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Turbiditi * - Geoznanosti


Turbiditi *

Povzetek

Razumevanje razvoja podmorskih kanalsko-režastih sistemov na pobočjih, na katera vpliva sol, je zahtevno, saj se ti sistemi odzivajo na subtilne, sinodna spremembe v topografiji morskega dna. Vpliv velikih blokirnih struktur na posamezne globokomorske sisteme je dobro dokumentiran, vendar je naše razumevanje prostorskega in časovnega razvoja obsežnih kanalsko-reženjskih sistemov na pobočjih, na katere vplivajo razmeroma skromne solne strukture, razmeroma slabo. Osredotočeni smo na pozno miocenske globokomorske sisteme odlaganja v c. 450 ms TWTT debel interval, posnet v 3D podatkih o potresnem odboju iz kontrakcijske solno-tektonske domene, na morju Angole. Napredno kartiranje potresnih lastnosti, povezano z analizo seizmičnih facij in spremembami debeline časa, razkriva širok spekter medsebojnih vplivov med strukturno povzročenimi spremembami reliefa pobočij, usmerjanjem globokomorskih usedlin, geomorfologijo in sedimentologijo. Pet potresnih enot beleži presenetljivo tektono-stratigrafsko vsebino v osmih mini bazenih. Opažamo postopno preusmerjanje kanalov s stransko migracijo v času razmeroma visoke strukturne stopnje rasti, v nasprotju z nenadnim gibanjem kanala skozi avulzijska vozlišča v času razmeroma visoke stopnje kopičenja usedlin. Naši modeli zajemajo odziv globokomorskih usedalnih sistemov na začetek, zorenje in propad kontrakcijskih struktur na pobočjih, na katera vpliva sol. Začetna stopnja je opredeljena z majhnimi, segmentiranimi gubami z globokomorskim sistemom usedanja, ki je v veliki meri sposoben prečiti več minibasinov. Nasprotno pa je za fazo zrelosti značilna velika, zdaj povezana visokoreljefna struktura, ki omejuje vidne mini bazene, kar vodi do preusmerjanja in obsežnega preusmerjanja kanalsko-reženjskih sistemov ter postavitve MTC, ki izhajajo iz bližnjih vrhov. Stopnja propadanja je izražena s strukturami, ki so krajše in bolj umirjene od tistih, ki označujejo fazo zrelosti, kar vodi do bolj zapletenega sistema kanalsko-reženjskih sistemov, na njihov razvoj še vedno vplivajo obvod, preusmeritev in vodni tok. V fazi razpada ostanki struktur še vedno izvajajo subtilen, a ključen nadzor nad razvojem in pozicioniranjem avulzijskih vozlov.

POUDARKI

  • Tektono-stratigrafski razvoj minibazenov poznega miocena na angolskem kontinentalnem robu.
  • Spremenljiv odziv podvodnih globokomorskih kanalsko-režastih sistemov na kompleksno strukturno nadzorovano topografijo morskega dna.
  • Medsebojno vplivanje strukturne stopnje rasti in stopnje kopičenja usedlin pri spreminjanju geomorfologije in usmerjanja kanalsko-reženjskih sistemov.
  • Modeli, ki prikazujejo razvoj globokomorskih sistemov usedanja na kontrakcijskih področjih soli med začetkom, zrelostjo in razpadom strukturnega razvoja.

Bouma zaporedje natančno opisuje idealno vertikalno zaporedje struktur, naloženih s tokom motnosti z nizko gostoto (tj. Nizko koncentracijo peska, drobnozrnatimi). Za idealno navpično zaporedje struktur, ki jih nalagajo tokovi z visoko gostoto, obstaja nadomestna klasifikacijska shema, ki jo na splošno imenujemo Lowejevo zaporedje. [1]

Zaporedje Bouma je razdeljeno na 5 ločenih slojev z oznakami A do E, pri čemer je A spodaj, E pa zgoraj. Vsaka plast, ki jo opisuje Bouma, ima določen nabor sedimentnih struktur in določeno litologijo (glej spodaj), pri čemer sloji na splošno postanejo bolj drobni od spodaj navzgor. Večina turbiditov, ki jih najdemo v naravi, ima nepopolna zaporedja - Bouma opisuje idealno zaporedje, kjer so prisotne vse plasti. [2]

Plasti so naslednje.

  • E: Masivni, nerazvrščeni blatni kamen, včasih z dokazi o fosilih v sledovih (tj. Bioturbacija). Sloj Bouma E pogosto manjka ali ga je težko ločiti od spodnjega sloja Bouma D.
  • D: Vzporedno laminirani mulj.
  • C: valovito lepljen drobnozrnat peščenjak. Pogosto se valovite laminacije deformirajo v zvite lamelacije in plamenske strukture.
  • B: ravninsko laminiran drobno do srednjezrnat peščenjak. Podnožje Boume B ima pogosto značilnosti, znane kot oznake podplatov, kot so ulitki za piščali, utor za utor in ločevanje.
  • O: Masiven do normalno razvrščen, drobno do grobozrnat peščenjak, pogosto s kamenčki in / ali raztrganimi grozdi skrilavca v bližini dna. Prisotne so lahko posode. Podnožje peščenjaka pod A je včasih erodirano v podložne plasti.

Bouma zaporedje se nalaga med padajočim tokom, ko se motnostni tokovi premikajo navzdol. Z drugimi besedami, pretoki nenehno izgubljajo energijo, ko se odzovejo na spremembe naklona površine, po kateri potujejo, in / ali ko se pretoki preusmerijo iz omejenega znotraj kanala v neomejene, ko zapustijo kanal in se razširijo. Prenapetosti in / ali hidravlični skoki, ki jih povzročajo spremembe naklona, ​​lahko na kratko poživijo pretoke, da povečajo pretočno energijo, vendar se na koncu energija zmanjša, ko se pretoki odmikajo od svojih izvornih točk. [2]

Kadar je energija znotraj pretoka največja, lahko prenaša največjo količino usedlin in največje velikosti zrn, toda ko se energija zmanjšuje, se nosilnost zmanjša in najgrublje zrnje se hitro usede, včasih skoraj takoj. Visokoenergijski tokovi lahko erodirajo tudi v spodnja ležišča in s tem v tok vključijo nov material, ki bo ponavadi zmanjšal energijo toka. Pretoki v kanalih lahko potekajo tudi skozi odstranjevanje toka, pri katerem se zgornji del toka, kjer se drobnejša zrna koncentrirajo, loči in potuje čez vrh kanala, pri čemer spodnji del toka zapusti, kjer se kopičijo groba zrna , znotraj kanala. Na koncu ostanejo le delci gline, suspendirani v mirujočem vodnem stolpcu, v bistvu brez trenutnega gibanja. [2]

Ko se pretoki premikajo navzdol, potekajo naslednji postopki za ustvarjanje plasti Bouma zaporedja. [2]

  • Bouma E je zadnja naložena plast. Rezultat je usedanje suspenzije, kjer v bistvu ni toka. Gline običajno ostanejo suspendirane, dokler se kemikalija vode ne spremeni in omogoči, da se gline flokulirajo in odstranijo. Ker plast Bouma E, če se sploh naloži, zlahka erodira s kasnejšimi motnostnimi tokovi, pogosto ni prisoten.
  • Bouma D se odlaga z usedanjem suspenzije, kjer obstaja majhen tok. Prefinjene spremembe trenutne energije povzročajo, da se izmenično laminiranje grobih in drobnejših zrn mulja umiri.
  • Bouma C se odlaga v pogojih z nižjim režimom pretoka, kjer je dovolj energije, da tok prenaša droben pesek s saltacijo, pri čemer zrna poskakujejo in se odbijajo po površini pod tokom. Ko se zrna usedejo, se razvijejo trenutne valove, pri čemer se razvijejo plezalne valove, če so stopnje sedimentacije dovolj visoke. Če potres in / ali prekrivajoči turbidit / motnostni tok na posnetke valov naloži strižne plasti, se lahko valovite laminacije deformirajo v zvite plasti in plamene strukture.
  • Bouma B se odlaga v pogojih z zgornjim režimom pretoka, kjer je energija dovolj visoka, da zrna peska z vleko prenašajo, pri čemer drsijo in se kotalijo po površini pod tokom. Trenutna energija je takšna, da se na podplatu pod tokom lahko tvorijo oznake podplatov, kot so ulitki za žlebove, ulitki za piščali in ločitve, in se ohranijo kot plesni in odlitki na spodnji strani Bouma B plasti.
  • Bouma A je prva plast, ki jo nanese tok, če ima tok dovolj energije. V nasprotnem primeru bo Bouma B, C ali D prva naložena plast. Bouma A se nalaga, ko je energija pretoka dovolj velika, da lahko turbulenca tekočine zadrži groba zrna v suspenziji. Ko energija pade pod kritično raven, se zrna naenkrat naselijo in tako ustvarijo masivno gredico. Če energija pretoka pade počasneje, se lahko groba zrna najprej usedejo, drobna zrna pa ostanejo v suspenziji. To ima za posledico grobo repno stelje, kar pomeni, da obstaja bimodalna porazdelitev velikosti zrn, pri čemer se groba zrna postopoma manjšajo proti vrhu postelje, drobnejša zrna pa se naključno porazdeljujejo med groba zrna (tj. velikosti zrn so nerazvrščene). Ko se zrna usedejo, se lahko voda, ki jo iztisne z zbijanjem zrn, premakne navzgor, da ustvari strukture posod. Prav tako lahko pride do erozije na dnu toka in raztrga skrilavca iz spodnjega sloja, tako da se klasti iz skrilavcev vgradijo v dno plasti Bouma A. Če je nekaj vzgona na razpokanih plasteh, potem lahko tvorijo plast nekaj razdalje nad dnom Boume A.

Bouma Interval turbidita, ki prikazuje posodne strukture s stebrnimi strukturami med posodami, Severna Kalifornija.


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* Prirejeno iz razširjenega povzetka, pripravljenega za predstavitev na letni konvenciji AAPG, Long Beach, Kalifornija, 1. do 4. aprila 2007.

1 Dipartimento di Scienze della Terra, Univerza v Parmi, Italija

2 Petrobras S.A., Rio de Janeiro, Brazilija

Večina sodobnih turbiditnih sistemov se oblikuje v globinah več kot tisoč metrov, podobno pa tudi nastavitve globokih voda na splošno temeljijo na izpostavljenih ali zakopanih starodavnih sistemih. Ti sistemi so značilno sestavljeni iz različnih facij, ki jih nalagajo gravitacijski tokovi usedlin. Razvrščene postelje iz peščenjaka na osnovi ostrih delcev, ki se izmenjujejo s splošno tanjšimi blatnimi enotami, so verjetno najbolj tipično nahajališče takih sistemov.

Naraščajoči dokazi kažejo, da so skoraj enaka nahajališča enako pogosta in stratigrafsko pomembna v plitvih vodnih območjih izpostavljenih starodavnih zalivov. Takšni sedimenti, ki jih večino na žalost že dolgo zamenjujejo z nevihtnimi nahajališči zaradi običajnega pojavljanja humastih križno stratificiranih peščenjakov (HCS) ali jim je bil dodeljen globlji vodni turbidit, so najbolj pristen izraz deltičnih sistemov, v katerih prevladujejo reke v poplave in zato s hiperpiknalnimi tokovi. Ti odlagališni elementi, bogati s peskom, običajno razvrščajo porečje v debele, v pobočju zaporedje, v katerem prevladujejo blatniki. Pravilno prepoznavanje izvora in okolja teh nahajališč, ki je ključnega pomena za razlikovanje deltskih sistemov, v katerih prevladujejo poplave, od bazalnih turbiditnih sistemov, je mogoče doseči le s skrbnim geološkim kartiranjem in stratigrafskimi korelacijami. in facies analize tako na površini kot na površini. .

Izraz "turbiditi", kot ga je prvotno opredelil Kuenen (1957), naj bi označeval globoko morske razvrščene postelje peščenjaka, ki jih nalagajo motnostni tokovi in ​​ponazarjajo terciarni peščeni "fliš" severnih Apeninov, kot sta formaciji Macigno in Marnosoarenacea (Kuenen in Migliorini, 1950). Do začetka sedemdesetih let se je pomen izraza razširil tako, da je vključeval sedimente tako sodobnih kot starodavnih globokomorskih sistemov, v katerih bi se kanalizirani tokovi motnosti širili na koncu kanala in razpršili svojo energijo v depozicijskih režnjah in sosednjih kotliških ravnicah (glej pregled v Mutti in Normark, 1991). Za večino sodobnih globokomorskih ventilatorjev je značilen ta način odlaganja, o podobnih vzorcih lahko sklepamo tudi iz starih sistemov usedanja, izpostavljenih v potisnih in pregibnih pasovih, čeprav lahko v tem primeru konfiguracija bazena in tektonska nastavitev znatno spremenita geometrijo in vzorce porazdelitve facij kanalskih, reženjskih in kotliških ravnin. V izpostavljenih starodavnih okoljih so ploščasti sistemi, sestavljeni iz peščenjakov in nanosnih ravninskih nanosov, volumetrično najpomembnejši elementi odlaganja (za posodobljen pregled glej Mutti in sod. 2003). Kot rezultat, geometrijska zasnova in notranja arhitektura teh sistemov običajno kažeta precejšnja odstopanja od sodobnih globokomorskih ventilatorjev, od katerih mnogi rastejo v v bistvu neomejenih bazenih. Vendar je treba omeniti, da lahko na številnih različnih kontinentalnih robovih (npr. Na brazilskem morju) razpadanje, zlaganje, gibanje soli in blata ter vulkanska dejavnost povzročijo znaten topografski relief, ki bo imel pomemben nadzor nad erozijo in nanašanjem. .

Lokalni geološki kontekst, razvrščeni peščenjak do ležišč blatnih kamnov (značilno po klasičnem zaporedju Bouma, čeprav z nekaj previdnosti), ki se izmenjujejo s hemipelagičnimi plastmi, ki vsebujejo globokomorske fosilne sklope, in pomanjkanje plitvih morskih značilnosti, ki jih povzročajo valovi in ​​plimovanje, že dolgo obstajajo najboljši dokaz za globokomorski izvor turbiditnih plasti. Spektakularni primeri globokomorskih turbiditov so bili med drugim opisani iz kotliških ravnic miocenske formacije Marnosoarenacea, severni Apenini v Italiji in skupina Eocene Hecho, južno-osrednji Pireneji v Španiji.

Kot smo zgoraj opredelili, globokomorski turbiditi tvorijo ogromne količine v zaporedjih, ki jih zapolnjujejo kotline, tako na različnih kontinentalnih robovih kot na izpostavljenih trčnih pasovih, njihov pomen v geološkem zapisu pa močno povečuje njihov naraščajoči potencial kot rezervoarji ogljikovodikov na številnih celinskih robovih (npr. , Zahodna Afrika, Mehiški zaliv, brazilska obala).

Trdno smo prepričani, da se v izpostavljenih nagibnih pasovnih kotlinah (npr. Južno-osrednji Pireneji, porečje Neuquen v Španiji, terciarno porečje Pijemonta v severozahodni Italiji) razvijajo podobno velike sedimentne količine vzporedno enostransko razvrščenega peščenjaka do ležišč blatnih kamnov. kot obalni in šestalni odlagališča na različnih globinah vzdolž lokalnega profila odlagališč in v nekaterih primerih v globljih vodnih strukturnih vdolbinah (in znotraj pobočja). Vertikalna in bočna stratigrafska razmerja ter skrbno kartiranje ne dvomijo, da so ti sedimenti del prednjega dela bodisi sistema ventilator-delta bodisi reka-delta - sklep, ki ga močno podpira ugotovitev, da je treba očitno dovajati velike količine plitvovodnega peska ob sosednji reki. Ti sedimenti so v bistvu režnja peščenjaka, ki jih nalagajo gosti hiperpiknalni tokovi (podtoki), ki izvirajo iz sorazmerno majhnih in visoko gradientnih poplavnih sistemov. Razen pojava humastih navzkrižno stratificiranih peščenjakov (HCS) (glej spodaj), obilnih fosilnih ostankov in lokalno razširjenega bioturbacijskega procesa ti tokovi ustvarijo facije, ki so zelo podobni tistim, ki jih povzročajo motnostni tokovi. Proti morju se ti peščeni sedimenti razvrščajo v prodeltajske sukcesije, v katerih prevladujejo blatniki, ki jih nalagajo bolj razredčeni in z blatom obremenjeni hiperpiknalni tokovi, pa tudi "običajni" rečni plumi (za podrobnejši prikaz teh usedlin glej Mutti in sod. 1996, 2003) .

Čeprav sta Goldring in Bridges (1973) že davno zaznala pomen teh plitvovodnih in lokalno zelo fosifernih nanosov turbiditov, ki so jih poimenovali "sublittoralni peščenjaki", so sedimentologi žal prezrli to temeljno vrsto sedimentacije. Zaradi pojavljanja HCS v številnih razvrščenih posteljah iz peščenjaka so običajne sedimentološke interpretacije že dolgo poudarjale izvor teh nanosov zaradi neviht in jih povezovale z visokoenergijskimi obalnimi črtami (npr. Walker, 1984 Duke et al., 1991). Jasno je, da ne zanikamo, da se lahko nevihtno razvrščene postelje peščenjaka lokalno razvijejo proti morju proti obali, vendar trdimo, da takšni procesi ne morejo predstavljati velike količine razvrščenih postelj iz peščenjaka s HCS, ki se pojavljajo v izpostavljenih zalivih v trkih. V potisnem in upognjenem pasu in bolj splošno v tektonsko aktivnih bazenih obrežne črte praviloma izražajo nizkoenergijske facije. Terciar vodnih bazenov v južnem osrednjem delu Pirenejev v Španiji in porečje Pijemonta v Italiji sta opazna zaradi odsotnosti visokoenergijskih plažnih nanosov. Tu imajo glavno vlogo samo plimski tokovi pri predelavi bližnjih in plitvejših delov delta sistemov, zlasti v estuarinskih kompleksih. Delovanje teh tokov pa se z globino zmanjšuje, kar povzroči, da na plimovanje in / ali valove distalnih in globljih delov poplavljenih delta prednjih peščenjakov skoraj ne vpliva plimovanje in / ali valovi, kar spominja na tipično menjavanje stopnjevanih ležišč peščenjaka in vmesnih blatnikov. globokomorski turbiditi.

Na sliki 1 so prikazane nekatere glavne značilnosti postelj s peskom, razvrščenimi po deltah. Tu posebej poudarjamo zelo diagnostični pojav struktur krogel in vzglavnikov, ki ga razlagamo kot rezultat diferencialne obremenitve (gradient gostote), povezane z geometrijo stiskanja in nabrekanja postelj iz peščenjaka, ki vsebujejo obsežen HCS.

Glede na gradient in fiziografijo regala, ki je v večini primerov povezan z lokalnim strukturnim nadzorom, lahko nastanejo hiperpiknalni tokovi, ki izvirajo iz ustja reke, pritrjeni na rečne ustnice (Mutti et al., 1996 Tinterri, v tisku) ali pa se lahko odmaknejo od obale na velike razdalje in tako tvorijo pomembne peščene nakopičene površine v območjih polic v globinah vode, ki so lahko precej pod globino, ki jo običajno dosežejo nevihtni valovi in ​​plimski tokovi. V drugih primerih se lahko te akumulacije tvorijo v depresijah, omejenih z napakami, kjer so gravitacijski tokovi prisiljeni upočasniti in nalagati svojo usedlino. V takih primerih je lahko razlikovanje med temi ločenimi telesi peščenjaka pred delto in globokomorskimi turbiditi težavno. Razlikovanje mora temeljiti predvsem na geološkem kontekstu, čeprav lahko lastnosti facijesa in fosili v sledovih predstavljajo dobra merila za ločevanje obeh vrst nahajališč. Zlasti deltaično razvrščena ležišča peščenjaka ponavadi kažejo facijezne značilnosti, ki kažejo na usedanje iz slabo učinkovitih pretokov, skupna pomanjkljivost drobnozrnatih delcev pa je verjetno posledica obvoza teh sedimentov proti bolj oddaljenim predelom prodelte.

Podobnosti med deltami, v katerih prevladujejo reke, in podmorskimi turbiditnimi sistemi (zlasti globokomorski ventilatorji) so bile prepoznane že od zgodnjih modelov podvodnih ventilatorjev, hranjenih s kanjonom (Mutti in Ghibaudo, 1972, njihova tabela II Mutti in Ricci Lucchi, 1972), ki primerjajo splošni vzorci nalaganja teh sistemov v smislu prenosa (kanali) in območja nalaganja (deltaične pregrade skozi kanal in ustnice turbiditnih kanalov v ustih). Primerjava je sčasoma postala veliko lažja in pomembnejša zaradi spoznanja, da rečne poplave v ustjih rek ustvarjajo hiperpiknalne tokove, ki se v bistvu obnašajo kot plitvotočni motni tokovi. Zato lahko motiv kanalskega režnja, ki ga opazimo v večini turbiditnih sistemov, in facialne poti, ki nastanejo pri odvajanju energije na koncu kanala, lahko s potrebno previdnostjo uporabimo tudi pri interpretaciji poplavno prevladujočih fluvio-deltaičnih sistemov. Glede na te koncepte je verjetno treba ponovno preučiti večino peščenih kamnov na obali in na šelfu. Po našem mnenju del teh nanosov že dolgo zamenjujejo bodisi z "obalnimi nanosi", povezanimi s plažo, bodisi celo s "turbiditi v dnu bazena", razvitimi na dnu razvijajočih se deltajskih klinoform, ki imajo v večini primerov relief, ki se giblje med nekaj metri in nekaj sto metrov - očitno relief, ki je premajhen, da bi ustvaril motnostne tokove z zadostno prostornino in zagonom, da bi dosegel bazalne, globokomorske bazenske regije.

Slika 2 je diagram treh glavnih vrst pojavnosti fabidijem, podobnih turbiditom, v morskih okoljih divergentnih, konvergentnih in trčnih kontinentalnih obrob. Diagram prikazuje (1) "plitvovodno domeno", kjer so razvrščeni peščenjaki v bistvu pritrjeni na svoje napajalne fluvio-deltaične sisteme, (2) "vmesno področje", kjer so razvrščeni peščenjaki večinoma ujeti v pobočjih kotlin (v obeh tlačnih in ekstenzijski režimi) in (3) „globokomorska, bazenska domena“, kjer razvrščeni peščenjaki beležijo končno območje usedlin tokov motnosti, ne glede na njihov izvor (hiperpiknalni tokovi, podmorski tobogani ali njihova kombinacija).

Jasno zaznavanje zgornjih težav je ključnega pomena za boljše razumevanje procesov nanašanja in značilnosti facij v pobočjih kotlin, ki se zdijo glavni cilj raziskovanja ogljikovodikov po vsem svetu. Verjetno razvrščene postelje iz peščenjaka tvorijo kontinuum od naplavinskih do globokomorskih okolij kot odziv na ciklična obdobja fluvialnih poplav, čeprav imajo lahko podmorski diapozitivi v morskem okolju skoraj enako pomembno vlogo pri sprožanju motenj močnih tokov.

Duke, W. L., Arnott, R.W.C. in Cheel, R. J., 1991, Polniški peščenjaki in humocky križna stratifikacija: Nova spoznanja o nevihtni razpravi: Geologija, v. 19, str. 625-628.

Goldring, R. in Bridges, P., 1973, Sublittoral pločevinasti peščenjaki: Journal Sedimentary Petrology, v. 43, str. 736-747.

Kuenen, Ph.H., 1957, Edine oznake stopnjevanih postelj iz sivke: Journal of Geology, v. 65, str. 231–258.

Kuenen, Ph.H., in Migliorini, C. I., 1950, Motnostni tokovi kot vzrok za razvrščeno posteljnino: Journal of Geology, v. 58, str. 91-127.

Mutti, E. in Ghibaudo, G., 1972, Un esempio di torbiditi di conoide sottomarina esterna: le Arenarie di San Salvatore (Formazione di Bobbio, Miocene) nell 'Appennino di Piacenza: Accademia delle Scienze di Torino, Memorie, Classe di Scienze Fisiche, Matematiche e Naturali, Serie 4, št. 16, 40 str.

Mutti, E., Davoli, G., Tinterri R. in Zavala, C., 1996, Pomen fluvio-deltajskih sistemov, v katerih prevladujejo katastrofalne poplave v tektonsko aktivnih bazenih: Memorie di Scienze Geologiche, Universita di Padova, v. 48 , str. 233-291.

Mutti, E. in Normark, W. R., 1991, Integrirani pristop k preučevanju turbiditnih sistemov, v Potresne facije in sedimentni procesi podmorskih ventilatorjev in turbiditnih sistemov, ur. P.Weimer in H. Link: Springer, New York, str. 75-106.

Mutti, E., in Ricci Lucchi, F., 1972, Le torbiditi dell'Appennino settentrionale: Introduzione all 'analisi di facies: Memori della Societa Geologica Italiana, v. 11, str. 161 199.

Mutti, E., Tinterri, R., Benevelli, G., Di Biase, D., in Cavanna, G., 2003, Deltaic, mešano in motno sedimentacija starih porečij predmestja, v Turbidites: Models and Problems, ur. E. Mutti, G. S. Steffens, C. Pirmez, M. Orlando in D. Roberts: Marine and Petroleum Geology, v. 20, str. 733-755.

Prather, B. E., Booth, J. R., Steffens, G. S. in Craig, P. A., 1998, Klasifikacija, litološka kalibracija in stratigrafsko zaporedje potresnih facij znotraj pobočnih bazenov, globokomorski Mehiški zaliv. AAPG bik., 82 (5A), 701-728.

Tinterri, R., v tisku, Spodnji eocenski rodni peščenjak (južno-osrednji Pireneji): primer poplavno prevladujočega sistema reka-delta v tektonsko nadzorovanem bazenu: Rivista Italiana di Paleontologia e Stratigrafia.


Turbiditi *

Ponedeljek, 7. maja, avditorij Hatfield Marine Science Center, Newport, OR. 18:30.

Pubični prikaz & quotnepripravljenega & quot OPB posebnega potresa, s panelno razpravo

Torek, 1. maja, avditorij srednje šole North Salem, 18.30.

Kratek tečaj podvodne paleoseizmologije, ki ga je organiziralo srečanje Geološkega društva Amerike v Seattlu

Tečaj je na voljo v soboto, 21. oktobra. Za podrobnosti in prijavo glejte GSA.

Izšel nov papir!

Ta članek prikazuje evedencijo erozije na morju, ki je nastala med kataklizmičnimi poplavami v Missouli.

Izšel nov papir!

Ta članek natančno preučuje strukturo, evolucijo in ukinitev severnega preloma San Andreas v Severni Kaliforniji

Izšel nov papir!

Ta članek modelira habitat morskega dna z uporabo Bayesovih metod

Izšel nov papir!

Ta teden je izšel nov članek, ki poskuša vključiti modele cunamija, podatke o paleoizmičnih podatkih na kopnem in na morju v južni Kaskadiji:

George R. Priest, Robert C. Witter, Y. Joseph Zhang, Chris Goldfinger, Kelin Wang, Jonathan C. Allan, 2017, Nove omejitve kozeizmičnega zdrsa med potresi v območju subdukcijske cone v južni Cascadia v zadnjih 4600 letih, ki jih povzročajo nanosi cunamija in morje turbiditi, Naravne nevarnosti DOI: 10.1007 / s11069-017-2864-9 http://activetectonics.coas.oregonstate.edu/paper_files/Priest%20et%20al.%202017%20offprint.pdf

Nacionalna akademija za znanost, inženirstvo in medicino

Skupno srečanje BESR / COSG - Območje subdukcije Cascadia: znanost, vplivi in ​​odziv

10. – 11. Novembra 2016, stavba Nacionalne akademije znanosti
2101 Constitution Ave NW Washington DC 20418

Goldfinger Active Tectonics Lab je leta 2016 prejel nagrado Geološkega društva Amerike Kirk Bryan.

TEDx Portland, 18. junija 2016. Revolucijska dvorana

Science Pub Corvallis & quotTresanje severozahoda, potres Cascadia v naši prihodnosti & quot; Majestic Theatre, Covallis 18:00. />

Delavnica NWEA, gostišče Hood River, 2. oktober.

Gospodarski vrh Oregonske obale, 27. avgusta, Grand Ronde.

Nove knjige

Nov roman: Stick Slip od Chrisa Scholza! Zabavno branje o velikem potresu v Cascadiji.

Naslednji cunami preučuje naš kratkoročni spomin na nesreče, Los Angeles Times, 21. marec 2014

Novi prispevki

Objavljen je drugi članek s podrobnimi podatki o morskem paleoizmičnem zapisu obrobja severne Sumatre.

Druga nova kanadska študija potrjuje in razširja Cascadia Marine Paleoseismic Record

Objavljena nova disertacija: Turbiditi južne kaskadije, ki jim sledijo spodnji profili CHIRP visoke ločljivosti.

Objavljena nova disertacija: Sumatra Paleoseismology

Izšel je nov članek: Cascadia Segmented Rupture Tsunami Modeli

Izšel je nov članek: Cascadia Csunami Models

Izšel je nov članek: Veliki potresni grozdi Cascadia

Objavljeni scenariji obalnega poplavljanja cunamija za Oregon

& quotSuperkveniki in supercikli & quot, Seismological Research Letters

Objavljen nov članek: Cascadia Turbidites in Forearc Lakes?

Predhodna preučitev obstoječih sedimentnih zapisov na jezeru kaže na zapis o velikih potresih.

Objavljen nov papir Cascadia: Segmentirani prelomi vzdolž južnega roba Cascadia

Novi odsevni podatki o jedru in visoki ločljivosti osvetljujejo paleoizmični zapis južne Cascadije.

Nova kanadska študija potrjuje morski paleoseizmični zapis Cascadia

Seizmično nastali turbiditi v zalivu Effingham, zahodni otok Vancouver.

Izdana druga v seriji paleoizmologije Sumatra

Druge stvari

Bayesova ekipa za prostorsko analizo je zmagala na oddelku za notranje partnerje za konzervacijo

Objavljeno poročilo o odpornosti proti potresom v Oregonu

Nagrada za delo v Oregonu zaradi cunamija

Uspešno geofizično križarjenje na krovu Dereka. M. Baylis zaključen z zelo nizkim ogljičnim odtisom

Cascadia, film! Animacija 10.000-letnega potresnega zapisa z morskih in obalnih paleoizmičnih krajev.

Pobuda za obnovo šol v Portandu za potresi

Ponavljajoči se modeli velikih potresov

Prisluhnite & quotNovi minuti & quot o sprožanju stresa

Ozadje

Leta 1996 smo začeli raziskovati paleoizmično zgodovino kaskadije na podlagi turbiditnih zapisov. Možnost obstoja dobrega zapisa o potresu ob robu je bila predlagana konec šestdesetih let prejšnjega stoletja, uradno pa jo je leta 1990 predlagal John Adams. Prvo večje križarjenje za preizkus te hipoteze smo izvedli leta 1999 na krovu R / V Melville. Od takrat smo objavili več člankov, ki podrobno razkrivajo razmerje med velikimi potresi in turbiditno stratigrafijo v Cascadiji.

Ena od stvari, ki jo je mogoče obravnavati z zelo dolgimi paleoizmičnimi zapisi, so modeli ponavljanja velikih potresov. V sedemdesetih letih prejšnjega stoletja so preiskovalci iskali modele, s katerimi so z omejenim uspehom razložili temeljne varnostne točke potresov. Zaradi velikega vzorca ponovitve potresa, ki je zdaj vzpostavljen v Cascadiji, je vredno ponovno preučiti idejo modelov ponovitve, da bi ugotovili, ali iz zapisa izhajajo vzorci, ki jih ni mogoče razložiti z naključnim pojavom.

Ljudje

Pri tem projektu je od leta 2002 vključeno veliko število soiziskovalcev, študentov, tehnikov in ladijske posadke, med njimi: Chris Goldfinger, C. Hans Nelson Joel E. Johnson, Ann E. Morey, Julia Gutiérrez-Pastor, Eugene Karabanov, Andrew T. Eriksson, Eulàlia Gràcia, Gita Dunhill, Jason Patton, Michaele Kashgarian, John Southon, Pete Kalk, Chris Moser, Bob Wilson, Jeff Beeson, Kelly Grijalva, Roland Bürgmann ter častniki in posadke R / V Melville in R / V Revelle in ladijske znanstvene skupine

Super potresi in supercikli

UVOD
Nedavni Mw = 9,0 Tohoku na Japonskem in Mw = 9,15 Sumatra-Andamanski potresi leta 2004 so ponižali številne raziskave potresa. Nobena regija ni bila sposobna potresov, ki presegajo Mw

8.4. Pritožba na predlagana razmerja za napovedovanje velikosti potresov v subdukcijskih območjih, na primer med močjo potresa in parametri, kot so nižja starost plošč in stopnja konvergence (Ruff in Kanamori, 1980), ter sklopka plošč na podlagi sidrnih plošč (Scholz in Campos, 1995), imajo vsaj veliko izjem in morda ne bodo veljavne. Oba potresa sta se zgodila tam, kjer je bil rob podložne plošče precej star,

50-130 moj. Vloga debelih usedlin, ki gladijo vmesnik plošče in povečujejo površino rupture, je bila pomemben dejavnik in se zdi, da vpliva na številne nedavne velike potrese (Ruff, 1989). Tudi dogodek v Tohokuju je v nasprotju s to hipotezo. Jasno je, da se je treba o teh velikih dogodkih še veliko naučiti, tako da bi bilo večino prejšnjih ocen največje moči potresa na mejah subdukcijske plošče sumljive in morda tudi druge sisteme prelomov (McCaffrey, 2007, 2008).

Naš pogled na to vprašanje očitno ovirajo kratki zgodovinski in še krajši instrumentalni zapisi. Zgoraj navedeni primeri kažejo, da ocene največje velikosti potresa ali modeli ponovitve potresa zgolj na podlagi takšnih kratkoročnih evidenc očitno ne morejo zajeti obsega vedenja napak, četudi so zgodovinski zapisi lahko tudi> 1000 let dolgi kot na Japonskem. Tukaj predstavljamo nekaj primerov področij, kjer lahko dolgi geološki in paleoseizmični zapisi osvetljujejo veliko širši spekter potresnih vedenj, kot so bila ugotovljena iz zgodovinskih in instrumentalnih podatkov, in špekuliramo o modelih dolgoročnega vedenja napak, ki temeljijo na zelo dolgih zapisih.

Severovzhodni japonski rov
Od pliocenskega časa je bil Japonski lok podvržen stiskanju vzhod-zahod predvsem zaradi konvergence pacifiške plošče proti zahodu pri Japonskem jarku s hitrostjo 70 mm / leto. (DeMets et al., 2010). Običajne napake, ki so verjetno posledica širjenja miocenskega hrbtnega loka, so bile v Plio-kvartarnem času ponovno aktivirane kot potisne napake zaradi spremembe regionalnih polj napetosti iz napetosti v kompresijo E-W. Geološke omejitve kažejo, da je stiskanje zgornje plošče le majhen del celotne celotne konvergence med Japonsko in pacifiško ploščo. Geodetsko opažena hitrost kratkotrajne deformacije v loku severovzhodne Japonske pa je bistveno večja od dolgotrajne deformacije. Triangulacija, trilaterala in GPS opazovanja med zadnjim

100 let je razkrilo, da se je japonski lok skrčil v smeri vzhod-zahod s hitrostjo do nekaj deset mm / leto. (Hashimoto, 1990 Suwa et al., 2006 Sagiya et al., 2000). Ta stopnja je skoraj za en red velikosti večja od geološko opaženih stopenj skrajšanja in je primerljiva z

Stopnja konvergence plošč pri japonskem jarku 83 mm / leto (slika 1). Podobno obstaja kontrast med nedavnim hitrim pogrezanjem obal in dolgoročnimi dokazi o dvigovanju terase vzdolž pacifiške obale SV Japonske. Podatki o plimovanju kažejo na neobičajno visoke stopnje (nekaj do 10 mm / leto) pogrezanja v zadnjem času

80 let (Kato, 1983). This subsidence is likely due to strong coupling dragging down the upper plate by the subducting Pacific plate beneath the Japan arc. However, late Quaternary marine terraces developing along the Pacific coast indicate uplift at 0.1-0.4 mm/yr. (Koike and Machida, 2001). The discrepancy between short-term (geodetic) and long-term (geologic) observations indicates that most of the strain accumulating in the last

100 years has been elastic, to be released by slip in large earthquakes on the subducting plate boundary. Although large thrust-type earthquakes with magnitude 7-8.4 have occurred at the Japan Trench during the last 100 years, they did not result in significant strain release on land. Thus, larger slip events are required to occur at intervals much longer than the period (

100 years) of instrumental observations (Ikeda, 2003, 2005). The recent Tohoku-oki Mw =9.0 earthquake was such a slip event with a slip based on submarine GPS of

24m (Sato, 2011), and slips greater than 50 m near the toe of the accretionary prism (e.g. Fujiwara et al., 2012) its rupture area encompassed those of numerous previous earthquakes of magnitude 7-8.4.

The most recent earthquakes in the Sendai area: 1933 (M 8.1), 1936 (M 7.5), and 1978 (Mw 7.6) did not leave a tsunami record in nearby Suijin-numa, a coastal lake (Sawai et al., 2008), nor did they leave extensive sand sheets on the Sendai Plain (Minoura et al., 2001). However, the older historical record in the Tohoku region in Japan includes a number of large earthquakes and associated tsunami, including large events in 869, 1611 and 1896. The largest of these events was likely the 869 Jogan tsunami based on the presence of tsunami deposits in the coastal lake (Sawai et al., 2008), the 3-4 km landward extent of inundation relative to the paleo-shoreline (Sawai et al., 2007 Shishikura et al., 2008 Sugawara et al., 2012) and tsunami modeling (Namegaya et al., 2010). ). The paleotsunami evidence also includes two predecessors to the Jogan event that also penetrated

4 km inland (though in Jogan time the shoreline was

1 km west of present). These large tsunami support the existence of periodic outsized earthquakes (Mw

9) along the Tohoku coast. The recurrence times are between 800 and1200 years, with numerous smaller events between that make up the majority of the historical record (Sawai et al., 2008 Shishikura et al., 2007).

Figure 1. (Left) Map showing recent vertical crustal movements and source areas of large interplate earthquakes. Blue line contours indicate rates of uplift (in mm/yr) revealed by tide gauge observations during the period 1955-1981 (Kato, 1983). Orange lines indicate source areas of interplate earthquakes of Mw > 7 since 1896. The epicenter and source area of the 2011 Tohoku earthquake of Mw 9.0 are indicated by an asterisk and orange shade, respectively NFM = Northern Fossa Magna. Open squares indicate tide-gauge stations station numbers correspond to those in the right figure. (Right) Selected tide-gauge records along the Pacific coast (Geographical Information Authority, 2010). See the left figure for location. Red arrows indicate large earthquakes (Mw > 7.0) that occurred near each station. Note progressive subsidence of the Pacific coast at rates as high as 5-10 mm/yr, except for the Onahama station, which has likely been affected by coal mining.

In Cascadia, several decades of paleoseismic work have yielded an unprecedented record of great earthquakes. Pioneering work (Atwater, 1987) established the repeated occurrence of great earthquakes and tsunami along the Washington coast, followed by widespread evidence of subsidence and tsunami from coastal sediments along the entire margin from Canada to northern California (Atwater et al., 1997 2004, Kelsey et al., 2005 Clague and Bobrowsky, 1994). The longest records available, those from deep-sea turbidites, reveal the complex behavior of this subduction zone over the past 10,000 years (Goldfinger et al., 2012). The offshore records are in good agreement with onshore paleoseismology where temporal overlap exists (variable from 3500-4600 years BP), and both offer consistent information about the relative size of paleoearthquakes, giving confidence that both are recording the same phenomenon (Goldfinger et al., 2012). The longer records reveal several important features not discernible with shorter records. One is that there is apparent clustering of the larger (rupture lengths greater than 600 km, Mw

8.7-9.0) events into groups of 4-5 events, with 700-1200 year gaps between the clusters (Goldfinger et al., 2012). Another is significant segmentation of the margin, with a group of shorter ruptures limited to southern Cascadia that are interspersed between the long ruptures as determined by intersite stratigraphic correlation (Goldfinger et al., 2008 2012 their Fig. 55).

Goldfinger et al. (2012) show that mass per event down core among four key Cascadia core sites is reasonably consistent among sites. They infer that the best explanation is that turbidite thickness and mass are linked to the relative levels of ground shaking in the source earthquakes. The magnitude of the AD 1700 earthquake is estimated to be

9.0 based on tsunami inversion of the tsunami heights along the Japanese coast, and the attribution of this &ldquoorphan tsunami&rdquo to Cascadia (Satake et al., 2003). The 9.0 magnitude could change in the future with more sophisticated modeling, but still provides a benchmark for other paleoseismic events. The connection between earthquake size and turbidite size is tenuous nevertheless, the correlation between size characteristics per event, among numerous cores along strike, strongly suggests a regional connection that can best be attributed to the magnitude or shaking intensity of the source earthquake ( Goldfinger et al., 2008, 2012). In the offshore turbidite record, the turbidite associated with the 1700 AD event is roughly &ldquoaverage&rsquo in mass and thickness relative to 19 inferred similar ruptures as compared between core sites along the 1000 km Cascadia margin (Goldfinger et al., 2012). Significantly, there are several turbidites that are considerably larger in terms of thickness and mass in the 10,000 year offshore record. Notable are the 11th and 16th events back in time, known as T11 and T16, that took place 5960 +/- 140 and 8810 +/- 160 years ago (Fig. 3). These two turbidites are consistently larger at all core sites along the length of Cascadia, being an average of 2.9 times (range 2.8-3.1) the A.D. 1700 turbidite mass. At most sites, 4-7 other events in the 10 ky turbidite record, (typically including turbidites T5, T6, T7, T8, T9, T13 and T18) are also larger than the 1700 AD turbidite, though by smaller margins of 1.3-1.7 times the T1 turbidite mass (range 0.2-1.7). Goldfinger et al. (2012) estimate Mw for all 19 Cascadia ruptures of 600 km and greater using estimated rupture length, width and slip parameters calibrated to the AD 1700 event, and setting that event equal to 9.0. They estimate Mw for T11 and T16 to be

9.1. The average mass increase in these two turbidites of 2.8 times the A.D. 1700 turbidite is roughly comparable to the energy increase of 1.4 times from Mw 9.0 to Mw 9.1. The event to event variability and consistency among sites are unlikely to be due to changes in sediment supply, oceanography, or other factors as they are replicated at numerous sites, including one (Hydrate Ridge) with no modern terriginous sediment supply. The outsized turbidites are unlikely to be due to a long prior sediment accumulation interval, as only T11 has such a prior interval (

1100 years interrupted by one small event), and because other events following

1000 year gaps were not outsized in thickness or mass (T6 for example). These data suggest that significantly outsized earthquakes may occur at a rate of 1-2/10,000 years in Cascadia.

Uniquely, the 10 ky Holocene Cascadia earthquake generated turbidite stratigraphy affords uncommon opportunities to examine recurrence models, clustering and detailed long-term (10 ka) strain history of a subduction zone. First, in Cascadia, the two outsized superquakes do not appear to occur in an otherwise random sequence. Cascadia earthquakes appear to cluster, with the larger events that include much of the strike length of the margin occurring within groupings of 4-5 events that comprise four Holocene clusters. There appears to be a weak tendency to terminate these clusters with an outsized event. The long time series also suggests that Cascadia is neither time nor slip predictable (Goldfinger et al., 2012). Because there appears to be a connection between earthquake size and turbidite size among core sites and across a variety of depositional environments, an opportunity exists to investigate the earthquake pattern further. This inference comes from the observation that correlated turbidites along strike in Cascadia vary considerably in mass and thickness per event at each site in the Holocene series, but that they are consistent in mass and thickness for the same event at multiple sites and multiple depositional environments as previously described (Goldfinger et al., 2012 e-supp. Fig. S4, Tables S4, S5 available as an electronic supplement to this paper). Because of this consistency for individual events along the margin, and despite the obvious simplifications involved, we infer that turbidite mass can be considered a crude proxy for seismic moment or intensity of ground shaking at offshore sites for at least the 19 larger ruptures of 600 km or greater described in Goldfinger et al. (2012).

If our assumption that energy release can be approximated by turbidite mass and thickness, we can then assemble and compare the Holocene series of earthquakes as a time series. First, we assume that while slip and moment of paleoearthquakes is unknown, that coseismic energy release may be modeled as proportional to the mass of turbidites triggered in seismic shaking. Second, we assume that plate convergence between earthquakes increases elastic strain energy in proportion to interevent time (a coupling coefficient of 1.0 is assumed but does not affect the outcome).To examine the energy balance between subduction earthquakes and accumulation of elastic strain, we scale turbidite mass (energy release) to balance plate convergence (energy gain) to generate a 10 ky energy time series for Cascadia (Fig. 4). We do not know the starting or ending values of course, thus we simply scale the plot such that the overall trend of the series has no net gain or loss of potential energy. The interval between the last earthquake and the next one is also unknown, and we set this equal to the average recurrence time. Sources of error also include the uncertainties in the radiocarbon ages for each event, which are taken from Goldfinger et al. (2012) and are shown on the plot. Both approximations undoubtedly comprise additional sources of error. The resulting sawtooth pattern reveals what we interpret as a complex pattern of long-term energy cycling on the Cascadia megathrust, with the vertical scale representing potential energy. If correct, we can then make some observations about the long-term behavior of Cascadia. Earthquake clusters including small to large events appear to have significant variations in energy balance within and between the clusters. Cluster four (

10000-8800 BP) appears to maintain a relatively even energy state comprising several seismic cycles before falling to a low after large event T16. Cluster three (

8200-5800 BP) climbs steadily in energy state through multiple seismic cycles until falling sharply to a similar low following large event T11. Cluster two (

4800-2500 BP) climbs then falls to a low energy value after T6, which also precedes a long gap of

1000 years, which then raises the energy state. Cluster one (

1600-300 BP) slowly declines from T5 to T1, the AD 1700 Mw

Overall, what is suggested by this pattern is that some events release less energy while others release more energy than available from plate convergence (slip deficit) and may have borrowed stored energy from previous cycles. This suggests that energy release in the earthquakes is not closely tied to recurrence intervals, that is, they are not obviously slip or time predictable, but the pattern of values suggests that it is not likely to be a Poisson process either. The highest energy states may result in either a very large earthquake, or a series of smaller earthquakes to relieve stress. A very low energy state may result in a long gap or in a series of smaller earthquakes with a net energy gain over time, something that also appears to describe NE Japan prior to the 2011 Tohoku earthquake.

Figure 2. Cascadia supercycle model. Plot showing long-term energy cycling of the Cascadia megathrust, and complex behavior over time. Cascadia Holocene earthquake time series at four primary sites expressed as energy gain and loss per event. Energy gain is proportional to recurrence between events in years. Energy loss is proportional to the mass of turbidite samples, scaled to result in no net gain or loss of energy through the Holocene. Four primary sites are shown with envelope showing variability, and dashed line showing maximum variability including error. The four sites are pinned at large and consistent event T11 (

5900 cal BP) for comparison. Mass values are extracted from the gamma density curves, using as a baseline the mass values for each baseline pair of bounding hemipelagic layers. Mass values (dimensionless) are then DC scaled to yield no net change when plotted against recurrence interval in years. (see Ⓔ Fig. S6 in the electronic supplement for scale factors). Core compaction is partially compensated for by this method, though some unknown compaction error remains in this plot. Error ranges are OxCal (Ramsey, 2001) 2s ranges from Goldfinger et al. (2012) in the X axis (time), and an estimated maximum value of 10% error applied to the mass values that includes possible air gaps in the core liner, bioturbation if present within the turbidites (rare), measurement error, error in establishing the baseline for each turbidite, and digitizing error. Final event assumed to occur 500 years from last event at AD 1700, a value equal to the average recurrence time (Goldfinger et al., 2012). See Cascadia Turbidites for core locations and other information about the CAscadia earthquake record.

Publications

Goldfinger, C., Ikeda, Y., Yeats, R.S., and Ren, J., 2013, Superquakes and Supercycles, Seismological Research Letters, v. 84, no. 1, p. 24-32

Goldfinger, C., Ikeda, Y., Yeats, R.S., 2013, Superquakes, Supercycles and Global Earthquake Clustering, 2013, EARTH Vol. 58 (No. 1), p. 34.

Goldfinger, C., Nelson, C.H., and Johnson, J.E., 2003, Deep-Water Turbidites as Holocene Earthquake Proxies: The Cascadia Subduction Zone and Northern San Andreas Fault Systems : Annali Geofisica, v. 46, p. 1169-1194.

—, 2003, Holocene Earthquake Records From the Cascadia Subduction Zone and Northern San Andreas Fault Based on Precise Dating of Offshore Turbidites : Annual Reviews of Earth and Planetary Sciences, v. 31, p. 555-577.

Goldfinger, C., Morey, A.E., Nelson, C.H., Gutiérrez-Pastor, J., Johnson, J.E., Karabanov, E., Chaytor, J., Ericsson, A., and shipboard scientific party, 2007, Rupture lengths and temporal history of significant earthquakes on the Offshore and Northcoast segments of the Northern San Andreas Fault based on turbidite stratigraphy, Earth and Planetary Science Letters, v. 254, p. 9-27.

Goldfinger, C., Grijalva, K., Burgmann, R., Morey, A.E., Johnson, J.E., Nelson, C.H., Gutierrez-Pastor, J., Karabanov, E., Chaytor, J.D., Patton, J., and Gracia, E., 2008, Late Holocene Rupture of the Northern San Andreas Fault and Possible Stress Linkage to the Cascadia Subduction Zone, Bulletin of the Seismological Society of America, v. 98, p. 861-889.

Goldfinger, C., Patton, J.R., Morey, A.M., 2009, Reply to comment on "Late Holocene Rupture of the Northern San Andreas Fault and Possible Stress Linkage to the Cascadia Subduction Zone, Goldfinger, C., Grijalva, K., Burgmann, R., Morey, A., Johnson, J.E., Nelson, C.H., Ericsson, A., Gutiérrez-Pastor, J., Patton, J., Karabanov, E., Gracia, E.", Bulletin of the Seismological Society of America, v. 98, p. 861-889, 8 pp.

Goldfinger, C., 2009, Subaqueous Paleoseismology, v Mcalpin, J., ed., Paleoseismology, 2nd edition, Elsevier, p. 119-169.

Goldfinger, C., 2011, Submarine Paleoseismology Based on Turbidite Records, Annual Reviews of Marine Science, v. 3, p. 35-66.

Goldfinger, C., Nelson, C.H., Morey, A., Johnson, J.E., Gutierrez-Pastor, J., Eriksson, A.T., Karabanov, E., Patton, J., Gracia, E., Enkin, R., Dallimore, A., Dunhill, G., and Vallier, T., 2012, Turbidite Event History: Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS Professional Paper 1661-F, Reston, VA, U.S. Geological Survey, p. 184 p, 64 Figures. http://pubs.usgs.gov/pp/pp1661f/ Appendices

Goldfinger, C., Morey, A., Black, B., Beeson, J. and Patton, J., 2013, in press, Spatially Limited Mud Turbidites on the Cascadia Margin: Segmented Earthquake Ruptures?, v Pantosti, D., Gracia, E., Lamarche, G., Nelson, C.H., and Tinti, S., eds., Research Conference Submarine Paleoseismology: The Offshore Search of Large Holocene Earthquakes: Obergurgl, Austria, Natural Hazards and Earth System Sciences. (150 mb!)

Gracia, E., Vizcaino, A., Escutia, C., Asioli, A., Rodes, A., Palla, R., Garcia-Orellana, J., Lebreiro, S., Goldfinger, C., 2010, Holocene Earthquake Record Offshore Portugal (SW Iberia): Testing turbidite paleoseismology in a slow-convergence margin, Quaternary Science Reviews, v. 29, p. 1156-1172.

Gutierrez-Pastor, J., Nelson, C.H., Goldfinger, C., Johnson, J.E., Escutia, C., Eriksson, A., and Morey, A., 2009, Earthquake Control of Holocene Turbidite Frequency Confirmed by Hemipelagic Sedimentation Chronology on The Cascadia and Northern California Active Continental Margins, in Kneller, B., Martinsen, O.J., and McCaffrey, W., eds., External Controls on Deep-Water Depositional Systems, Society for Sedimentary Geology Special Publication, Volume 92: London, Society for Sedimentary Geology p. 179-197.

Gutierrez-Pastor, J., Nelson, C.H., Goldfinger, C., Escutia, C., 2012, Sedimentology of Seismo-Turbidites off the Cascadia and Northern California Active Tectonic Continental Margins, Northwest Pacific Ocean, Marine Geology, doi: 10.1016/j.margeo.2012.11.010.

Nelson, C. H. Escutia, C., Goldfinger, C., Karabanov, E., Gutiérrez-Pastor, J., 2009, In Press, Tectonic, volcanic, sedimentary, climatic, sea level, oceanographic, and anthropogenic controls on turbidite systems SEPM Special Paper on turbidites, in prep.

Priest, G. R., Goldfinger, C., Wang, W., Witter, R. C. Zhang, Y., 2009, Confidence levels for tsunami-inundation limits in northern Oregon inferred from a 10,000-year history of great earthquakes at the Cascadia subduction zone, Natural Hazards v. 54, p. 27-73. DOI 10.1007/s11069-009-9453-5.

Priest G.R, Goldfinger C, Wang K, Witter RC, Zhang Y, Baptista A.M., 2009, Tsunami hazard assessment of the Northern Oregon coast: a multi-deterministic approach tested at Cannon Beach, Clatsop County, Oregon. Oregon Department of Geology Mineral Industries Special Paper 41, 89p. plus Appendix and GIS files.

Witter, R.C., Zhang, Y., Wang, K., Priest, G.R., Goldfinger, C., Stimely, L., English, J.T., and Ferro, P.A., 2011, Simulating tsunami inundation at Bandon, Coos County, Oregon, using hypothetical Cascadia and Alaska earthquake scenarios, Oregon Department of Geology and Mineral Industries Special Paper 43, Salem, Oregon, 63 p. and GIS files

Selected Bibliography

Alexander, J., and Mulder, T., 2002, Experimental quasi-steady density currents: Marine Geology, v. 186, no. 3-4, p. 195-210.

Adams, J., 1990, Paleoseismicity of the Cascadia subduction zone: Evidence from turbidites off the Oregon-Washington Margin: Tectonics, v. 9, p. 569-584.

Beattie, P.D., and Dade, W.B., 1996, Is scaling in turbidite deposition consistent with forcing by earthquakes?: Journal of Sedimentary Research, v. 66, p. 909-915.

Beck, C., Mercier de Lépinay, B., Schneider, J.-L., Cremer, M., Çagatay, N., Wendenbaum, E., Boutareaud, S., Ménot, G., Schmidt, S., Weber, O., Eris, K., Armijo, R., Meyer, B., Pondard, N., Gutscher, M.-A., Turon, J.L., Labeyrie, L., Cortijo, E., Gallet, Y., Bouquerel, H., Gorur, N., Gervais, A., Castera, M.H., Londeix, L., de Rességuier, A., and Jaouen, A., 2007, Late Quaternary co-seismic sedimentation in the Sea of Marmara's deep basins: Sedimentary Geology, v. 199, p. 65-89.

Bertrand, S., Charlet, F., Chapron, E., Fagel, N., and De Batist, M., 2008, Reconstruction of the Holocene seismotectonic activity of the Southern Andes from seismites recorded in Lago Icalma, Chile, 39°S: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 259, p. 301-322.

Blumberg, S., Lamy, F., Arz, H.W., Echtler, H.P., Wiedicke, M., Haug, G.H., and Oncken, O., 2008, Turbiditic trench deposits at the South-Chilean active margin: A Pleistocene–Holocene record of climate and tectonics: Earth and Planetary Science Letters, v. 268, p. 52-539.

Dallimore, A., Thomson, R.E., and Bertram, M.A., 2005, Modern to late Holocene deposition in an anoxic fjord on the west coast of Canada: Implications for regional oceanography, climate and paleoseismic history: Marine Geology, v. 219, p. 47-60.

Doig, R., 1990, 2300 yr history of seismicity from silting events in Lake Tadoussac, Charlevoix, Quebec: Geology, v. 18, p. 820-823.

Goldfinger, C., Patton, J., Morey, A.E., and Nelson, C.H., 2009, Reply to “Comment on Late Holocene Rupture of the Northern San Andreas Fault and Possible Stress Linkage to the Cascadia Subduction Zone" Bulletin of the Seismological Society of America, v. 99, p. 2599–2606.

Goldfinger, C., Patton, J.R., Morey, A., and Witter, R., 2010, Segmentation and Probabilities for Cascadia Great Earthquakes based on Onshore and Offshore Paleoseismic Data, Seismological Society of America Annual Meeting: Portland, OR, Seismological Research Letters.

Goldfinger, C., Witter, R., Priest, G.R., Wang, K., and Zhang, Y., 2010, Cascadia Supercycles: Energy Management of the long Cascadia Earthquake Series: Seismological Society of America Annual Meeting, v. 81, p. 290.

Gorsline, D.S., De Diego, T., and Nava-Sanchez, E.H., 2000, Seismically triggered turbidites in small margin basins: Alfonso Basin, Western Gulf of California and Santa Monica Basin, California Borderland: Sedimentary Geology, v. 135, p. 21-35.

Gorsline, D.S., Shiki, T., Chough, S.K., and Einsele, G., 1996, Depositional events in Santa Monica Basin, California borderland, over the past five centuries, Elsevier, Amsterdam, Netherlands, p. 73-88.

Guyard, H., St-Onge, G., Chapron, E., Anselmetti, F., and Francus, P., 2007, The Ad 1881 Earthquake-Triggered Slump And Late Holocene Flood-Induced Turbidites From Proglacial Lake Bramant, Western French Alps, Submarine Mass Movements and Their Consequences, p. 279-286.

Huh, C.A., Su, C.C., Liang, W.T., and Ling, C.Y., 2004, Linkages between turbidites in the southern Okinawa Trough and submarine earthquakes: Geophysical Research Letters, v. 31.

Huh, C.-A., Su, C.-C., Wang, C.-H., Lee, S.-Y., and Lin, I.-T., 2006, Sedimentation in the Southern Okinawa Trough -- Rates, turbidites and a sediment budget: Marine Geology, v. 231, p. 129-139.

Ikehara, K., 2000, Deep-sea turbidite record of great earthquake along the eastern Nankai Trough and eastern margin of Japan Sea, Active Fault Research for the New Millenium. Proceedings of the Hokudan International Symposium and School on Active Faulting: Hokudan-cho, Awaji Island, Hyogo, Japan, p. str. 119-120.

—, 2000, Paleoseismicity analysis using earthquake-induced sediments: Bull Geol. Survey Japan, v. 51, p. 89-102.

—, 2004, Estimation of recurrence intervals of large earthquakes using deep-sea turbidites around Japan, in Satake, K., Goldfinger, C., ed., Workshop on Turbidites as Earthquake Recorders: Tsukuba, Japan, AIST, Geological Survey of Japan.

Ikehara, K., and Ashi, J., 2004, Deep-Sea Turbidite Evidences on the Recurrence of Large Earthquakes Along the Eastern Nankai Trough: Eos Trans. AGU, v. 86, p. Fall Meeting Supplement, Abstract T11A-0354.

Inouchi, Y., Kinugasa, Y., Kumon, F., Nakano, S., Yasumatsu, S., and Shiki, T., 1996, Turbidites as records of intense palaeoearthquakes in Lake Biwa, Japan: Sed. Geol., v. v. 104, p. str. 117-125.

Johnson, J.E., Paull, C.K., Normark, W., and Ussler, W., 2005, Late Holocene Turbidity Currents in Monterey Canyon and Fan Channel: Implications for Interpreting Active Margin Turbidite Records: Eos Trans. AGU, v. 86, p. abstract OS21A-1521.

Karlin, R.E., and Abella, S.E.B., 1994, A history of past earthquakes in the Puget Sound area recorded in Holocene sediments from Lake Washington: Proceedings of the workshop on Paleoseismology Open-File Report - U. S. Geological, v. Survey, p. 90.

—, 1996, A history of Pacific Northwest earthquakes recorded in Holocene sediments from Lake Washington: Journal of Geophysical Research, B, Solid Earth and Planets, v. 101, p. 6137-6150.

Karlin, R.E., Holmes, M., Abella, S.E.B., and Sylwester, R., 2004, Holocene landslides and a 3500-year record of Pacific Northwest earthquakes from sediments in Lake Washington: Geological Society of America Bulletin, v. 116, p. 94-108.

Karlin, R.E., Verosub, K., and Harris, A., 1996, A paleoearthquake record in varved Holocene sediments from ODP Leg 169S, Saanich Inlet, British Columbia: Geological Society of America, Cordilleran Section and associated societies, 96th annual meeting abstracts Abstracts with Programs - Geological Society of America, v. 32, p. 22.

—, 2000, A paleoearthquake record in varved Holocene sediments from ODP Leg 169S, Saanich Inlet, British Columbia: Geological Society of America, Cordilleran Section and associated societies, 96th annual meeting abstracts Abstracts with Programs - Geological Society of America, v. 32, p. 22.

Kastens, K.A., 1984, Earthquakes as a triggering mechanism for debris flows and turbidites on the Calabrian Ridge: Mar. Geol., v. v. 55, p. str. 13-33.

—, 1984, Earthquakes as a triggering mechanism for debris flows and turbidites on the Calabrian Ridge: Marine Geology, v. vol. 55, p. pp. 13-33.

Lozefski, G., McHugh, C.M., Cormier, M., Seeber, L., Cagatay, N., and Okay, N., 2004, PROVENANCE OF TURBIDITE SANDS IN THE MARMARA SEA, TURKEY: A TOOL FOR SUBMARINE PALEOSEISMOLOGY: Geological Society of America Abstracts with Programs, v. 36, p. 120.

Nakajima, T., 2000, Initiation processes of turbidity currents implications for assessments of recurrence intervals of offshore earthquakes using turbidites: Bulletin of the Geological Survey of Japan, v. 51, p. 79-87.

—, 2000, Initiation processes of turbidity currents implications for assessments of recurrence intervals of offshore earthquakes using turbidites: Chishitsu Chosajo Geppo = Bulletin of the Geological Survey of Japan, v. 51, p. 79-87.

—, 2001, Translated: Initiation processes of turbidity currents implications for assessments of recurrence intervals of offshore earthquakes using turbidites: Bull Geol. Survey Japan, v. v. 51, p. str. 79-87.

—, 2003, Earthquake potential inferred from turbidites on the Sado Ridge, in the eastern margin of the Japan Sea,: Earth Planest and Space.

—, 2004, Earthquake potential north of Sado Ridge, Japan Sea, inferred from turbidites, in Satake, K., Goldfinger, C., ed., Workshop on Turbidites as Earthquake Recorders: Tsukuba, Japan, AIST, Geological Survey of Japan.

Nakajima, T., and Kanai, Y., 2000, Sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the Japan Sea: Sedimentary Geology, v. 135, p. 1-19.

Noda, A., 2004, Turbidites along Kushiro Canyon, in Satake, K., Goldfinger, C., ed., Workshop on Turbidites as Earthquake Recorders: Tsukuba, Japan, AIST, Geological Survey of Japan.

Noda, A., Tsujino, T., Furukawa, R., and Yoshimoto, N., 2004, Character, Provenance, and Recurrence Intervals of Holocene Turbidites in the Kushiro Submarine Canyon, Eastern Hokkaido Forearc, Japan: Eos, Trans. AGU, Fall Meeting Abstracts, v. 86, p. T13C1369.

Noda, A., TuZino, T., Kanai, Y., Furukawa, R., and Uchida, J.-i., 2008, Paleoseismicity along the southern Kuril Trench deduced from submarine-fan turbidites: Marine Geology, v. 254, p. 73-90.

Okamura, Y., 2004, Paleoseismology of deep-sea faults based on marine surveys in Japan Sea, in Satake, K., Goldfinger, C., ed., Workshop on Turbidites as Earthquake Recorders: Tsukuba, Japan, AIST, Geological Survey of Japan.

Patton, J.R., Goldfinger, C., Morey, A., Erhardt, M., Black, B., Garrett, A.M., Djadjadihardja, Y.S., and Hanifa, U., 2009, 7.5 ka earthquake recurrence history in the region of the 2004 Sumatra-Andaman earthquake: Geological Society of America Abstracts with Programs, v. 41, p. 408.

—, 2010, Temporal Clustering and Recurrence of Holocene Paleoearthquakes in the Region of the 2004 Sumatra-Andaman Earthquake, Seismological Society of America Annual Meeting, Volume 41: Portland, OR, p. 408.

Prins, M.A., Postma, G., and Weltje, G.J., 2000, Controls on terrigenous sediment supply to the Arabian Sea during the late Quaternary the Makran continental slope: Marine Geology, v. 169, p. 351-371.

Prunier, C.F., Karlin, R.E., and Pratt, T.L., 1996, Seismic landslides in Puget Sound (SLIPS) IV, Holocene neotectonics and mass-wasting in Lake Sammamish related to the Seattle Fault: Enriched: AGU 1996 fall meeting Eos, Transactions, American Geophysical Union, v. 77, p. 500.

Sarı, E., and Çağatay, M., 2006, Turbidites and their association with past earthquakes in the deep Çınarcık Basin of the Marmara Sea: Geo-Marine Letters, v. 26, p. 69-76.
Schnellmann, M., Anselmetti, F.S., Giardini, D., McKenzie, J.A., and Ward, S.N., 2002, Prehistoric earthquake history revealed by lacustrine slump deposits: Geology (Boulder), v. 30, p. 1131-1134.

Shiki, T., Cita, M. B., and Gorsline, D. S., 2000a, Sedimentary features of seismites, seismo-turbidites and tsunamiites&mdashan introduction: Sedimentary Geology, vol. 135, p. vii-ix.

Shiki, T., Kumon, F., Inouchi, Y., Kontani, Y., Sakamoto, T., Tateishi, M., Matsubara, H., and Fukuyama , K., 2000b, Sedimentary features of the seismo-turbidites, Lake Biwa , Japan : Sedimentary Geology, v. 135, p. 37-50.

Skinner, M.R., and Bornhold, B.D., 2003, Slope Failures and Paleoseismicity, Effingham Inlet, Southern Vancouver Island, British Columbia, Canada, in Locat, J., and Mienert, J., eds., Submarine Mass Movements and Their Consequences: 1st International Symposium: Nice, France, Kluwer Academic Publishers, p. 375-382.

Soh, W., 2004, Coseismic seafloor displacement along Enshu fault detected from NSS coring, in Satake, K., Goldfinger, C., ed., Workshop on Turbidites as Earthquake Recorders: Tsukuba, Japan, AIST, Geological Survey of Japan.

Sternberg, R. W., 1986, Transport and accumulation of river-derived sediment on the Washington continental shelf: J. Geol. Soc. London, v. 143, p. 945-956.

St-Onge, G., Mulder, T., Piper, D.J.W., Hillaire-Marcel, C., and Stoner, J.S., 2004, Earthquake and flood-induced turbidites in the Saguenay Fjord (Québec): a Holocene paleoseismicity record: Quaternary Science Reviews, v. 23, p. 283-294.

Syvitski, J.P.M., and Schafer, C.T., 1996, Evidence for an earthquake-triggered basin collapse in Saguenay Fjord, Canada: Sedimentary Geology, v. 104, p. 127-153.

Thomson, J., and Weaver, P.P.E., 1994, An AMS radiocarbon method to determine the emplacement time of recent deep-sea turbidites: Sed. Geol., v. 89, p. 1-7.

Ujiie, H., Hyun, S., Oyakaa, T., Nakamura, T., Miyamoto, Y., and Park, j.-O., 1999, Holocene turbidite cores from the southern Ryukyu Trench slope: Suggestions of periodic earthquakes: Geol. Soc. Japan, v. v. 103NO. 6.

Ujiie, H., Nakamura, T., Miyamoto, Y., Park, J.-O., Hyun, S., and Oyakawa, T., 1997, Holocene turbidite cores from the southern Ryukyu Trench slope suggestions of periodic earthquakes: Chishitsugaku Zasshi = Journal of the Geological Society of Japan, v. 103, p. 590-603.

Völker, D., Reichel, T., Wiedicke, M., and Heubeck, C., 2008, Turbidites deposited on Southern Central Chilean seamounts: Evidence for energetic turbidity currents: Marine Geology, v. 251, p. 15-31.


Carl Froede and Jack Cowart investigated the outcrop of sandstone and shale found at Dougherty Gap in Walker County in the northwest corner of Georgia. They argue that turbidity currents are a better model to describe how these sediments were laid down than the uniformitarian pro-grading delta model. [1]

Tiny animals left burrows that were fossilized as casts, and it is argued that this "bioturbation" or mixing from biological activity, is found in sediment deposited in turbidity currents as well as in deltas. Large spans of sandstone without these fossils is difficult to explain if the sand was laid down a few layers at a time because the animals would have plenty of time to look for food and construct vertical escape structures. The lack of fossil traces would seem to imply large amounts of deposition at one time. Burrows made in salt water are often lined with clay, but clay lined burrows were not found. A large number of animals should have destroyed the ripple marks at the top of each sand layer, but traces were only found at the bottom of the layer as if the animals survived for a time at the bottom but did not have time to penetrate and destroy the ripple patterns. Incoming sand may have preserved traces found at the top of previous layer. [1]

Froede and Cowart suggest that the outcropping formed from pulses of sediment laden water at the beginning or middle of the flood (Lower to Middle Flood Event Timeframe). [1]


Turbidites*

Dawn Summer, University of California Davis, Department of Geology, University of California-Davis

When last checked this resource was offline Our automated link checker has alerted the folks responsible for the part of our site where this problematic link is referenced. If you have further information about the link (e.g. a new location where the information can be found) please let us know.

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This website, designed for a Sediments and Strata course at the University of California- Davis, contains numerous photographs of turbidite sequences in outcrop. Photos are divided into two categories turbidites in the Cretaceous Pigeon Point Formation and turbidites in the Cretaceous Great Valley Sequence. Users may also follow a link to other sedimentary photos.

This description of a site outside SERC has not been vetted by SERC staff and may be incomplete or incorrect. If you have information we can use to flesh out or correct this record let us know.

Part of the Cutting Edge collection. The NAGT/DLESE On the Cutting Edge project helps geoscience faculty stay up-to-date with both geoscience research and teaching methods.


Turbidite Sequences

The turbidites are characterized by layers (bed) with great lateral continuity, bedding regularly and generally gradational with thinning of the grains to the top of each stratum (layer), ripple marks, association of hemipelagic sediments, base-layer structures as sole marks, flutecasts, marks objects (toolmarks, grooves). Each stratum of turbidite (bed) is deposited in a single one event (flow). The partition of energy between dense and turbulent flow during a turbidity event gives the typical features of these deposits. In Bi-partite flows dense and fast deposition commonly form massive sandstones while turbulent flow will deposit fine sediments (pelites).The deceleration of the turbulent flow may form ripple marks before decanting the less dense materials and the finer particles, such as clays and silts.


The characterization of some facies and processes associated with siliciclastic turbidites comes primarily from the observation of the structures formed in the ignimbrite flows, which are volcaniclastic rocks.


Turbidites*

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Turbidite Event History—Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone

Povezave

Povzetek

First posted July 12, 2012

Active Tectonics and Seafloor Mapping Lab
Oregon State University
College of Earth, Ocean, and Atmospheric Sciences
Burt 130, Corvallis OR 97331

Turbidite systems along the continental margin of Cascadia Basin from Vancouver Island, Canada, to Cape Mendocino, California, United States, have been investigated with swath bathymetry newly collected and archive piston, gravity, kasten, and box cores and accelerator mass spectrometry radiocarbon dates. The purpose of this study is to test the applicability of the Holocene turbidite record as a paleoseismic record for the Cascadia subduction zone. The Cascadia Basin is an ideal place to develop a turbidite paleoseismologic method and to record paleoearthquakes because (1) a single subduction-zone fault underlies the Cascadia submarine-canyon systems (2) multiple tributary canyons and a variety of turbidite systems and sedimentary sources exist to use in tests of synchronous turbidite triggering (3) the Cascadia trench is completely sediment filled, allowing channel systems to trend seaward across the abyssal plain, rather than merging in the trench (4) the continental shelf is wide, favoring disconnection of Holocene river systems from their largely Pleistocene canyons and (5) excellent stratigraphic datums, including the Mazama ash and distinguishable sedimentological and faunal changes near the Pleistocene-Holocene boundary, are present for correlating events and anchoring the temporal framework.

Multiple tributaries to Cascadia Channel with 50- to 150-km spacing, and a wide variety of other turbidite systems with different sedimentary sources contain 13 post-Mazama-ash and 19 Holocene turbidites. Likely correlative sequences are found in Cascadia Channel, Juan de Fuca Channel off Washington, and Hydrate Ridge slope basin and Astoria Fan off northern and central Oregon. A probable correlative sequence of turbidites is also found in cores on Rogue Apron off southern Oregon. The Hydrate Ridge and Rogue Apron cores also include 12-22 interspersed thinner turbidite beds respectively.

We use 14 C dates, relative-dating tests at channel confluences, and stratigraphic correlation of turbidites to determine whether turbidites deposited in separate channel systems are correlative - triggered by a common event. In most cases, these tests can separate earthquake-triggered turbidity currents from other possible sources. The 10,000-year turbidite record along the Cascadia margin passes several tests for synchronous triggering and correlates well with the shorter onshore paleoseismic record. The synchroneity of a 10,000-year turbidite-event record for 500 km along the northern half of the Cascadia subduction zone is best explained by paleoseismic triggering by great earthquakes. Similarly, we find a likely synchronous record in southern Cascadia, including correlated additional events along the southern margin. We examine the applicability of other regional triggers, such as storm waves, storm surges, hyperpycnal flows, and teletsunami, specifically for the Cascadia margin.

The average age of the oldest turbidite emplacement event in the 10-0-ka series is 9,800±

210 cal yr B.P. and the youngest is 270±

120 cal yr B.P., indistinguishable from the A.D. 1700 (250 cal yr B.P.) Cascadia earthquake. The northern events define a great earthquake recurrence of

500-530 years. The recurrence times and averages are supported by the thickness of hemipelagic sediment deposited between turbidite beds. The southern Oregon and northern California margins represent at least three segments that include all of the northern ruptures, as well as

22 thinner turbidites of restricted latitude range that are correlated between multiple sites. At least two northern California sites, Trinidad and Eel Canyon/pools, record additional turbidites, which may be a mix of earthquake and sedimentologically or storm-triggered events, particularly during the early Holocene when a close connection existed between these canyons and associated river systems.

The combined stratigraphic correlations, hemipelagic analysis, and 14 C framework suggest that the Cascadia margin has three rupture modes: (1) 19-20 full-length or nearly full length ruptures (2) three or four ruptures comprising the southern 50-70 percent of the margin and (3) 18-20 smaller southern-margin ruptures during the past 10 k.y., with the possibility of additional southern-margin events that are presently uncorrelated. The shorter rupture extents and thinner turbidites of the southern margin correspond well with spatial extents interpreted from the limited onshore paleoseismic record, supporting margin segmentation of southern Cascadia. The sequence of 41 events defines an average recurrence period for the southern Cascadia margin of

240 years during the past 10 k.y.

Time-independent probabilities for segmented ruptures range from 7-12 percent in 50 years for full or nearly full margin ruptures to

21 percent in 50 years for a southern-margin rupture. Time-dependent probabilities are similar for northern margin events at

7-12 percent and 37-42 percent in 50 years for the southern margin. Failure analysis suggests that by the year 2060, Cascadia will have exceeded

27 percent of Holocene recurrence intervals for the northern margin and 85 percent of recurrence intervals for the southern margin.

The long earthquake record established in Cascadia allows tests of recurrence models rarely possible elsewhere. Turbidite mass per event along the Cascadia margin reveals a consistent record for many of the Cascadia turbidites. We infer that larger turbidites likely represent larger earthquakes. Mass per event and magnitude estimates also correlate modestly with following time intervals for each event, suggesting that Cascadia full or nearly full margin ruptures weakly support a time-predictable model of recurrence. The long paleoseismic record also suggests a pattern of clustered earthquakes that includes four or five cycles of two to five earthquakes during the past 10 k.y., separated by unusually long intervals.

We suggest that the pattern of long time intervals and longer ruptures for the northern and central margins may be a function of high sediment supply on the incoming plate, smoothing asperities, and potential barriers. The smaller southern Cascadia segments correspond to thinner incoming sediment sections and potentially greater interaction between lower-plate and upper-plate heterogeneities.

The Cascadia Basin turbidite record establishes new paleoseismic techniques utilizing marine turbidite-event stratigraphy during sea-level highstands. Te tehnike je mogoče uporabiti v drugih specifičnih okoljih po vsem svetu, kjer obsežen prelom prečka celinski rob, ki ima več aktivnih turbiditnih sistemov.

Predlagano citiranje

Goldfinger, C., Nelson, CH, Morey, AE, Johnson, JE, Patton, JR, Karabanov, E., Gutiérrez-Pastor, J., Eriksson, AT, Gràcia, E., Dunhill, G., Enkin, RJ , Dallimore, A. in Vallier, T., 2012, Zgodovina dogodkov turbiditov - metode in posledice za holocensko paleoizmičnost območja subkukcije Cascadia: US Geological Survey Professional Paper 1661 – F, 170 str. (Na voljo na https://pubs.usgs.gov/pp/pp1661f/).

Študijsko območje

Kazalo

  • Povzetek
  • Uvod
  • Pomen paleoizmologije turbidita
  • Subdukcijsko območje Cascadia in potencial velikega potresa
  • Metode
  • Rezultati
  • Diskusija
  • Posledice za potresne nevarnosti v porečju Cascadia in severnem San Andreasu
  • Napaka
  • Zaključki
  • Naučena lekcija
  • Zahvala
  • Navedeni viri
  • Priloge 1–11

Del ali celo poročilo je predstavljeno v obliki prenosnega dokumenta (PDF). Za najboljše rezultate pri ogledu in tiskanju dokumentov PDF je priporočljivo, da jih prenesete v računalnik in odprete z Adobe Readerjem. Dokumenti PDF, odprti iz brskalnika, se morda ne bodo prikazovali ali natisnili, kot je predvideno. Brezplačno prenesite najnovejšo različico programa Adobe Reader. Več informacij o ogledu, prenosu in tiskanju datotek s poročili najdete tukaj.


Poglej si posnetek: Amazing Flash Flood. Debris Flow Southern Utah HD (September 2021).