Bianco, F.

Castellano, M.

Milano, G.

Vilardo, G.

Earth-prints Repository

PERIODICO DIMINERALOGIA
CRISTALLOGRAFIA GÉOCHII\4ICA GIAC, fuIINERARI I\4INERALOGIA PETBOGBAFIA VULCANOLOGIA
Fondato da F. l\4illosevich
VOLCANOES IN TO\íN
a IAVCEI Conference
on Volcanic Hazard
in Densely Populated Regions
Roma 27-.10 Septembeî 1995
Pubblicazione quaddmesùal6
Proprielà dell'Unive|sità d€gli Sludi di Roma
 
Pq. Mneral. (1995), ó4, 289-29A
IMRoDUcIIoN
The last eruprior of Mt. Vesùvius occured
i n  I 0 4 4  a n d  w a s  a c c o m p a n i e d  b v  l 5 0 o
seismic eveEls (Casenano, i9s6a). Afier ùar
rhere was weak to n i t  se ismic i r Ì  on ML.
Vesuvìus up to 19ó4 when, dùdns a seismrc
crisis, some húndreds of ev;nrs were
recoded (Casenano 195ób). Sti now (199s)
senqally sevqal hlmdreò of events per year
The seismic dara col lecred by the
permúeúr nersork and dur ins lou;  held
sgúeys, caried out in the ye;s 198ó-82,
I 9 8 9 .  1 9 9 3  a n d  t 9 9 4 ,  p r o ; i d e d  a  s e L  o f
t n l o r m a r i o n  t h a l  a l l o w e d  u s  t o  d r a w  a
quanúLaLive p icrure o i  L]1e present  se ismr!
b e h a v i o u r  o f  r h e  M r .  S o m m a - V e s u v i u s
DÀTA aNAtj.sts Al\.D coNcrùsroNs
For location puposes, a simple velociry
model was obtained on rhe basi; of a direcr
modelling of borh filst aùivat detavs and
rime differences berween pared :rivats of
direcl ùd contfled phdes. tr Fact, a 
"heffpbase arival. inlemedjaLe lo p- and S.wavc
arrivals, was observed on horìzontat
recordjne5. This pallem, b) paricle molior,
a b a l y s i s .  w a s  a r r r i b u t e d  L o  a  p , r o _ S
conveEion rhar could be tinked ro rhe abrupr
mpedúce contr6r ber$een rhe consolidated
b o r r o m  o i  M L .  S o m m a  s  c a t d e r a  a n d  i r s
plroclasric [iì]. The calcutaLed depLh of r]ris
inlerface rabour 500 m b.(.1.) is in;ereemen,
Shallow heterogeneities aud seismic activity of Mt. Vesuvius
G. Vn-ìRDo, F. BraNco, M. CasrErLANo anal G. MÌ"qNo
ossenarorio vesuliano, via Md4ni 249, I-8012J Napoii,IlaÌy
wi th rhe recons(rúcr ion ot  rhe volcani .
envrronmenr in respecr ro the carbonaric
b a s e m e n r ' s  L r e t r d ,  a s  o b l a i n e d  b y
volcùologic, and eeophysicaj dara (CÀssanu
and La Tolle, 1987j pljn ciDe et aL. t9B7\.
An tugh velociry zone beneath rÀe Vesuvius
cone is  sr ronsly  marked by neear ive p_
resrouar obserued ar rhe sraùons locared iìrlhe_cenrral ùea of ihe votcaoi. (omplex, as
w€"ll as by the rema.Ìkable srgnal amplirudes
drr  rerences obserued ber$een per iDheral
srarioN and ihose tocared on lhe tra,à This
t e a t u r e  w a s  a t r e a d y  o b s e r v e d  i n  o t h e .
vor@nic dismfls te.g. Mr. Lrna dd Vulcano
rs lancl l  ancf  was iorerprered as e i rher  otd
Dùeo vorcarrc shlcrures or ùùusive bodies(Hi)m.et al., 1991, Ferrucci 
"r 
a?., l99t). For
rÉmework, Lhis hiah vetocirv
anomaly could be tin_ked ro rhe io[apse of
t l le  teeding conduir  af ier  the Ig4t f ina l
erupLion and i rs  cemenrat ion due lo ihLpercolatioÌ of hyaìrcdjemal fluids wirhin rhebro&en-down wal ls  and roof .  Anorherpossibtlity could be rhar the positive velocirv
aùomaly marks the thermo-metamorDhi ;
zone sMounding the feediDg slsrem.
_ 
rrom a seismic pojn! of ùew, low acrivirv
both in energy and in aents number occuÀ
at Mî. Soma-Vesuvius vol@ic @mDlex ar
the Fesent stage of volcanic quiece;ce. No
tremór,-Iike evenrs are observed. tndeed,
monocnromarrc low_trequency events ale
recor . red in  rhe Vesuvian area,  but  rhey
resùts b-om arrificial blasts orieinated bv
smus8lins fisbemen.
The events location, pel{olmed by meryins
290 c. vr]],oo. F. grANto. M. CasrlllaNo and G. MBNo
the 148 best recorded earthquakes withiD a
tbÌee-dimensionaÌ heterogeneous medium,
revealed l-har lhe seismic acriviry had most ot
irs epiceúen located around the crater area.
The whole seismicity analyzed in ,hjs srud)
displayed locations confined in depth within
five kilometres {r.om the top of the volcanic
cone. In panicuÌar, tllìs seismicity corsisted
primarily of extremely small events (M < 1)
associaied with cracking inside the volcanic
cone of the Vesuvius. On the otller hmd, the
larger magnitude sejsmjc events (1.1 < M <
3 2ì shówed deeDùlocatioG and mav be wel
associated with ìectonic àùltins. ln iacr Mt.
Sorma-Veiuvius comple.x is emplaced on a
resional NE-Sw-trendine faults system
(M^rzocchi  et  a | . ,1993).  Best  fauÌ t -p lane
solutions, for tle deeper seismicity anal)zed
in this stùdy, showed the presence of a plare
approximately along the NE-SW direction.
Ihis $ssested that, il ùe presert. the most
energet ic  se ismic i ty  af [ect inS the Ml .
somma-vesúviús volcùic comDl* is maiilv
soveúèd by the sÚess field acttng on à
ihe rcle played by resional dynamics ir
the s€ismic behaviou of this area was aÌso
evidèncèd by the occurrence of seisDiic
actlvity related to seismogenetic strrctres,
periaining to the tectonic lireaments with
NE-SW trcnd, located close the volcanic
complei. For istance, the earthqùake
occuned on June 16th, 1987, (M-2.9) $,as
located a lors the NE-SW latera l
discontinuity, inferred from DSS daia
(caste[ano et aL, 1988; Fe]n@i er al, 1989),
separaiiDg the Phlegrean Fields ftom Mt.
Somma-Vsùviu volcmic aeas. Moreover, a
shot sequence of foú earthquakes occured
on Ausust 1991 (1.8 < M < 3.3) wft located
at about 40 km outside the culf of Naples
aÌons the prolonsation of one of the faldts
rhat, frÒm the volcano basement propagates
towdds SW into the Neapolitan Guff (Milqno
et a.1.. r99l)-
In  corc lus ion.  Mt .  Somma-Vesuvius
voÌcanic complex displays an highly
heiero8ereous structure bd a very low level
oÉ activity at present rifle.In facl, as alftady
poin led out  by Berr ino et  a l .  (1993),  io
i i g D i l i c a  n r  v a r i a l i o n s  o f  g e o p h y s i c a l
paramerers, such as ground delormaúon o,
glavimeric anomalies. h e been obsened at
Vesuvius in tbe last 20 years.
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Shallow heterogeneities and seismic activity of Mt. Vesuvius

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Shallow heterogeneities and seismic activity of Mt. Vesuvius

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