Động đất, sóng thần và núi lửa phun trào

I KHOA HOC DONG DAT, S6NG THAN VA NUI L O A PHUN TRAO Nguyen Xuan C h a n h dng dit, sdng than vd nui liia phun ttdo la nhimg hien tuqng thien nhien gay nhilu thdm hoa cho ngudi va ddi song tren trdi dit Cac Men tuqng rit khac dd lai gidng d chd xdy rit Mat thudng, viing nhilu, vung it noi nay, noi nq cd hang ttdm, hang nghin nam khdng xay ra, nhung cd lai din dap bet tran den ttan khac mdt thdi gian ngdn, khd sdm bilt trudc Cdc hien tuqng cd nguyen rMan sau xa la chuye'n dqng cac mang kien tao, cd lien quan vdi nhung khdng phdi dl dang tim duqc nhiing quy Mat chat che Ky trudc (Khoa hqc to' qudc so 4/2010) chiing ta da tun hieu ve ddng dit, d ky ndy chung ta xet Mem mqt so dac diem bieu hien ciia ddng ddt de' tu tim hieu sdng than va niii liia phun ttao D ldp khd ddy dat da ciing, nen tao luc ma sat rat ldn kim giu hai mang Vi vdy nang luqng lam cho hai mang chuyen ddng duqc tich luy lai Manh nang luqng biln dang d mat phay, tuong tu nhu nang luqng tich luy d Id xo Id xo bi bdp vdo hay keo Cii cang lau nang luqng tich luy cang ldn den mqt liic nao dd nang luqng bien dang qua ldn, ldp dat da ciia mat phay khdng chiu nd'i, mat phay bdt diu bi vd dmot cho xung yeu nao dd, roi nhanh chdng lan rpng Nang luqng biln dang tich luy duqc giai phdng rat nhanh d cho mat phay bi pha vo; cd nhiet luqng ldn tod va chdn dqng ldn lan tniyin: dqng dat bat dau D O N G DAT Noi mat phay bi phd vd Id tieu diem cua dqng dat (focus Ta da Met bl ngoai trai dit Id mdt ldp vd cung hay hypocenter) Tu tieu diem gidng thing len mat iMung bi nut thdrM tung mdng ldn gqi la mang dat la tdm chin (epicenter) Mqt trdn ddng dat Ion kiln tao Cd tit ca mang ldn vd ban mdt chuc mang hay nhd My thudc vao nang luqng biln dang da tich nhd mdi mang cd bl day tten 80 km, phin tten cung luy duqc giai phdng d noi mat phay bi phd vd va cd luc tdc dung cd the bi Men dang cong hoac tat nhien la cho bi pha vd cdng lan rdng thi nang gay vd Phin dudi cua cdc mangmlmhonbibiln dang luqng giai phdng cang ldntiicla ddng dat cdng manh, deo Dudi ciing la mqt ldp sen set, rdt ndng Cd mang sdng cua dqng dat keo dai (tii vdi chuc gidy den bon nhu Id mqt khdi dich chuyen chdm chap cd I cm din nam phiit) 13cm ttong mqt ndm Khi hai mang kl chuyen Noi noi khac bi dqng dit, nhd cua cdng tiinh dqng doi vdi chiing gay ling suit d chd mat bi sap chinh la sdng d noi mat phay bi phd vd tilp xiic hai mang tiic la mat phay Mat phay la mdt lan truyln den vung dd I thang 5-2010 KHOA H O C i nhe hon, xem nhu chdt ran d iMiet ndng chay Cd ldi ttong vd ngoai cMem 1/3 khdi luqng trdi ddt nhung cU cMem 1/6 the tich Cdc ldp vd d ben ngodi ldi My ldp ttong cung hoi sen set nhung todn bd cd thexem la vat ran bi phan nhieu tdng Ncri mat phay bi phd vd bat ddu phat sinh sdng ddng dat thirdng d sau ttong vd ttdi dat, can thi cdng sdu dudi mat dat 70km, loai trung binh cimg d sdu vdo khoang M 70 din 130km, cdn loai sau thi tren 130 km Sdng sinh noi mat phay bi pha vd la sdng co va truyen di ttong ttai dit dudi hai hang: sdng P (Primary - so cip hay Pressure - nen ep) la sdng dqc, cac hat vat chit (dit da) dao ddng dqc theo phuang ttuyen sdng vdi toe trung binh cd 6km/ giay vd sdng S (Secondary - thu cdp hay Shear - cat) la sdng ngang, dao dqng vudng gdc vdi phuongttuyensdng tdc cd4km/ gidy KM truyen Vdy sdng ddng dat nhu thi ndo va lan truyln Meo din gdn mat dat, sdng P den trudc, sdng S den sau each ndo? vd chii yeu la sdng S lam cho mat ddt dao dqng len Cd the xem dai the' trai ddt Id mqt qua ciu rdn xuong nen mdng nha ciia len xuong theo, nha cua nhung khdng dong nhit Cf giiia tam la loi ttong, chu lac lurdt de bi do" sap vi xay dung nhd cua ngudi yeu la sat d nhi8t cao binh thudng thi ndng ta chu trqng ling suit theo chilu thang diMg rit it chay long, nhung vi dp suit ciing rat cao nen cd Me chu y su chiu dung ling suit theo chieu ngang Khi xem la ran Ldi ngoai rat ndng nhung gdm cac chat din mat dat hai sdng P va S chuyen hai sdng bl mat Rayleigh vd Love truyen theo mat ddt, chung phdi hqp ldm cho mat dat dao ddng len xudng tiep tuc gay sup dd nhd ciia Viec theo ddi cac sdng duqc thuc hien tuong ddi de ddng bdng cdc mdy dia chin Thuc chat dd Id mdt vat kha nang treo tren mdt cai gia linh dqng Biit ghi gdn vao vat nang va he thdng giay ghi dat tren gia gdn vdi mat ddt Khi ddng dit xdy ra, sdng ddng ddt den lam cho mat dat rung ddng va he thong giay ghi rung ddng theo Con vat nang cd qudn tinh ldn nen van diing yen Vi vdy khdng phai but ghi chuyen ddng ve dd thi tt8n gidy ma nguqc lai giiy chuyen ddng, biit ghi dirag yen Nhd nhilu may dia chan nhu vay bd tri d nhilu noi, can cii vao Hinh Bong dat ngdy 8/11/2005 a mien Nam - nut chdn tudng ^0 I KHOA HOC thdi gian bat dau gM duqc ciia timg loai sdng cdng nhu phuong hudng, bien ngudi ta cd the xac dinh cu the ti8u diem cung nhu tdm chin, ldn cung nhu nhieu dac diem khdc ciia dqng dat SONG THAN Sdng than la mdt loat cac dqt sdng d bien cdn d xa bd tM nMn thiy khdng cd gi ndi bat nhung kM din gan bd tM rit cao va manh cd Me phd hoai nha cua, ldi cuon thuyen be, vat dung, ngudi, sue vat dat di rat xa bd Sdng than Mnh Mdnh mdt the tich rat ldn nude ddai duong bi dich chuyen nhanh chdng Tilng Anh sdng thdn Id tsunami bdt nguon M tieng Nhat tsu Id cang (tan) va nami la sdng (ba) Thuat ngu ndy ngu dan Nhdt dat vi hq thay rd tac hai ghe gdm ciia sdng thdn dang cao d cdng cdn liic dngoai khoi xa hq khdng thiy duqc Sdng than trudc tiing duqc coi la sdng thuy trieu vi cd tinh chat nhumdt dqt thuy trilu cue manh tiln vao Nhung thuc tl sdng Man khdng lien quan den thuy trieu Cac nha dia chat trudc thudng gqi Id sdng dpng ddt dbien vi thuc chat nd lien quan den ddng dat Sdng thin sinh hai mang kiln tao kl chuyen dqng lai gan hoac xa nhau, mat ranh gidi giua hai mdng vi ma sdt ldn n8n khdng dich chuyen theo ma bi bien dang chiu ung sudt ldn, tich luy nang luqng Den ung suat qud ldn, mat ranh gidi bi vdradot ngqt lam cho nude bien dbenttendich chuyen nhanh theo chieu thdng diing Dilu xay kM tieu diem ciia ddng dit d sdu dudi ddy bien ria cua mdng dai duong nam tren, ria ciia mang luc dia ludn xuong dudi Khi ddng dat xdy hai mdng tniqt theo mat phay nhung bi dinh lai mdt phan n8n d day dai duong cd mdt the tich ldn nhd len (sdng thin dang manh nude vdo bd) hoac chim xudng (sdng Min keo nude xa bd) Sdng thin the Men tren mat bien d bien cao hay thap va budc sdng (khoang each giua hai dinh song) ddi hay ngan O xa bd, nude sau budc sdng dai nhung bien thap, khd thay Cang vao gan din bd, nude can nen budc sdng thu ngan lai cdn bien sdng rit ldn Chinh vi vdo bd bi8n sdng rit ldn nen nude bien dang cdt cao dd* nude vao bd (nude dang len) phd hoai nhd cua v.v Sdng thdn cdn sinh bit cii nguyen nhdn nao lam cho nude bien bi dot ngdt dich chuyenmqt khoi ldn so vdi luc can bang Hinh Bong ddt ldm ddy bien ndng len hay xuong tao song thdn Nhung trdn ddng dit ldn cd the gay truqt Id dat d day bien cung cd Me tao sdng than Khi truqt lo d day bien, muc nude bien dang can bang bi May doi manh dat da dudi day bien chuyen ddng Tuong tu nui liia dudi day bien boat ddng manh, mot khdi luqng Idn vat chat phun ttdo lam nude bien ddtngdt dang len gay sdng than SdngMdng Mudng tr8n mat bien Id gid gay thirdng cd chu ky cd din 20 giay va budc sdng cd 100 den 200 met Sdng thin cd chu ky dai M 10 phiit den gid cdn budc sdng cd the din 500 km Vi sdng thin cd budc sdng khd ddi nen sdng cd the di rat xa vdi toe ldn ma mat rit it ndng luqng Dieu cdn My thudc vdo sau ciia nude bien Thi du,biencddqsaucd6km, sdng than cdthlchuyen dqng vdi toe din 900kni/ gid ngang vdi toe may bay phdn luc Sdng thin cd the di tii bd sang bd ciia Thai Binh Duong Tdc ciia sdng than cang nhd neu sau nude bien cang gidm Nhung nang luqng td'ng cdng truyln di thi van giii nguyen Vi vdy cdng vao gan bd, sau nude bien cang giam thi cao sdng (bien do) cang ldn Do dd, mit thudng nhin bien tu xa khdng thiy duqc sdng thin truyen din Khi sdng Mdn d8n bd, nd nhanh chdng dang nude 18n that cao, nude xudng that thip gay sdng phd vd hodc ddo sau Nhimg noi nhieu thuyen be dau, vinh, ciia sdng, nhimg cong trinh kiln tnic dbien, nghieng ciia bd bien diu cd the lam thay dd'i sdng than vao bd Muc nude d bd cd the tang len nhi8u met Trong nhimg trudng hqp sdng than manh nhung tu xa tdi nude cd the dang cao 15m, cdn sdng than gan tam chin cd the cao din 30m Sdng din diu tien khdng phdi la sdng manh nhat ttong chuoi sdng den Dien tich bi ngdp cd the vdo sau each bd hang ttam den hang nghin met Khi sdng than den nhd cua bi dd, ciia cai bi mat sdng day xa vao bd nhung sdng than lui thi rat de cuon theo ngudi bien Dac biet sdng Man d Vinh LiMya, Alaska nam 1958 dit da truqt d day be sinh tao muc nude cao Hinh Ndi lira Macma long ddt Dat dd Ong ddn Chdn nui lua Mach ngang KHOA HOC I dac biet den 525 met Khoa hqc hien chua du doan duqc sdng than, khdng the biet chinh xac d ddu vd liic nao sdng than sinh ra; nhung nhd tdng ket lich su vd cac phuong phdp md phdng, dac biet cd mdt he thdng qudc te phat hien vd du dodn hudng di ciia sdng thdn, nen phan ndo td' chuc duqc bdo ddng sdng thdn NUI L O A Nlii Ilia Id nui cd mieng d dinh, qua tung Mdi ky cac chdt khoang ndng chdy vdi nhiet va dp suat cao bi phun ngodi Liic phun ttao nhu vay la liic niii Ida boat ddng Tr8n thi gidi Indonesia, Nhat Ban vd My la ba nude cd nhi8u mii lua boat ddng nhat Nguy8n nhdn hinh mii lua va mii liia boat ddng cimg la chuyen ddng cdc mdng kien tao Khi hai mdng tiln lai gin nhau, dau miit ciia mqt mdng bi miit cua mang de len nen dim sau xuong dudi, dit da ndng chay chat long Cac chat ndng chay neu nhu tim duqc chd ttdng se Moat len tten Neu chd ttdng dd la d ttong mdt ngqn mil ilia da phun trudc day, tM dd la Men tirqng nui life phun ttao Neu cM la chat da macma ndng chay ttao bi day len tten Mi tir mieng niii liia cM cd dung nham chay Neu ttong chat ndng chay cd ca nhieu chat gay no thi niii liia vua cho dung nham chay ra, vira phun tto bui vd cdc loai kM len cao Thudng thi hai mdng chuyen ddng lai gan nhau, mang cd mut bi de xudng la mdng dai duong vd truqt dudi mang Id mdng luc dia n8n cdc nui liia nam d gan dai duong thi du cac mii lua d vanh dai liia Thai Binh Duong Hai mang kien tao chuyen dqng xa nhau, thudng la hai mang cd raiM gidi la rang dinh (ddt da nhd len d dudi dai duong) dd xa tao khe hd cdc chat ndng chdy d bdn ttong ttao ngodi theo khe hd bi nude ciia dai duong lam ngudi hinh thdrM mdt ldp vd mdi mdng dudi dai duong Nlu nhu dp sudt d ttong ldn, lam pha vd mqt chd ndo dd ciia ldp vd mdng de thodt thi 10 Hong ndi lua Ong dan nhdnh cd hoat ddng mii lua d day dai duong Nhimg Lap tro dpng lai tu 11 Chdp ky sinh chat phun trao d niii liia loai ndy se tao 12 Bdng dung nham truac nhimg day dai duong mdi Khi rang dinh ddt 13 Ld thodt Sudn nui liia Lop dung nham dong 14 Mieng nui lua da iMd len d ddy dai duong la kha cao tten lqi tie trudc 15 Mdy tro bui thane 5- pm n B B B B B W I A J.WWJB 15 I KHOA HOC muc nude bien, liic dd se hinh thdnh ddo mii Ilia Iceland Id mdt vi du cd ca mqt day dao mii Ilia rit Mudng xuyen hoat ddng Niii lua hoat dqng gay nMeu hau qua tai hai Cd nhilu kieu phun ttao mii liia vd nhieu hien tuqng di kem: phun hd, phun trdo bung nd' ciia nham Mach silicat cao, phun ttao nham thach silicat thip, phun trao dung dich ndng, phun trao mdnh vun,ttobui,phat raCOjVV Tit cadluldnguy Mem cho ddi song ngudi Kem theo niii lua phun ttao thudng la dqng dit, dqt ndng dot ngdt, biin chdy nhu ddng sdng, nude nong gin nhu sdi toa nhu suoi Cdc loai kM Mniii liia phun ciing thay dd'i rat nhi8u vl thdnh phin vd ndng do, phu thuqc vao tiing loai mii Ilia Hoi nude thudng cd nhilu nhit mii lua phun ra, sau dd la CO; va SO; Nhung loai chinh khac hay thay d nui lira phun la SH, HCi, HE Anh hudng tai hai nhit ciia cac phun Mniii lua la su chuyen M SO; phun H2SO4 (axit sunMric) nhanh chdng ngung tu d ting binh luu tao sol luu huynh dnh hudng xau den su hd hap ciia ngudi va sirM vat Nhu vay ddng dat, sdng than vd niii liia phun ttao cd li8n quan vdi rdt chat che vd ttong may chuc nam qua khoa hoc da cd nMeu tien bd ldn ttong viec phan tich, ly giai tung hien tuqng gan lien vdi chuyen ddng cua cdc mdng ki8n tao Tuy vay cdc Men tuqng rit phiic tap, ly thuyet xdy dung duqc chua hodn chinh Thi du, khdng phdi tat cd cac tran ddng dat xdy deu d gdn ranh gidi cac mang kien tao, md cd den gin mudi phan tram xay d giira mdng kiln tao Ddng dit ldn vua qua d Thanh Hai Trung Quoc la ddng dit vdi tieu diem nam d giiia mang kiln tao Nhung CO ban nhiing hieu biet Men vl dqng dit, sdng thin vd mil liia da cho phep giai Mich diing duqc nhieu hien tirqng xay M xua cho din gan day nhat nhu dqng dat d CM-Le, sdng than d Mdonexia, Thdi Lan cung nhu mii lua phun tto bui d Iceland Tli nhung ly thuylt da xay dung duqc cac nha khoa hqc cung da bat ddu dua nhimg ly gidi vl boat dqng ciia ngudi cd the gdy ddng dat ldn, thi du ddng dit d Tii Xuyen duqc mdt so nha khoa hqc gia thilt Id xdy dung cac ho chua nude qua ldn d cao nguy8n Tay Tang tao mot sue nen ldn d mat phay gin dd, kich thich su pha vd mat phay gay ddng dat •N!WS!ffii.lJ.WaB thang 5-2010 ^ f^S*^.' i Oceanic crust Lhhosphere Aittienosphere \ \ "\ \ Ocesnic-con linental convergence Lithosphere i Hinh Hai mdng dqi duang vd luc dia lqi gdn Ria ciia mdng dai duang ludn xuong mdng luc dia, mdng luc dia bi dpi len tqo thdnh niii Ilia Phdn bi dim vdo sdu bi ndng chdy vda phun len thdnh nui lua hoqt dqng vua bi nguoi di thdnh dd ndng chdy So vdi the gidi, ddng ddt d Viet Nam vao loai trung binh ylu Nhung d miln bdc Viet Nam cung timg ghi nhan nMlu ttan ddng ddt manh nhu ddng dit 6,8 Richter d Dien Bien Phu nam 1935, ddng dit 6,7 Richter d Tuin Gido, Lai Chdu nam 1983 Theo cac tdi lieu luu trii thi khoang M 1915 den 1972 Viet Nam da tiing cd dqt sdng thin Neu di vao khu vuc Da Lat, Ldm Dong ta de dang thay nhieu ngqn mii phia tren ngang bang, dd la nhung mii Ilia M xua, ngung boat ddng Ngay 15 Mang nam 1923 cu lao Hdn Mudc Phan Thiet da xdy ddng dat lam rung chuyen nha ciia keo ddi Mdn Thuy thu tren tdu Vacasamaru ciia Nhat phat bien mdt ddm khdi den dung dung kem theo mdt cdt hoi day dac bdc cao hon 2000 met cimg vdi nhttng tilng nd manh phat tiing dqt Den 20 thdng cung nam ddng dit vd nm lua lai xdy lan niia Nhu vay Viet Nam ciing can day manh nghien ciiu ve ddng dit, sdng thdn, niii liia; tham khao de lap ban dd du bao chinh xac han cac tam dilm co thi gay dqng ddt, sdng than, nm liia vd phoi hqp vdi qudc te to' chiic cdc ttam dac, quan ttac vl nhung hien tuqng Rdt nhieu hoat ddng xa hqi ddi song hi8n nhu doi phd vdi anh hudng xiu ciia bien do'i hau, xay dung cac hd chua nude, nhd may thuy dien, rMa may dien hat nhdn v.v ddi hdi phai tiln hdnh nghi8n ciiu dqng dit, sdng thin, mii liia d Viet Nam theo each hien dai, d quy md nhd nude • ... Cd nhilu kieu phun ttao mii liia vd nhieu hien tuqng di kem: phun hd, phun trdo bung nd'' ciia nham Mach silicat cao, phun ttao nham thach silicat thip, phun trao dung dich ndng, phun trao mdnh... nhilu nhit mii lua phun ra, sau dd la CO; va SO; Nhung loai chinh khac hay thay d nui lira phun la SH, HCi, HE Anh hudng tai hai nhit ciia cac phun Mniii lua la su chuyen M SO; phun H2SO4 (axit... cd mieng d dinh, qua tung Mdi ky cac chdt khoang ndng chdy vdi nhiet va dp suat cao bi phun ngodi Liic phun ttao nhu vay la liic niii Ida boat ddng Tr8n thi gidi Indonesia, Nhat Ban vd My la