Magma reservoir at Mt. Vesuvius: Size of hot, partially molten, crust material detected deeper than 8 km
ABSTRACT One- and two-dimensional Vp models were obtained by TomoVes experiment, all characterized by low Vp in the uppermost 500 m and a sharp discontinuity at about 2-3 km beneath the volcano. Large amplitude late arrivals were identified as P- to S-phases converted at the top, between 8 and 10 km deep, of a low-velocity layer with a dramatic drop of Vs, from approximately 3.6 km/s to less than 1.0 km/s. Here, we synthesize the interpretation of Rayleigh wave dispersion measurements, made by several authors, to delineate the extent of such anomalous layer of hot, partially molten, crust material. Our non-linear inversion of broad-band dispersion measurements evidences a main feature of Somma-Vesuvius deep structure consisting of low Vs layers at about 8-10 and 20 km of depth. The depth of the shallower low-velocity layer and the Vs value above it are in agreement with TomoVes results, but the Vs velocity reduction is of about 10%. If we assume Vs equal to 1.0 km/s in our non-linear inversion, a thickness not
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ABSTRACT: A research project to define the feeding system of the Vesuvius volcano and the upper crustal structure of the area was started in 1993. The core of the project is the high resolution seismic tomography study by using explosive sources. Results of a preliminary 2D seismic profile have been discussed by Zollo et al. (1998) [J. Volcanol. Geotherm. Res., this volume]. The study of local seismicity at Vesuvius has many implications for the determination of the substructure of the volcanic area. The shape and size of the seismic volume and the study of the focal mechanisms put important constraints on the stress field of the area. The local seismicity can greatly improve the knowledge of the tridimensional velocity distribution of both P and S seismic waves inside the volcano, using passive tomographic techniques. In this paper we obtain a first three-dimensional tomographic image of the volcanic structure, obtained by inversion of first P and S arrival times of local earthquakes. The results show the existence of a sharp velocity contrast, along a lineation oriented NW–SE, cutting the crater along the line separating the relict of the Somma caldera from the southwest part of the volcano. This study confirms, also for S wave velocities, the absence of indications for a magma chamber in the first 4–5 Km below the sea level, as already evidenced, just for P waves, by 2D tomography. Furthermore, we discuss the improvement of resolution obtainable by deploying a small set of three component seismic stations to get a better coverage of the area.Journal of Volcanology and Geothermal Research 01/1998; 82(1-4):175-197. · 2.19 Impact Factor
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ABSTRACT: We applied a revised version of the 1-D t - p inversion method to first P-arrival times from the active seismic experiment performed at Mt. Vesuvius (southern Italy) in 1996 (TomoVes96 Project). The main objective of this work is to obtain 1-D velocity models of Mt. Somma-Vesuvius volcano complex and surrounding area. Moreover we show that combining the 1-D information we provide a reliable 2-D initial model for perturbative tomographic inversions. Seismic and geological surveys suggest the presence of a refractor associated with the contrast between carbonate basement and volcanic:alluvial sediments; synthetic simulations, using a realistic topography and carbonate top morphology, allowed us to study the effect of topography on the retrieved velocity models and to check that the 1-D t -p method can also approximately retrieve the refractor depth and velocity contrast. We analysed data from 14 on-land shots recorded at stations deployed along the in-profile direction. We grouped the obtained models in three subsets according to the geology of the sampling area: Models for carbonate outcrop area, models for the Campanian Plain surrounding the volcano edifice and models for Mt. Somma-Vesuvius volcano complex. The found 1-D P-velocity models show important vertical and lateral variations. Very low velocities (1.5-2.5 km:s) are observed in the upper 200-500 m thick shallow layer. At greater depths (3 km is the maximum investigated depth) P velocities increase to values in the range of 4-6 km:s which are related to the presence of the carbonatic basement. Finally we interpolated the 1-D models to demonstrate an example of misfit for a 2-D interpolated model whose residuals are confined in a narrow band around zero.Pure and Applied Geophysics 01/2000; 157(10):1643-1661. · 1.62 Impact Factor
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ABSTRACT: The Somma-Vesuvius volcanic complex and surroundings are characterized by topographic relief of over 1000 m and strong 3-D structural variations. This complexity has to be taken into account when monitoring the background volcano seismicity in order to obtain reliable estimates of the absolute epicentres, depths and focal mechanisms for events beneath the volcano. We have developed a 3-D P-wave velocity model for Vesuvius by interpolation of 2-D velocity sections obtained from non-linear tomographic inversion of the Tomoves 1994 and 1996 active seismic experiment data. The comparison of predicted and observed 3-D traveltime data from active and passive seismic data validate the 3-D interpolated model. We have relocated about 400 natural seismic events from 1989 to 1998 under Vesuvius using the new interpolated 3-D model with two different VP/VS ratios and a global search, 3-D location method. The solution quality, station residuals and hypocentre distribution for these 3-D locations have been comparedGeophysical Journal International 01/2001; 146:313-331. · 2.85 Impact Factor
Magma reservoir at Mt. Vesuvius: Size of the hot, partially molten,
crust material detected deeper than 8 km
Concettina Nunziataa,⁎, Maddalena Natalea, G. Luongoa, Giuliano F. Panzab,c
aDipartimento di Geofisica e Vulcanologia, Università di Napoli “Federico II”, Largo San Marcellino 10, 80138 Napoli, Italy
bDipartimento di Scienze della Terra, Università di Trieste, Via Weiss 4, 34127 Trieste, Italy
cThe Abdus Salam International Centre for Theoretical Physics, SAND group of the Earth System Physics Section, Trieste, Italy
Received 24 September 2005; received in revised form 2 December 2005; accepted 3 December 2005
Available online 18 January 2006
Editor: R.D. van der Hilst
One- and two-dimensional VPmodels were obtained by TomoVes experiment, all characterized by low VPin the uppermost
500 m and a sharp discontinuity at about 2–3 km beneath the volcano. Large amplitude late arrivals were identified as P- to S-
phases converted at the top, between 8 and 10 km deep, of a low-velocity layer with a dramatic drop of VS, from approximately
3.6 km/s to less than 1.0 km/s. Here, we synthesize the interpretation of Rayleigh wave dispersion measurements, made by
several authors, to delineate the extent of such anomalous layer of hot, partially molten, crust material. Our non-linear inversion
of broad-band dispersion measurements evidences a main feature of Somma-Vesuvius deep structure consisting of low VSlayers
at about 8–10 and 20 km of depth. The depth of the shallower low-velocity layer and the VSvalue above it are in agreement
with TomoVes results, but the VSvelocity reduction is of about 10%. If we assume VSequal to 1.0 km/s in our non-linear
inversion, a thickness not greater than 0.35 km results. The volume occupied by this very low-velocity layer, sill-shaped, is
compatible with the size of Mt. Vesuvius cone, but it develops above a much larger hot mass, which could be the parental
source as the erupted products are only few percent of magma chamber.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Rayleigh group velocity; shear velocity models; crustal system; Somma-Vesuvius volcanic complex
Over the past 10 yr, intensive efforts have been
made to study details of the inner structure of Mt.
Vesuvius. A preliminary three-dimensional tomo-
graphic image of the Somma-Vesuvius structure was
obtained from the inversion of first P and S arrival
times of local earthquakes . Such model showed a
central, high rigidity core of the volcano extending to
a depth of about 5 km, interpreted as magma solidified
in the main eruptive conduits. During 1994–1997,
multi-two-dimensional seismic refraction experiments
(TomoVes) were performed. One- and two-dimension-
al VPvelocity models of the shallow structure (up to
3–4 km of depth) were obtained by using different
methods . Although they differ in the details, all
the models are characterized by low P velocities (1.5–
2.5 km/s) in the shallow layer (b500 m) and a sharp
discontinuity at about 2–3 km of depth beneath the
Earth and Planetary Science Letters 242 (2006) 51–57
⁎Corresponding author. Tel.: +39 81 2538349; fax: +39 81
E-mail address: firstname.lastname@example.org (C. Nunziata).
0012-821X/$ - see front matter © 2005 Elsevier B.V. All rights reserved.
volcano, interpreted as the top of the Mesozoic
carbonate horizon [3–6]. Large amplitude late
arrivals were identified as P- to S-phases converted
at the top of a low-velocity zone with a dramatic
drop of VSfrom approximately 3.6 km/s to less than
1.0 km/s. The depth of this interface is at about 10
km  or about 8 km , by assuming a VP/VSratio
of 1.8. It was interpreted as due to the presence of a
very extended layer of hot, partially molten, crust
material . A still open question is the depth
extension of this very low S-wave velocity layer
whose top can be placed at a depth between 8 and
Surface waves represent a quite effective tool to
investigate the extension of low-velocity layers,
particularly powerful when stringent a priori con-
straints can be placed at the stage of inversion on the
value of the velocity . The properties of the crust
and upper mantle below Mt. Vesuvius (Fig. 1) have
been delineated by intensive broad-band (0.3–100 s)
measurements of Rayleigh waves [9–11], shown in
Fig. 2a–b, combined with available body and surface
waves tomographic inversions [12–16]. Average VS
models have been obtained for a set of very local
dispersion profiles by means of non-linear inversion
. To investigate the VS models of the crust, a
total of 12 parameters have been inverted, which are
seven S-wave velocities (VS) and five thicknesses.
The parameter's space of VS (Fig. 2c) has been
chosen based on typical ranges of variation of
volcanic and sedimentary rocks, but very wide at
depth greater than 5 km to explore the presence of
very low VS (near zero values), as obtained by
TomoVes studies [6,7]. From the set of solutions, we
accept as representative solution the one with rms
(root mean square) error closest to the average rms
error of the solution set, and hence reduce the
projection of possible systematic errors  into the
structural model. All relevant solutions (Fig. 2c) are
characterized by VS velocities increasing from 0.6
km/s, typical of tuff material , to about 2 km/s in
the shallower 0.5–1 km of depth. Instead, anoma-
lously high VSaround 3.3 km/s characterize the area
where the SMC station is located. At greater depths,
about 2–3 km, VSincreases to 2.40–3.05 km/s, very
probably in the limestone horizon, calibrated in the
Trecase well, close to the FTC station (Fig. 1), and
to 3.30–3.65 km/s at 3–6 km of depth. A main
feature of Somma-Vesuvius crustal structure is
represented by low VSlayers at about 8–10 and 20
km of depth. The deeper low VS layer is found
below all stations formed by mantle or by a mélange
of crust and mantle material, with sizeable phenom-
ena of partial melting. It is a regional feature and can
be interpreted as magmatic reservoir of Campania
active volcanoes . From our study , the
shallower low-velocity layer is at 7–11 km of depth,
with velocities decreasing from 3.40–3.65 km/s to
Fig. 1. Topographic map of Somma-Vesuvius (modified after Vilardo et al. ) with location of the examined seismic stations and the Trecase well.
Simplified stratigraphy of Trecase well  is also shown on the right.
52C. Nunziata et al. / Earth and Planetary Science Letters 242 (2006) 51–57
Fig. 2. (a) Regional group and phase velocities of Rayleigh waves, with error bars, obtained for the cell containing Mt. Vesuvius from teleseismic
tomography . (b) Average Rayleigh wave group velocity dispersion curves, with error bars, measured from local events at the stations shown in
Fig. 1. (c) Results of the non-linear inversion (lines) obtained at all stations from the simultaneous inversion of group (T=0.3–35 s) and phase
(T=25–100 s) velocities. The area delimited by dashed line represents the investigated parameter space. As in Natale et al. , the root mean square
(rms) of the chosen solution (thick line) is as close as possible to the average rms, computed from all solutions.
53C. Nunziata et al. / Earth and Planetary Science Letters 242 (2006) 51–57
2.45–3.05 km/s, and is absent at the VIS station (Figs.
1 and 2c), at a distance of about 15 km from the
crater, i.e. outside of the volcano. According to Taylor
and Singh , this VSreduction, corresponding to a
minimum velocity inversion of about 10%, may
correspond to the presence of 5–10% partial melting,
depending, for a solid matrix with isolated inclusions
of melt, on the aspect ratio of the melt inclusions.
The depth of the discontinuity and the VS value
above it are in agreement with TomoVes results
(VS=3.61 km/s after Auger et al. ). The structural
models below Mt. Vesuvius (Fig. 3) indicate
moderate lateral variations and an average Rayleigh
group velocity dispersion curve can be considered to
define the average properties of Mt. Vesuvius cone
(BKS, BAF, SGV, BKN and BKE stations). The non-
linear inversion of such average group (0.3–35 s) and
phase (10–100 s) velocities gives a representative VS
model characterized by a 5% VSreduction at about
8 km of depth (Fig. 4a–b), which may correspond to
the presence of less than 5% partial melting. Below
the discontinuity, if we impose as a priori information
the value of 1.0 km/s, from Auger et al. , the
result of our inversion indicates a thickness of 0.050–
0.350 km for this very low-velocity layer, which
cannot be resolved (too thin) inverting our data with
unconstrained VS velocity (Fig. 4c–d). The dimen-
sions of this very low-velocity layer suggest the
presence of a sill with a volume compatible with the
size of Mt. Vesuvius cone, but it develops above a
much larger hot mass, which could be the parental
source as the erupted products are only few percent
of magma chamber. Finally, a scheme of Mt.
Vesuvius feeding system can be drawn (Fig. 5),
starting from Tyrrhenian Sea . The shallower low
VS layer seems to have a local feature, as it is not
found outside Somma-Vesuvius volcanic complex,
while the deeper low VSlayer has a regional feature
We thank two anonymous reviewers for constructive
comments that improved this paper. This research has
been supported by INGV-DPC 2004-2006, Vesuvio
Project, UR_V3_4/07 (scientist responsible: C. Nun-
ziata) and UR_V3_4/12 (scientist responsible: A.
Peresan), and Italian MIUR Cofin funds 2004
(2004045141_003: the multi-scale geophysical Earth
Fig. 3. The chosen VSmodels are shown along a SE–NW–SW–NE cross-section through Mt. Vesuvius (Fig. 1). The grey bands indicate
the boundaries between layers that can well be transition zones in their own right and the group of numbers indicate the ranges for VS
54 C. Nunziata et al. / Earth and Planetary Science Letters 242 (2006) 51–57
Fig. 4. (a) The VSsolutions from hedgehog inversion of the average Rayleigh wave group velocity dispersion curve computed, in the period range
0.3–2 s, for all stations on Mt. Vesuvius cone (BKS, BAF, SGV, BKN and BKE in Figs. 1 and 2b), and regional group (T=10–35s) and phase
(25–100s) velocities (Fig. 2a). The root mean square (rms) of the chosen solution (red line) is as close as possible to the average rms, computed
from all solutions. (b) The chosen VSmodel for Mt. Vesuvius cone. The grey bands indicate the boundaries between layers that can well be
transition zones in their own right and the group of numbers indicate the ranges for VSin km/s. Red patches on the cone refer to seismic
stations. (c) The VSsolutions from hedgehog inversion (red line represents the chosen solution with the rms criterion) of the average Rayleigh
wave group velocity dispersion curve as used in (a), if we impose, as a priori information, the value of 1.0 km/s  for the low-velocity layer at
8 km of depth. (d) Uppermost part of the chosen model from solutions in (c).
55 C. Nunziata et al. / Earth and Planetary Science Letters 242 (2006) 51–57
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