SEISMIC ZONNING MAPS OF VIETNAM FOR THE BUILDING CODEa Nguyen Dinh xuyen, Nguyen Le Minh, Nguyen Quoc Cuong, Nguyen Tien Hung, Tran Thi My Thanhtmythanh@igp.vast.vn; tmythanh@yahoo.com

a. Institute of Geophysics – Vietnam Academy of Science and Technology

The seismic zoning maps of Vietnam were included in the Vietnamese Building Code TCXDVN 375-2006: Seismic Design Standards in 2006 for the first time. The maps were characterized with the Peak Ground Acceleration(PGA) with a return period of 500 years on ground type A. In 2012, the Association of Structure and Construction Techniques of Vietnam required to implement seismic design in seismic regions for ground type B to meet thecurrent requirements of the design and construction of structures for seismic safety in Vietnam. To meet the above requirements, another version of seismic zoning map for the territory of Vietnam under the MSK-64 scale has been
built by using and updating the 2006’s seismic zoning map for Vietnam, with an exceedance probability of 10%, 5%, 1% and 0.5% in 50 years, respectively (corresponding to a return period of 250, 500, 1000, 5000, and 10000
years, respectively). These results are based on the catalogue of earthquakes and the map of the seismogenic zone map for Vietnamese territory then calculated with the CRISSIS99 program based on probabilistic analysis
methods, by using the vibration attenuation relationship proposed by Nguyen Dinh Xuyen and Tran Thi My Thanh.

Tectonic Faults in Viet Nam
UnderofN-S

In the past, earthquakes with intensity of 8 andVietnam

haslarger in the MSK-64 scale (estimated magnitude MS = 6-

developed a NW-SE trending fault system, a N-S7) occurred in Hanoi (1278, 1285), in lower section of thetrending fault system and a NE-SW trending fault

Ma river (1635) and at the Ca river (1821). More recently,system (Nguyen Dinh Xuyen et al. 2004). Amongin 1935 and 1983, earthquakes of magnitude MS 6.7 - 6.8

these systems, the NW-SE trending fault system isoccurred in the north west of Vietnam, namely the Dienthe most significant, including the Red River (SongBien Phu earthquake ( November 1935) and the Tuangiao

Hong), Chay River (Song Chay), Ma River (Song Ma)

earthquake (June 24, 1983). Both destroyed and heavily

and Son La faults. Most of the large and moderate

damaged many houses, buildings and agricultural lands incompression,

the
the

tectonicstressnorthwestoffield

Ground Motion Attenuation Relationships

earthquakes in the northwest region of Vietnam havean area covering about 13,000 km2. Many people died oroccurred in this fault system. The N-S trending fault

were injured by the collapse of houses. These were thesystem is also an important system. The main fault oflargest earthquakes recorded in Viet Nam since 1900. Inthe system is the Dien Bien – Lai Chau fault, the fault

addition to the above earthquakes, several moderate

shown in Figure 1 at the western termination of theearthquakes that were known by many people haveSong Hong, Son La and Song Ma Faults. On the otheroccurred in recent years. These include the Ta Khoa

hand, the NE-SW trending fault system is rather

earthquake with magnitude of M = 4.9 in 1991, the Lai

inactive.

chau earthquake with magnitude of M = 4.9 in 1993, theThe NW-SE trending system includes major faults that

Muong Luan earthquake with magnitude of M = 4.8 incould produce large magnitude earthquakes. In
particular, the Red River Fault zone, represented inThe PGA attenuation curves and the observed data

1996, the Lai Chau earthquake with magnitude of M = 4.8Fig. 1. Seismic tectonic map of Vietnam

earthquake in 2001 and the Dien Bien earthquake with

Viet Nam by the Song Hong and Song Chay Faults, atmagnitude of M = 5.3 in 2001. The earthquake catalogue

over 900 km length rivals New Zealand’s Alpine Faultup to 2010 including the data sources: Historical up toin length, and could potentially produce similar

1900, the Seismological network of VietNam and others

magnitude earthquakes. It is a major tectonic feature,(ISC, NEIC, NOAA, …). The epicenter's distribution map

separating the Indochina and South China blocks.

in Vietnam and adjacent area is shown in Fig 1.

Local Magnitude Scale

Potential source zones

The laws of seismicity manifestation serve the basis for delineation of seismogenic (source) zones

Fig. 2: The seismic source zones in VietnamSeismogenic faults are considered potential seismic source zones (Fig.2).The width of the zones is taken

and estimation of their seismic characterestics (Mmax, depth h, earthquake occurrence frequency). The

equal to one of the destruction zone related to the faults; for a single fault it is about 10 km.

following laws of seismicity manifestation in Vietnam were identified in results of study on earthquake

Magnitude of maximum possible earthquake in the zones is estimated bydistribution, focal characterestics...

-Geological extrapolation method: the maximum earthquake which occurred in any part of fault may arise

Relation between earthquake focus and tectonic structure: The focus of the earthquakes Ms≥4.5 arein remain parts of this fault and also in the other faults with similar tectonic condition.

closely connected with the deep faults seperating the main tectonic units.

-Gumbel's asymtotic distribution of extrems G3

Distribution of earthquakes in depth: Although the faults may reach to the depth of 40-50 km the-Correlation between upper limit magnitude and dimension of fault segment established for Vietnam
Msmax ≤ 2logL + 1.77

earthquake focus depth don't exceed 30 km and varie from zone to zone.Maximum focus depth h=25-30 km

Msmax ≤ 4logH + 0.48

are observed in Sonla,Ma River fault zones and in northeast border of Hanoi depression,in the Red Riverfault zone the focus depth is h≤25 km,in the other fault zones h≤15-20 km.
Magnitude-frequency relation

L,H- fault segment length and active layer thickness in km.

Gurenberg-Richter formulaAttenuation law
Seismic hazard maps
The PGA map of 500, 5000 and 10000 years return period on ground type A have been calculated andcompiled in scale 1:1.000.000 (Fig 3, 4, 5, 6).

2006: Applied the Campbell 97 attenuation law (Campbell, 1997).
2013: The Vietnam attennuation law (Nguyen Dinh Xuyen and Tran Thi My Thanh, 1999).

The relationship between the new local magnitude
obtained in this study and the duration magnitude
currently being used in the Vietnam official
earthquake bulletin.

Fig. 3. The PGA map, 500 years - Campbell
W. Kenneth, 1997

Fig. 4. The PGA map, 500 years

Fig. 5. The PGA map, 5000 years

Fig. 6. The PGA map, 10000 years

References
Nguyen Dinh Xuyen, Tran Thi My Thanh, 1999, Defining a peak ground motion attenuation relationship for Vietnam. Journal of Earth Sciences,Vol.21, 3, 207-213
Campbell W. Kenneth, 1997, Empirical near-source attenuation relations for horizontal and vertical components of peak ground acceleration, peak ground velocity, and Pseudo-absolute acceleration response spectra, Seismological research letters, 68(1), pp. 154-179