Francesco Panzera

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Panzera

First Name

Francesco

ORCID

0000-0003-3062-4044

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Publications 1 - 10 of 48

Reconstructing a 3D model from geophysical data for local amplification modelling: The study case of the upper Rhone valley, Switzerland
Panzera, Francesco; Alber, Jonas; Imperatori, Walter; et al. (2022)
Soil Dynamics and Earthquake Engineering
The geometry of three-dimensional subsurface structures plays an important role in determining local seismic site effects as in the case of alpine valleys. Detailed knowledge of these structures is fundamental in seismic hazard and risk studies. In this study we investigate an area in the upper Rhone valley around Visp, in the southwestern part of Switzerland. A large dataset of geological and geophysical data, consisting of borehole logs, microtremor horizontal to vertical spectral ratios and shear-wave velocity measurements, was compiled to build a detailed 3D model of the subsurface. By combining fundamental frequency information from noise recordings and shear-wave velocity profiles, three main geophysical discontinuities were identified and their physical properties constrained through a stepwise process. First, the bedrock depth was estimated; in a second step a generic velocity model was defined and finally, combining all the available geological and geophysical information, we developed a 3D geophysical model. The model was compared with a local 3D geological model and a model derived from gravimetric data. The study area is a complex alpine valley where 2D/3D wave propagation phenomena occur. In such case a purely 1D response assumption is considered to be invalid. In order to test the 3D model, we modelled different ambient-vibration wave fields and compared observed and synthetic H/V spectral ratios. We slightly modified our 3D geophysical model in some areas based on this comparison. Finally, a good match between simulated and empirical spectral ratios corroborated the model. The results suggest that the use of ambient vibration techniques are a powerful and cost-effective tools to reconstruct three-dimensional models of the subsurface. Finally, we used the 3D model to predict amplification of earthquake ground motion in the basin. Again, the match between observed and modelled amplification at the locations of the seismic stations is good. This allows us to map amplification inside the study area.
On the correlation between earthquake coda horizontal-to-vertical spectral ratios and amplification functions at the KiK-net network
Panzera, Francesco; Bergamo, Paolo; Perron, Vincent; et al. (2022)
Frontiers in Earth Science
The Japanese KiK-net network comprises about 700 stations spread across the whole territory of Japan. For most of the stations, VP and VS profiles were measured down to the bottom borehole station. Using the vast dataset of earthquake recordings from 1997 to 2020 at a subset of 428 seismic stations, we compute the horizontal-to-vertical spectral ratio of earthquake coda, the S-wave surface-to-borehole spectral ratio, and the equivalent outcropping S-wave amplification function. The de facto equivalence of the horizontal-to-vertical spectral ratio of earthquake coda and ambient vibration is assessed on a homologous Swiss dataset. Based on that, we applied the canonical correlation analysis between amplification information and the horizontal-to-vertical spectral ratio of earthquake coda across all KiK-net sites. The aim of the correlation is to test a strategy to predict local earthquake amplification basing the inference on site condition indicators and single-station ambient vibration recordings. Once the correlation between frequency-dependent amplification factors and amplitudes of horizontal-to-vertical coda spectral ratios is defined, we predict amplification at each site in the selected KiK-net dataset with a leave-one-out cross-validation approach. In particular, for each site, three rounds of predictions are performed, using as prediction target the surface-to-borehole spectral ratio, the equivalent of a standard spectral ratio referred to the local bedrock and to a common Japanese reference rock profile. From our analysis, the most effective prediction is obtained when standard spectral ratios referred to local bedrock and the horizontal-to-vertical spectral ratio of earthquake coda are used, whereas a strong mismatch is obtained when standard spectral ratios are referred to a common reference. We ascribe this effect to the fact that, differently from amplification functions referred to a common reference, horizontal-to-vertical spectral ratios are fully site-dependent and then their peak amplitude is influenced by the local velocity contrast between bedrock and overlying sediments. Therefore, to reduce this discrepancy, we add in the canonical correlation as a site proxy the inferred velocity of the bedrock, which improves the final prediction.
Preliminary results of estimating the non-linear site response in the Lucerne area
Janusz, Paulina; Bonilla, Luis Fabian; Perron, Vincent; et al. (2022)
Abstract Volume 20th Swiss Geoscience Meeting
Reference soil condition for intensity prediction equations derived from seismological and geophysical data at seismic stations
Panzera, Francesco; Bergamo, Paolo; Fäh, Donat (2021)
Journal of Seismology
In 2011, an amplification map achieved by macroseismic information was developed for Switzerland using the collection of macroseismic intensity observations of past earthquakes. For each village, a Delta Imwas first derived, which reflects the difference between observed and expected macroseismic intensities from a region-specific intensity prediction equation. The Delta Imvalues are then grouped into geological/tectonic classes, which are then presented in the macroseismic amplification map. Both, the intensity prediction equation and the macroseismic amplification map are referenced to the same reference soil condition which so far was only roughly estimated. This reference soil condition is assessed in this contribution using geophysical and seismological data collected by the Swiss Seismological Service. Geophysical data consist of shear-wave velocity profiles measured at the seismic stations and earthquake recordings, used to retrieve empirical amplification functions at the sensor locations. Amplification functions are referenced to a generic rock profile (Swiss reference rock condition) that is well defined, and it is used for the national seismic hazard maps. Macroseismic amplification factorsAf, derived from empirical amplification functions, are assigned to each seismic station using ground motion to intensity conversions. We then assess the factorsd Delta fdefined as the difference betweenAfand Delta Im. The factord Delta faccounts for the difference between the reference soil condition for the intensity prediction equation and the Swiss reference rock. We finally analysed relationships betweenAfand proxies for shear-wave velocity profiles in terms of average shear-wave velocity over defined depth ranges, such asV(S,30), providing an estimate of the reference shear velocity for the intensity prediction equation and macroseismic amplification map. This study allows linking macroseismic intensity observations with experimental geophysical data, highlighting a good correspondence within the uncertainty range of macroseismic observations. However, statistical significance tests point out that the seismic stations are not evenly distributed among the various geological-tectonic classes of the macroseismic amplification map and its revision could be planned merging classes with similar behaviour or by defining a new classification scheme.
Geophysical surveys for the characterization of the seismic local response at instrumented sites: a case study from a station of the Swiss strong motion network
Bergamo, Paolo; Panzera, Francesco; Hobiger, Manuel; et al. (2022)
Proceedings of the Third European Conference on Earthquake Engineering and Seismology – 3ECEES
Site characterization surveying is one of the key efforts for the understanding of local amplification effects in earthquake engineering. In this perspective, geophysical measurements for the estimation of the physical properties of the subsurface at instrumented sites are particularly important. For instance, the comparison between simulated site amplification based on the retrieved Vs profile and empirical local response observed at the station allows assessing whether the site is characterized by a purely 1D response or additional 2D-3D effects are present. We present a case study involving a site characterization measurement at a station of the Swiss strong-motion network. The survey includes active seismic data acquisition along two geophone lines, of 15 and 115 m length, for the imaging of the near-surface and deeper layers, respectively. The acquired data were interpreted in terms of P-wave refraction and Rayleigh-wave multi-modal propagation analysis. The reconstructed Vs-Vp profiles achieve a high level of accuracy over a wide depth range and allow modelling the SH-transfer function of the local soil column; the latter is in excellent agreement with the local amplification function estimated by means of empirical spectral modelling of the station’s recordings. The agreement confirms a purely 1D site response for the surveyed station.
Insights into the dynamics of the Nirano Mud Volcano through seismic characterization of drumbeat signals and V/H analysis
Antunes, Verónica; Planès, Thomas; Obermann, Anne; et al. (2022)
Journal of Volcanology and Geothermal Research
Mud volcanoes are rapidly-evolving geological phenomena characterized by the surface expulsion of sediments and fluids from over-pressurized underlying reservoirs. We investigate the Nirano Mud Volcano, Northern Italy, with seismic methods to better understand the dynamic evolution of the system and shed light on its subsurface structure. Our study allowed to detect and characterize three different types of high-frequency drumbeat signals that are present in the most active part of the mud volcano plumbing system. With a back-projection method based on the cross-correlation envelope of signals recorded at different station pairs, we can determine the source location of the drumbeats. These coincide with the location of V/H (vertical-to-horizontal) amplitude peaks obtained from an ambient vibration profile and resistivity anomalies identified in a previous study. We observe that the drumbeats are P-wave dominated signals, with characteristics similar to those found in magmatic settings, i.e. LPs (long-period signals). We suggest that such tremors originate from the migration of mud and gas inside the mud volcanic conduits. The source location, waveform and frequency content of the drumbeats evolve over time. We found that drumbeat occurrence is directly linked with morphological changes at surface.
Integrated use of ambient vibrations and geological methods for seismic microzonation
Panzera, Francesco; Romagnoli, Gino; Tortorici, Giuseppe; et al. (2019)
Journal of Applied Geophysics
A revised earthquake catalogue for South Iceland
Panzera, Francesco; Zechar, J. Douglas; Eberhard, David A. J.; et al. (2015)
Pure and Applied Geophysics
Modello di amplificazione sismica per la Svizzera basato su indicatori di condizione di sito e sulla risposta sismica locale misurata alle stazioni sismiche
Bergamo, Paolo; Panzera, Francesco; Cauzzi, Carlo Virgilio; et al. (2022)
Atti del 40° Convegno Nazionale
Cultural heritage and earthquakes: bridging the gap between geophysics, archaeoseismology and engineering
Pecchioli, Laura; Panzera, Francesco; Poggi, Valerio (2020)
Journal of Seismology

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Francesco Panzera

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