Tiiu hem: Cdc Khoa hgc vi Trdi ddt ISBN: 978-604-913-016-8
TONG QUAN VE DANH GIA D Q NGUY HIEM SONG THAN VUNG VEN BIEN VIET NAM
AN OVERVIEW OF TSUNAMI HAZARD ASSESSMENT IN COASTAL ZONE OF VIETNAM
Tran Thi My Thanh, Vien Vat ly Dja ciu
18 - Hoang QuIc Viet, Ciu Giiy, H i Ndi Email: tmythanh(a)yahoo.eom
Tdm tat:
Tir sau thdm hog sdng thdn gdy ra bai dgng ddt Sumatra Mw 9.3 ngdy 26-12- 2004 vdn di nguy hiim sdng thdn a viing ba biin Viit Nam tra thdnh mdi quan tdm lan a nuac ta. Mdt sd di tdi nghiin cim theo huang ndy da dugc tiin hdnh dem lgi nhung kit qud ddnh gid budc ddu vi nguy ca sdng thdn a viing ba biin Viet Nam. Trong bdi ndy chung tdi xem xet cdc kit qud nghiin cim vi xdc dinh, ddnh gid cdc viing ngudn ddng ddt sdng thdn tiim dn trong viing Biin Ddng, xdy dung cdc kich bdn ddng ddt diing tinh lan truyin sdng thdn di ddnh gid nguy ca sdng thdn a cdc viing ba bien vd hdi ddo Viet Natn. Bdi bdo ciing giai thiiu bdn do nguy hiim sdng thdn viing ven biin Viet Natn. Kit qud trinh bdy trong bdi cho thdy birc tranh tdng quan vi nghiin cim sdng thdn vd cung se gdp them cdc sd lieu mai phuc vu cdng tdc nghiin cim ddnh gid nguy ca sdng thdn a nuac ta.
Abstract:
After the tsunami caused by the Sumatra earthquake magnitude 9.3 on 26 December 2004, the tsunami hazards along the coast of Vietnam has become a major concern for our country. A number of research studies in tsunami risk along this coast has been undertaken and has produced some preliminary results to help evaluating this risk. In this paper, we will investigate the results of the studies to determine and evaluate the earthquake sources that can cause tsunami in the Eastern Sea. We will build some scenarios using the tsunami propagation model to evaluate the tsunami hazards along the Vietnam coast and the offshore islands. This paper also introduces the tsunami hazards map along the Vietnam coast. The result presents an overview of the tsunami research studies and help to gain a better understanding of tsunami risk in Vietnam.
I. M O DAU
Nhirng nim trudc diy Viet Nam cd it nghien cim ve ST, chii yeu li cic edng bd de cap den ehe do ddng dit d Bien Ddng v i co ehe hinh thinh sdng thin eua tie gii Pham Van Thue.
Tir sau thim hga ST Sumatra ngay 26 - 12 - 2004 (Mw = 9.3) vin de nguy hiem ST d cic viing bd bien nude ta trd thinh mdi quan tam ldn cua nhi nude v i nhin din. Trong giai doan nay d i tien hanh mot sd nghien cim cd tinh chit quy md va ehi tiet ve nguy hiem ST nhu eac de tii nghien cim cip Vien KH & CN Viet Nam: 'Nghien cuu dinh gia do nguy hiem ddng dat v i sdng thin d viing bd biin Viet Nam v i d l xuit cic giii phip cinh bio, phdng trinh', ( Nguyen Dinh Xuyen, 2005 - 2006); "Quy Uinh edng nghe dinh gii do nguy bilm sdng thin v i cinh bio nguy eo sdng thin tren viing ven biin Viet Nam (phii hgp yeu eiu eua he thing
cinh bio khu vyc)", (Trin Thj My Thinh, 2007 - 2008); Dy in KHCN cip Bd Tii nguyen vi Mdi trudng "Xiy dung bin dl cinh bio nguy co sdng thin eho eic vimg bd bien Viet Nam" (Vu Thanh Ca, 2007-2008); Dy in hgp tie khoa hgc giiia Vien Vat ly dja ciu ya Vien Khoa hgc dja chit vi Hat nhin Niu Di Lin "Dinh gii do nguy hiem vi nii ro sdng thin vi sy img phd ciia Viet Nam" (2007-2008); D I tii cip nhi nude "Nghien cim dinh gii do nguy hiem eua ddng dit vi sdng thin tren viing ven bien vi hii dio Viet Nam vi de xuat cac giii phip phdng trinh vi giim nhe hiu qui", (Biii Cdng Que, 2007 - 2009). Cic ket qua nghien cim mang tinh tdng quan ve do nguy hiem dgng dit vi ST vi eic bien phip phdng trinh tren viing ven bien Viet Nam.
II. NGUON GOC SONG THAN VA CAC KET QUA KHAO SAT SONG THAN O VUNG BO BIEN VIET NAM
Lich sir the gidi ghi lai nhieu trin ST thim khdc gay thiet hai khdn ludng ve ngudi vi ciia.
Ddng Nam A li khu vyc phit sinh nhieu sdng thin ngudn gdc khie nhau, giy nhirng thim boa sdng than ldn nhit, dien hinh nhu tran sdng thin ngudn kinh hoing ngudn gdc ddng dit xiy ra ngiy 26-12-2004 d Sumatra. Theo eic danh muc ddng dit sdng thin ciia NOOA (My), Indonesia, Philippin,... cho thiy ST giy thiet hai nghiem trgng trong lich su li it ed khi ning xiy ra d viing ven bien nude ta. Tuy nhien trong eic nghien cim eua eic nhi khoa hgc Viet Nam [14] cho thiy trong ljeh sir ed the di tirng xiy ra ST vdi cudng do manh. Viee tim hieu nguyen nhin vi khi ning giy ST d bd bien Viet Nam duge tien hinh bing eich thu thip, dieu tra trong nhin din nhirng sd lieu thyc ve hien tugng sdng thin, sdng bio da xiy ra d cic viing bd bien trong qui khir. Nguyen Dinh Xuyen [14] di dua ra 3 khi ning ST ljeh sir tai bd bien Viet Nam dd li bien Tri Cd (1978), bien Dien Chiu (cudi the ky 19 diu the ky 20) vi ST d Nha Trang (1923). Vii Thanh Ca [15] sau khi di tien hinh khio sat lai tai cie viing bien tren da dua ra ket luin tai bd bien Dien Chiu ed the li sdng thin cd nguyen nhin trugt Id dit. Nam 2007, cae tic gii Cao Dinh Trieu, Ngd Thj Lu [] eiing edng bd mdt sd ket qui ban diu ve phuong phip nghien cim cd ST. Tuy eic ket qui edn chua rd ring vi chic chin nhung ciing da mang den eho ngudi dgc mdt suy nghT ve khi ning ST di xiy ra tren bd bien nude ta. Nhu viy cic ket qui nghien cuu eho thiy ST cd khi ning da xay tren bd bien Viet Nam, vdi 3 nguyen nhin: do ddng dit, do trugt Id dit vi do niii lira sinh ra ST tren bien Viet Nam.
III. CAC VUNG NGUON CO KHA NANG PHAT SINH DONG DAT SONG THAN VUNG BIEN DONG
Khu vyc Ddng Nam A ndi chung vi Bien Ddng Viet Nam ndi rieng ed eiu tnic kien tao vi ljeh sir phit triln dja ddng lye rit dde dio vi phiie tap [8]. Vinh dai ddng DNA tren thyc te ed eiu tnic rit phire tap, bao gdm eic ming vi tieu mang cd ngudn gdc khie nhau. Chiing hoac thudc vl luc dja chiu A, hoac la cic minh vd phieu di tir phia An-Uc hoac Thii Binh Duong.
Sy tin tai va phit trien eua eic ddi tieh eye vinh dai ddng DNA la cie ngudn cd khi ning giy ddng dit va sdng thin manh. Dya vio dieu kien phit sinh sdng thin, tir cie tii lieu da cd ve kiln tao dja ddng lye khu vyc Ddng Nam A, ket qui nghien cuu boat ddng mii lira, khi nang trugt Id d viing them lue dja Viet Nam theo eic tii lieu dja chin thim dd diu khi, eic nghien cuu trude da xie djnh mdt sd viing ngudn cd khi ning giy sdng thin khu vyc Bien Ddng: Ddi hiit chim Manila; Ddi hiit chim bien Sulu gdm 2 doan vdi chieu dai 368km vi 642 km; Ddi hut chim Celebes; Ddi hut chim Makasart; Cie ddi hut chim bien Banda Bic vi Nam; Ddi dirt gay thim lue dja Bic Bien Ddng; Ddi dirt giy Tay Biin Ddng hay dirt gay kinh tuyen 109°';
Ddi dirt gay bic Borneo; Ddi dirt gay bien Jawa. Cie die trung cua cic viing ngudn dugc danh gia nhu sau (bing 1):
Tiiu ban: Cdc Khoa hgc ve Trdi ddt ISBN: 978-604-913-016-8
- Vi tri, phuong vj eua eic viing xic djnh theo ban dd bin dd.
- Hudng cim, gdc dd xie dinh theo mat eit phan bd chin tieu theo do siu.
- Ddng dit eye dai Mmax xie dinh theo cic phuong phip thdng ke Gumbel, ngoai suy dja chit vi quy md dirt giy.
- Tin suit ddng dit dinh gii theo quan he magnitude-tin suit, van tdc dich ehuyen eiia dut gay vi djch chuyen trong chin tieu.
Bing 1: Tham sl die trung eic viing ngudn ed khi ning giy ST viing Biin Ddng TT
1
2
3
4
5
6
7 8 9
10
Ten vimg ngudn Ming siu Malina - Doan 1
- Doan 2
Bie Bien Ddng
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- Nam Hii Nam-nam Tiy Bien Ddng
- Doan 1: nam Hii Nam-Tuy Hoi
- Doan 2: tir Tuy Hoi ve phia nam
Palawan - Doan 1 - Doan 2 Bien Sulu - Doan 1 - Doan 2 Bien Celebes
- Doan l(bie Sel. Sea) - Doan 2 (nam Sel. Sea)
Bien Banda bac Bien Banda nam Makasart
- Doan 1 - Doan 2
Bien Jawa (nam Bomeo) - Doan 1
- Doan 2
Die trung kien tao Ddi hut chim Dut giy trugt bing -
thuin Dirt giy trugt bing-
thuin
Diit gay nghjch Ddi hut
chim Ddi hut
chim Ddi hut
chim Ddi hut
chim Ddi hiit
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do dii, km 1153
292 1087
548 811
158 533 368 642 346 648 632 304
167 326 592 200
Mmax
8,2 7,3 7,2 7,0 6,1 6,6
6,9 7,7 7,5 7,8 7,4 7,8 7,8 7,2
7,0 7,4 7,8 7,1
B 0,88
0,80 0,80 0,80 0,90
0,86
0,86
0,86
0,86 0,86 0,86
0,86
V
(Mo=5.) 0,95
0,12 0,06 0.06 0,0103
0,42
0,42 0,75
0,33
0,57
IV. NGUY CO XAY RA SONG THAN - KET QUA TINH LAN TRUYEN SONG THAN VUNG BOf BEN VIET NAM
Nguy eo sdng thin viing tren viing bien vi hii dio Viet Nam, duge danh gii dya tren do cao vi thdi gian lan truyen eua sdng thin tir ngudn tdi eic vi tri ven bien va hii dio theo cac
nhu MOST, MIKE21, DELFT3D, INGV... Cae nghien cim cua Viet Nam ehu ylu sir dung chuong trinh MOST ( Method Of Splitting Tsunami model, do V.Titov vi Gonzalez xiy dyng) [28] de tinh lan truyin ST viing bien Viet Nam. MOST li mdt chuong trinh cd the md phdng lai mdt eich trgn ven mdt trin sdng thin duge tao ra bdi ddng dit: phit sinh, lan truyen. Chuong trinh dugc viet bing ngdn ngir Fortran vi chay tren he dieu hinh Linux hoac Unix. Tuy nhien chuong trinh chi cho ket qui tdt d nhiing noi ed do siu diy bien ldn hon 10m. Md hinh MOST hien dang duge sir dung rdng rii tren the gidi vi duge USGS diing tinh eho quy md toin eiu.
Sd lieu do siu diy bien Cd nhieu ngudn sd lieu do sau Bien Ddng. Ngudn sd lieu hien dang duge sir durig rdng rai nhit d Viet Nam hien nay li sd lieu dja hinh ET0P02 eua Hoa Ky.
Diy li ngudn sd lieu dja binh diy bien ciia Trung tim dii lieu bien Anh Qude (BODC - British Oceanographic Data Centre) vdi do phin giii 1' x 1'. Ngudn sl lieu niy cd do chinh xic chip nhan duge tai khu vyc giira Bien Ddng, noi ed do siu ldn. Tuy viy, d gin bd, sai sd do siu bien xae djnh theo bd sd lieu niy li rit ldn vi eic ket qui tinh toin thanh tao va lan truyen sdng thin tren bien sir dung do siu bien xie dinh theo ngudn sd lieu niy khdng the sir dung.
Cae kjch bin ddng dit sdng thin duge xiy dyng cho tirng viing ngudn rieng biet theo quan diem kjch bin gay sdng than cd the li mdt tran ddng dat manh hoac td hgp cua nhieu (hai hoac hon) trin ddng dit xay ra d eic vi tri lin can xic djnh khie nhau. Cae thdng sd ddng dit diing de tinh lan truyen sdng thin bao gdm toa do chin tim, chieu dii ddi dirt gay (L), chieu rdng ddi dirt gay (W), do sau chin tieu ddng dat (h), gdc cim {5), gdc trugt (2.), gdc phuong vi (6*). Magnitude eye dai dugc xie djnh theo eic edng thirc thyc nghiem lien quan tdi kich thudc dirt gay [Wells va Coppersmith (1994)]. Theo ket qui dinh gii nguy hiem sdng thin eua nhieu kjch bin ddng dat sdng thin (10 kjch bin (Nguyen Dinh Xuyen, 2006), 25 kjch bin (Vii Thanh Ca,), 35 kjch bin ( TMT), 10 kich bin (BCQ)) cho thiy Viing ngudn nguy hiem nhat li ddi hiit chim Manila. Thdi gian lan truyen ST tir ddi niy tdi bd bien Viet Nam khoing 2 gid. Khu vyc cd khi nang chju inh hudng manh nhit cua sdng than la khu vyc Trung Trung Bd, tir Di Ning tdi Quing Ngii.
V. BAN DO Yi() NGUY HIEM SONG THAN VUNG VEN BIEN VIET NAM
Bin dd nguy hiem sdng thin dugc xiy dyng tir ket qua tinh lan truyen sdng than eua cic tran ddng dat kich bin, nd bieu dien do cao eye dai mi sdng thin cd the dat tdi iing vdi cic chu ky thdi gian khae nhau. Bin dd do NHST duge xay dyng gidng nhu bin dd do NHDD theo ly thuyet Cornel (1968). Phuong phip tinh theo do NHDC dugc phat trien rdng rii trong nhirng nam 2000 [18, 21, 45, 57, 58, 59] thudng cd 3 budc tinh: 1) Xic djnh tham sd ciia vimg ddng dit va khoing sai sd. 2) Xac djnh phuong trinh (d day la do eao ST tai bd bien phu thudc vio ngudn). 3) Tinh xac suit.
Tiiu ban: Cdc Khoa hgc ve Trdi ddt ISBN: 978-604-913-016-8
Cic nghien cim trudc d i cho ket luan vl khi ning lan truyin sdng thin trong viing Biin Ddng cua eic ddng dit sdng thin xiy ra tren ddi hiit chim Manila la cd inh hudng ldn nhit tdi viing ven bien Viet Nam. Tir kit luan quan trgng nay cac kjch bin ddng dit xiy ra tren ddi Manila (bing 2) li duge chgn lim eo sd sd lieu tinh bin dd NHST vimg ven bien Viet Nam chu ky 950 nam (hinh 1).
Cac kit qui cho thiy khu vyc mien Trung la vimg ed khi ning chju inh hirdng sdng thin ldn nhit. Viing Tam ky, Quing Ngii do eao sdng len tdi hon 6m d chu ky 950 nim. Mien bic vi mien Nam li viing it bj inh hudng eua sdng thin.
Hinh 1: Bin dd do nguy hiem sdng thin viing ven bien Viet Nam ehu ky 950 nim Bing 2. Cae kjch bin ddng dit giy ST viing bien Ddng diing xiy dyng bin dd nguy hiem
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Chieu dii 201.3 243.9 234 223.5 242.3
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Gdc truot 90 90 90 90 90
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Mw 8.5 8.6 8.5 8.3 8.4
8.0 VI. KET LUAN
Cie ket qui nghien cim ST trong giai doan niy deu cd mdt sd ket luin ehung sau diy:
- Viing ngudn ddng dit giy ST nguy hiem nhit eho viing ven bien Viet Nam li ddng dat xiy ra tai ddi hiit chim Manila.'
- Viing bien mien Trung tir Ddng Hi tdi Phan Rang li khu vyc chju inh hudng ST ldn nhat tren viing linh thd Viet Nam. Khu vuc bien mien Bic v i mien Nam it ed khi ning bj inh hudng eua ST.
- Cin tiep tue nghien cim bd sung de cd the ning cao mirc do ehinh xic trong vin de xic djnh vi dinh gii cic tham sd viing nguon cd khi ning giy ST anh hudng tdi bd bien Viet Nam. Ciing nhu khi ning xiy ra sdng thin do cac nguyen nhin khie nhu trugt Id dit, phun trio niii lira ngim.
TAI LIEU THAM KHAO
1. Abe K. (1975). Reliable estimation of the seismic mement of large earthquakes; J.
Phys. Earth, 23, 381-390.
2. Aida, I. (1969). Numerical experiments for the tsunami propagation-The 1964 Niigata tsunami and the 1968 Tokachi-oki tsunami. Bull. Earthquake Res.Inst., Tokyo Univ.
47, 673-700.
3. Aida, I. (1988). Tsunami hazard probability in Japan. Bull. Seism. Soc. Am. 78, 3, 1268- 1278.
4. Bautista P. Leonila Ma., Kazuo Dike. Estimation of the Magnitudes and Epicenters of Philippine Historical Earthqukes. Teetonophysics 317 (2000) 137-169.
5. Donald L. Wells and Kevin J. Coppersmith (1994), "New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area, and surface Displacement", Bull. Seism. Soc. Am., 84(4), pp. 974-1002.
6. Geist, E. L., Tom Parsons, 2006. Probabilistic analysis of Tsunami hazards. Nutural hazard, 37, 277 - 134.
7. Le Nhu Lai, Phiing Van Phich, Biii Cdng Que, Nguyen The Tiep, Trin Vin Trj, Pham Ning Vii, Phan Trung Dien, Ngd Vin Dinh. Bin dd eau tnic kien tao viing bien Viet Nam vi kl can, ty le 1: 2000 000. D I tii KHCN-06 vi KC-09-24. Vien Dja chit va Dja vit ly Bien, Ha Ndi 2006.
8. Bill Cdng Que, Phiing Vin Phich. Ve nhiing yeu td cau tnic-kien tao chinh tren vimg bien Viet Nam vi ke can. Tap chi Khoa hgc vi Cdng nghe bien. 4(T.l), Ha Ndi 2001.
9. Titov V.V. and F. I. Gonzalez. 1997. Implementation and testing of the method of splitting tsunami (MOST) model. NOAA technical memorandum ERR PMER-112, Pacific Marine Environmental Laboratoty,
10. Nguyen Dinh Xuyen, 2006. Nghien cim dinh gia do nguy hiem ddng dit vi sdng thin d vimg bd bien Viet Nam va de xuit cic giii phap cinh bao, phdng tranh. Bao cao de tai cap VKHVN, luu thu vien Vien Vat ly Dja ciu.
