Tuyin tip cac cdng trinh nghien cdu Dja chit va Dja vit ly biin - Tap IX 69
M 6 HINH DAN H 6 I TINH TOAN CAC THAM s6 BAN DAU SONG THAN DO NGUYfeN NHAN B6NG D X T TRONG CHU TRINH DANH GIA
DO NGUY H I £ M , THifiT HAI DO SONG THAN.
Nguyen Hdng Ldn"\ Pham The'Truyen'^'
Phdng Vdt ly khi quyen vd Dgng luc bien-Vien Dia chdt vd Dia vat ly Bien
TOM TAT:
Sdng thdn Id mdt hien tugng thiin tai nguy hiem. Sdng thdn dugc tao ra do su chuyen ddng ddt ngdt ddy bien, su trugt Id ddy bien hodc do cdc khd'i ddt dd, khdi bdng, vdt the cd kich thudc Idn rai xud'ng bien. Bdi bdo ddt vdn de nghien cvtu su liin quan giita cdc tham sd sdng thdn vdi cdc tham sd'ddng dd't sit dung md hinh ddn hdi. Ket qud tinh todn cho phep xdc dinh hinh dang, dd cao, chu ky sdng ban ddu hinh thdnh ngay sau khi xdy ra ddng ddt.
M d D A U
Viet Nam cd horn 3000 km dudng bd biin va nam trong vung biin cd nguy co xay ra sdng thdn. Sdng thdn trong khu vuc Biin Ddng xay ra tuong ddi hilm va chua cd ddy du bdng chdng xac thuc v l viec sdng thdn da xay ra vd gdy anh hudng din vung ven biin Viet Nam [1]. Viec nghien cdu ddnh gid dd nguy hilm sdng thdn cung nhu tinh todn trudc cdc rui ro thiet hai gdy ra do sdng thdn gdp phdn ndng cao kha ndng dng phd khi sdng thdn xay ra ddng thdi lam giam nhe thiet hai gdy ra do sdng thdn ddi vdi cdc khu dd thi, khu ddn cu, khu cdng nghiep ven biin.
Quy trinh danh gid thiet hai do sdng thdn gdy ra dd'i vdi cdc vung ven biin cd thi dugc trinh bay theo so dd sau [10]:
Xac djnh vung nghien ciiu, d6 nguy hilm ddng ddt.
Xac dinh ddng ddt -N kich ban, cac tham Vl sd ngudn ddt gay.
Tinh toan hinh dang, cac tham sd song hinh thanh
ban ddu.
• < - > •
Tinh toan lan truyin song thdn. Thdi gian lan truyen, d6
cao cue dai tai vung ven bd.
Hinh 1: Sadd ddnh gid thiet hai do sdng thdn.
Cdc md hinh tinh todn cho tdng phdn trong so dd tren ddng vai trd quan trgng dl ddnh gid tdng thi thiet hai do sdng thdn gdy ra dd'i vdi vung ven biin. Trong dd viec tinh toan md hinh dua ra ddnh gia v l hinh dang, tinh chd't sdng hinh thanh ban ddu dua theo cac tham sd kich ban cua mdt trdn ddng ddt ngoai biin ngay sau khi xay ra ddng dd't dugc sd dung ldm dd lieu ddu vdo cho vide tinh todn lan truyin sdng thdn tren biin.
70 Tuyin tip cac cdng trinh nghiin cCru Dja chit va Dja vit ly' biin - Tip IX CO S 6 L t THUYET
1. Ngudn gdc song than, danh gia cac tham so dong d^t.
Mdt trong nhttng nguydn nhdn gdy ra sdng thdn Id do ddng dd't ngodi biin, thdng thudng do cac trdn ddng dd't tai cdc ddt gay dang chdm nghich, thudn (dip-slip) khi ma cd su dich chuyin len tren cua mdt canh ddt gay va chuyin ddng xudng dudi cua cdnh ddt gay kia. Theo cdc nghidn cdu thuc nghiem va md hinh da chi ra rang vdi cdc trdn ddng dd't cd cudng dd (magnitude) Idn hem 7 dd Rich te thi cd kha ndng gdy ra sdng thdn nguy hilm ddi vdi vung ven biin [9].
Theo thd'ng ke cua tac gia Pham Van Thuc [1, 2] tai khu vuc ria phia ddng Biin Ddng cd su lien he gitta sd ddng ddt N vd cudng dd M theo cdng thdc sau:
LogN=4.692-0.566M (1) Ngoai ra dd boat ddng ddng dd't khu vuc qudn dao Trudng Sa va Idn cdn thudc khu
vuc Biin Ddng cd dang:
LogN=3.41-0.45M (2) Nhu vdy tai ria phia ddng Biin Ddng dd boat ddng ddng dd't Idn hon nhilu so vdi
cac khu vuc khac va vdi cudng dd ddng dd't cd thi Idn tdi 7-8 dd Rich te.
Viec xdc dinh md'i lien he thdng ke gitta cdc tham sd ddt gay (dd dai doan ddt gay, dien tich, gdc nghieng...) vdi cudng dd trdn ddng dd't xay ra rdt quan trgng cho muc dich ling dung thuc t l trong viec tinh todn dd nguy hilm, thiet hai do sdng thdn gdy ra. Tac gia [3] da dua trdn viec thdng ke horn 500 trdn ddng ddt (vdi cudng dd td 5.0 din 9.6 dd) trong dd cd 69 trdn ddng dd't xay ra ngoai biin dl dua ra cac cdng thdc vl md'i lien he dudi ddy.
Dd dich chuyin trung binh u (cm) cd thi tinh theo M (cudng dd) va S (dien tich bl mat ddt gay) theo cdng thdc:
MQ = uSu, Log Mg = 1.5 M + 16.1
trong dd M^ tmh bang dyn.cm (Hanks & Kanamori 1979).
Mdi lien he gitta cdc tham sd doan ddt gay gdy ra ddng dd't: L(km), S(km^), vdi cudng dd trdn ddng ddt xay ra trdn doan ddt gay dd dugc xdy dung cho cac trudng hgp khac nhau cua cac loai ddt gay khdc nhau:
a) Ddt gay dang chdm nghich, thuan tren da't lien (xem hinh 2):
LogL = 0.50M-1.86, 6 = 0.13, 6.0<M<7.5
LogS = 0.78M 2.56, 6 = 0.21, 6.0<M<7.5 (3) LogW = 0.28M - 0.70, 6.0<M<7.5
Logu = 0.72M 2.82, 6.0<M<7.5
Tuyin tip cac cdng trinh nghidn cdu Dja chit va Dja vit /j? biin - Tip IX
1000 p
100 r
10 r
.1 . T T 1 . 1 1 I I . 1 . ( • • • • | M ' l | l < l ' | , i . , 1 l l , l | . l l l | , < . , 1000 1000
100 100
10 10 r S
i l i . i l i i n l , i i i l i i i i l i . i , l i i . i ' , , i . l , . . i L i , l (
6 6.5 7 7.5 8 8.5 9 9.5 M -*
"i""r""i""i""i""i' (b)
n-«9
I...,.., 1000
100
•5 10
I - - - I I. . . . I , .
1000
1(10
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-T
..."
6 6.5 7 7.5 8 8.5 9 9.5 M -»
1000
100
10
71
6 6.5 7 7.5 8 8.5 9 9.5 M -»
Hinh 2: Suphdn bd bie'n thien cua L (km) theo M dd'i vdi ditt gdy trugt bdng, [3].
10000
1000
100
' • - - ^ T - ^ ' - ' ^ T ' ^ " '
- (!)
ICit
x>
t
•..>.XJ...J.J..»,
; .'.'rrjTT.'Tyn-.-.TTT'r'
* A' r *
i...t...i...*.i.t...i.ij.
T ' ^ - ' T " ' -
-
- :
100OO
tooo
10000
1000
100 100 y^,f
10 10
rtT-l-jT-T-ri-J-l'l-T-t' yn-r t-T-ITTT
r n*i3
).S 7 7.5 8 e.S 9 9.S
^ J.il.1.. .i-l-lJ.4.».*.iJ.J.J..<.i~I-hJ.J.«.I..w
6 6.5 7 7.5 8 M - »
. 10000
1000
100
j.i...j..i a * .
e.5 9 9.5
100000 L W
F n<l1
10000 r
100000
10000
1000
Hinh 3: Suphdn bdbie'n thien cua S (km^) theo M ddi vdi ddt gdy trum chdm thudn, nghich tren ddt lien. [3].
72 Tuyin tip cac cdng trinh nghien ctki Dja chit va Dja vit lyt biin - Tip IX b) Durt gay dang chdm nghich, thuan dudi bien (xem hinh 2,3,4):
LogL = 0.55M 2.19,6 = 0.18, 6.7<M<9.3 LogS = 0.86M 2.82,6 = 0.25, 6.7<M<9.3
LogW = 0.31M - 0.63, 6.7<M<9.3 Logu = 0.64M 2.78, 6.7<M<9.3
(4)
Ngoai ra theo [5] chu ky Idn nhd't trong tdp hgp sdng do ddng dd't gdy ra cd mdi lien he vdi cudng dd ddng dd't theo cdng thdc sau:
LogT„=-0.2+0.23M (5)
2 . 5 -
o 2 -
1.5-
1
2.5
*
CB
.2 1.5
1 3.5
2.5
1.5
I I I I I I I I I I I 1 I I I I I I I " • ' I " " I " " I • • 1 ' J
Dlp«llp (nMucllon)
I I I I I I I H I I I I I I I I I I I I I I I I I I I I I I I I I I I
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II I II I I
I • . .
6.5
•'•••''••••'••••'••••'••••
7JS 6 M
8.5 9 9.6
Hinh 4: Suphdn bdbie'n thien cua L(km), w(km), u(cm) theo M, [31.
Tilp theo dd cdc tham sd ddt gay ddng dd't dugc tinh toan theo cudng dd ddng ddt dua tren cdc cdng thdc thdng ke dugc sd dung trong md hinh ddn hdi d l tinh cdc tham sd sdng thdn hinh thanh ban ddu do ddng ddt.
Tuyin tip cac cdng trinh nghien curu Dja chit va Dja vit lyf biin - Tip IX 73 2. Mo hinh tao song ban ddu
Theo cac cdng trinh [6, 7, 8] sdng ban ddu hinh thanh khi xay ra ddng ddt dugc tinh toan dua trdn md hinh ddn hdi. Kit qua tinh toan da giai thich dugc mdi lien he gitta cdc tinh chdt cua sdng vdi cdc tham sd cua trdn ddng ddt nhu: dd sdu chdn tieu, hudng, kich thudc ddt gay, hudng va vdn tdc chuyin ddng cdc canh ddt gay.
Bdi todn tinh cdc tham sd sdng thdn dua trdn md hinh ddn hdi dugc xdy dung nhu sau: Ldp nude ddng nhd't dugc ddt nam trdn ldp vd Trai Ddt d day biin ddng nhdt ddn hdi vd ca hai nam trong trudng trgng luc khdng ddi. Gia sd H - Dd day ldp nude (dd sdu), ngudn chdn tidu ddng dd't ndm tai dd sdu h dudi day biin, ngudn ddng dd't la doan ddt gay dugc md phdng dudi dang nhu sau (hinh 5).
Hinh 5: Md hinh ngudn ddng ddt.
Phuang trinh Lame tinh din anh hudng cua trgng trudng dugc vilt dudi dang sau:
Vograd{divu)- g.divu -k^^d^u/dt^ 0<z<H,
F(r,0,z,t) + ( F / - V^)grad[divu)+ F/AM - gdivu -1 = 0^^/81^ z> H, (6) Tuong dng vdi cdc dilu kien bien nhu sau:
[v,'divZ-guX.^=0, kL=w+o=kL//-o'
du,. du,
— - I - - — - dz dr z=W+0
1 du, dUg
r dG dz = 0,
(7)
r=//+0
(v^-2Vs')divZ + 2Vs'^-gu,
= ^hdivZ-guX__„_,.
Jz=H+0 P\
74 Tuyin tap cac cdng trinh nghien cdu Dia chat va Dia vit ly biin - Tip IX 6 ddy u{r,9,z,t)={u,.,u^,Ug} vector dich chuyin; g gia td'c trgng trudng; k vector dan vi theo hudng z; p^ - mdt dd nude biin; FQ - vdn td'c dm thanh trong nude bien; F Ham ngudn chd'n ddng; yO,, F^, F, mdt dd, vdn td'c truyin sdng dgc va vdn tdc truyin sdng ngang trong ldp day biin; true O^.- hudng xud'ng dudi day biin. Cac gia tri ban ddu cac trudng dugc cho bang 0 khi t=0.
AP DUNG
Viec tinh toan thd nghiem dugc dp dung dd'i vdi gia dinh ddt gay nam d ria phia ddng Biin Ddng giap Philippin cd vi tri nhu binh 6.
SMih C U n S(9 Idurfs
C H I N A
H o n g ^ o n f ) C n h l i u n i *
P H I L I P P I N E S
OfMfl
M U M ! Mrt
K0«71 (AOWI^i • • »
Hinh 6: Vi tri ddt gdy si/dung trong mo hinh.
Tuyin tip cic cdng trinh nghien cCru Dja chat va Dja vit ly biin - Tip IX 75^
Ddt gay dugc gia dinh thudc loai chdm nghich hoac chdm thudn. Cac tham sd thd nghiem dugc tinh cho trudng hgp ddng ddt cd cudng dd 7.5 dd Rich te. Vdn tdc truyin sdng dgc Vp=8 km/gidy, vdn tdc truyin sdng ngang V,=5 km/gidy. Theo cdng thdc (4) ta tinh dugc cdc tham sd doan ddt gay gdy ra ddng dd't:
L= 86 km; S= 4300 km^ W= 50 km; u= 104 cm.
Kit qua tinh todn chi ra rang dd sdu ngudn ddng ddt, gdc nghieng ddt gay va kilu chuyin ddng cua ddt gay anh hudng Idn din gid tri dd cao sdng hinh thanh ban ddu tren mat biin tai nod xay ra ddng dd't. Cdc ylu td cua ngudn ddng dd't khac nhu vdn td'c lan truyin sdng, thdi gian dich chuyin hdu nhu khdng anh hudng din bien dd cung nhu dang sdng hinh thanh ban ddu. Dilu nay phu hgp vdi kit qua tinh todn theo [8].
Kit qua tinh todn cd thi md phdng sdng ban ddu cd mat cdt ngang dang clip vdi chilu cao sdng tai tdm dat 3m vd cd dang hinh sin giam ddn vl ria vung nghien cdu.
Sdng ban ddu cd budc sdng khoang 250 km, chu ky sdng Idn nhd't dat gia tri gdn 33 phdt.
Kl^T LUAN:
Td nhiing kit qua nghien cdu tren cd thi dua ra mdt sd kit ludn nhu sau:
1. Vide xdc dinh mdi lien he thuc nghiem, thdng ke cdc tham sd ddt gay lien quan din cdc tham sd ddng ddt ddng vai trd quan trgng trong viec xac dinh ngudn gdy ra sdng thdn.
2. Td cdc tham sd cua trdn ddng dd't cd thi tinh todn va dua ra mdt sd cdc tinh chdt cua sdng hinh thanh ban ddu tren mat biin nhu chu ky sdng, sd sdng, bien dd cung nhu hinh dang sdng. Cac ylu td' tinh dugc, se dugc dung trong md hinh lan truyin sdng thdn nhu la cac tham sd' ban ddu, dl tinh todn thdi gian lan truyin sdng va dd cao sdng tai vung ven bd.
3. Viec tinh toan dua tren cdc nghien cdu vl ddt gay, cdc tham sd ddng dd't. Do vdy rd't cdn bd sung them cdc danh gid thd'ng ke cac dai lugng tren cua cdc chuyen gia nghien cdu vl ddng ddt ngoai biin cung nhu cdc sd lieu thdng ke vl cac trdn ddng dd't trong lich sd gdp phdn ndng cao dd chinh xdc cua kit qua tinh todn.
TAI LifeU THAM KHAO:
1. Pham Van Thuc. Sdng thdn d biin ddng va vdn dl du bao. Tuyin tdp bdo cdo khoa hgc Hdi nghi khoa hgc biin "Biin ddng-2000" Tr. 35 i-365.
2. Pham Van Thuc. Nhdng dac dilm cua sdng thdn khu vuc Biin Ddng. Tap chi Khoa hgc va Cdng nghe biin T. 1 (2001), sd 2. Tr. 52-64.
3. Papazachos B. C , Scordilis E. M., Panagiotopoulos D. G., Papazachos C. and Karakaisis G. F. GLOBAL RELATIONS BETWEEN SEISMIC FAULT PARAMETERS AND MOMENT MAGNITUDE OF EARTHQUAKES. Geophysical Laboratory, School of Geology, Aristotle University of Thessaloniki.
4. Thomas C. Hanks and William H. Bakun. A billinear source-scaling model for M-log A observations of continental erathquakes.
5. Mitrina M.R., Pelinovski E.H.. Md'i lien he gitta chu ky sdng thdn tai vung ven bd vdi kich thudc ngudn ddng dd't. Vien vdt ly dng dung, Vien HLKH Nga, 1979. Tr. 1218-
1219. (Tilng Nga).
76 Tuyin tip cac cdng trinh nghien cdu Dja chat va Dja vit ly biin - Tip IX 6. Gusiakov V.K. Mdi lien he gitta sdng thdn vdi cac tham sd ngudn ddng ddt. Nha xudt
ban: VHLKH Nga, 1974. "Cac vd'n d l todn hgc va dia vdt ly", Tr. 118-140.
7. Padiapolski G.C. Su tao thanh sdng dai do ngudn ddng ddt. Tap chi: "Vdt ly dia cdu", VHLKH Nga, 1968, t r . 1-24.
8. Martruk An.G., Chubarov L.B., Sokin lU.L. Md hinh sd tri sdng thdn. Nha XB khoa hgc, VHLKH Nga, chi nhdnh Siberi. 1983. 170 tr.
9. EM 1110-2-1414. Water Level and Wave Heights for Coastal Engineering Design.
Chapter 4, TSUNAMI.
10. Quy c h l bdo tin ddng ddt, canh bdo sdng thdn. Ban hanh theo Quylt dinh sd 264/2006/QD-TTg ngay 16 thdng 11 ndm 2006 cua Thu tudng Chinh phu.
SUMMARY
ELASTIC MODEL APPLIED TO EVALUATING TSUNAMI PARAMETERS CAUSED BY EARTHQUAKE IN THE PROCESS OF
TSUNAMI RISK AND HAZARD ASSESSMENT.
Nguyen Hong Lan, Pham The Truyen Institute for Marine Geology & Geophysics.
Tsunami are generated by sudden movements of the ocean bed or by objects such as subaerial landslides and bolides falling into the ocean. Relationship between the faults' characteristics and parameters of initial waves tsunami are evaluated by using elastic model in this report. Results of this experiment let to determine the form, the maximum height and period of initial wave of tsunami.
Ngudi sita bdi: TS Bui Xudn Thdng Trung tdm Khi tugng thuy vdn Bien.
