More about severe frost as a triggering agent of micro-

seismic activity in the neighbourhood of large Dam amI 

about the geodynamical conditions leading lo il 

r. CALOI (*) - ][. :'orIGA};I (**) - M. O. SPADEA (*) 

Reecive,l on .\ray 28th, l !l73 

SU~[~['\RY. In this sceond notc it is cvinceneed as t.lle (·ontrflst in 
the roeky.nH'dinlll downstl"rllili aTHI upstl"eulII or the Pieve di l':u\on' ,\alll 
dllc to severc frost, is the triggerillg agent of the lIIinoseiSlllieity. 'l'II(' frozen 
liqui,1 c](>lIIent (·:.pansion in thc r01'ky.mcdillm imbuc,\ wit.h wilt{'r (!o\\"u-
strrllm or thc dalll brings out the struins into the IIIc(!inlll hi(!(!t·n .. \rOl"eov('r 
fhe geo(!Yllalllica! con,litions which originate the lIIierOlshoeks are stlHli(',I, 
putt.ing forwilr,l; l) t.1!/' lllÌ('roshoeks repdrildly st.ar up during swlolen 
chllnges Olr tCIlI]JCrnture; 2) UJ{'y espeeially oc('nr dllrilli! the rew llOur~ of 
(lilll·nal heatini!, eharacLerized II.\' a partial snrfarial thawin).!; \\"ith ('n~ning 
IIhrupt. "filll" of t.hc {!fUll dOlWnstn'illil. The ilfon'Sflid jlhenOlllP1Hlll n'prp· 
scnt.s one or thc OI"igin-llIce!wnislll or thc earthqllukes in sdslllic ZOlWS Il.\' 
lOlcal strains eOlntrast eharaeterized. 

1. - On summ>lrizing in n. }lrcviolls note (') thc me>ln behavior 
of a large (bm (}lart.ieularly of the rieye di Cadore Jlalll) wit.hin a 
s}mn of fOllI" seasons, the exeeptional interest })ertaining to })erio(ls of 
severe frost· has been reyeu,lel! for thc first t·imc. It eOllll! be sho\\"n how 
the lllediulll anI! thc (Jam are a(lversclr aHeet.ed by the almormal belm-
vior of wat.cr if t.emperature falls below zero . 

.Alllong the phenOlllenu, brought 1,0 light that of miero8eislllieitYI 
eaused by cont.msting stmins within the roeky mediulll U}lf;trcalll 

{*l Istituto NaziOlnale di Gcofi~icu, ROllia. 
{Hl E.K.E.T,. COlllpartilll{'nto di Venczia. 



a!H[ I[owniltream oI thc I[am a!H! partiruhuly adiye at tile dum bottom, 
calllC qllitp llnc.:qwetell. 

fn the previolls 1I'0rk spedal attention wa,~ giypn to the seaHonal 
I[eyelopmcnt oI tilc phcnomcnoll. Il l'l'I'· Wl' .~halllook }lal't.ieularly illl0 
itil daily CO\ll'HC, 

:!, - To POilll Ollt lhiil mirroilciilmil'it~, we availel! our~clyei; oI three 
~('i~llli(' ~tatiOll.~ caril oI whieh wai; in~talled in \IlH!el'grolllld rooms 
oI centralil,el[ ('ontrol ('ahi11, Ollll Oll thc l'ighl hand .~hOl'e IlI'lU' lhe dam-
top, onc in a sta}lle-}lit. of ash!al' 1\'1' XI\' (('1.1) imide lhe dam (at. 
an hight of mil m) alH! one in a .~laple-pit. of ailhhl1' NI'. \' (C5), al an 
hight. of U:-Hl m, likewi,~e insil[e lhe I[am (fig. 1). ('l-j i~ in a eentml 

pOililion oI the dam, ('il is nCH1' its left l'!Hl. Tlw seismo;.;mph~ '\'cre of 
llw "Oirla!H!a" typc with the samc in,~tnll11enta! ehal'l\('tcristiC',~ cX(,C}lt 
thc l[mnlstl'eam-u}l~t.l'pam (\'-M) ('ompo11cnt of a Hei.~nlOgl'a}lh ill,~t,alled 
i11 Cii ,dlO~e dynamir magniliration pnwails oyel' the otlll'l' lwo. 

i\liel'O~h()('kil triggcrcI[ by fro,~1 are l'erol'ded by t,holl~a1l(!H in 
Wintcl' hctwecn ]lecembel' and )Iarrh whcn ail' tempeml1u'e Ialls 
('!eal'ly hclow zero I!egrces or os('illatci; wil!ely 1'0ll!H[ iL 

Onl,\' onc sel'ies i.~ ('omidel'ed hcrc, 1'(leo1'(!ed bCt,wCC11 Janllary lWi2 
ani! ,Janllary-Feln'\U\l'Y ln7:'l, 

AH a ge1l(~ml Il'all1l'c oI tlll' mirro.~hoek.~ tl'iggel'ed h~' the fro.~t. it 
~!J()1l](l be ob.~crvcl! tlmt ai; a rnlc tiley are rcro]'(!cl! 011/,/1 by thc ~ci~­
mie ~tations ill,~talled withill the dam, Rc('o]'(1ing,~ are 110t UnifOl'lll, 
ilmnwel', IlOt, eY(lll t.ho.~e of the t,wo aHh!al',~; ~ome mi('l'oHho('k,~ ('0111d be 
l'I'('ol'dl'd l'leal'ly in ('1-~ alH! wca\{ in C:'l, or yi('e ver~a, olhcrH were 
l!c1aYI'I! in ('5 01' in ('14, still othcrH only in C'H or only in ('5, T!Jc 
rea,~OIl of t.his 111lllVelll\('C.~H of l'el'ol'ding",~ may hl' atll'ibllt.ed ahoye ali 
to thc diJlerent arl'angemcnt oI thc ~cismie ~taliom, onc being" loeatcd 
in tile ('cntml ashlar oI tile dam (t'H), lhc ot!Jcr in a }lcl'i}lilerieal 
aHhlar (('f)) (hg. 1). 

Among t.he hUlH[rel[s oI miC'roHhoek~ rcro]'(!cl! belwcen ,Tallllal'y :1 
alld 12, 1ni2, t,he Olle of 2:'l111:!m of Jalluaryi (tig, 21X) wa,~ not rcco]'(lcd 
in C5. Oh"iou~1y, tilc mierosiloe\{ inlel'esled HlOl'e ('1·1 thal1 the 11IH!el'-
lying J'()('k (aH a mattl'r of faet, tlle high rrcqnGney vibratiOI1R, pcell!inl' 
to thc lat,tel', arc llliHSi11g): the I!am l'CHPO!U!CI[ Jìl',~t with lhe 11ninodal oI 
lheaHhlal', a!H! then with lilcI11ndamenta! of the entirc I[am Ll1 c-01.5·· (a)J 
,\'hich !m,~ no a}lpl'cdable alll}llitUl!C in ('5 a~ it is llllH1' the 1101!e, 

Fol' \'hc .~amc l'ca.~on.~ :dRO the te11,~ of miC'l'osiloeks oI Jìg. 2~ do 110t 
l'earh ('5, 



011 the othcr hnlld, fig:, '2,( Hhow~ a lnirl'oshock whi('h was J'('('()l'dpd 
ollly ill ('5: o bviomly, t he lWl'hll'bntion ol'igi11H ted n t. Cil \\ hieh l'e~llolHlPll 
Hr~1 with it~ pl'Oller uninodnl, followell b~' Ih(' hight'r hal'mOllil' of the 
cntire Ilam (T = 1- ab,), A ~imi]ar ob~E'rYnti()n waH madl' fol' IhE' 
two mieroHho('k.~ of fig:, '20 (20h.3~m and 2lh.3.!m of Jnnuary ~), t!H' SN'OIHI 
of \\'hirh wns lll'c('l'ded by high fr('qne11('Y vihl'ntiom, tltu" lll'oving thl' 
fad Ihat the mirl'oHhl)('k was also al'tivl' ill t!w ]'()('k I)(']ow tllll n~hlnl', 

Fig, 210 ~hows two lllil'l'o~hoC'k~ (thc lnltl>l', at t]H' O,;,) ~E'I'()]ld'~ 
Ili~b\lH'e nh, wa~ ~tl'ong'el' than tll!' fOl'mel') \\'hi('h ol'ig:inntE'lllll'ubabl,\' 
in the l'OC'k in ('onlnd with ('1-l whi('h m('r('l,\' l'l'a('t!'(! lo tll!' HtTe,,~, 

Fnl'theJ' tholl~nnllH oI llIi('l'o~hoek~ Ilue tu Im~t WE'rc l'E'('urdt·d in 
l,he dam from ])l'(,l'mhel' 1972 tu MarcII 1973. 

'l'hi~ ext.rl'lllely n111lWl'on~ Heries of mirl'O~IIO('k~, too, fentul't'd 
('a~cs a~ the ahove oI whil'h Wl' ill'l' nll'nt.io11i11g hel'e ollly h'\\'. 

Thc lllil'l'o~l!()('k of Jnnuary 8, 1973 (HjhG,Jon ... ) wa~ l'('('onl('d llln('h 
~t.l'Ollgel' in ('5 Ihn11 in ('H (Iig, :3), MOl'eovel', it real'lll'd {'l-l with 
a delay of ahout O,Ul ,~Cl'. rrhi~ ]ll'O\'l;H that tllll ~ho('k origillnt.ed llPaJ' 
('5, 

At 18 1>20'" of ,Jannnl'y 11, 197:3 a mirl'osho('k is l'ceordE'11 both in 
the dam (lig111'l'~ -ln and -lh) alld ill UlIl ('()]ltrol ('ahi n (fig11l'!'~ ~'(' alld ~d), 
yet with a ]owel' amlllitudc owing to thc lowI'r ~l'miti\·I'n('H.~ oI thl' 
Hei~mographs imtallell. Thi~ iH ~llggeHtiYe of the shoC'k orig:i11atillg ill 
I Ili' l'orky-plain do\\'mt.l'eam of the lIam, a~ iH lll'Oved hy tlw bu'k of 
l)J'O]lCl' o~I'ÌJJntiollS uf thc ('onl'rele H1..J'lldmc, Otht'r frnetme~ in thl' 
l'orI{ al'e tho~e l'e('(ll'I\l'11 nt Hlh20m of ,Jallunl'y l~, 'l'll!'il' Ol'igin \\'n~ 
mtlwl' elo~c to Cl.1, n~ pl'oved hy tlt(· majUl' nlll]llitndt' OhHt·rvt·d and 
by the vel'y sllOl't :lIlva1H'e iI ('olllllared to Himihn l'eC'ol'dillgs made in 
('il (!ig'. ;')). 'l'hl' ~t.l'Ol1g:e~t of the two mi('l'o~lll)('k~ ('il1l~ed light tl'a('eH 
in the C'ontl'ol l'ahi Il. Anothl'l' mi('1"o~llOek originatcII in thc l'oek wn~ 
that of ,JnllUnl'y 13, at l\J IL'2-l m (lig. (i), ('loHel' to ('l.! thall t.o ('G. ()ll!pl' 
exalllplc~ of mirl'oHhorl{H lll'Ovoked hy l'1)('k fra('tnl'l',~ )]rl' l'l'pur(('d in 
lig.7; thl',\' luul \'ariom intcmitie~, nlthough theil' Ol'igi11 l'lo~e to (:':') 
nllllcar,~ l111ique, 

'l'hl' ~ome lift,eell mi('l'o~hu('ks l'l'purt('d in lig. 8, on thc othcl' hand, 
l'E'g:l1'Il almo~t tlXl'lll~ively thc dam allii theil' ())'igill mllHt he ~ongh( 
hehind this: the 1ll0l'e ()J' ]e~H long Herics of usrillations al'c nnimatC'll, 
in fart, hy allomn]ollH Ili~pE'l'~ion, a stl'ikillg featul'tl of the Ilam'H fl'('l' 
osrillationH, They al'l' l'erol'ded ahuv(' ali in ('1-1 wher(' thc fnndaml'ntnl 
uf thc elltil'e dam allPl'an! bcttcl' dE've]ollllE'11. ]t is ob~el'vl'1I that. hl'-
twecn the ht'ginning oI t.he val'ion~ pl'1'tll1'lmtio\lH and the hl'ginninK' uf 



506 l'. CALOI -~!. ~[[flA-";I - ~1. C. SPAllE A 

free o~cillation~ of CH (or of t.h" one~ concel'lling the cntire dam) t.hcre 
are diHtn"ent t.im" interval~. 

']'hi~ mean~ that t.h" (1i~t.ance oI origin oI t.he variolls microshocks 
to the ~ei~mic ~tation oI Cl-! varics. The nearest to CH appears to 
be, Ior in~tanee, t.h" one uf 18 '1 .!7 m oI January 26, followed by that. uf 
191>3-1 m of January Il; the Iarthest is apparently tlmt of 20l\·J,6'" oI 

J anuary 2ii . 
. .i\nyway, the order oI magnit.ude of t.he relat.ive diRtanees may be 

calcuJa.ted after the formula, (3). 

n ./ l,' 1 
v~ -

.JT l i " l' , 
where v is the pru]lagation velueity of a frN, osdllation of the ]lcrioa 'J' 

.l E 
in an ashlar oI the thicknClSS b, l! - ilHliNltes tlw lH·ollagation vCllu-, 
city of tlw (1am's ln·ol)el" ordinary longitmlinal waves. 

'g 
POI' l r; "-' 4500 m/seI', b = 16.5 m, one gets v "-' 1 366 l' . 
ThcrcIore, the velocity results to be inversely ln·ol)ortional to the 

l)eriod of the consider"d free "\vave. 'Fur a lwriud of l' = l ' , une gets, 
for instanec, v = 366 m/seI'; for T = 0.6 ' , v = 470 m/sec. ab, for 
'J' = 1.5 ' , v "-' 300 mjsel'ab.; fur l' =.03.0 ' , v = 210 m/seI' ab. I<Jvidently, 
t.he~e arn }Jurcly indieative valneR. 'Vith re8]lcrt to the IrN, wave of 
about O.ii ", the secon<l oI the abovc microshoeks appears to be, thcre-
fore, some one hundred m"ters farthcr, with its oI"igin, than the first. 
']'Iw mieI"o~hol'k of 2()11.j,ti m of JanlHll"y 2ii, might have it.s origin at. t.he 

l)lug·bottom, ete. 
The microshocks originating near the base of the centraI ashlar 

(OH) not. only bring ,.bOllt the fundamental useillations of the entiI"e 
dam, but oftcn give l'iRe aR well to vibrations in thc or(1cr of abollt 3 -
whieh may be considered vibmtions of thc concretc building fixed at 
one of it.8 end8 (tI w left) and "fr"e" Iwar tlw plug, always bearing in 
mimI that these are mÌeromovenwntR. The exeitation oI t.he~" oscil· 
lat.ions may be more or less retar<led: consideration should be given, 
for inRtanec, to mirrusllOeks of ngs (le, 11 (01 h07 m of J alH1ary 29, 19(3), 
9b, (la, 12b, 12a. The microRhock a]lpearÌng in fig. 91' seClms t.o l'OmCl 
Irom right. below CH, c:xactly as the first oI fig. lO. At 23 h 35 m oI 
J alHHlry 28 (fig. 11), them was "vidently a sm·ies of mieroshocks, as 



MO!\}; AnOUT SEVERE ~ ROS'[ AS A ,[RIGGERI~G AG:EXT, ETC. 507 

well as at 14 11 57 m of Jannary 29 (Hg. 9b). 'l'he mkroshoek of Hg. 11 
(at 081<02"') evidenlly took its origin Irom tbc rock, cven though it 
exteIllle<l fmtber to lhe dam, simi\a.rly as lbe mil'roshoek of fìg. 12b 
(OP.!9 m) caused succc~sive microfrad-nres in thc rode In Hg. 13a 
(f. in. at 15 1126 m and aì 17 11 14 no ) tbc vibrations oI the dam or ils pa.rts, 
farle in about. 4 sec, while in fìg. 1:3b (at 1Jh2Sm) they deyelop at (lis-
tinct. intervals and persist. for abont. 50 seeonds, which is indieahve 
oI the far origin oI t.he micro,~hock (possibly at the 1)lng-hol10m). 

Among the fractures originating from t.be roek, that oI 14 11 22"' 
of January 2!J, 1973 (fig. 9a) whieh wa~ reeorded only at C14 and i~, 
bence, very clo~e t.o t.bis ashlar, deserves att.ent.ion. Contrary t.o t.his, 
t.he fraetnre of Jannary 31 originated on lhe right side, at. t.wo or three 
bnndre<l metres dist.anee from the eontrol eabin, extelHling from S\V 
t.o SS\V. Unly t.races of it conld be recorded in C5, fig. 1-1. Here it 
should be remembered that the eontrol eahin is spparatcd hom the 
rockY-l)\a.in by a gorge of about 120m deep in which t.he plng fìts. 
:Fig. 15 shows a microsho('k in t.he rock, reeorded merely at ('5 a11(l 
neces~arily with its origin rather dose to t.his a~hlar, ami, moreover, 
in C5 only tbe microshocks oI fig. 16 are record ed. 

3. - Four series of microshoeks due to host bave been exa.mined, 
between January 6 and 12 ami between January 15 and 1!J, 1972: 
between January 11 ami 16 and between January 26 and }'ebruary 2, 
1 !J73. The variou~ thousands oI mieroshocks thus originat.ing were 
divided into one hour interva.ls with the fn·st. t.wo series, and into 
t.wo hour intervals wit.h t.he third ami fonrt.h ~eries, as far as their 
ehronological order is concerned. 

Fig. 17 refers t.o the lìrst. two series and shows as well the bchavior 
of temperat.ure and oI the wafer-Ioading moreover the II0wn.~tTeam -
upstream component (V-~I) of tbe clinogmphic station inst.ai1{'d at tbe 
base of CH of t.he Pieve di ('a<lme Dam. Figs 18,19 are referre<l to 
lhe otber two series, the first consi<lering t.emperat.ure, waler-Ioading 
alHI clinogral)hiC recor<lings, simultaneously measnred at the hights 
oI 682, 660 alHI 625 metres of C14, t.he ~eeolHl these same llata plus 
elinographic recordings obtained by the ~lation installed in the ro('k 
at 625 ms height in a staple-pit. of t.he right SUPl)Ort. 

One fact emerge.~ immediately Irom the figureH: the micro.~ho('ks 
l)ertaining to severe Irost mass logefher espeeia.lly in time periolls oI 
swlden t.emperat.nre change~. 'l'hm, sinee eooling olr requires much 
more time than warming up, it is in periods of the lat.t.er that miero-



l', C,H OI - l I. ~f1GA~1 - ~l. C. SPADEA 

f!hocks OCCllr with maximlllll f\'equency, rt is not SO much the tC'llll)('l'a· 
ture val'iation in it,~clf whil'h i8 J'(jspon,~ihl!' fol' micl'ofradures Wl thc 
rnpidity at which it takcH plnee. Dl1l'ing thc day, p\'ovidel1 there is 
,~uIl8hille, tempemtul'e recovers what it 10Ht the night. bcfo\'e. H!nveveT, 
~ilwe t!'lllperatu\'e lw'overy oceUl'8 much faster than !oRHes, (Iming the 
few hours in whil'h the t.em}leratlll'e inc\'ea~es, .iust then t.he cncl'gy 
whieh is capablc of b\'inging in plasto-elastil' field In'!'a].;:8, more gathers. 

'T'he fact iR 'vcll ontlincll al.~o by t.hc l'!inognl]lhic \'ecol'l1illgs which 
allow, besides, to 11eJinc its cnuses. 11: iH known tllat. 1:111' "diu\'nal wave" 
following the sun rndiat.ions anl1 }larticulal'ly ampIe near the llam·toll 
l'mlnees its alllplitude ns it pnll'eel1s towal'11 the (Iam-bottolll when' 
it vi\'tllally is a,nnlllled. III tlw \Vinte\' nlOnths i1: is stl'ongly relluccll 
al~o near the l]am-toll aIHI at. Ia.Rt dif!aplle~U'f! in the lle\'iod when the 
sun is 1m\". 

At Pieve 11i ('aI10re, t.oo, wit.h temperature above zero dcgrceR, the 
'~dimnal wave" nt the 11am-bottmn of 62;) 1m height is reconlcll only 
ns a tl'll,Ce, if an~'. Tts belw.viol' in pet'iolls of seveTe frust is a.ltog'cthf'l' 
ditIel'ent, 'T'Ili' l'(wk 11owllstl'eam of the danl iInbibed with water swc1h! as 
it fl'cezef! and ]J\lshcH t,Ile 11am l1j)stl'eam (:\I). rl'lti~ is shown by tigs J 8-21 
w11ieh l'eveal also another fact.: the cont.ra~ting Iwhavioll\' of the top 
and the dam-hot.f,om nnllel' t,he sa/il(' aetillg cause, 'T'hc ~inkillg of 
tempc\'atu\'e hmll1.~ the uppc\' lla\'t of the danl downst.l'eam (Y), 'vhile the 
bottom is pUf!hcll llllRt.ream (111), aIHI viceverf!a. SIJ('l'e,~sively, wlwn the 
upper jJal'Ì of the da m, exartly t.he side opposi te the lakc, is wal'lned 
up hy sUllnillPss, hends upst.l'eam (:\I), whi1!' at the snme time t.he warmed 
a.i\' part.ly meltR thc fl'ozen wate\' within the \'ol'ky lllnin, eall8ing the 
contraction oI the rocky medium with a smal1 downstream (V) bendillg 
of tlw dam bott.onl. A t the lower }lart of the 11am anl1 in periods oI 
severe Irost t.hif! rewl1:s in the fmmatiml of an i-nvtrtlJd IliUl'nal n'ave 
(lue to the anomalous behavior of water when t.he temlle\'a.tlll'e is 
llll(Jm ze\'o degl'ees, The mentioned ligurcs shmv that for the Pieve di 
Cadore }lam the height. of mdi l'otn.tion is few metl'e8 below 660m~ 
whel'e the clinogra}lhic eom]lonent 11owmtl'ealll - llpst.I'C~\m (V-:\[l is 
stili, thOllgh slightly, ill pha~e with t.he correspolHlin,l!; eomponent of 
the !lam-to}l station ({j82ms), 

('omillg bfi.ck to the connecting' phenomenon of mi('Tofl'aetu\'es, 
it is observell t.llat 11nring t.lw gnulunl ;;inking oI temjleratl(J'e belo\\' 
Z!'\'O 11egrees the dam is grnllunlly pl(f!llPd llpst\'mun CM) [).!l11 that only 
in the Ked.ionfl wll('I'!' eooling is more rapi!l, t,hi~ 11llSh may hrillg ahont 
mÌC'l'oshocks, fn other terlllH, dlll'illg cooling the mellium general1y 



MOllE ABOV1' SEVERI:> l"1\081' A.~ A TmGGEHI~G AG1':~T, ETC. ;, Ofl 

reacts withiu t1w plastie tìelil. In tlw few hOUl·S oi sumhine, ,dlCn 
tem}lerature rapillly nwovers ,dm.t, il hall lost Illlriug" the night, thc 
outer parto of t.hc medium releases rat.hcr suddcnl.\' fllHI allows the dalll 
to "fa.ll" downst.ream (V) (figs. 17 -1 D) in too l'al)id a wa)" to bc l'outainell 
oy thc nWIlillm wit,hin thc plafltic tìe!ll. So, aftoCr overeoming the 8tl'cng"th 
limit, microshocks Ol'CUl' \\'it.h highcr frclj1Wnl'Y. .As is shown b~' the 
clinographic rccorllings j t.he defiection dcscribell oy tlle Ilam-oottom, iu 
one way or the OP1)(),~ite way, is more or less the same; howevcr, Ilul'iug 
t.he st.age of wanl1il1g uV it. is covered much qlliekIier than during' the 
cooling olI stage which aecounts for the outgrow of the pla~tie }lhHSe 
aJl(1 for t.he follO\dug microfraeturcs as a re~lllt of a morc fll'centuatell 
monwntllm. 

This 1JhcllumclluJ! s7wuld be secli ([S a '('(Ilua/Jlc indication o/ thr 
mcchanism which accomptmies scismicily in ail a/'(([ subjrl't to contraslilly 
st/'ains, 

'l'he Ol'der of magnitude of tltc st,l'CSSCS sltal'ing with tlte mie1'o-
fracturcs rising in the l'(){'k can oe oest. valued if one comillers that the 
t.angential st.mim actillg Ilowllst.nmm at tlw dam-llOttom j the rcservoil' 
being completely filled

j 
are abollt, 30 kg/cm~. 1'heHe are t.he Iorees 

whieh ad a.gaiust t,he medium downstream when
j 
furt.hcl' t.o the yielding 

of the rol'ky system whieh lo~es in strength Ilue to }lartial t.hawiug of 
t,he flUl'face, the Ilam "falls" towan! the roekY-lllain. Hllt, thiH will be 
dealt wit.h in dctaii in another pfl,pcr. 

4. - In ordcr to lllUlerflbulI! always hcttcr the behavior of the 
Pieve di Callore Dam closely linked by seasonal variat.ioufl it, was 
couflillcl'cd hel}lful to eompare the course of tempemt.llres (and of the 
water-loalling) to t.lw ~imult.aueous Ilevelopment, of 1:he clinogmphic 
recordings taken in CH at, thc height,fl of 08:J

j 
liOtl

j 
ti~5 ms in t,lw months 

of Feoruary aJl(1 )Ll1'ch 1!H3 which, from the geodynami('al viewllOint, 
are t.l'fl,mit,ion months, 

At t.he height. of 682 ms, and le~Her a.t. tillO ms, t,he fir~t groups 
ai diurnal waves lllH!el' the cnect o[ sunniness begiu to avpcar, while 
the dam stm-ts ocnding uIMt,rcam CM), also t.hrough the ahatement of 
t.he watel'-loading. This behaviol' C(Hlt.inues thc whole of March, a.s 
[al' as the height of 66t1 ms i~ concerncll

j 
ami until :'\Iar('h :20 [or tlle 

height. of 682m~, t.he Ilam-tov which beginning at. that Ilate starts to belld 
Ilownstnmm (Y) rfl,t,hcl' t,han upstream (:U). 1'his allomaly is explainell 
by t,he ucllfl,viOl' of air temlleratUl'e, which meanwhile is aI1Ill'Ofll'hing 
8-10 <>C, and of the watoCl'-loadillg limited to heights below tiOtl ms, On 



i:;IO P. CA L,J r -)f. )[[GA~r -)f. C. f'PADEA 

the reservoir side the part of the liam ('overed by water lws a teml)era-
turc or about -i uC which accountR for the Ul)stream pressure of the 
lower l)art of the (lam up to the sai(l heig-ht whieh haH (10\\"11st.ream a 
mean temperat.ure of over ..1 0e being reaehe(1 by thc Sllllniness. }'rom 
660 ms upwan1, howcver, alRo the part or the (hun on the l'eservoir sidc 
is sllbjed. to progressive hcating a.s a. consequcnee of the inerease or 
air tcml)erature, eontrar:,>' to the submerged part whieh is governeli 
by a lower temperat.ure. This cont.rast inereases wit.h t.he height. 
Thus one has a relative motion of the emerged vart l'ontrast.illg with 
t.he Rubmerged part., that is a (lowllst.ream (Y) bcnding, as is elearly 
dmnonstrated by Hg. 21. 'l'hiH Hhows aH welI the alteration of thc 
diurnal wave as a· eonsequellec or thc eontraf!ting thermieal Ritua.tion. 

At any rate, the bchavior or the dam-botlom is mueh more 
interesting: in February the above sa id il1vcl'tcd dilll'l1allWVC (in op})osite 
phaRe to that or the top (liunml-wave) COlltinues to lievelop regularly 
allli with uniform succession (ill the mean t.ime t.he microseismieit.y (lue 
t.o frost., as shown, start.~). In the early part or flIareh, however, wit.h 
tempcrature rca.ehing gradualIy vahlCR abovc zcro degrccs, the llm1u-
lation a.t thc hei~ht of ti25 loseR eontinuously its unirormity of sueees-
sion, its rhythm iR brcaking uv, and in the serond parto of thc mont.h, 
when temperaturc variations are exelusively a.bove zero !legrees, it 
shows only sporadie and inegular perturbations and at the emi slaekells 
(10wn into a. line without aPlH·eeiable movementR. 'l'his mcans that 
t.he outer layer of the rocky-plain is now warmed up above zero 
!legrces and that. any valuable eont.rast agaillst. t.he liam 1ms eease(l. 

5. - 'l'o eonehllie t.hiH note, the interest roused by this l)artieular 
spceimen of invest.igat.ed mieroseismicit.y allli by its unexpeC-ted origin 
iR UlH1crlinc!l. Both have bcen broug-ht t.o light t.hrough the valuable 
hell) of two instruments whirh alrcady permit.ted to look into the geo-
dynamical behavior of a large liam and 
seismogra·1Jh alHl tlle photo-elillograph. 

its Vhysiral surroundillg: t.he 
The former has revcalc(1 thc 

phenomenon, t.hc latt.er has eontrilmte(l decisively t.o its eXllla.nation. 
Consù1ered in(livi!lualIy, t.he mieroshoeks triggen,(l by the frost 

are of a very limited intensity (on an averagc in thc order of 101u erg). 
It shollid not be overseen, however, that. in mountain areas they may 
originate in Eme RVallS of thrce, four mont.hs and by t.ens of thousands. 
Sinee each microshoek lH·oves the cxistcnre of a mierofI"arture in t.he 
roek, wit.h a very slow but eOllt.inuous weakillg or the medium in whieh 
thc dam haR bcen bllilt. 



)IOHE ABOUT SEVERE FROST AS A 'rHIGGEIU,>G AGE:\T, ETC. 5 11 

An inlcnsificd, accu/'ale contl'ol o/ Ihr r/m;/ic rcspOIiSC o/ Ihc mrdium-
to which Ille dam i,~ ancho/'etl - and o/ ils l'arialionsin Ow lime ilJ, 
t1lr/'e/o/'(', an 1//'gcnl ncccslJily. 

REFERE~CEtì 

(I) (',.>,T.OI }l., ~I!GA:\1 ::\L, SP.\J)EA::\L c., lUi2, - Uehavior ,,/ Ihe large dam 
al setere frust, "Annali oli Geofisica", XXV, 4, 5HJ·525. 

(' ) eALm 1'., SeADE.> 'L C., '''<HL - S"Il" "'1'0.1" ""1/,,, d.ll, d"h,. "Il" 
loro varia:;ione 'liel Icmpu. "Allunli (li Gl'uJhica", XXII, l. 

{') CALOI 1'., HI5G. - Sui periodi di oscillazio/le liberI! dei cO/lci di tO/a diga 
l' sulle loro re/azioni COli le l'araI/eristiche daR/iclle del calcestruzzo. "l; Enpr-
gia Elettrica", XXXIII, 12,