic test and application to a selected Swiss site. Our method is suitable for sites with low-velocity zones and it provides reliable estimates of solution uncertainty.
  • Joint multizonal transdimensional Bayesian inversion of surface wave dispersion and ellipticity curves for local near-surface imaging
    Item type: Journal Article
    Halló, Miroslav; Imperatori, Walter; Panzera, Francesco; et al. (2021)
    Geophysical Journal International
    Physical properties of near-surface soil and rock layers play a fundamental role in the seismic site effects analysis, being an essential element of seismic hazard assessment. Site-specific mechanical properties (i.e. shear- and compressional-wave velocities and mass density) can be inferred from surface wave dispersion and horizontal-to-vertical or ellipticity data by non-linear inversion techniques. Nevertheless, results typically exhibit significant inherent non-uniqueness as different models may fit the data equally well. Standard optimization inversion techniques minimize data misfit, resulting in a single representative model, rejecting other models providing similar misfit values. An alternative inversion technique can be formulated in the Bayesian framework, where the posterior probability density on the model space is inferred. This paper introduces an inversion approach of surface wave dispersion and ellipticity data based on a novel multizonal transdimensional Bayesian formulation. In particular, we parametrize 1-D layered velocity models by the varying number of Voronoi nuclei, allowing us to treat the number of layers as an unknown parameter of the inverse problem. The chosen parametrization leads to the transdimensional formulation of the model space, sampled by a reversible jump Markov chain Monte Carlo algorithm to provide an ensemble of random samples following the posterior probability density of model parameters. The used type of the sampling algorithm controls a model complexity (i.e. the number of layers) self-adaptively based on the measured data's information content. The method novelty lies in the parsimonious selection of sampling models and in the multizonal formulation of prior assumptions on model parameters, the latter allows including additional site-specific constraints in the inversion. These assumptions may be based on, e.g. stratigraphic logs, standard penetration tests, known water table, and bedrock depth. The multizonal formulation fully preserves the validity of the transdimensional one, as demonstrated analytically. The resultant ensemble of model samples is a discrete approximation of the posterior probability density function of model parameters and associated properties (e.g. V-S30, quarter-wavelength average velocity profile and theoretical SH-wave amplification function). Although the ultimate result is the posterior probability density function, some representative models are selected according to data fit and maximum of the posterior probability density function. We first validate our inversion approach based on synthetic tests and then apply it to field data acquired from the active seismic survey and single-station measurements of ambient vibrations at the SENGL seismic station site in central Switzerland.
Publications 1 - 10 of 21