50 research outputs found
Structural health monitoring and earthquake early warning: preliminary studies for application in eastern Sicily
In this work, the reduction of seismic hazard in eastern Sicily is addressed by both studying the fundamental resonant frequency of strategic
buildings through low cost geophysical investigation techniques, and exploring a practical approach to earthquake early warning EEW)
system. The fundamental period and the corresponding amplification of some selected strategic buildings has been estimated using ambient
vibration and earthquake data. We analyzed the basic dynamic parameters of buildings chosen as target, by using continuous vibration
measurements at different floors. The dynamic behavior of structures was evaluated considering both small strains induced by
ambient vibrations and larger excitation levels due to the earthquakes occurrence.
A practical approach to earthquake early warning in the investigated area was dealt with by using empirical relationships between parameters
measured on the initial portion of seismic recordings and related to the earthquake magnitude and peak ground motion. In particular,
we performed the first preliminary tests by using empirical relationships calibrated for the considered area and taking into account
the geometry of the existing permanent seismic network deployed in the eastern Sicily. The estimated relationships have been used to
provide onsite warning around a given seismic station and evaluate the potential damaging effects. The joint of EEW system and geophysical
investigation shown in this work may be deemed a useful guide for the future implementation of the in real time seismic monitoring
in the region.This work has been supported by the following
project: âAttivitĂ di sviluppo sperimentale finalizzata alla
riduzione del rischio sismico nella Sicilia Orientaleâ inside the
PO-FESR 2007-2013 Sicilia; MED-SUV funded from the European
Union Seventh Framework Programme (FP7) under Grant agreement
n°308665. This work is sponsored by European Unionâs
Horizon 2020 research and innovation programme under the
Marie Sklodowska-Curie grant agreement n° 798480. We are
thankful to Salvatore Rapisarda and Danilo Contrafatto to support
us in the field work
Seismic amplification effects and soil, to, structure interaction study nearby a fault zone: the Tremestieri fault and Madre Teresa di Calcutta School (Catania)
Results of passive seismic surveys, in terms of both amplification and polarization effects in a section of the Tremestieri Etneo Fault (Sicily
Eastern center - Catania) are discussed. For the purpose, velocimetric and accelerometric records of seismic ambient noise were analyzed.
The polarization analysis of particle motion was performed and azimuthally dependent resonant frequencies were estimated. Ambient
noise data were also used to assess the dynamic properties of a reinforced concrete building, located on the fault zone. The fundamental
modes have been estimated through ambient noise recordings acquired by three-directional accelerometers, installed at the highest
accessible floor and outside the building. The study revealed a clear oriented seismic amplification in the fault zone. This effect was observed
in intensely jointed rock masses, located inside the fault area, as the result of specific geometries and significant directional
impedance contrasts characterizing the area under study. The analyses show that the direction of the largest resonance motions has
transversal relationship with the dominant fracture orientation. The directional amplification is inferred to be produced by stiffness
anisotropy of the fault damage zone, with larger seismic motions high angle to the fractures. The results obtained are in complete agreement
with those obtained by a previous study which analyzed the fault section located to the north-west.Finally, comparing the dynamic
properties of the school building and the vibrational characteristics of the soil in the direction of maximum amplification, no clear resonant
effect in the soil-structure interaction has been observed.This paper has been funded by the following
research projects: âAttivitĂ di sviluppo sperimentale finalizzata
alla riduzione del rischio sismico nella Sicilia
Orientaleâ inside the PO-FESR 2007-2013 Sicilia; MED-SUV
funded from the European Union Seventh Framework Programme
(FP7) under Grant agreement n°308665. This work is
sponsored by European Unionâs Horizon 2020 research and innovation
programme under the Marie Sklodowska-Curie grant
agreement n° 798480
Interplay between Tectonics and Mount Etnaâs Volcanism: Insights into the Geometry of the Plumbing System
Mt. Etna lies in front of the southeast-verging Apennine-Maghrebian fold-and-thrust belt,
where the NNW-trending Malta Escarpment separates the Sicilian continental crust from the
Ionian Mesozoic oceanic basin, presently subducting beneath the Calabrian arc (Selvaggi
and Chiarabba, 1995). Seismic tomographic studies indicate the presence of a mantle plume
beneath the volcano with a Moho transition at depth less than 20 km (Nicolich et al.,2000;
Barberi et al., 2006). Geophysical and geological evidences suggest that the Mt. Etna magma
ascent mechanism is related to the major NNW-trending lithospheric fault (Doglioni et al.,
2001). However, the reason for the Mt. Etna mantle plume draining and channeling the
magma from the upper mantle source to the surface is not yet clear. All models proposed in
literature (Rittmann, 1973; Tanguy et al., 1997; Monaco et al.; 1997; Gvirtzman and Nur,
1999; Doglioni et al., 2001) do not explain why such a mantle plume has originated in this
anomalous external position with respect to the arc magmatism and back-arc spreading
zones associated with the Apennines subduction. Some ideas on the subduction rollback
must be better developed through the comparison with new regional tomographic studies
that are being released. Moreover, tomographic studies reveal a complex and large
plumbing system below the volcano from -2 to -7 km a.s.l., wide up to 60 km2 that reduces
itself in size down to -18 km of depth close to the apex of the mantle plume. Chiocci et al.
(2011) found a large bulge on the underwater continental margin facing Mt. Etna, and
suggested that the huge crystallized magma body intruded in the middle and upper
continental crust was able to trigger an instability process involving the Sicilian continental
margin during the last 0.1 Ma. This phenomenon induces the sliding of the volcano eastern
flank observed since the 90s (Borgia et al, 1992; Lo Giudice and RasĂ , 1992) because the
effects of the bulge collapse are propagating upslope, and the continuous decompression at
the volcano summit favors the ascent of basic magma without lengthy storage in the upper
crust, as one might expect in a compressive tectonic regime. Taken together, these new
evidences (tomographic, tectonic, volcanic) are concerned with the exceptional nature of Mt.
Etna and raise the need to explain the origin of the mantle plume that supplies its
volcanism. The lower crust and the uppermost mantle need to be better resolved in future
experiments and studies. The use of regional and teleseismic events for tomography and
receiver function analyses is required to explore a volume that has only marginally been
investigated to date. The relation between the magma source in the mantle and the upper
parts of the system, as well as the hypothesis above reported on the relation between
tectonics and volcanism and the role of lithospheric faults, could be resolved only by
applying seismological techniques able to better constrain broader and deeper models.
Finally, although the recent tomographic inversions have progressively improved our
knowledge of Etnaâs shallow structure, highlighting a complex pattern of magma chambers
and conduits with variable dimensions, the geometry of the conduits and the dimensions
and shapes of small magmatic bodies still require greater investigation. Their precise
definition is crucial to delineate a working model of this volcano in order to understand its
behaviour and evolution. For this purpose, at least within the volcanic edifice, the precise
locations of the seismo-volcanic signals can be considered a useful tool to constrain both the
area and the depth range of magma degassing and the geometry of the shallow conduits. In
this work, we furnish evidences that the tremor and LP locations allowed to track magma
migration during the initial phase of the 2008-2009 eruption and in particular the initial
northward dike intrusion, also confirmed by other geophysical, structural and volcanological observations (Aloisi et al., 2009; Bonaccorso et al., 2011), and the following
fissure opening east of the summit area at the base of SEC. All these evidences, obtained by
the marked improvement in the monitoring system together with the development of new
processing techniques, allowed us to constrain both the area and the depth range of magma
degassing, highlighting the geometry of the magmatic system feeding the 2008-2009
eruption
Source geometry from exceptionally high resolution long period event observations at Mt Etna during the 2008 eruption
During the second half of June, 2008, 50 broadband seismic stations were
deployed on Mt Etna volcano in close proximity to the summit, allowing us to
observe seismic activity with exceptionally high resolution. 129 long period
events (LP) with dominant frequencies ranging between 0.3 and 1.2 Hz, were
extracted from this dataset. These events form two families of similar
waveforms with different temporal distributions. Event locations are performed
by cross-correlating signals for all pairs of stations in a two-step scheme. In
the first step, the absolute location of the centre of the clusters was found.
In the second step, all events are located using this position. The hypocentres
are found at shallow depths (20 to 700 m deep) below the summit craters. The
very high location resolution allows us to detect the temporal migration of the
events along a dike-like structure and 2 pipe shaped bodies, yielding an
unprecedented view of some elements of the shallow plumbing system at Mount
Etna. These events do not seem to be a direct indicator of the ongoing lava
flow or magma upwelling
Recent Developments and Applications of Acoustic Infrasound to Monitor Volcanic Emissions
Volcanic ash is a well-known hazard to population, infrastructure, and commercial and
civil aviation. Early assessment of the parameters that control the development and evolution of
volcanic plumes is crucial to effective risk mitigation. Acoustic infrasound is a ground-based remote
sensing techniqueâincreasingly popular in the past two decadesâthat allows rapid estimates of
eruption source parameters, including fluid flow velocities and volume flow rates of erupted material.
The rate at which material is ejected from volcanic vents during eruptions, is one of the main inputs
into models of atmospheric ash transport used to dispatch aviation warnings during eruptive crises.
During explosive activity at volcanoes, the injection of hot gas-laden pyroclasts into the atmosphere
generates acoustic waves that are recorded at local, regional and global scale. Within the framework of
linear acoustic theory, infrasound sources can be modelled as multipole series, and acoustic pressure
waveforms can be inverted to obtain the time history of volume flow at the vent. Here, we review
near-field (<10 km from the vent) linear acoustic wave theory and its applications to the assessment
of eruption source parameters. We evaluate recent advances in volcano infrasound modelling and
inversion, and comment on the advantages and current limitations of these methods. We review
published case studies from different volcanoes and show applications to new data that provide a
benchmark for future acoustic infrasound studies.Silvio De Angelis and Alejandro Diaz-Moreno are funded by NERC grant number NE/P00105X/1.
Luciano Zuccarello has received funding from the European Unionâs Horizon 2020 research and innovation
programme under the Marie Sklodowska-Curie grant agreement No. 798480
Uncertainty in Detection of Volcanic Activity Using Infrasound Arrays: Examples From Mt. Etna, Italy
SD and LZ acknowledge the support from the EUROVOLC
project under the European Unionâs Horizon 2020 research
and innovation programme (grant agreement No. 731070). The
authors thank the staff of the Istituto Nazionale di Geofisica e
Vulcanologia Sezione di Catania, in particular Salvo Rapisarda,
Daniele Pellegrino, Mario Pulvirenti, and Danilo Contrafatto for
their valuable support in the field.The injection of gas and pyroclastic material from volcanic vents into the atmosphere is
a prolific source of acoustic waves. Infrasound arrays offer efficient, cost-effective, and
near real-time solutions to track the rate and intensity of surface activity at volcanoes.
Here, we present a simple framework for the analysis of acoustic array data, based
on least-squares beamforming, that allows to evaluate the direction and speed of
propagation of acoustic waves between source and array. The algorithms include a new
and computationally efficient approach for quantitative assessment of the uncertainty
on array measurements based on error propagation theory. We apply the algorithms to
new data collected by two 6-element infrasound arrays deployed at Mt. Etna during the
period JulyâAugust 2019. Our results demonstrate that the use of two infrasound arrays
allowed detecting and tracking acoustic sources from multiple craters and active vents
associated with degassing and ash-rich explosions, vigorous and frequent Strombolian
activity, opening of new eruptive fractures and emplacement of lava flows. Finally, we
discuss the potential use of metrics based on infrasound array analyses to inform
eruption monitoring operations and early warning at volcanoes characterized by episodic
intensification of activity.NERC Natural Environment Research Council
NE/P00105X/1European Union (EU)Geoscientists without Borders grant from the Society of Exploration Geophysic
Fibre optic distributed acoustic sensing of volcanic events
Understanding physical processes prior to and during volcanic eruptions has improved significantly in recent years. However, uncertainties about subsurface structures distorting observed signals and undetected processes within the volcano prevent volcanologists to infer subtle triggering mechanisms of volcanic phenomena. Here, we demonstrate that distributed acoustic sensing (DAS) with optical fibres allows us to identify volcanic events remotely and image hidden near-surface volcanic structural features. We detect and characterize strain signals associated with explosions and locate their origin using a 2D-template matching between picked and theoretical wave arrival times. We find evidence for non-linear grain interactions in a scoria layer of spatially variable thickness. We demonstrate that wavefield separation allows us to incrementally investigate the ground response to various excitation mechanisms. We identify very small volcanic events, which we relate to fluid migration and degassing. Those results provide the basis for improved volcano monitoring and hazard assessment using DAS
VINEDAâVolcanic INfrasound Explosions Detector Algorithm
Infrasound is an increasingly popular tool for volcano monitoring, providing insights of the
unrest by detecting and characterizing acoustic waves produced by volcanic processes,
such as explosions, degassing, rockfalls, and lahars. Efficient event detection from large
infrasound databases gathered in volcanic settings relies on the availability of robust and
automated workflows. While numerous triggering algorithms for event detection have
been proposed in the past, they mostly focus on applications to seismological data.
Analyses of acoustic infrasound for signal detection is often performed manually or by
application of the traditional short-term average/long-term average (STA/LTA) algorithms,
which have shown limitations when applied in volcanic environments, or more generally
to signals with poor signal-to-noise ratios. Here, we present a new algorithm specifically
designed for automated detection of volcanic explosions from acoustic infrasound data
streams. The algorithm is based on the characterization of the shape of the explosion
signals, their duration, and frequency content. The algorithm combines noise reduction
techniques with automatic feature extraction in order to allow confident detection of
signals affected by non-stationary noise.We have benchmarked the performances of the
new detector by comparison with both the STA/LTA algorithm and human analysts, with
encouraging results. In this manuscript, we present our algorithm and make its software
implementation available to other potential users. This algorithm has potential to either be
implemented in near real-timemonitoring workflows or to catalog pre-existing databases.This research was partially funded by KNOWAVES TEC2015-
68752 (MINECO/FEDER), by NERC Grant NE/P00105X/1,
by Spanish research grant MECD Jose Castillejo CAS17/00154
and by VOLCANOWAVES European Unionâs Horizon
2020 Research and Innovation Programme Under the Marie
Sklodowska-Curie Grant Agreement no 798480
THE SHALLOW MAGMA CHAMBER OF STROMBOLI
AbstractIn this work, we integrate artificial and natural seismic sources data to obtain highâresolution images of the shallow inner structure of Stromboli Volcano. Overall, we used a total of 21,953 P readings from an active seismic experiment and an additional 2731 P and 992 S readings deriving from 269 local events. The wellâdefined Vp, Vs, and Vp/Vs tomograms have highlighted the following: (i) the region where magma cumulates at shallow depths (2â4 km below sea level (bsl)), forming an elongated NEâSW highâvelocity body (Vp â„ 6.0 km/s and Vs â„ 3.5 km/s), with a very fast velocity core (6.5 †Vp < 7.0 km/s) of ~2 km3; (ii) the presence of some nearâvertical pipeâlike structures, characterized by relatively high P velocities values, mainly linked to past activity (e.g., Strombolicchio); and (iii) a nearâvertical pipeâlike volume with high Vp/Vs (1.78 Ă· 1.85), located beneath to the craters (down to ~1.0 km bsl), overlying a deeper region (1.0 to 3.0 km bsl) with low Vp/Vs (1.64 Ă· 1.69), interpreted as the actual and preferential pathway of magma toward the surface. Our results demonstrate the importance of combining passive and active seismic data to improve, in a tomographic inversion, the resolution of the volcanic structures and to discover where magma may be stored