Wavefield Polarization in Fault Zones of the Western Flank of Mt. Etna: Observations and Fracture Orientation Modelling

Panzera, Francesco; Pischiutta, Marta; Lombardo, Giuseppe; Monaco, Carmelo; Rovelli, A.

doi:10.1007/s00024-014-0831-x

Cited by 33 publications

(13 citation statements)

References 46 publications

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“…Furthermore, it is commonly accepted that, although the single components of ambient noise can show large spectral variations as a function of natural and cultural disturbances, the HVNR spectral ratio tends to remain invariant, therefore preserving the fundamental frequency peak (Cara et al 2003). The reliability of ambient noise recordings in different geological and topographic conditions has been tested, with good results, in recent years (Galluzzo et al 2009;Tramelli et al 2010;Panzera et al 2011a;Burjànek et al 2012;Panzera et al 2012Panzera et al , 2014.…”

Section: Forewordsmentioning

confidence: 97%

Seismic site effects observed on sediments and basaltic lavas outcropping in a test site of Catania, Italy

et al. 2015

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Ambient noise measurements and a set of 44 moderate magnitude earthquakes were used to study the role of local geology and morphology on the site response of a small hill in the northern part of Catania, on top of which the University Astronomical Observatory is located. The study area has a gentle topography with a flat surface at the top, and it is characterized by a complex sedimentary sequence lying between a clayey basement and an upper volcanic formation. The recorded data were processed through standard spectral ratio and horizontal-to-vertical spectral ratio techniques. Directional effects were also investigated by computing the spectral ratios after rotating the horizontal components of motion and performing polarization analysis. Results of noise and earthquakes analysis, although showing significant differences in amplitude, are comparable in frequency, especially in the sedimentary terrains. On the lava flows, spectral ratios show significant amplification of the vertical component, which appear related to a higher P velocity contrast with underlying soft sediments. Directional effects were identified in two frequency bands (0.2-0.4 and 1.0-10.0 Hz). The effects observed at the lower frequency interval are rather stable, and it spreads out in all the studied area. At higher frequencies, directional effects are variable and mostly observed on the slopes rather than at the hill top. Our findings appear linked to the complex wave field generated by the lithologic heterogeneities existing in the area which seem to be related to the alternation of sediments and basaltic lavas.

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Section: Forewordsmentioning

confidence: 97%

Seismic site effects observed on sediments and basaltic lavas outcropping in a test site of Catania, Italy

et al. 2015

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“…Such correlation between wavefield polarization and brittle deformation pattern is postulated to occur also on the western flank of Mt. Etna by Panzera et al (2014). The link of seismic anisotropy with the stress regime and anisotropic distribution of open crack features is confirmed in other Acocella (2007-2009 (Shelley et al 2014;Pischiutta et al 2015;Li and Peng 2017;Vignaroli et al 2018).…”

Section: Introductionmentioning

confidence: 71%

“…Etna by Panzera et al . (). The link of seismic anisotropy with the stress regime and anisotropic distribution of open crack features is confirmed in other volcanoes or fault zones by recent numerical and experimental studies (Shelley et al .…”

Section: Introductionmentioning

confidence: 97%

Using a vibratory source at Mt. Etna (Italy) to investigate the wavefield polarization at Pernicana Fault

Giulio

Punzo

Bruno

et al. 2019

Near Surface Geophysics

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The paper presents the results of a controlled‐source seismic experiment performed using a vibratory source capable of producing harmonic vibrations. The survey aimed at investigating the horizontal directional amplification mechanism observed at the Pernicana Fault (Mt. Etna in Sicily, Italy) along an N150°/N330° orientation. With the vibratory source (a shaker truck) working in shear‐wave mode in the frequency range 5–40 Hz, we recorded seismic data using both three‐component velocimeters and 4.5 Hz geophones. These two types of receivers were arranged in linear configuration along two orthogonal orientations: radial and transverse to the direction of the main polarization observed within the fault zone. The two lines of seismic stations allowed us to investigate the polarization evolution as a function of the distance from the source. Results show that when the shear excitation induced by the source is parallel to the direction of observed polarization of the ground motion, the seismic signal propagates efficiently, maintaining the same horizontal polarization induced by the active source. This polarization is well recorded up to distances as large as 300 m from the source. On the contrary, when the shear excitation is orthogonal to the predominant site polarization, the ground excitation loses its initial polarization in less than 50 m away from the source position. At larger distances, the transmitted energy propagates with the natural site polarization independently from the original source polarization. The observations in terms of polarization were combined with surface‐wave analysis, aimed at investigating the dispersion characteristics of the wavefield on the geophone lines. The data suggest that the experimental Rayleigh‐wave dispersion spectra show a more coherent signal over the frequency range along the same orientation of the observed site polarization, supporting a preferential direction in the propagation of surface waves. From inversion of the Rayleigh dispersion curves, we inferred the shear‐wave velocity (Vs) to be in the range of 120–450 m/s in the first 30 m deep of Quaternary volcanic sediments. The dispersion curves are not constant along transverse and radial directions, suggesting the presence of fracture‐induced seismic anisotropy in the near surface.

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“…Furthermore, ground motion polarization that is commonly observed in fault zones is interpreted as fracture-controlled (e.g. Pischiutta et al, 2012;Panzera et al, 2014). These studies show that the frequency bands at which directional amplification occurs reflects asymmetry in rock damage.…”

Section: Introductionmentioning

confidence: 94%

Defining fault avoidance zones and associated geotechnical properties using MASW: a case study on the Springfield Fault, New Zealand

Duffy

Campbell

Finnemore

et al. 2014

Engineering Geology

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a b s t r a c tThe Springfield thrust fault at Dalethorpe, west Canterbury, New Zealand, provides a test case to explore the correlation between shear wave velocities at a range of scales, and direct field observations of distributed deformation and outcrop properties. The Springfield fault ruptures to the surface through hard Torlesse greywacke, overlain on a flight of late Quaternary glacio-fluvial terraces by~5 m of gravel. Fault slip has displaced all but the lowest terraces, revealing the geometry and location of faulting. We used multi-channel analysis of surface waves and meter-scale cross-hole measurements to map shear wave velocities below the lowest, apparently undisplaced, terrace. We correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory. Both field and laboratory results indicate that the shear wave velocity of Torlesse greywacke declines sharply with increasing fracture density. Field surveys further indicate that relatively unweathered, high velocity greywacke is being exhumed in a bivergent wedge between two oppositefacing thrusts. The fracturing and low shear wave velocities are focused in a wide, low-velocity damage zone that has developed in the hanging wall of the main thrust, and a smaller but similar feature in the hanging wall of the backthrust. This is consistent with the geomorphology of the site. Our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain. This type of analysis has utility for land use planning on, or close to, active faults, especially where they are obscured by fluvial deposits.

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Wavefield Polarization in Fault Zones of the Western Flank of Mt. Etna: Observations and Fracture Orientation Modelling

Cited by 33 publications

References 46 publications

Seismic site effects observed on sediments and basaltic lavas outcropping in a test site of Catania, Italy

Seismic site effects observed on sediments and basaltic lavas outcropping in a test site of Catania, Italy

Using a vibratory source at Mt. Etna (Italy) to investigate the wavefield polarization at Pernicana Fault

Defining fault avoidance zones and associated geotechnical properties using MASW: a case study on the Springfield Fault, New Zealand

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