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More about severe frost as a triggering agent of microseismic activity in the neighbourhood of large Dam amI about the geodynamical conditions leading lo il

2011; National Institute of Geophysics and Volcanology; Volume: 26; Issue: 4 Linguagem: Inglês

10.4401/ag-5022

2037-416X

P. Caloi, Marco Migani, M. C. SPADEA,

Landslides and related hazards

More about severe frost as a triggering agent of microseismic 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 .\ray28th, l !l73 SU~[~['\RY.In this sceond notc it is cvinceneed as t.lle (•ontrflst in the roeky.nH'dinllldownstl"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.mcdillmimbuc,\ wit.h wilt{'r (!o\\"ustrrllm 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.ingforwilr,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.sone or thc OI"igin-llIce!wnislll or thc earthqllukes in sdslllic ZOlWS Il.\' lOlcal strains eOlntrast eharaeterized.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.ieularlyilll0 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'eIlI'lU' lhe damtop, 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'(!edbCt,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.edahoye 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 Ll 1 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 .~amcl'ca.~on.~:dRO the te11,~ of miC'l'osiloeks oI Jìg.2~ do 110t l'earh ('5,