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26.05.2017 15:53

Re­search­ers drill deep to un­der­stand why the Sumatra earth­quake was so severe

Ulrike Prange Pressestelle
MARUM - Zentrum für Marine Umweltwissenschaften an der Universität Bremen

    An in­ter­na­tional team of sci­ent­ists has found evid­ence sug­gest­ing the de­hyd­ra­tion of min­er­als deep be­low the ocean floor in­flu­enced the sever­ity of the Sumatra earth­quake, which took place on Decem­ber 26, 2004. Find­ings of a study on sed­i­ment samples found far be­low the seabed are now de­tailed in a new pa­per led by Dr An­dre Hüpers of the MARUM-Cen­ter for Mar­ine En­vir­on­mental Sci­ences at Uni­versity of Bre­men – pub­lished in the journal Sci­ence.

    The earth­quake, meas­ur­ing mag­nitude 9.2, and the sub­sequent tsunami, dev­ast­ated coastal com­munit­ies of the In­dian Ocean, killing over 250,000 people.

    Re­search into the earth­quake was con­duc­ted dur­ing a sci­entific ocean drilling ex­ped­i­tion to the re­gion in 2016, as part of the In­ter­na­tional Ocean Dis­cov­ery Pro­gram (IODP), led by sci­ent­ists from the Uni­versity of Southamp­ton and Col­or­ado School of Mines.

    Dur­ing the ex­ped­i­tion on board the re­search ves­sel JOIDES Resolution, the re­search­ers sampled, for the first time, sed­i­ments and rocks from the oceanic tec­tonic plate which feeds the Sumatra sub­duc­tion zone.  A sub­duc­tion zone is an area where two of the Earth’s tec­tonic plates con­verge, one slid­ing be­neath the other, gen­er­at­ing the largest earth­quakes on Earth, many with de­struct­ive tsuna­mis.

    Ex­ped­i­tion co-leader Pro­fessor Lisa McNeill, of the Uni­versity of Southamp­ton, says: “The 2004 In­dian Ocean tsunami was triggered by an un­usu­ally strong earth­quake with an ex­tens­ive rup­ture area.  We wanted to find out what caused such a large earth­quake and tsunami and what this might mean for other re­gions with sim­ilar geo­lo­gical prop­er­ties.” 

    The sci­ent­ists con­cen­trated their re­search on a pro­cess of de­hyd­ra­tion of sed­i­ment­ary min­er­als deep be­low the ground, which usu­ally oc­curs within the sub­duc­tion zone.  It is be­lieved this de­hyd­ra­tion pro­cess, which is in­flu­enced by the tem­per­at­ure and com­pos­i­tion of the sed­i­ments, nor­mally con­trols the loc­a­tion and ex­tent of slip between the plates, and there­fore the sever­ity of an earth­quake.

    In Sumatra, the team used the latest ad­vances in ocean drilling to ex­tract samples from 1.5 km be­low the seabed.  They then took meas­ure­ments of sed­i­ment com­pos­i­tion and chem­ical, thermal, and phys­ical prop­er­ties and ran sim­u­la­tions to cal­cu­late how the sed­i­ments and rock would be­have once they had trav­elled 250 km to the east to­wards the sub­duc­tion zone, and been bur­ied sig­ni­fic­antly deeper, reach­ing higher tem­per­at­ures.

    The re­search­ers found that the sed­i­ments on the ocean floor, eroded from the Hi­m­alayan moun­tain range and Tibetan Plat­eau and trans­por­ted thou­sands of kilo­metres by rivers on land and in the ocean, are thick enough to reach high tem­per­at­ures and to drive the de­hyd­ra­tion pro­cess to com­ple­tion be­fore the sed­i­ments reach the sub­duc­tion zone. This cre­ates un­usu­ally strong ma­ter­ial, al­low­ing earth­quake slip at the sub­duc­tion fault sur­face to shal­lower depths and over a lar­ger fault area – caus­ing the ex­cep­tion­ally strong earth­quake seen in 2004.

    Dr An­dre Hüpers of the Uni­versity of Bre­men says: “Our find­ings ex­plain the ex­tent of the large rup­ture area, which was a fea­ture of the 2004 earth­quake, and sug­gest that other sub­duc­tion zones with thick and hot­ter sed­i­ment and rocks, could also ex­per­i­ence this phe­nomenon.

    “This will be par­tic­u­larly im­port­ant for sub­duc­tion zones with lim­ited or no his­toric sub­duc­tion earth­quakes, where the haz­ard po­ten­tial is not well known.  Sub­duc­tion zone earth­quakes typ­ic­ally have a re­turn time of a few hun­dred to a thou­sand years. There­fore our know­ledge of pre­vi­ous earth­quakes in some sub­duc­tion zones can be very lim­ited.”

    Sim­ilar sub­duc­tion zones ex­ist in the Carib­bean (Lesser An­ti­lles), off Iran and Pakistan (Makran), and off west­ern USA and Canada (Cas­ca­dia).  The team will con­tinue re­search on the samples and data ob­tained from the Sumatra drilling ex­ped­i­tion over the next few years, in­clud­ing labor­at­ory ex­per­i­ments and fur­ther nu­mer­ical sim­u­la­tions, and they will use their res­ults to as­sess the po­ten­tial fu­ture haz­ards both in Sumatra and at these com­par­able sub­duc­tion zones.

    Con­tact for fur­ther in­form­a­tion: 
    Dr. An­dre Hüpers
    Tele­fon:0421-218 65814
    E-Mail: ahuepers@marum.de

    Original publication: 
    An­dre Hüpers, Marta E. Torres, Sa­toko Owari, Lisa C. McNeill, Brandon Dugan, Timothy J. Hen­stock, Kitty L. Mil­liken, Ka­ter­ina E. Pet­ro­notis, Jan Back­man, Sylvain Bour­lange, Farid Che­male, Jr. Wen­huang Chen, To­bias A. Colson, Mar­ina C.G. Fre­derik, Gilles Guèrin, Mari Hama­hashi, Brian M. House, Tamara N. Jeppson, Sarah Kachovich, Abby R. Kenigs­berg, Mebae Kur­anaga, Stef­fen Kut­ter­olf, Freya L. Mitchison, Hideki Mukoy­oshi, Nisha Nair, Kevin T. Pick­er­ing, Hugo F.A. Pouder­oux, Ye­hua Shan, In­sun Song, Paola Van­nuc­chi, Peter J. Vrolijk, Tao Yang, Xixi Zhao: Re­lease of min­eral-bound wa­ter prior to sub­duc­tion tied to shal­low seis­mo­genic slip off Sumatra. Sci­ence 2017, DOI: 10.1126/science.aal3429

    Weitere Informationen:

    http://www.marum.de/en/Discover/Researchers-drill-deep-to-understand-why-the-Sum...

    Bilder

    IODP Ex­ped­i­tion 362 IODP crew and Co-chief Scientists Lisa McNeill and Brandon Dugan help carry the last coresci­ent­ists ex­am­ine the work­ing and archive halves of a freshly split core.
    IODP Ex­ped­i­tion 362 IODP crew and Co-chief Scientists Lisa McNeill and Brandon Dugan help carry t ...
    Photo: Tim Fulton, IODP-JRSO
    None

    IODP Ex­ped­i­tion 362 sci­ent­ists ex­am­ine the work­ing and archive halves of a freshly split core.
    IODP Ex­ped­i­tion 362 sci­ent­ists ex­am­ine the work­ing and archive halves of a freshly split cor ...
    Photo: Tim Fulton, IODP-JRSO
    None

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    Englisch

     

    IODP Ex­ped­i­tion 362 IODP crew and Co-chief Scientists Lisa McNeill and Brandon Dugan help carry the last coresci­ent­ists ex­am­ine the work­ing and archive halves of a freshly split core.


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    IODP Ex­ped­i­tion 362 sci­ent­ists ex­am­ine the work­ing and archive halves of a freshly split core.


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