Mqt trdn ddng dat Ion hay nhd My thudc vao nang luqng biln dang da tich luy duqc giai phdng ra d noi mat phay bi phd vd va tat nhien la cho bi pha vd cdng lan rdng thi nang luqng giai ph
Trang 1DONG DAT,
S6NG THAN
PHUN TRAO
Nguyen Xuan C h a n h
Ddng dit, sdng than vd nui liia phun ttdo
la nhimg hien tuqng thien nhien gay ra
nhilu thdm hoa cho con ngudi va ddi song
tren trdi dit Cac Men tuqng rit khac
nhau dd lai gidng nhau d chd xdy ra rit Mat thudng,
viing nay nhilu, vung kia it 6 noi nay, noi nq cd
khi hang ttdm, hang nghin nam khdng xay ra, nhung
cd khi lai din dap bet tran nay den ttan khac trong
mdt thdi gian ngdn, khd sdm bilt trudc
Cdc hien tuqng nay cd nguyen rMan sau xa la do
chuye'n dqng cac mang kien tao, cd lien quan vdi
nhau nhung khdng phdi dl dang tim ra 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 do
tim hieu sdng than va niii liia phun ttao
1 D O N G D A T
Ta da Met bl ngoai trai dit Id mdt ldp vd cung
iMung bi nut ra thdrM tung mdng ldn gqi la mang
kiln tao Cd tit ca 7 mang ldn vd ban mdt chuc mang
nhd mdi mang cd bl day tten 80 km, phin tten cung
khi cd luc tdc dung cd the bi Men dang cong hoac
gay vd Phin dudi cua cdc mangmlmhonbibiln dang
deo Dudi ciing la mqt ldp sen set, rdt ndng Cd mang
nhu Id mqt khdi dich chuyen chdm chap cd I cm din
13cm ttong mqt ndm Khi hai mang kl nhau chuyen
dqng doi vdi nhau chiing gay ra ling suit d chd mat
tilp xiic hai mang tiic la mat phay Mat phay la mdt
ldp khd ddy dat da ciing, nen tao ra 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 khi Id xo bi bdp vdo hay keo ra 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 ra Nang luqng biln dang tich luy duqc giai phdng rat nhanh d cho mat phay bi pha vo; cd nhiet luqng ldn tod ra va chdn dqng ldn lan tniyin: dqng dat bat dau Noi mat phay bi phd vd Id tieu diem cua dqng dat (focus hay hypocenter) Tu tieu diem gidng thing len mat dat la tdm chin (epicenter) Mqt trdn ddng dat Ion hay nhd My thudc vao nang luqng biln dang da tich luy duqc giai phdng ra d noi mat phay bi phd vd va tat nhien la cho bi pha vd cdng lan rdng thi nang luqng giai phdng ra cang ldn tiic la ddng dat cdng manh, sdng cua dqng dat keo dai (tii vdi chuc gidy den bon nam phiit)
Noi nay noi khac bi dqng dit, nhd cua cdng tiinh
bi do sap chinh la do sdng d noi mat phay bi phd vd lan truyln den vung dd
Trang 2Vdy sdng ddng dat nhu thi ndo va lan truyln Meo
each ndo?
Cd the xem dai the' trai ddt Id mqt qua ciu rdn
nhung khdng dong nhit Cf giiia tam la loi ttong, chu
yeu la sat tuy d nhi8t do cao binh thudng thi ndng
chay long, nhung vi dp suit ciing rat cao nen cd Me
xem la ran Ldi ngoai rat ndng nhung gdm cac chat
^0
nhe hon, xem nhu chdt ran d iMiet
do 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 ra nhieu tdng Ncri mat phay bi phd vd bat ddu phat sinh ra 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 ra 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 do trung binh cd 6km/ giay vd sdng S (Secondary - thu cdp hay Shear - cat)
la sdng ngang, dao dqng vudng gdc vdi phuong ttuyen sdng tdc do cd4km/ gidy KM truyen din gdn mat dat, sdng P den trudc, sdng S den sau
vd chii yeu la sdng S lam cho mat ddt dao dqng len xuong nen mdng nha ciia len xuong theo, nha cua lac lurdt de bi do" sap vi khi xay dung nhd cua ngudi
ta chu trqng ling suit theo chilu thang diMg rit it chu y su chiu dung ling suit theo chieu ngang Khi din mat dat hai sdng P va S chuyen thanh 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 ra sup dd nhd ciia Viec theo ddi cac sdng duqc thuc hien tuong ddi de ddng bdng cdc mdy do 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 do
cd qudn tinh ldn nen van diing yen Vi vdy khdng phai but ghi chuyen ddng ve ra dd thi tt8n gidy ma nguqc lai giiy chuyen ddng, biit ghi dirag yen Nhd nhilu may do dia
Trang 3thdi gian bat dau gM duqc ciia timg loai sdng cdng
nhu phuong hudng, bien do ngudi ta cd the xac dinh
cu the ti8u diem cung nhu tdm chin, do ldn cung
nhu nhieu dac diem khdc ciia dqng dat
2 SONG THAN
Sdng than la mdt loat cac dqt sdng d bien khi 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 khi 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 do ngu dan Nhdt dat ra 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 kia 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 kia thudng
gqi Id sdng dpng ddt dbien vi thuc chat nd lien quan
den ddng dat
Sdng thin sinh ra khi hai mang kiln tao kl nhau
chuyen dqng lai gan nhau hoac ra 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 khi ung suat qud ldn, mat ranh gidi bi
vd ra dot ngqt lam cho nude bien dben tten dich chuyen
nhanh theo chieu thdng diing
Dilu nay xay ra 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 ra 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 do 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
do thap, khd thay Cang vao gan din bd, nude can
nen budc sdng thu ngan lai cdn bien do sdng rit ldn
Chinh vi khi vdo bd bi8n do sdng rit ldn nen nude
bien dang thanh cdt cao dd* do nude vao bd (nude
dang len) phd hoai nhd cua v.v Sdng thdn cdn sinh
ra do bit cii nguyen nhdn nao lam cho nude bien bi
Hinh 2 Bong ddt ldm ddy bien ndng len hay ha xuong tao ra song thdn
Nhung trdn ddng dit ldn cd the gay truqt Id dat d day bien cung cd Me tao ra sdng than Khi truqt lo d day bien, muc nude bien dang can bang bi May doi manh do dat da dudi day bien chuyen ddng Tuong
tu khi nui liia dudi day bien boat ddng manh, mot khdi luqng Idn vat chat phun ttdo ra lam nude bien ddtngdt dang len gay ra sdng than SdngMdng Mudng tr8n mat bien Id do gid gay ra thirdng cd chu ky cd 5 din 20 giay va budc sdng cd 100 den 200 met Sdng thin cd chu ky dai M 10 phiit den 2 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 do ldn ma mat rit it ndng luqng Dieu nay cdn My thudc vdo do sau ciia nude bien Thi du,biencddqsaucd6km, sdng than cdthlchuyen dqng vdi toe do din 900kni/ gid ngang vdi toe do
Trang 4sang bd kia ciia Thai Binh Duong trong 1 ngay Tdc
do ciia sdng than cang nhd neu do sau nude bien
cang gidm Nhung nang luqng td'ng cdng truyln di
thi van giii nguyen Vi vdy cdng vao gan bd, do sau
nude bien cang giam thi do cao sdng (bien do) cang
ldn Do dd, mit thudng nhin ra bien tu xa khdng
thiy duqc sdng thin truyen din
Khi sdng Mdn d8n bd, nd nhanh chdng dang nude
18n that cao, ha nude xudng that thip gay ra sdng
phd vd hodc ddo sau Nhimg noi nhieu thuyen be
dau, vinh, ciia sdng, nhimg cong trinh kiln tnic dbien,
do nghieng ciia bd bien diu cd the lam thay dd'i sdng
than khi 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 do sdng day xa vao bd nhung khi
sdng than lui ra thi rat de cuon theo ngudi ra bien
Dac biet sdng Man d Vinh LiMya, Alaska nam 1958
do dit da truqt d day be sinh ra tao ra muc nude cao
Hinh 3 Ndi lira
1 Macma trong long
ddt
2 Dat dd
3 Ong ddn
4 Chdn nui lua
5 Mach ngang
6 Ong dan nhdnh
7 Lap tro dpng lai tu
truac
8 Sudn nui liia
9 Lop dung nham dong
lqi tie trudc
10 Hong ndi lua
11 Chdp ky sinh
12 Bdng dung nham
13 Ld thodt
14 Mieng nui lua
15 Mdy tro bui
dac biet den 525 met Khoa hqc hien nay 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
3 NUI L O A
Nlii Ilia Id nui cd mieng d dinh, qua do tung Mdi
ky cac chdt khoang ndng chdy vdi nhiet do va dp suat cao bi phun ra 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 thanh mii lua va mii liia boat ddng cimg la do chuyen ddng cdc mdng kien tao Khi hai mdng tiln lai gin nhau, dau miit ciia mqt mdng bi miit cua mang kia de len nen dim sau xuong dudi, dit da ndng chay thanh chat long Cac chat ndng chay nay 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
ra bi day len tten Mi tir mieng niii liia cM cd dung nham chay ra Neu ttong chat ndng chay
cd ca nhieu chat khi gay no thi niii liia vua cho dung nham chay ra, vira phun tto bui vd cdc loai kM len cao Thudng thi khi hai mdng chuyen ddng lai gan nhau, mang cd mut bi
de xudng la mdng dai duong vd truqt dudi mang kia Id mdng luc dia n8n cdc nui liia nay nam d gan dai duong thi du cac mii lua
d vanh dai liia Thai Binh Duong Hai mang kien tao chuyen dqng ra xa nhau, thudng la hai mang cd raiM gidi la rang dinh (ddt da nhd len d dudi dai duong) do dd khi
ra xa nhau tao ra khe hd cdc chat ndng chdy
d bdn ttong ttao ra ngodi theo khe hd bi nude ciia dai duong lam ngudi hinh thdrM ra mdt ldp vd mdi mdng dudi dai duong Nlu nhu
do dp sudt d ttong ldn, lam pha vd mqt chd ndo dd ciia ldp vd mdng nay de thodt ra thi
cd hoat ddng mii lua d day dai duong Nhimg chat phun trao ra d niii liia loai ndy se tao ra nhimg day dai duong mdi Khi rang dinh ddt
da iMd len d ddy dai duong la kha cao tten
Trang 5muc 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 ra nMeu hau qua
tai hai Cd nhilu kieu phun ttao mii liia vd nhieu
hien tuqng di kem: phun h d , phun trdo bung nd' ciia
nham Mach silicat cao, phun ttao nham thach silicat
thip, phun trao dung dich ndng, phun trao mdnh
vun, tto bui,phat raCOjVV Tit cadluldnguy Mem
cho ddi song con ngudi Kem theo niii lua phun ttao
thudng la dqng dit, dqt ndng dot ngdt, biin chdy ra nhu
ddng sdng, nude nong gin nhu sdi toa ra nhu suoi
Cdc loai kM Mniii liia phun ra 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 trong khi
mii lua phun ra, sau dd la CO; va SO; Nhung loai
khi chinh khac hay thay d nui lira phun ra la SH,
HCi, HE Anh hudng tai hai nhit ciia cac khi phun
ra Mniii lua la su chuyen M SO; phun ra thanh H2SO4
(axit sunMric) nhanh chdng ngung tu d ting binh
luu tao sol khi 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 nhau 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
nay rit phiic tap, ly thuyet xdy dung duqc chua hodn
chinh Thi du, khdng phdi tat cd cac tran ddng dat
xdy ra deu d gdn ranh gidi cac mang kien tao, md cd
den gin mudi phan tram xay ra 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 nay vl dqng dit,
sdng thin vd mil liia da cho phep giai Mich diing
duqc nhieu hien tirqng xay ra 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 ra nhimg ly gidi v l boat
dqng ciia con ngudi cd the gdy ra ddng dat ldn, thi
du ddng dit d Tii Xuyen duqc mdt so nha khoa hqc
gia thilt Id do xdy dung cac ho chua nude qua ldn d
cao nguy8n Tay Tang tao ra mot sue nen ldn d mat
phay gin dd, kich thich su pha vd mat phay gay ra
ddng dat
^ - - f ^ S * ^ ' i
O c e a n i c c r u s t
Lhhosphere
Aittienosphere
O c e s n i c - c o n
\ \ Lithosphere
" \ \ i
l i n e n t a l c o n v e r g e n c e
Hinh 4 Hai mdng dqi duang vd luc dia lqi gdn nhau 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
do Richter d Dien Bien Phu nam 1935, ddng dit 6,7
do Richter d Tuin Gido, Lai Chdu nam 1983 Theo cac tdi lieu luu trii thi trong khoang M 1915 den
1972 Viet Nam da tiing cd 5 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, nay ngung boat ddng
Ngay 15 Mang 2 nam 1923 cu lao Hdn Mudc Phan Thiet da xdy ra ddng dat lam rung chuyen nha ciia keo ddi 1 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 ra tiing dqt Den ngay
20 thdng 3 cung nam ddng dit vd nm lua lai xdy ra 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 ra dqng ddt, sdng than, nm liia vd phoi hqp vdi qudc te to' chiic cdc ttam do dac, quan ttac vl nhung hien tuqng nay
Rdt nhieu hoat ddng trong xa hqi ddi song hi8n nay nhu doi phd vdi anh hudng xiu ciia bien do'i khi 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 •
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