TheTheAssociationforthe Association for the Geological Collaboration in Japan (AGCJ){AGCJ)
ttf!ptXIFI;57#, {2003IT{) 73 Earth Scic･uce73-82(Cl]i]{yLiKf,Ls.aku) x'ol,57.73S2, 2003
. Liquefaction structures ln peat - - a case studydeformationin Kan'etsuarea, central Japan
OTSUKA Tomio'
Abstract Derorinations duc to liguefactien in peat bcds are describcd i'ruin threc localities : Takasaki City･ und 'Ib",n, 'Fakasaki ltakura Gumma Prefccture tmd Ect]igo-Kawaguehi Tl'}wn, Nii.o ata Prefccture. The 1igueiaction in Nblcane. occurs in a iatc P]eistocene pumice bed, parl of the Macbashi Peat Formution. eriginated from Asama The thickncss ofthe pu]nice bed is laterall}, highl}, variahle shewing fltimc-like sLructurc in places. The age ef the liquefacrion is estimaied to bc 16 thousand },ears BP froni radiomerric ages ot' lhe peat bed and ovcrtying Due to pumice i'all. The liqucfactiop Lrace at ltakura Town is observcd in the Hotoccne peat and sand beds. ]uteral ilow of sand bcd at the time of [iquefaccion, ",eds,e and batl structures are fon]ed, ,ALt Echigo-Kawaguchi, structures due to latcral moveinent of sand bcds ",ithin pear beds of thc river terracc deposiLs are observed. In all the cases clea]' Lipza,ard-intrusions and sand dikcs are not seen. but the de rormutien ef pear beds accompanying in struetures, Itisimpossibleto niake a lateral n]ox,ement ef Liquefied materials are observed resulting chaotic '1'he conclusion that thcse structures havc been formed b>, paleo-carthquakcs. but rhere is a large pessibility lci'r. rcco.gnition of thcse charactcri stic fe atures tna), bc cffective to clarify a tecal seismic hisLory,
ballstrucrui'e. eurthquuke, ()uaternar},, l(2yIVbrdty:LiqucfacLion dct'ormation, peat, ]v･{aebashl Pcar,tlanie-1ikesLructurc, weds,e and
at the tatest stage of liquei'action and various othei' deforma- Introduction tion structurcs. Takahama and Otsuka (2001) diseriminated 'rhis stages in Lhc same arca aiid briefl.v de- report is on some sequenccs ofJiquel'ied strocture ub- two inore Jique['action in to bcclcscribed served in thc late Pleistocenc to Holocene peat dcposits. scribcd liquefaetion ofpumice deposils peat Horiguchi et al. (1985) rcported sand and gravcl dil
Seismitc tntcrprcted as earthquake-indueed liquefaction has eravhquake, man}, ot' lictuefaction in the Pleis- becn reported in the 1acustrine sedimenLs (Sims 1973 : Hi bisch Ihavc observed traces on liquc- ct al. ] 997 : Alftilo et a]. 1 997 : Rodoriguez-Paseua ct al. 2000}. teccne and lIelocene peat deposits. Obscrvations
within deposits svere carricd out at threc Otsuka eutl, (1997) discriminated t'our dlfferent periods of factiontraces peat and Itakura Town. Ora liquefaction wilhin tephra deposits dcrix,ed from Asama Vt)1- localiticsjneludingTakasaki Cit>, Prefecture.and Echigo-Kawaguchi cano in the middlc reach of the Karasutfiawa River drainage County. both in Gummu 'l'hey They basin, Gumrna Pfefecture. described draw'-in strucLures Tk)wn. Kita-Uonurna Count>,. Niigata Prefocture 200L7. Accepted Fchruar}･ 12, 20()3. ReccivedAugstS. 'tbwn, 'i' Gumma I'ref.. 3.79-22t4. Japan, Otsuka prix,ute schooL, Shhnofurei1044.Akaberi C 7:), ) NII-Electronic Library Service The AssooiationAssociation for the GeologioalGeological Collaboration in Japan (AGCJ)（AGCJ ｝ 14 ．． 1K ’’ （．）T Sl．．， ．Y ic・．〕lni し．． 自 用 ’’ 139 E［ 38 s9 4s ］ 詈1齷 1 覊 ミ・・ 黷 鑞纛 ・ ’ F三 ・LL … lili… fth・ ・mdy … a … ］ m ・ ： … maP ・ ・ 9 dleca iLy P・A L lity fTak ・saki ・1c ・． B ・L ・c Uity maP ・f lt・k ・lr・ u ．… ．C ・ L ・ diLy map ・f − 」 ’’ ’bqjiya’7 Echigo Kawaguchi llrCEI．UsingIo top（〕 illap graphic Takasaki∵ Kog ビ ar】d scalc 1：25，000 by【．he Gc 〔〕graphic［LI Survey 【nstitute ． ’ ’ show characteristic ’ lllorl〕holc）gies． The 1ecogni1 ．ion 〔）f thosc mud 亅1〔〕w dじ P（）si 且丶 1）umice Jall deP〔：）sitcd in the waler ， volca − morphologics wo lld し bc irnpc）rtant to idcntify liquefaetion ln llic ash ． and p じat 〔Fig．2）． Thc｝sc purnicじ ｛．Lnd v 〔）lcan．ic ash lh じ ficld． werc derived froEn th¢ Asama V 〔｝lcamo situatcd 30 km to thc ’ ’ w est 〔｝」吐．his localily． Takasal （三 district ’ − Thc stratigraPhy o1 this location is a 〜 follQws in desccnd Site descr三 inL，． OrdCr ， ． Pdon L 1 loca］ （：）ut south （， he ityjsab l knl fthcTakasaki SしatiQn 〔｝f Tal（asaki Mudflow． （TMf ） Tlle Takasaki M しlcM ．ow collsists ’・ ． the丑 Lkasaki L ．i．ne Fig．1A ／ （ ），．ak しsakj area ．is Ialgご1ycc）vorcd lとugciyof loan1y malcriaiswith abundant pumicc． It has thirl ’ 「 ， ’ ・ bytheTakasakiMudllo− orwhich sur ゼace formsthe lhkasaki andesitc glavel beds ncar thc base．． At thc cu1 rcllt． locahty the Daichi ． ． （upiand ）． Thc western edge of Lhc Takasaki Daichi is estiTnated thicknc ．ss is 3 n1 ． τakahama alld Otsuka（2〔｝0 D cu 亡 ’ −− by 1he Karasugawa River． Thc relative heightbctween 1eported occul 1ellces of equivalentb じd aloPg the Karasugawu the river bcd and the Daichi ． surface i℃ achcs about 15m ．Tlユe Rivじ r at ［he s （．）utl 】crn R，ot of thじ Haruna Volcan 〔， and ut 「 − observed outcrop is situated orl thc riverside cliff． Sakutno〔o ． Nla〔sutd とL ［Own in thc uPper reach o 【the Usui ’ TheTakasakiDaichiigmade of ］atc Plcigtoccneto Hol．ocene Rivcr、 Because itdirecdy ove1 lies］iqueficd bcds， they illter一 （7 ・1 ） 一 NII-ElectronicN 工 工 Eleotronio Library Service The AssociationfortheGeologicalAssociation for the Geological Collaboration in Japan (AGCJ){AGCJ) !.icll.lefE-lctioll (Lc･formEltic)11 s,t]'Llc.'turus in peat 75 bccause it contains a ]argc ainount of mica flakes. The age is TakasakiMudflow Thickness [TMf] estirnatcd to bc 19 to 20 thousand >,eurs (Nakarriuru et al. 300 cm+ [997).AsamaItahanaBrownPumice Volcanic sand [VS] 1 5 cm Formation (As-BP) Thiscon- * 44 cm sists ot' brown sandy of 30 crn thick and is originated AS-YP(13-J14ka) pumiee from the Asama Vit)lcano. Its estimated age is 20 to 24 thou- Pt4(161sO ± 2sOy*Bp*) 1Ocm - sand years (Nakamura et td. 1997 : Committee for Gunma Pt3 pruoa--scoroOoasEJPi'efectui'al ("Jeologic ),Tap 1999), Mudflow This is ovcr 25 cm thiek, but the 48 cm Maebashi (MMf) *** is unknown, Il conlains an.ou]ar andesitic wilh AsOkP-1(16-J17ka) bottoin gruvels an indurated inatrix oi' ash. It is dcrived l'rom theAsama Vk)1- Debris Avalanche Dep(}sit Pt2 *** 30 cm cano and correlatcd to the Ol MaebashiMudflow cm+ [MMf] Daichi. It is alse t'ecos,niied in the part ofthe Takasaki Daichi. about cm thick and subdi N,ided unlts --- Intrusive The peatis 1OO intofour pl-"-1･i-I-I-:-I-I MudflowVolcanicM Peat horjzonLiquefactionfrom Peat 1 te Peat 4 {Pt1 to Pt4) (Pig. 5). Eaeh unit is cla.ve.v sand Peat pcat,. and fresh surface is dark brown in color, but it turns Lo -tt Pumice Ash [!E] horizon dark bro",nish bkick immediatcl>, ailerexposurc. Nirei (]997) reporLed radiomctric carben agcs ('or Ptl and Pt4 of this lo- * after Comittee for Gunma Prefectura[ caliL}, are 20,040 ,-L 290 ancl ]6.150 ± 250 respec- Geoiogic Map (1 999) yBP yBP, ** tivelx,,Deformatjon after Nirei (1 997) *** structures afterNakamuraetal,(1997) 'i'akasttki Detaits ef deferniation structures are shown in Figs, 3 and Fig. 2, Colurnnar secLion ei' tel}hra and pe:u la.yerb in arca. 4. Thc dcforination structures are restrietcd within the As- OkP-1 and oN･erlying PL3. Thc KbP[' ",hich underiies Pt2 is prcted inudflow to be caused by the carthquake. Arai et ai, slightl}, deformed. <[993) attribLtted the origin ol' rhe inudflesv to a largc earth- The thickncss of the As-OkP- 1, "'hcrc most del'ormation quake or hcavy r'ain occurrcd about }O.OOO },cai's ago. occLLrs, varies widely frem 1 to 20 cm. This bed shows flamc- Fjne-gra{ned volcanic sand bed (VS) : provisional name This like shape (not a dikc-likc i'orm) un the cross section intrud- is 15 cm thick, ",ell-]aminated interbecls of volcanic sand and ing into os'crlying becis. ZI'hc tlamcs decrease their individual ash which direeLl>, overl the As-YP becl, ",idths upward. The Pt3 unit shows det'onnalion conl'orm- >,ing 'I'he Asama Itahanafellow Pum{ce Formation (As-YP) This is ablc to that ot' the As-()kP-1. base of i"Ls-OkP-l is de- 44 cni thiek >,ello", puniiec bcds. a key tcphra betL in northern formed, but the degree ol' deformation is not more advanced lowcr of Kanto area, and a product of ,tYsama V')lcano about 13 to ]4 lhaii the upper portion ofAs-OkP-i. The portion thousand >,ears ago cNakamura et a!, 1997 z Committee fer As-OkP-1 has been lntruded inte under]ying Pt2 unit with Gunma PreC'ecturat Gcoiogic NTap ]999), lo"' ang, lc, Atl those deft)rtnation sti'uctures are clearly eov- Olcubozawa Daiichi Pumice (As-OkP-i) This is white me- ered bvvInterpretation un-deformed Pt4 unit, dium- to coarsc-graincd pumicc bcds. Bccausc its primar>･ ofdeformation structures dcpositional structure is disTuvbed by liquefaction, the exacz The deformation structLtre is mostl>, cemplcx and caused thickncssis not also originated theAsama b>, laterat fiow of ljquefied As-OkP-1. Strong variatjen ot' known, This is L from liq- va')]cano and its age is estimated to be 16 to ]7 thousand >,ears liqucfied beds thickncss. flame-like shooting up shapc of (Nakamura eL at, 1997), ucC'ied matcrial indicatc its comptexity, Kumoba Pumice bcds is originated from theAsama Vblcano. ,tYt soui'ce it fbi'rns lhe deposition ol' the ,'Ns-OkP-1. The history ot' deformation pumice flQ"i but hcrc it is ash fall. It is cusily idcntifiabicC7is summarizcd in Fi.g, 5. The tiniing o(' liquefaction isjud.g.ecl t5 ) NII-Electronic Library Service The Association for thetheGeological Geological Collaboration in JapanJapan{AGCJ) (AGCJ) 76 rl'oinio O'I'SUK,N A before 16 ka Pt3As-OkP-1Pt2 As-BPMMf Fig, 3, F]atnc-like structure (t]ot a dike-Likc forin) ol' thc As-OkP-1 layer in the N･laebashi Peat Fei'niation. C 13･-14ka v -a ve (vs)As-\PPt4 Oe TakasakWudflow[TMf] e o'(,Q T,rrr=\"g-=-L7.trr'Ttt,,..,.....g.. t..ttt.t. t tt .t tt.'(vs)AA' AAAAAAAAA A As-YP AAAAAAA AAA AAAAAAAAA TMf t ･A･ tt . ･1t t t. ･./,.t.'.Al t, ,..i :: b,,. .･.-..' ･･.,., 1･ i･ IA.s.-B?･,:, /.1'A >' ･/ ( l'.2d 6. i/)'K4a'e{Ia:iiMld ftow[MMf] o lm n t Fig, 4. Suhcinutic sketch orancicnL Hqucfaetion htructure sho"'ing flainc-tike strLicturc F]arne-tike strucLLere ol'As-OkP-1 t.t-d Ptr, is cut of ancient area, by Pt4. 1;ig,5, Historicalprocess liqvet'actioninTakasaki to be betwcen A and B in thc figure, and on the basis ol' depo- Itakura clistrict sitionui ages of the As-OkP- 1 and Pt4. it is estimaLed to be 16 thousand years ugo, Site description Rikahamu and Otsuka (200] ) confi rmed occurrence of liq- ltakura district is located about g km east of Tatcbayashi, LtefacLion ot' the same age about 1S kt]i northwcst of this Io- GLunma Prct'ecturc. The district is closc to thejunction of cality on the right bank of the Kara,sugawa River, wherc the Guinma. Saitama, and Tochigi Prefectures and at the uon- As-OkP-] is drawn in. Thedra",-jn uccuvring at the [ast stages fiuence of the Waturasc and lbne Rivers. Thc locality is 1 of liquefaction is a good indicator of agc of Iicsuefactien as ktn nerLhwest of the [[b},odaimac Station of thc IIk)bu Nikko rfakahama havc been out by Otsuka et pointed al. (]997)and Line (Fig. IB), and in an alluviaL plajn .gcntly sloping south- et al. (2000). castward ot'the northein Kanto Plain, The observation is made (76) NII-Electronic Library Service The AssociationforAssociation for the Geological Collaboration in Japan (AGCJ){AGCJ) T.jquerucLion dc･formaLicm structurc}s iii peal 77 Thjckness SO cm+ 11Ocm 35cm27 cm 62 cm Fig, 7, Ancientliquefaction strucuturc ln Itakura area, 15cm30cm i ln the eeiiter of this t'igurc the stmd and peat beds are dcfornied forming as>,mmetrical duwnward pointing wedges. To the right ef cenLrulwedgeisaballsLructurc. 60cm 40 cm+ :: silt,,iiiii i{}tg,rc,adiaiAodnday . . . intercalation ciay ' ' " g of sand and peat ua peat i:;:i[i:i:i:i sand Fig, 6. Co]uu]nar section in ILakura aretL BIack circte indietucs 1iquefaction horizon, and bEack arrow intrusive heri zon rcspcetivcl},. at a site of the bridgc foundation work. Thc sides ot' the exea- vated foundation work are ideal for obserx'ation o1' sott ground, Fig, 8, Skctch ot' ancieTit liqueftLcLion in ltakura iirca. as secping ",atcr is foreibly drained, The dcposlts consist of From thc deferniatiun of peat bed i1 is clear that the batl is ro[atcd tnainly, Holocene clay, silt, sand, beds and interca]ation peat 90e anLi-clockwisc. Mcdjuin-erained sand bed shows preferred resulting from flo-'age. of sand and silt (Fig. 6). Thelr･ ure deposits of flood plain and orientutiun murshland along the lbne Rivcr and its tributuries. Deformation structures bLLt this is noL major deformation, To the The deformation caused by liqucfaction is obserx,ed in thc intrusionupward, right of centfal wcdgc is a ba[1 stnictLtre with diameter of 1O interbeds c)1' fine-s,raincd sand and peat, Details of the defer- anti-clockwise from thc surround- niation are shown in Figs, 7 and 8, In thc center of Lhe t'igures ctn. Thebullisrotated 90U of bed, This is also i'esultcd 1'rom the the origina] depositional struetures of sancl and peut beds urc in.udeformationpeat lateral ilowage of thc sand bed, AL 1o",erleft side ofthe wedge det'ormcd forming as>,mmetrical downward pointing ",edges. schcniati- In the t'igures. right-1iand sides show higher anglcs while left- thc peat is sheared. Those phenomena ure shewn hand sides abuul 45', and oi,erlying mediuin-.grained sand is cal]}, in Fig. 9. sand bed movcd lcft resulting in forming dragged downward. Surrounding peat bed shows conform- Medium-grained half able shape. The dra.o.oed dov,'n mcdium-.orained sand bed in- tensional crucks inthe center and the left shirted tothe with topographic crcases its thickness from 2 to 8 cm te thc left and sho",s' left. The direction ot' movement is the samc js ",eak pre ['errcd orientation, sloping djrection !hough thc sloping angle gentle, Interprctatlon ofdeformation structures Thosc feat ures deseribed above suggest that thosc phenom- '1'he structure is a result of let'tward nio},cTncnt of Tncd{um- cntt havc been formcd from llquci'action. grained sand bcd. In part of this sand beds is snial] scule(77) NII-Electronic Library Service The AssociationforAssociation for the Geological Collaboration in JapanJapan{AGCJ) (AGCJ) 78 OTSUK J, To]･mio Thickness intercalation of sand and silt peaty 50 cm :obl-o=c･o'pvasvo=v= 150cm Fig, 9, Sehematic [lgure or ancient Liqucfactlen in Itakura area. Medjuni-grained sand bcd mox,cd left, [hickcning to the let'r, in the 50 cm+ ccnter et' the 11gure, there is an asyiiimcrrical downwuvd pointing wedge. whose Ieft-hand sidcs shows a lower an."le rhan its ri.g.hl- iXt lo"er lcft side of the xs,cdgc the is handsides't'hesedoes. peat partl.v sheared. fearures described above su.g.gest thar its lel't-hand soilintercalation side sii'tcd ro the lcft. To the right of the wed.oe is a bail gtrucLure. mnL-t -,hich is rotated 90' anti-c]ocksvise. Its Enovcincnt is eonforinuble to Lhut ot' medium-grained sand bed. of sand and peat t:eeijiterrace grave[ Fig. IO, Co]Etmnar sectien in Echi.g.o-Ka",aguehi iLrLa. Echigo-Kawaguchi district 13 lack arrow indieates liquefaetion herizon. Site description The localit>, is in Echigo-Kawiguchi. Niigata Prefecture. in the middle reach ot' the Shinano.ga",'a Rivcr. It is on the lcft bank ol' thc Shinanogawa River about 500 m east of Echigo- Ka",aguchi Interehangt of Kan'etsu ExpTessway (Fig. IC). 'I'he relativc hcight of the localit>, is 50 m abovc the Shinano- gaxK,a River bed and on the rix,er terrace surface, which is gcnt!>, slopin.g to the river, The age of the terrace deposils is esti- mutcd to bc 13 thousand yLars according to Furuka",a and Neotectonics Research Group of thc Niigata Shinano Rivcr Region (2002), The area including thc locality is known as the Shinanegawa Scismic Zone (Omori 1907) and miu]>, pu- pers have been written on the actix,e structures (Ota 1969 : Ota er al. I973 ; Thnuka 2000 ; Ncotectonics Rescarch Group ef the Nijgata Shinane Rix,er Restion 2002). Fig, 11. AncicnL licluefactLon Qf peat and sancl layer in Echigo- column of the sho",n K'a",aouchlarea. Thc geologic localityis inFig.IO. o The deposits consist of terruce gravets, interca[ation of peaL and sand. and cu]tivated soil in the ascending order. Deformation structures plane and cont'ormablc to the moving, directioii ot' the sand 'Fhe beds. In the del'ornied scldom observed deforniation is observed in the [errace gravcls and in- partis .oravels de- rived underl tcrrace axcs tercatation ever]>,,ing the former, Dctails of deft)rmations are from >,in.o .orai,el deposlts.Thc long of are u]so to tbe ter- shown in Figs. 11 and 12･. In thc intercalation of peat and .gravels paratlel horizontalplane.The smd, bed is shearcd off or biocks and race at thc locality shows wcl1-developed imbrication peat partly forming ,o,ravels rarelx, uthickness balls occur with 20 cm dianicter in sand beds. Thc as priniar>, depositional stTueture (Fig. 13A), Thc directic}n of the sand js x,ariab]e. ol' gravcls in the liquelled pat't. ho",ever, is random (Fig. 13B), Interpretation of deformation structures I;roin the above mentioned observations, it is safe to con- The sand bed (lew sideways containing peaL btocks or balls, clude that the sand in the tcrrace gravektnd interca]ated beds niox,ed Iuterallyshearing bccl, The long axcs of peat ball tcnd to bc pura]lel to the horizontal(78) arc ltqueficd and peat NII-Electronic Library Service The AssociationfortheGeologicalCollaborationAssociation for the Geological Collaboration mJapan{AGCJ)in Japan (AGCJ) T.iquofaetion clt,formation srructu]'es m pc'al 79 {ffil･,pmiewewezewtttzzvatva･xu'kzZ%evetlj,ew#'ZZIDiscussion Characteristic features ofthe deformation in peat The charucteristics 1'eatures obsers ccl in the three loca]ities ' tll'e 1, The lique[lcd inaterlalg are pumice, sand and tJraNel, Thiee peul hecis are deformed in thc eonformable form to thc 1iquefaction. 2. J.iquefaelion and resulEing sand boi] ttre acco]npanied -ith high anglc sand dikeg, hut peat docs not rorm dikcs. 3. Det'ormation accornpanyjng liquefaction in pcat is tnostly complex and caused by Iatcral 1'low Stron.o x,ariation ofliq- O 10cm iFig, ueficd sand thickness. flamc-like shooting up shape ol' ]iquc- a]1 12, Sketuh of ancTcnt hguciacLion m Echige-Kawaguchi area, fiedintuerial. batlstructurc and itsrotution. indicateits Gravelh ate dern ed f'roni underl.s,iny, Leri[Lce .o.raNel. complexity. Liquefaction due to paleo-earthquakes Sin]ilar defortpution structures can be (ound in peat}, ter- vace deposits in Tatsunokuchi. Tsunan Town. and west of Shinmachi-Shindcn, Kawanighi Tb"n. both in Nakauonuma Count>,, Nii.gata Pretccture (Fi.g. 14), Gtuurei et al. (2000) reported ball-and-pillow structure in an silt and sund rich in carbonatt7ed interculatcd fine-grained L niaterial at a ren]ple t'oundation cxcavation in Kathniandu, Nepal, Thc deformution gtructure has ymilarities with ones describecl hcrc. The> reporlcd that homogeni[cd 7one had heen formed b> streng agitation. eoinpression und extension det'orrnational structurcs had been l'ormed at a same timc. Because of thesc. thc} attributcd thc origin of the dei'orma- tion tu an eurthquake, Therc may be a pogsibMty ol' those deformatiens to be phc- nomena et' pevi-.olacial orJgin, Thc phenomcna are character- ved hy iee wcdge cast and inxolution in japan CNogami et al. 1980). Ice wcdge cagt is fillcd with inaterials carried from wed.ee wall and ground gurface without the underlying mule- rials rhege phenomcna eccur commonly within the samc bed. Ketvc{]996) gug.ocgted that ice wedge cagts are ar- ranged at regu]ar intervalg of 3 Lo 5 m in Hokkuido urea. Tt is common, however. that in liquefacLion phenoinena thc un- dcr]ymg rnuterialb inLi'ude up" ard and the phcnomcna is ob- serx,ed in restrictcd areas. Thc peat bed dcformaLion in /['akasaki and Echigo- Kawaguchi occurs in regtricted areas. I[' those deformation struetures are origtnated from freezing-melting cycles, simi- lar deformations ure cxpecled to occur comnionly within thc sume bed. but they are not being observed. The deforination Fig. 13. DeposiUonal structure ot the terraee s,ruvel. occurs m restricted horizon, whcre materiaJs dcrived from A , 1]ie terrtLce gruxels at sun ounding area ei the 1ique l'ied part she" g the guTfacc arc not observed at all, In fact "'ell-deyeloped iinbdLcutionK. B In Lhe liquefactlen piut the Tcrrace ground peri-glacial gras e] dose not sho- iTnbricaLions cleai'].v. dei'ormations have iiot been rcported trem either iow land of (79) NII-Electronic Library Service The AssociationforAssociation for the Geological Collaboration in JapanJapan{AGCJ) (AGCJ) 80 OTtt't'K.iL Toinio ee:if due to liquet'action, it may give an imprcssion ol' homoge- asasec neous bed, lt' sampling is clone without cnough precaution as to the possjbjlity of mixing -,ith liquefaction. incorrect re- ee sutLs niight be obtained, Identifieution of liqueficd interi,al i' ii' and itscharacteristic fcatureswould be essential to obtain re- i\' liubledatu, /- Summary , eew Three locaiities where Iiquefaction is developed have been ,, ･ , i･s,,IX, c]osely examined and clescribed. Liquet)'ed pumice and sand $ ., beds within peat beds tend t() s. how lateral movement while , , sand dikes are not well developed. The liquefied materials $ high]y vuriable thickncss and sometimes tlame- 1,shew show , like cross section. ba]i stnietures, and rotation. Peat beds en- closing the liquefied beds jtselfis deformed accompan)'ing tiflosi, dct'ormation of liqucfied materials, Thosc liqucfaction are interpreted to be due to paleo-earthquake. The last peint is important to inteiprct seisrnie histc)r>' of the area. Aclmowledgements Prof. TAKAHAMA Nobuyuki, Nligata University, gave vatuab]e .guidunce in the fieid and niun>, ,suggestions to this paper, Proil KOS"XKA Tomoyoshi, Shinshu Unis,ersiry, and Mr. NAKASMO Hiroomi,Agriculturai En.gincering lnstitute, Ministry ot' Agriculture, Mr. NAKAMURA Masayoshi and othcr members of Macbashi Branch ol' AGCJ, members ol' ShinanogawaRiverNeotectonicsRcgearchGroup,kindlydis- F{g. 14. Del'ormatien structLires Ln peut beds. iX : Downward ",ed.tres cussed the subjcct of this in the field and invalu- pointing 'Town, in sand ancl peat beds. tLt west of paper gave Shininachi Shinde], Kau,anishi )NiigaLa Prel'ecture. ab]e advicc. I'd like to express sincere graLitude to those B : Mud bull in silt and peat beds, uL Tatunokuchi, Tsunan To",n, Niigata Prefccture. people. References norLh Kanto regions or iniddle reach of the Shinanoga",a River ,ALIfaro ll Dv{oretti rv'T and Soria JDvt Dish'ict, japan, Sci Rep E]aculty Edu (}unina LJniversity, 1e : l- As brietly reported by Otsuka et al. (1 997), we tnterpretcd 75,**AraiDvl,YaguehiH,Naka]nuraM.HayakawaYandTakasukiChjgaku that the deformations in this papcr represent liquefaction duc Lo paleo-eaithquake, Aikoukai C1993) Origin and distribution of the Takasaki lahar, ca. Problems related to liguefaction trace in peat IOka, Abstraets Annu Meeting Geol See Japan, 1{}5 : 296," CommLttee for Gunma Prefectural GeoLogic k"lap Gcelegie tncrease in knowlcdge ot' thc deformation similar to the ones (1999) Map ( 1 / ] OO.OOO) of Gunma Prefecture and cxp]anation text. described here may contribute more further understanding of Nais,ai Map Inc, Tokyo, 114p.' the meehanism of liquefaetion and bc used for disas- pTocess FLijita Y (1983J On the regularaty and origin ot' sand crater caused ter preventien. The features described herc along with Lhose by the earthquake- Disasrer b}, sand crater at W'akami-inachi and Akita harbour, AkiLa l'eeture-. Anll Rep Saigai-ken Niigata Univ, rcported in Sangawa (1992) and Otsuka et al. (1997) wou]d prc no. 5 / 5. 3-69.** be useful to recognize in the older beds. pa]eo-1iquefaction IrurLtkawaAundNeotectonicsResearchGroupol'thcNiiuga[aShinano Peat beds are widely used to deduce paleo-environmental Rivcr Region (2002) Tephrochrone]o.gy oHate Quaternai'y fluvial conditlons. Ifa bed is rich in peat, despite extcnsive mixing{80) terraces a]ong the Shinaiio River, ccntral Japan. Abstracts Annu NII-Electronic Library Service The AssociationforAssociation for the Geological Collaboration in Japan (AGCJ){AGCJ) Liquefaction deformati(')n structiires in peat 81 Meeting Geol Soc Jupan, 109 : 48.'i' scismites in laeustrine sediments oi' the Prebetie Zone, SE Spain, GajurelAP, Huyghe R IJpreti BN and Mugnier JL (2000) Palaee- and thcir potcntial use as indicators of earrhquakc magnitudes seismisity in the Keteshwor area of the Kathmandu Valley, Nepat, durjng tbe Late Miouene. Sedimcntar>, Geo]ogy, 135 : 117-[35. infcrred frorri the soft sedimeiit deformationaL structures. Jeur SangawaA (1992) EarthquakeArcheotogy, Chuo Keron Pubt Ltd, Nepal Geol Soe, 22:547-556. 251p."Sei]acherA Hattori I{, I'ukushinia Nl and Kami.io T ([996) C]astic dlkes ofsand C1969) Fault-graded bcds intcfpreted as seismites. Scdi- and loam in the TaTna New Tow'n Housing Distriet, Tekyo, Jour mentelogy13/155-159, Geol Soc Japan, 102:391-403,"' Sims JD (1973) Earthquake-induced structures in sediments ofllan IIibsch C, Alvarado A, Yepes II, Pcrez UH and Sibrier rvl (l997) Norman Lake, San Femando, Califbrnia. Scienee 182 : 161-]63. HoLocenc tcetonics and liqucfactiont soft sediment det'orma[ion Takahama N, Otsuka T and Brahmantyo B (2000) A new Phenonenon in rhc Quite CliquadoD : a paleoseismic history record in laeus- in ancienr liquefaetion-draw-in proeess. its final stage. Sedi- trine scdiments. Jour Geodinaniics, 24 : 259-280. mcntary ]35:]S7-165. c]-4) geology, 'l' Horiguehi M, Tsunoda E MachiduA and Hiruma A {1985) Ancient 1lakahnma N und Otsuka (2001) Geo-1iistory of the Late Quater- inM1ing sand ofcruck is fOuncl on thc Fuka},u Bypass Site, Saitama nary ancienl liguefaction in thc Karasu Rix,er Region, C]unma Pre- 1]refecture. Jour College I.iberal Arts, Saitamu Upiv, 33 : 24)'- fecture, ccntra] Japun. Eurth Science (C.hik}'u Kagaku}, 55:217- 251,,/,,i, 226.**Takcmoto Kuizuka S and Chiiizci K ([986) Mountains in Japan ( Nihon-no- H and Kubo S 099S) Tephra in Gunma Prefecture, Nature in japan JI, Iw'ananii, 259p.* MiyamaBunko,Maebasbi,180p.*' yama), 't', Kazaoka O, Kusuda KuTnura K, Nirei H, Sato K, HaraY, Furuno Tanaka M (2000) A Stud}, oi' Activc FauLts Related te Folding, K, Ka.gawaJ and NIorisaki "C Cl995) Mechanism and the realities Estimated frem the Defortnation of F!uvial Terraees in the ot' lique('action and tluidization. Abstracts Annu A,reeting 6eol Tokamachi Basin, Central Japan. Quat Res, 39:411-426.'* Soc Japan, 101 / 125-1 26."' Yoshika-'a S, Mitamura M, Uehiy, ama T, Nagahashi Yl Tsugcki N, '['anakaS. Koaze 996) FogsH in the northwestern SunardiE. SatogichiY, I'Iashimoto S, YuinatnotoI, (] pcri.crlacial phenomena part - of Tokachi Planc wedgc and invoLution- Inventor>, of Quarcr- 1('atnazaki H. SuLo T and Ichikawa H (1997) Fossile liquefactions -1lephras nary Outcreps in Japan-, Japan Asseciation for Quater- due to earthquakes in the Sayama-ike sedimcnt, Osaka Prefcc- nary Research 40th ,Anniversar.v Special Pub]ication : 1 16.'i' ture. Japan, Jour Geol Sec Japan,1C}3:892-9g9."' tsCatsuda J (2000) Seismic deformaLion sLructurc c)1' the pest-2300 u * BP muddy sediments in Kawachi lowland plain. Osaka. Japan. in Japanese E';" Sed GcoL 135:99-1l6. in Japancsc with English abslract i`C Nakamura T, Tsuji S, Takcinoto H and Ikeda A ( 1997) age mea- surements with aecelerator mass spcclromctry of Asama Tcphra stratigraphiesamplesaroundMinami-Kuruizawu,TheLatcstPleis- toeene. Na.gano Prefecture, centrat japan. Jour Geot Soc Japan, 103:990-993.*･ Ncotcctonics Researeh Group ot' the Niigata Shinano Rh,er Rcgjon QO02) Chronology and Dcvelopmcnta[ Proeess of Late Quater- -- i., narv J }"'luviaLTerraccsinthe TsunanAreaot'thcShinanoRiver. m y･ti g L ft: }ti! .g, ai- lwa 1M'olfig Centrat Japan, Rcs, 41 / 199-212,*"' Quat ,a,sal]la ike" Echigo Kawaguchi ou.EJ1iM NirciT CI997) Paleovegitarional andPuleoclimatic Changes ofJ.ast Fukaya i'2ZS Itahana tb( fi Itakura ･tug Glacial Stage in Takasaki-cit},, Gunma Prel'ecture. Central Japan. KawanishVI[di Kumoba AbsLracts Ann Mectillg Japan Associatioii Quaternary Reserch, Karasugawa,kJl[ :-za 27 I li6.t17.fi, Maebashi rtf/IJde]s･Iatsuida i2L'"EH Nogami M. Koaze T and FukudaM Pcriglacial cm,ironment (19SO) OkubozawaXeeiFl Okuwa J(rk Ora i\ in Japan:prcsent and past. Geojournal.4:125-132, Shinanogttiva ftt neJlIShinmachi Shindun wtm'rsm Omorj F (1907) Rccent strong earthquakcs in Shinanogawa Va]lc},. 'i'atsunoktichi Takasaki mT$ullull Toyo Gakugeizassi, 24 : 1 14-117.'i' zatsi trE 'lt OtaY {1969) ('rustal movcments in Lhe late Quatemar.y considercd Toyodaiinae M}1: rkii Tsukuino th, l-JL npt froin de(brrned terracc in Northeastern Japan. Japan Jour pluins LJonuma .ft,.?e IJsui EitZ< Geo] Geogr, 40:41-61. Ota Y, MachidtL T, Ikeda H, Shirai T and Suzuki T (t973) Active i'olding e[' the tluvial teT'ruces a]ong the Shinano River, eentrul Japan. Thc Crust and Uppcr Mafitlc of thc Japancsc Area, PttrL II, Geology and Geochemjstry : 121-[2･ 9, Geological SL]rvey of Ja- PELn,OtsLtkaT, 1lakahama N, Nakasato N and Noinuru S Ancient <1997)'1'cphra 1iquefactions und Lheir signil'icance in the tatc quaternary layers in the Kurasu River val]ey, Guntna Prct'ecturc, Japan, (2uar Res. 36 : 123-]36,"'' Rodoriguez-Pasucua PvlA, Cal vo JR De Vicente G and G6mci-Gras D {2000) Soft-scdjmcnt defermation strucLures interpreLed as (81) NII-Electronic Library Service The AssooiationAssociation for the GeologioalGeological Collaboration in Japan (AGCJ)（AGCJ ｝ 82 （．）TSUKA TOIm 〔．） 大 塚 富男．2003 ． ピ ー ト層 中 に 認 め ら れ る液状化構造一関越地域 に お け る 事例一．地球科学，57，73−82， ・− − 』 OTSUKA Tomio．2003． LiqucfacLkm defoiM ［ltioll sLructures ill peaL acase stud ＞・ ill Kan eLsu area ， ccntraI − ． − Japan． Earth Science（Chik｝u Kagaku），57、73 82， 要 旨 ー ピ ト層中 に 認 め られ る 占い 液状化 の 跡 を ，群馬県高崎市 と 同県板倉U］お よ び 新潟県越後川 ［「町 の 3 地点 で 観 察 し，そ の 特 徴 を 記 載 し た ．高 崎 市 の も の は ，浅問 火 山 起 源 の 軽 石 1曽が 後 則梗 新統 の 前橋 泥 炭 層 中 で 液 状化 した も の で ，側方 へ の 層厚変化 が 激 し く ，火 炎状 に 吹 き Eが る 特徴的な 形 態 を 示す，こ の 液状化 の 時期 ー は，軽石層 の 降 F年代 とビ ト「両の 堆 積年代 か ら ，約 L6 万 往 前 で あ る と結論 され る ．板 倉町 の 液状化跡 は， ・一 一． 完新 世 の ピ ト 層 と 砂 層 の 互 層鄙分 で 覯察 さ れ る ．そ こ で は 液状 化 に よ る 砂 層 の 側方 へ の 流 動 に よ ） て ，ク ー一 サ ビ 構造 や ボ ル 構造 の 形 成 を 読み 取 る こ と が で き る ，さ ら に 越 後 川 咽 」の 液 1犬化 も ．後期史新統 の 河 成段 ー 巳堆積物 の ピ ト層中 で 認 め られ．液状化 し た 砂 層が ダ イ ナ ．ミッ ク に 偵ll方 へ 流動 し て い る 構造 が 観察 さ れ た ． ー一 ・一 い ず れ の ケ ス で も 明確 な 液状化物質 の 貫 入 吹 き上 げ や ll月瞭な砂脈は 形 成 さ れ ず，また ピ ト僭は液 状化物 質 の 流 動 に 伴 っ て 大 き く 変 形 し，全 体 と し て カ オ テ ィ ッ ク な 構造 を 示 す ．こ こ で は ．液 状 化 の 原因 を 特定 す る こ と は で き な い が ，占地震 に よ る 叮 能性が 高い ． 〔82 ） 一 NII-ElectronicN 工 工 Eleotronio Library Service