ASSESSMENT OF VIỆT
ON THE BASIS OF DETERMINISTIC APPROACH
1CAO ĐÌNH TRIỀU, 2GIULIANO
F. PANZA, 2A. PERESAN, 2F. VACCARI,
2F. ROMANELLI, 1NGUYỄN HỮU TUYÊN, 1PHẠM
1LÊ VĂN DŨNG, 1MAI XUÂN BÁCH, 1THÁI ANH TUẤN, 3CAO ĐÌNH TRỌNG
1Institute of Geophysics, VAST, 18 Hoàng
Quốc Việt, Cầu Giấy, Hà Nội;
2Dept of Earth Sciences, University of Trieste, Italy;
3Peoples Friendship University of Russia, Moscow
Abstract: The catalogue of earthquakes in the
The bilateral project
"Establishing approaches to increase
earthquakes preparedness in Việt Nam (Index 10EE1)" between Department
of Earth Sciences, University of Trieste, Italy and Institute of Geophysics,
VAST, Việt Nam had been approved on July 10-11, 2002. The main objective of the
Cooperation Project is to enhance the capability in decreasing vulnerability of
- Characterization of the
seismotectonic framework of Việt
- Realistic modelling of seismic ground motion as the base for pre-disaster activities (hazard prediction, risk assessment, and their mapping); and
- Intermediate-term medium-range earthquake prediction, providing the base for earthquake preparedness.
This bilateral project
brings a big long-term benefit in the field of seismic study in Việt
- Establishing the Việt Nam catalogue of the earthquakes;
- Identification of seismic zones; and
- Seismic hazard assessment
II. THE EARTHQUAKE CATALOGUE OF VIỆT
1. The Catalogue of Earthquakes of the Institute of Geophysics to the end of 2003
The Catalogue of Earthquakes of the Institute of Geophysics (VNCAT), VAST to the end of 2003 was established on the basis of three data sources as follows:
- Catalogue of Historical Earthquakes up to 1900.
- Catalogues of Macroseismic Data, investigating in public documentation (1900-1976).
- Earthquakes recorded from
seismic network of Việt
The VNCAT catalogue reports an estimation magnitude for each event. Magnitudes can be of different type (from intensity, from surface waves, local magnitude, and duration magnitude) depending on the source data. The reference magnitude is MS.
2. Comparison of different catalogues for establishment the sufficient catalogue of earthquakes on the Việt Nam territory to the end of 2003
Sufficient catalogue of earthquakes on the Việt Nam territory established to the end of 2003 is based on documentary sources and methodology of comparison of different catalogues as follows [15, 16]:
A. Software used for comparison of different catalogues
The following softwares are used for comparison of different catalogues:
- EDCAT - to edit catalogue and transform it into standard format;
- CATAL - to select sub-catalogues, merge and compare catalogues;
- HIST - to make histograms for any parameter of catalogue.
These softwares provide various facilities for data analysis.
B. Comparison of different catalogues and
establishing the catalogue of earthquakes in Việt
a. The comparison
performed among the NOAA, ISC and NEIC data sets for the Việt Nam region. We
had compiled an earthquake catalogue for Việt
In order to perform the magnitude comparison, the events common to different catalogues are identified according to the following rules: a) time difference Dt £ 1.00 Min; b) DLat = DLon £ 0.50 degree; and c) DM £ 9.00; DH £ 999.00 km (no limitation imposed on magnitude or depth differences).
- The ISC catalogue is preferable for the time interval after 1994, since it contains more events while only a few are missing with respect to the other data sets.
- Before 1994 NOAA is preferable to NEIC, since NEIC contains only 47
additional events, but all of them have epicenter outside Việt
- NOAA contains also information about historical events (before 1900 - 34 events).
b. Enlist all the data sets available and description (area, time interval, number of events, type of magnitude, etc.).
Description of the new VNCAT catalogue: by time interval from 1278 to 2003 and covering an area approximately within Lat: 4.63 - 23.30 N, Lon: 100 - 118 E. The catalogue contains about 2610 events with Ms: from 0 to 7.50; depth from 0 to 350 km.
the NEIC-VNCAT catalogue NE20.dat (its format - 20), we have compiled an earthquake
catalogue for Việt
the ISC-VNCAT catalogue IS20.dat (its format - 20), we have compiled an
earthquake catalogue for Việt
Description of the VNCAT-NOAA catalogue: We compare the Việt Nam catalogue and NOAA one. The catalogue compiled for the Việt Nam territory spans the time interval 1137-2003 and covers an area approximately within Lat: 4.63 - 23.30 N; Lon: 100 - 118 E. The catalogue, structured according to the standard 20 binary format, is stored in the file NO20.DAT. The starting point has been provided by the Việt Nam catalogue, referred as VN hereinafter, has been checked and corrected for time ordering and formal mistakes (e.g. seconds = 60), events from the NOAA dataset (SEASIA) have been selected for the Việt Nam territory: Lat: 4.63 - 23.30 N; Lon: 100 - 118 E. The time interval covered by the NOAA data is 1900-1995. The catalogue is obtained adding the events from NOAA to those reported in the VN catalogue. Comparing the catalogues we observe that there are 793 events in NOAA that are not reported in VNCAT. In this catalogue used kind of magnitude: Mb, Ms, Ml, Mw and MR = Rautian magnitude Kondorskaya and Shebalin, 1982.
Therefore a new catalogue has been then obtained adding the events from NOAA to those reported in the VNCAT catalogue. Formally identical events have been removed from the initial VNCAT and NOAA catalogues. Then the NOAA data are merged into the VNCAT data, giving the priority to the VNCAT catalogue. Practically, whenever similar events are found only events from the VNCAT catalogue are retained . If for such events no magnitude is reported, then the maximum magnitude provided by NOAA is placed in the MP position. The analysis of the completeness of the resulting catalogue VNCAT-NOAA seems to indicate that it can be considered rather complete for magnitude of 3.0 and above.
The sufficient catalogue of
earthquakes in Việt
III. IDENTIFICATION OF SEISMIC ZONES
1. Distribution of earthquakes
Although some earthquake occurrences have been recorded at high magnitude, but research work was poorly conducted, in some cases, the seismic depth and magnitude could not be determined properly. Parameters of some earthquake events were determined at the highest reliability as follows [3, 9, and 10]:
1. Earthquake occurrence in
the Điện Biên area (1935) - M=6.8, occurring in 23 h 22' (Hà Nội time)
2. Earthquake in the Lục Yên (Yên Bái) 1953-M=5.4.
3. Earthquake in the Lục Yên (Yên Bái) 1954-M=5.4, the earthquake epicenter was located quite near to that occurring in 1953. These two earthquake events occurred at the same seismic intensity but the width of isoseismic (1954) was narrower and its length was longer.
4. Earthquake in the Bac
Giang, 1961-M=5.6, which occurred at 16 h 58' (Hà Nội time) in
5. Earthquake in Sông Cầu,
1970-M=5.3. Sông Cầu earthquake occurred in
6. Sông Cầu earthquake in 1972-M=5.3. The event happened on
7. Tuần Giáo earthquake
1983-M=6.7. It happened in 14 h of
8. The Mường Luân Ms5.0
9. The Thin Tóc Ms5.3
2. Identification of various levels of the earthquakes
The level of the earthquake activity has been divided into 5 ranks:
1- Feeble, MS < 4.0;
2- Low, MS = 4.0 ¸ 4.9;
4- High, MS = 6.0 ¸ 6.9; and
5- Large, MS ³ 7.0.
On the Việt Nam territory, there were only earthquakes of the first 4 ranks: feeble, low, moderate and high ones.
3. Identification of active fault zones and seismogenic fault zones
This analysis focused on determining active fault zones, which are earthquake sources. Six groups of seismogenic fault zones characterized by potential to generate earthquakes were determined. They are as follows:
1- Non-seismogenic fault zones, underneath that there had not been any earthquake generated so far.
2- Feeble seismogenic fault zones, that are active fault zones where earthquakes are generated with the magnitude less than 4.0 (MS < 4.0).
3- Low seismogenic fault zones, that are active fault zones where earthquakes are generated with the magnitude of from 4.0 to 4.9 (MS = 4.0 ¸ 4.9).
4- Moderate seismogenic fault zones, that are active fault zones where earthquakes are generated with the magnitude of from 5.0 to 5.9 (MS = 5.0 ¸ 5.9).
5- High seismogenic fault zones, that are active fault zones where earthquakes are generated with the magnitude of from 6.0 to 6.9 (MS = 6.0 ¸ 6.9).
6- Large seismogenic fault zones, that are active fault zones where earthquakes are generated with the magnitude equal or more than 7.0 (MS ³ 7.0).
The main seismogenic fault zones with the earthquake magnitudes more than 5.0 on the Việt Nam territory and surrounding areas have been determined.
4. Seismogenic zones on the Việt Nam territory and surrounding areas
a. Principles of identification of seismogenic zones
For identification of seismogenic zones the following principles are used:
1. The possible earthquake genesis zones are that active faults or a system of tectonic active faults where the tectonic movement was quite differentiated. The possibilities of earthquake occurrences in deep faults depend on their scope, characteristics and intensity of tectonic activities. The most likely earthquake occurrences (seismic activities are stronger, more regularly happened) are the marginal deep faults, which are bounded by the neotectonic structural zones. Earthquake could occur inside (internal part) of fault zones, but the intensity is weaker.
2. The width of earthquake genesis zones and relative location in comparison with the projection profile of the fault on the surface depend on the movement style, dipping direction of the faults and thickness of active layers.
3. Based on the extrapolation principles the faults are regarded as having the same characteristics and the possibility of earthquake genesis is the same.
The analysis resulted in classification of the study areas into seismogenic classes based on the combination of 4 factors, including: seismogenic fault zones, seismotectonic structure zones, focal source parameters, and seismic stream density zone [1-8, 17-28].
b. Seismogenic zones
According to the study results
obtained from the above-applied method 30 seismogenic zones could be determined
on the Việt Nam territory and surrounding areas: 1. The strongest earthquake
occurring in the Mường Tè seismogenic zone with the magnitude MS=7.1;
2. Phong Sa Li (MS=6.8); 3. Ou Dom Xai (MS=6.8); 4. Lai
Châu - Điện Biên (MS=5.3); 5. Xiao Jiang (MS=6.8); 6.
Sông Hồng (
IV. SEISMIC HAZARD ASSESSMENT OF VIỆT
Microseismic map for urban area has been only established for Hà Nội area. In this project the calculation and mapping of seismic hazard parameters are carried out by using the probabilistic analysis method (Cornell & Allin model) and Mc Guire program EQRISK to estimate PGA values (with probability 10 % of exceed within 20, 50, 100 years).
The international cooperation activities have been carried out on
dealing with SHA in region is the "Global Seismic Hazard Assessment Program in Continental
Asia - GSHAP" which has been
accomplished for the whole Asia Continental region at large scale. As the
primarily results, the Việt Nam territory has been roughly studied and
estimated the SHA. In general, the GSHAP is almost concerned with the marine
region and the northwest area of Việt
The Neo-Deterministic Seismic Hazard Assessment (DSHA) is approached in
The advanced characters of applying the DSHA approach possibly address aspects largely overlooked in the probabilistic seismic hazard assessment (PSHA) ones, such as:
- Direct evaluation of resulting maps in term of design parameters, without requiring the adaptation of probabilistic maps to design ground motions;
- Effect of crustal properties on attenuation;
- Derivation of ground motion parameters from synthetic time series, instead of using only simplified attenuation functions; and
- Generalization of design parameters to locations where there is little seismic history.
The procedure of Neo-Deterministic Seismic Hazard Assessment (DSHA) is
based on the computation of synthetic seismogram by the modal summation
technique and has been applied for several countries in the world. The hazard
is computed in terms of peak ground displacement (D), peak ground velocity (V)
and design ground acceleration (DGA) using the neo-deterministic approach
(Costa et al., 1993). The numerical synthesis of the ground motion, taking into
account the source, the wave propagation path and the local site geology,
represents the key element for the ground motion predictions. Complete P-SV and
SH seismograms are generated by modal summation technique (Panza, 1985; Florsh
et al., 1991) on a regular grid covering the whole Việt
*** Preparing the parameter of Fault Plane Solution file (*.fps),
Normally we define the seismogenic zones basing on fundamental data, such as: crustal structure, tectonic, seismotectonic and earthquake distribution in regarding to select one the most appropriate solution focal mechanism in each zone. In fact, to select the focal parameter that is extracted directly from detailed study on fault parameters. In this field, the active fault (seismic fault) is considered as the dominating the dynamics parameters of earthquake (focal mechanism), in addition of the experience and expert's mindset in considering the data set.
In order to define focal parameters, there are some of these parameters
extracted through seismograph by the wave-form inversion program, but these
results are not specific enough to present for entire seismogenic zones in Việt
*** Preparing the catalogue (*.dat)
It is established based on the basically source of Việt
*** In order to define the seismogenic zones (*.pos) we almost use the most recently upgraded date form Geological, Geophysical, Seismic, Seismotectonic database. For identification of seismogenic zones, the following principles are used:
- Possible earthquake genesis zones, that were the active faults or a system of tectonic active faults where the tectonic movement is quite differentiated. The possibilities of earthquake occurrences in deep faults depend on their scope, characteristics and intensity of tectonic activities. The most likely earthquake occurrences (seismic activities are stronger, more regularly happened) are marginal deep faults, which are bounded by neotectonic structural zones. Earthquake could occur inside (internal part) of faulted zones but the intensity is weaker.
- Width of earthquake genesis zones and relative location in comparison with the projection profile of the fault on the surface depending on the fault movement style, dipping direction of the faults and thickness of the active layers. Based on the extrapolations principle the faults are regarded as having the same characteristics and the same possibility of earthquake genesis.
- Analysis resulted in classification of the study areas into seismogenic
classes based on the combination of 4 factors, including: seismogenic fault
zones, seismic tectonic structure zones, focal source parameters, and seismic
stream density zone. According to the studied results obtained from the
above-applied method 30 seismogenic zones could be determined in the
Figure 1. Maximum
displacement (Dmax) in the mainland of Việt
Figure 2. Maximum velocity (Vmax) in the
mainland of Việt
Figure 3. Design Ground Acceleration (component for max between .sns and .sew)
V. DESCRIPTION OF SOME PRIMARY NEW RESULTS
Design Ground Acceleration (DGA) values are computed using synthetic response spectra together with design response spectra (the default is EC8) for A, B and C. Structural models in a default run are by definition soils A, since the lowest velocities are anyway larger than 900 m/s (other important factor such as PGV, PGD). The results showed in the Figs. 1, 2 and 3, where: D-Pick ground displacement; V- Pick ground velocity; and DGA- Design ground acceleration.
part of the Việt Nam mainland region (from Binh Trị Thiên structure unit to the
south) is a quite stable region with the lower DGA values (£ 0.020g) which correspond to the
IV-Earthquakes Intensity in MM scale. The highest DGA values in this region
belongs to the north part of the Hà Tiên structure zone with the maximum DGA
values of about 0.015-0.020 g (corresponding to earthquake intensity-IV in MM
scale). The southeast part of the Kon Tum and Đà Lạt zone are slightly higher
DGA values, which is approximately 0.040 g. The maximum DGA values of
The used documents for this
work are the latest data that have been possessed by the
1. The catalogue of
earthquakes on the
2. The Điện Biên 1935-M=6.8 and Tuần Giáo 1983-M=6.7 earthquakes are the two strongest ones that happened in the Việt Nam mainland in the 20th century. These events caused heavy losses to the Điện Biên and Sơn La provinces.
3. The total amount of 30 seismogenic zones could be determined on the territory of Việt Nam and surrounding areas; among that, the high rank of the earthquake activity are: Mường Tè (7.1), Xiao Jiang (MS=6.8), Sông Đà - Sơn La (MS=6.7), Sam Nua - Thái Hòa (MS=6.8), Sông Cả - Rào Nậy (MS=6.8), Lingshan - Hạ Long (MS=6.8), Huyền Nhai - Vạn Ninh (MS=7.5), Guangzhou (MS=7.3), and North Hoàng Sa (MS=6.8).
4. The scenarios of seismic hazard pictures for the whole territory are showed including: Mo-Magnitude distribution, M- Magnitude of seismogenic zones (after discrimination and smoothing), PGD- Pick ground displacement, PGV- Pick ground velocity, DGA- Design ground acceleration. The highest DGA value of the Việt Nam mainland is the Northwest Region, Bình Thuận province and a part of the Hà Nội Basin, with DGA in range of 0.150-0.350 g which correspond to the maximum earthquake intensity-VIII in the MM scale.
The authors would like to express special thanks to the Italian Ministry of Foreign Affairs, Italian Embassy in Hà Nội, SAND of ICTP, DST of University of Trieste, Việt Nam Ministry of Foreign Affairs, MOST, VAST and IGP of VAST for the help and facilities provided in the process of the project implementation.
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