Seismic wave scattering in volcanoes

Volcano-tectonic (VT) earthquakes produce high-frequency seismograms characterized by impulsive shear mech- anism; their seismogram coda re ects the random inhomogeneity of the volcano structure. Consequently, this inhomogeneity can be investigated through the analysis of the coda wave envelopes of the VT events. In this chapter, I will review the main observational results obtained from volcanoes around the World, with the aim of quantifying the scattering and attenuation properties of the volcanic areas. First, I will review the coda-Q observations and their frequency dependence, then I will report on attempts that have been made to sepa- rate the intrinsic from the scattering attenuation using multiple scattering and di¤usion models, and nally, I will report on the interpretations based on these results. The results show that the coda-Q absolute values characteristic of volcanoes are slightly smaller than those measured in non-volcanic zones, and that sometimes their frequency dependence is di¤erent. It is impossible to deduce by coda-Q observations only whether this di¤erence is controlled more by the intrinsic or the scattering attenuation. The application of multiple scatter- ing models allows separate estimates of the intrinsic and the scattering attenuation coe¢ cients. Results show that volcanoes are highly heterogeneous structures, with a mechanism of seismic wave energy dissipation that tends to be controlled by the scattering phenomena with increasing frequency. For Mt. Vesuvius, Mt. Merapi and Deception island volcano scattering attenuation prevails at frequencies higher than 2-3 Hz. At Mt. Etna, intrinsic dissipation prevails or is comparable with scattering attenuation for frequencies lower than 8 Hz. At high frequencies, di¤usion approximation is appropriate to describe the energy seismogram envelope. The intrinsic dissipation of shear waves [possibly connected with magma reservoirs, which should decrease the intrinsic Q values for shear waves] only has an important role at low frequencies. Key words: Seismic scattering, coda waves, volcanoe

Wood Anderson Magnitude Scale for Mt. Vesuvius

A Mathcad-8 program to calculate a revised magnitude scale is presented. An application to Mt. Vesuvius is included as a program test. Wood-Anderson seismograms for 131 local earthquakes recorded at station BKE (Osservatorio Vesuviano seismic network) were synthesized to estimate local magnitude from the original definition: Ml=log Amax(D) - logAo(D) The distance correction logAo(D) was empirically determined simulating a wave packet which propagates in a structure with assigned Q. Moment magnitude (calculated both with Kanamori and Tatcher-Hanks formulas) was also determined from the displacement spectra. Finally a relation between Wood-Anderson magnitude and duration magnitude was derived, allowing the estimate of local magnitude from the duration of the earthquake

30 years of coda observations: Qc, Qi and Qs

A summary of the main results obtained worldwide, in memory of Keiiti Aki

Inside Mt. Vesuvius: a new method to look at the seismic (velocity and attenuation) tomographic imaging

Mt. Vesuvius have been obtained using the programming facilities as well as the enhanced graphical power of Mathematica8TM. The velocity and attenuation space distributions, already calculated inverting respectively P-wave travel times and amplitude spectra of local VT quakes, are first optimally interpolated and then graphically represented in a new Mathematica8TM code notebook (a powerful computational document with more facilities than a simple code) developed by the present authors. The notebook aims at interactively and friendly representing 3D volume distributions of velocity and attenuation parameters. The user can easily obtain vertical sections (N-S, E-W, NE-SW and NW-SE oriented) and define color scales to represent velocity or attenuation variations or prefer iso-surface plots to represent the pattern of peculiar geological structures. The use of dynamic graphical representation, allowing the sliding of any (horizontal and/or vertical) slice through the volume under study, gives an unusual and powerful vision of any small velocity or attenuation anomaly. The (open source) code, coupled with the friendly use of internal routines of Mathematica, allows to adapt the graphical representation to any user necessity. The method appears to be particularly adapt to represent attenuation images, where the space variations of the parameters are strong with respect to their average. The 3-D plots of the interpolated velocity and attenuation fields enhance the image of Mt. Vesuvius structure, evidencing low-velocity associated with high attenuation anomalies which appeared unfocused in the plots reported by Scarpa et al. [2002] and De Siena et al. [2009]

Pasquale del Pezzo, Duke of Caianello, Neapolitan mathematician

This article is dedicated to a reconstruction of some events and achievements, both personal and scientific, in the life of the Neapolitan mathematician Pasquale del Pezzo, Duke of Caianello

Stochastic Finite-Fault Ground Motion Simulation in a Wave Field Diffusive Regime: Case Study of the Mt. Vesuvius Volcanic Area

The main aim of the present work consists in the validation of stochastic method for simulating weak ground motion in a diffusive regime due to low-to-moderate magnitude earthquakes, and in particular in its application to a volcanic area. We simulated the peak ground acceleration and the response acceleration spectra caused by two earthquakes scenarios (MD = 4.3 and MD = 5.4) at Mt. Vesuvius volcanic area by using the stochastic finite-fault simulation method. We validated the stochastic methodology by combining source, path and site parameters of the investigated area considering the time duration parameter, Trms, calculated on the study seismograms. The values of time durations are confirmed by calculating the same parameter, Trms, on the seismogram energy envelope described by multiple scattering models, in terms of scattering and the intrinsic dissipation coefficient. Initially, the simulations were evaluated for 10 local earthquakes (1.7 ≤ MD ≤ 3.6) that occurred at Mt Vesuvius in 1999 and are then compared with the observed data. The comparison between simulated and observed seismograms has been used to calibrate the stochastic procedure, and has been considered as the starting point for simulating ground motion for the scenario earthquake (MD > 3.6) that could occur in the study area. The scenario earthquake and the relative fault features were chosen on the base of statistical, tectonic, structural and historical studies of the study area. We simulated ground motions for a maximum magnitude value, Mmax, of 4.3, determined from examination of the Gutenberg-Richter law for the study area, and also for an Mmax = 5.4, a magnitude that is associated with the earthquakes that struck the ancient town of Pompei 17 years before the eruption of Mt Vesuvius that occurred in 79 AD. The largest values of Amax for the MD = 4.3 seismic event are in the range of 0.140 g to 0.029 g. In the case of MD = 5.4, we obtain PGA values in the range between 0.17 and 0.55 g

Space-weighted seismic attenuation mapping of the aseismic source of Campi Flegrei 1983-84 unrest

Peer reviewedPublisher PD

Comments on " Separation of Qi and Qs from 1 passive data at Mt. Vesuvius: A reappraisal

n.a

Re-calibration of the magnitude scales at Campi Flegrei, Italy, on the basis of measured path and site and transfer functions

The quantification of the seismic energy of earthquakes occurring in volcanic regions is of great importance in order to better understand the dynamics of the volcano. The amount of the released energy and its variation during seismic crises can be considered as an indicator of the source processes acting inside the volcano. In this context, the effect of the propagation in attenuative media should be considered to correct for path effects and to properly estimate the seismic energy released at the source. Moreover, in order to allow a comparison with the dynamic processes occurring in different volcanic areas, the use of magnitude scales as homogeneous as possible is strongly recommended, In this framework, new duration-based Local (Ml) and Moment (Mw) magnitude scales are obtained for the Campi Flegrei area (southern Italy), by analysing a data-set of local volcano-tectonic earthquakes. First the S-wave quality factor for the investigated area was experimentally calculated and then the distance-correction curve, logA0(r), to be used in the Richter formula Ml = logAmax − logA0(r), was numerically estimated by measuring the attenuation properties and hence propagating a synthetic S-wave-packet in the earth medium. The Local magnitude scale was normalized in order to fit the Richter formula valid for Southern California at a distance of 10 km. Ml magnitude was estimated by synthesizing Wood-Anderson seismograms and measuring the maximum amplitude. For the same data-set, Moment magnitude from S-wave distance and site corrected displacement spectra was obtained. Comparisons between Local and Moment magnitudes determined in the present paper, and the old Duration magnitude (Md) routinely used at the Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano are presented. Moreover, relationships between Ml and Mw calculated for two reference sites are also derived

Shear wave splitting changes associated with the 2001 volcanic eruption on Mt. Etna

The time delays and polarizations of shear wave splitting above small earthquakes show variations before the 2001 July 17–August 9 2001 flank eruption on Mt Etna, Sicily. Normalized time delays, measured by singular value decomposition, show a systematic increase starting several days before the onset of the eruption. On several occasions before the eruption, the polarization directions of the shear waves at Station MNT, closest to the eruption, show 90◦- flips where the faster and slower split shear waves exchange polarizations. The last 90◦-flip being 5 days before the onset of the eruption. The time delays also exhibit a sudden decrease shortly before the start of the eruption suggesting the possible occurrence of a ‘relaxation’ phenomena, due to crack coalescence. This behaviour has many similarities to that observed before a number of earthquakes elsewhere