MISCARI SEISMICE(CUTREMURE)Cum se formeaza un cutremur?Ce sunt undele seismice?Cum se inregistreaza cutremurele?Pot fi prevazute cutremurele?

Ce este un cutremur?

DEFINITIIMiscari bruste si rapide ( - zguduire), de scurta durata;Datorate unei eliberari de energie in zona rigida de la exteriorul Pamintului;Adincimea maxima de formare este de 700 km;Energia eliberata se transmite sub forma undelor seismice;Cine produce cutremurele?Cutremurele se produc aproape continuu dinamica interna a planetei (1.000.000/zi);Sunt asociate zonelor unde se poate acumula / elibera energie;Foarte rare cutremure datorate unor factori externi (maree, meteoriti) sau antropici (explozii).

Relatia stress deformare pentru materiale (roci)

- Cutremurele datorate factorilor tectonici reprezinta peste 95% din totalul cutremurelor- Se produc datorita deplasarii bruste a unor blocuri tectonice in lungul zonelor de fractura, sub influenta unor miscari de forfecareEliberare de energie - socul seismic -Deformare cu acumulare de energie

Elementele miscarilor seismiceUndele seismice ale unui cutremur radiaza dintr-o zona relativ restrinsa FOCAR (HIPOCENTRU) Planul falieiEpicentruFalieFrontul undelorFocar (Hipocentru)Adincimea focarului = adincimea cutremuruluiIn EPICENTRU intensitatea este maxima

Propagarea undelor seismice

Tipurile de unde seismiceP unde longitudinale (primare) viteza 5 8 km/sS unde transversale (secundare) viteza cu 40% mai micaL unde de suprafata lente si numai la suprafata

Principiile undelor P si S

Undele de suprafata sunt rezultate din interferenta undelor P si S. Sunt de doua tipuri: unde de tip Love si unde de tip Rayleigh Unde LoveUnde Rayleigh

Forma si impactul undelor de suprafata- Au lungime de unda mare (simbol L)- Undele superficiale provoaca cele mai mari distrugeri- Se propaga in toate directiileMiscare lateralaDirectia de propagareDirectia de propagareMiscare ondulatorieUnde de suprafata

PSLModul de manifestare la suprafata a celor trei tipuri de unde seismice

Caracteristicile cutremurelor

Un seism este definit prin energia eliberata lucrul mecanic produs in focar;Se inregistreaza magnitudinea cutremurului si intensitatea sa;Timpul la origine (GMT);Durata timpul scurs de la decalnsare pina la amortizarea sa;Inregistrarea seismelor se face cu ajutorul SEISMOGRAFELOR / SEISMOGRAME

Inregistrarea undelor seismiceSeismografSeismogramaStatie seismica

SeismogramelePrimele sosesc undele P si reprezinta prima faza precursoare (5 7 s);Undele S au vibratii mai ample a doua faza precursoare (10 13 s);Faza paroxistica oscilatii ample, determinate de undele L (zeci de s);In final o faza de amortizare si revenirea la semnalul de baza.

Localizarea epicentrului/focarului

- Cunoscind timpul de sosire a undelor L si P si viteza lor de propagare se poate determina distanta fata de locul de inregistrare

Relatia timp - distanta

Relatia timp / distanta pentru curbele P si S

Localizarea epicentruluiLocalizarea epicentrului se realizeaza prin triangulatie / locul de intersectie a cercurilor ce reprezinta distanta primelor unde sosite

EpicentruPSNucleu solidNucleu extern lichidZona de umbra pentru PZona de umbra pentru PMantaLipsa unde SUnde P si SUnde P si SPropagarea undelor P si S si structura interna a pamintului- Undele P se propaga atit in mediii solide cit si lichide- Undele S se propaga numai in medii solide

Propagarea undelor P si S si structura interna a pamintului- Undele P se propaga atit in mediii solide cit si lichide- Undele S se propaga numai in medii solideSursa: Glencoe, Earth Science, McGraw Hill, 2008

Propagarea undelor P si S si structura mantalei (tomografii)Sectiune verticala prin mantaPlacaViteza undelor seismiceMicaMareSursa: Glencoe, Earth Science, McGraw Hill, 2008

Utilizarea metodelor seismice in prospectiunea geologica - Seisme provocate; Inregistrare si prelucrare; Interpretarea structurilor geologiceSursa: Glencoe, Earth Science, McGraw Hill, 2008

Distributia cutremurelor (adincime / suprafata)Clasificare functie de adincimeCutremure superficiale epicentrul sub 10 kmCutremure normale epicentrul intre 10 si 60 kmCutremure intermediare - epicentrul intre 60 si 300 kmCutremure adinci - epicentrul intre 300 si 700 km

Zone seismice si grad ridicat de riscZona circumpacifica 68%Zona mediteraneeana 21%Riftul Est-african si atlantic 11%Zone aseismiceZone cu seismicitate redusa, regiuni stabile

Zone seismiceIndice de seismicitate nr cutremure /100.000 kmp;Primul loc Japonia (382), Chile, Noua Zeelanda, Italia;Romania zona mediteraneeanaLinii de seismicitatecu intensitate mai mareSunt legate de fracturi in zonele alpine sau de platforma (sariaje, falii crustale);Sunt mai multe zone epicentraleVrancea cu cea mai mare energie si frecventa, cutremure intermediare;Fagaras polikinetice (surse multiple), moderate, scufundarea Bazinului Transilvaniei)Pontice DanubieneSecundare: tirnave, Dorohoi Botosani, Urziceni,

Harti de risc seismic(zona mediteraneana)

Harti de risc seismic (globala)

Relatia dintre placile litosferice si localizarea cutremurelorRiftFosaAdincime micaIntermediareAdincime mare

Localizarea zonelor majore seismice

Sursa: Glencoe, Earth Science, McGraw Hill, 2008

Sursa: Glencoe, Earth Science, McGraw Hill, 2008

Efectele cutremurelor

- CF Richter si B Gutenberg (1947) propune o metoda cu indici masurabili;- Magnitudinea logaritmul zecimal al valorii amplitudinii maxime (A) masurate in microni, a unei seismograme inregistrate la o distanta de 100 km de epicentru;Se corecteaza printr-o constanta de atenuare C1 si constanta C2 dependenta de parametrii litologici si structurali M = C1 logA + C2 Fiecare grad este de 10 mai puternic decit precedentul; Rosi Mercali si Sieberg 12 grade intensitate / efecte Romania scara a intensitatilor MSK si Mercali modificata 12 grade Harti cu IZOSEISTE (izolinii de egala intensitate) zone de risc seismic

Mercali si Sieberg EFECTEAmoriACCELERATIERichterMAGNITUDINEGradCaracteristiciGradmm/s2Grad1Microseisme (numai de aparate)I2,512Foarte slabe (persoane foarte sensibile)II2,5 523Slabe (majoritatea persoanelor)III6 1034Moderate ( vibreaza geamurile)IV11 253,55Semitari (penduleaza obiectele suspendate)V26 5046Tari ( suna clopotele, panica)VI51 1004,57Foarte tari (cad obiecte, panica)VII101 25068Distrugatoare (crapa zidurile, cad cosurile)VIII251 5007 7,59Pustiitoare (se darima ziduri, prabusire cladiri)IX501 10007,5 - 810Nimicitoare (distrugere cladiri din temelii, crapaturi ale scoartei, alunecari de teren)X1001 25008 8,511Catastrofale (toate cladirile, baraje, relief)XI2501 50009 -9,512Catastrofa seismica (toate constructiile, modificarea reliefului)XII500010

Scara Mercali - efecte

Predictia cutremurelorCutremurele apar in zonele de contact intre placile litosferice convergente, divergente, transformante;

Predictiile ofera un interval de timp si nu o data exacta;

Metodele de predictie variaza dar nu sunt sigure 100%.

MetodeColectarea de date permite o prezicere asupra locatiei si magnitudinii

Inregistrari continue (GPS) (Valabila pentru cutremure mai mici)Relatia dintre magnitudine si frecventa;3. Gap analysis

Cind apar aceleasi conditii exista sansa aparitiei unui cutremur;Depinde de o cantitate mare de date istorice

Studiile precursorilor si evenimentelor ce aparCresterea ratei seismice a zonelor de frecare si miscarea lenta in lungul unei falii;Curbarea gradata a reliefului in zona de falieModificarea nivelului apei in fintiniLumini, descarcari electriceComportamentul animalelorMasurarea miscarilor in lungul faliilor;Crapaturi in lungul faliilor;

1. Inregistrari continue

2. Relatia dintre magnitudine si frecventa(Legea Gutenberg Richter)Legea exprima relatia dintre magnitudine si numarul total de cutremure dintr-o regiune, intr-un interval de timp

Unde N = numarul de cutremurea, b = constanteM = magnitudinea

Sursa: http://en.wikipedia.org/wiki/Gutenberg%E2%80%93Richter_law

3. Gap theory

Gap theory (Turcia)Sursa: Glencoe, Earth Science, McGraw Hill, 2008

Sisteme de inregistrare continua (Romania, Mediterana)Noiembrie 10, 1940 (7.7, 160 km);

Martie 4, 1977 (7.5, 100 km);

August 30, 1986 (7.2, 140 km);

Mai 30, 1990 (6.9, 80 km).

Sisteme de inregistrare continua (global)

Harta de risc seismic

Sursa: Glencoe, Earth Science, McGraw Hill, 2008Efectele cutremurelor (subaerian)

Sursa: Glencoe, Earth Science, McGraw Hill, 2008Efectele cutremurelor (submarin)

Curenti de turbiditate (secvente Bouma)

1985 - Mexico CityNu cutremurele omoara oamenii, constructiile da!

Northridge, California, ianuarie 17, 1994Magnitudine 6.7Photo Credit: J. Dewey, U.S. Geological Survey

Loma Prieta, Octombrie 17, 1989Oakland, CaliforniaMagnitude: 6.9Photo Credit: H.G. Wilshire, U.S. Geological Survey

Santa Monica, ianuarie, 17, 1994, Magnitudine 6.7Photo credit: M. Celebi, U.S. Geological Survey

Armenia, decembrie 7, 1988Magnitudine 7,9Photo Credit: C.J. Langer, U.S. Geological Survey

San Francisco, octombrie 18, 1989Magnitudine 6.9Photo Credit: D. Perkins, U.S. Geological Survey

TsunamiFlores Island, IndonesiaSeptembrie 1, 1992Magnitudine 7.0Photo Credit: Harry Yeh, University of Washington

TsunamiSursa: Glencoe, Earth Science, McGraw Hill, 2008

Cele mai mari cutremure dupa 1900

NrLocatieDataMagnitudine1.Chile1960 05 229.52.Prince William Sound, Alaska1964 03 289.23.Off the West Coast of Northern Sumatra2004 12 269.14.Near the East Coast of Honshu, Japan2011 03 119.05.Kamchatka1952 11 049.06.Offshore Maule, Chile2010 02 278.87.Off the Coast of Ecuador1906 01 318.88.Rat Islands, Alaska1965 02 048.79.Northern Sumatra, Indonesia2005 03 288.610.Assam - Tibet1950 08 158.611.Off the west coast of northern Sumatra 2012 04 118.612.Andreanof Islands, Alaska1957 03 098.613.Southern Sumatra, Indonesia2007 09 128.514.Banda Sea, Indonesia1938 02 018.515.Kamchatka1923 02 038.516.Chile-Argentina Border1922 11 118.517.Kuril Islands1963 10 138.5

Cele mai distructive cutremureData Locatie Morti Magnitudine Comentarii1556 Jan 23 China, Shansi 830,000 9? 1737 Oct 11 India, Calcutta** 300,000 1976 Jul 27 China, Tangshan 255,000* 8.0 1138 Aug 8 Syria, Aleppo 230,000 1927 May 22 China, near Xining 200,000 8.3 Large fractures856 Dec 22Iran, Damghan 200,000 1920 Dec 16 China, Gansu 200,000 8.6 Major fractures, landslides2004 Dec 26 Banda Aceh, Indonesia 175,000+ 9.3 Tsunami in Indian Ocean893 Mar 23 Iran, Ardabil 150,000 1923 Sept 1 Japan, Kwanto 143,800 8.3 Great Tokyo fire1948 Oct 5 USSR 110,000 7.3 Turkmenistan, Ashgabat1908 Dec 28 Italy, Messina 70-100,000 7.5 Earthquake and tsunami1290 Sep ? China, Chihli 100,000 2005 10 08 Pakistan 80361 7.61667 Nov ? Caucasia Shemakha 80,000 1727 Nov 18 Iran, Tabriz 77,000 1755 Nov 1 Portugal, Lisbon 70,000 8.7 Great tsunami1932 Dec 25 China, Gansu 70,000 7.6 1970 May 31 Peru 66,000 7.8 Great rock slide, floods1268 ? ? Asia Minor Silicia 60,000 1693 Jan 11 Italy, Sicily 60,000 1935 May 30 Pakistan, Quetta 30-60,000 7.5 Near complete destruction1783 Feb 4 Italy, Calabria 50,000 1990 Jun 20 Gilan, Iran 50,000 7.7Landslides

Concluzii

Fenomene legate de miscarile din zona solida externa (700 km); Peste 95% legate de placile tectonice Degajare mare de energie; Impact si forta de distrugere mare Hazard Predictie, risc seismic, scadere impact.

Prezicerea cutremurelor nu este posibila in prezent- monitorizare, relatia magnitudine/frecventa, gap theory

Prezicerea cutremurelorAlerta cu citeva ore inainteSistem de alerta / monitorizare a cutremurelor

***Northridge, California Earthquake, January 17, 1994, Set 2 Title: Collapse of apartment building over garage in Reseda (Second view of same building ) Caption: Reseda This is a view of the back side of the same collapsed apartment building shown in slide No. 14. The building's soft story has collapsed onto cars. Photo Credit: J. Dewey, U.S. Geological Survey Main url: http://www.ngdc.noaa.gov/seg/hazard/slideset/19/19_slides.shtml Photo url: http://www.ngdc.noaa.gov/seg/hazard/img/200_res/19/19_389.tif*October 17, 1989, Loma Prieta, California, Title: none Caption: Support-column failure and collapsed upper deck, Cypress viaduct (Oakland, CA). Photo Credit: H.G. Wilshire, U.S. Geological Survey Main url: http://pubs.usgs.gov/dds/dds-29/web_pages/oakland.html Photo url: http://pubs.usgs.gov/dds/dds-29/screens/023sr.jpeg Higher-res photo: http://pubs.usgs.gov/dds/dds-29/photocd/IMG0023.PCD

*Title: Failed bridge support, Northridge earthquakeCaption: Bridge column supporting Interstate 10 (Santa Monica Freeway) at the La Cienega-Venice overcrossing failed in the 1994 Northridge earthquake. Photo credit: M. Celebi, U.S. Geological Survey

Main url: http://www.ngdc.noaa.gov/seg/hazard/slideset/22/22_slides.shtmlPhoto url: http://www.ngdc.noaa.gov/seg/hazard/img/200_res/22/22_459.tif*Title: Collapse of Composite Structure, Spitak, Armenia Caption: Partial collapse of composite structure with stone masonry infill walls near Spitak. More than 21,000 residences were destroyed and 700,000 people in northern Armenia were affected by this event. Photo Credit: C.J. Langer, U.S. Geological Survey Main url: http://www.ngdc.noaa.gov/nndc/struts/results?eq_1=11&t=101634&s=0&d=4&d=44 Photo url: http://www.ngdc.noaa.gov/seg/hazard/img/200_res/11/11_225.tif*Loma Prieta Earthquake, October 18, 1989, Part 2Title: View of Damage along Jefferson Street, San FranciscoCaption: Another view along Jefferson Street in the Marina District. Tenants try to salvage items from the rubble. Photo Credit: D. Perkins, U.S. Geological Survey

Main url: http://www.ngdc.noaa.gov/seg/hazard/slideset/13/13_slides.shtmlPhoto url: http://www.ngdc.noaa.gov/seg/hazard/img/200_res/13/13_267.tif

*Title: Effects at Wuhring, Floress Island, IndonesiaCaption: The effects of the tsunami at Wuhring, Flores Island. Although the tsunami heights at this location were lower than elsewhere (only about 3.5 m) the waves swept entirely over the 400 m by 200 m peninsula inundating the densely populated community of Wuhring and killing 100. Here the damage was not as severe as on Babi Island. The waves left conical sand accumulations inside the houses, and at some locations the depth of the debris was about one meter. Photo Credit: Harry Yeh, University of Washington

Main url: http://www.ngdc.noaa.gov/nndc/struts/results?eq_1=26&t=101634&s=0&d=4&d=44Photo url: http://www.ngdc.noaa.gov/seg/hazard/img/200_res/26/26_540.tif