Đặc điểm phát triển kiến tạo đới đứt gãy lai châu điện biên bản tóm tắt tiếng anh

VIETNAM ACADEMY of SCIENCE and TECHNOLOGY
Institute of geological sciences
X  W



Van Duc Tung



DEVELOPMENT CHARACTERISTICS OF THE
LAI CHAU-DIEN BIEN FAULT ZONE

Major: Geotectonic
Code: 62.44.55.05


ABSTRACT OF THESIS OF DOCTORATE IN geological








Ha Noi - 2011
Research finished at Department of Tectonic - Institute of Geological
Sciences-VIETNAM ACADEMY of SCIENCE and TECHNOLOGY

Supervisors:

1. Dr. Tran Van Thang
Institute of Geological Sciences - Vietnam Academy of Science and
Technology

2. Assoc. Prof. Dr. Tran Thanh Hai
Hanoi University of Mining and Geology

Examiner 1: Prof. Dr.Sc. Dang Van Bat
Hanoi University of Mining and Geology

Examiner 2: Assoc. Prof. Dr. Sc. Phan Van Quynh
Hanoi University of Science - Vietnam National University Hanoi

Examiner 3: Dr. Pham Van Hung
Institute of Geological Sciences - Vietnam Academy of Science and
Technology

This thesis is going to be defended at the council of doctorate thesis
examiners of Institute of Geological Sciences - Vietnam Academy of
Science and Technology on………date………month………year 2011

This thesis can be found at Hanoi National Library or Library of Institute
of Geological Sciences - VIETNAM ACADEMY of SCIENCE and
TECHNOLOGY
INTRODUCTION

Study urgency
The Lai Chau - Dien Bien fault is a large scale fault which plays an
important role in structural formation and geotectonic development of

the North-West region of Vietnam.
In the modern period, the fault active zone is quite active where
many related geological disasters have occurred along the Lai Chau -
Dien Bien fault zone such as earthquake, landslide, mudflow which
cause great damage to people of Lai Chau and Dien Bien provinces.
This fault zone has been studied by many geologists, both domestic
and overseas researchers. However, there are still many issues need to be
further clarified such as the position of tectonic center, the formation and
development of the zone. Especially, the segmentary feature of the fault
zone and the role of the segments in the formation and development of
various types of geohazards should be interpreted to provide scientific
basis for proposal of hazard prevention and mitigation solutions.
Based on the above-mentioned issues, the doctoral student had
selected study topic “Development characteristics of the Lai Chau-
Dien Bien fault zone".
The study objective: clarification of the tectonic and geodynamic
features, historical development process of the Lai Chau - Dien Bien
tectonic fault zone and the relationship between the modern activity of
the zone with some typical geological hazards.
Study tasks
- Study of formation and development history of the Lai Chau -
Dien Bien fault zone through the combination study of geotectonics and
deformation characteristics in order to clarify the environment of
geodynamics of the fault zone in each stage of its development.
- Study of the characteristics of the Lai Chau - Dien Bien fault's
segments in the modern period on the basis of differences in
characteristics such as geomorphological, geological, geological
structural, dynamic zone, movement mechanism, magnitude and
movement rate and expressions of modern activities of the fault
segments.

- Restoring of processes of the regional tectonic development
related to the development stages of the Lai Chau - Dien Bien fault zone.
- Study of the conditions of formation and development of some
geological hazards associated with the modern activity of the Lai Chau -
Dien Bien fault zone.
Scientific and practical importance of the study
- Clarification of the history of formation and development in stages
and deformation phases, restoration of the tectonic and geodynamic
regime for each stage.
- Contribution to confirmation of the role of intraplate tectonics in
in study of regional geological structure and geodynamics.
- Provision of scientific basis for determining the causes and
mechanism and for zonation of hazard risk: earthquake, landslides,
mudflows, etc.
- Provision of scientific basis for planning development and
exploitation and sustainable utilization of territory and proposing
solutions to prevent and mitigate natural disasters for socio-economic
development and enhancing national security, etc.
Thesis data and documents: the following are three main data
sources:
Study results and data of projects and studies in which the student
has participated since 1999:
- Report “Survey for Lai Chau hydropower plant: Investment
preparation stage (2000), Feasibility and technical design (2004),
Technical design (2008); “Supplementary geological survey for Dien
Bien Phu town” (2002); Survey for Nam Na hydropower plant 2 (2009).
- Independent governmental studies; KC 08.10; ĐTĐL.2009T/09;
Studies of Vietnam academy of science and technology.
Published archive documents:
- Data and documents of geological and mineral mapping of

different scales (1:500,000; 1: 200,000; 1: 50,000; 1: 25,000)
- Special reports, doctoral and master theses and articles related to
the study contents.
Field data, results and analysis which fully or partially made by
the student since 1999:
Results of processing of 300 geological and geomorphological
survey points and tectonic fracture measurement data in 18 sections
through the Lai Chau - Dien Bien fault and adjacent; collecting and
processing of more than 735 measurements of scratches and slipping
surfaces; results of detailed study of three key areas: Lai Chau , Na Pheo
and Dien Bien on the Lai Chau - Dien Bien fault; analysis of 80 samples
for orientation and micro structure study along with petrographic
analysis; five samples for relative age analysis by the method of pollen
spores in the Quaternary Division-Institute of Geological Sciences, 4
samples for analysis of absolute age by means of LA-ICPMS U-Pb in the
laboratory of the University of Tasmania, Australia; results of detailed
study with air photos for 10 areas along the Lai Chau - Dien Bien fault.
Study object and area
The study object is the Lai Chau - Dien Bien fault zone in Vietnam
territory within the coordinates:
21
0
08’ - 22
0
41’ Latitude
102
0
48’ - 103
0
20’ Longitude

New discovered study points
1. The Lai Chau - Dien Bien fault zone was formed in the early-
middle Jurassic (198-158 million years) in the first phase of deformation
and intraplate nature. In the history of development since the formation
of the fault zone until now it has gone through five phases of
deformation.
2. For the first time it had been discovered the Mio-Pliocene
sediments and their deformation in the Lai Chau - Dien Bien fault zone,
which gave proof about sinistral slipping activity phase in the Pliocene-
Quaternary period.
3. For the first time the tectono-petrography assemblage 7a, a light
colored granite complex with 33-35 million years old intruded into
foliation surfaces of 198 to 158 million years in Lai Chau formation, was
discovered.
4. It had been established a young deformation phase of thrust type
under the third deformation phase aged 33 to 28 million years developed
along the Lai Chau - Dien Bien fault zone in the Cenozoic.
5. For the first time the segmentary characteristics of the Lai Chau -
Dien Bien fault zone had been clarified with three development stages in
Vietnam territory.
Defensive points of view:
Point of view 1. The Lai Chau - Dien Bien fault zone was formed in
early-middle Jurassic and belongs to deformation phase 1 and went
through five phases of deformation with different deformation
mechanisms: the first phase is characterized by the plasticity which is a
shear zone, right-lateral strike-slip with the age of deformation of about
198-158 million years; the second phase is also characterized by plastic
deformation mechanism and also is a shear zone, right-lateral strike-slip
occurred in about 135-80 million years ago; the third phase was plastic to
brittle-plastic deformation mechanism and is characterized by reverse

fault with 33-28 million years old; the fourth phase is characterized by a
brittle deformation mechanism and is a right-lateral strike-slip fault zone
which began after deformation phase 3 and ended about 5.3 million years
ago; the last phase is also characterized by brittle deformation
mechanism and is a left-lateral strike-slip fault with start about 5.3
million years ago and still continues to the present.
Point of view 2. The Lai Chau - Dien Bien fault zone in the Modern
period quite clearly demonstrates segmentary nature and divided into
three segments with very different characteristics and activity levels: the
first segment is Ma Lu Thang - Chan Nua with normal left-lateral strike-
slip fault with a weak modern activity; the second segment is Chan Nua -
Huoi Leng also with normal left-lateral strike-slip fault with relatively
strong modern activity; the third segment is Huoi Leng - Thin Toc with
normal left-lateral strike-slip fault with strong modern activity.
The thesis has the following structure
Introduction
Chapter 1. Overview of the past studies and study methods
Chapter 2. Characteristics of tectonical structure of the Lai Chau -
Dien Bien fault zone
Chapter 3. S
egmentary characteristics of the Lai Chau - Dien Bien
fault zone in the modern period

Chapter 4. Geotectonic development history of the Lai Chau - Dien
Bien fault zone
Chapter 5. The relationship of modern activity of the Lai Chau -
Dien Bien fault zone with typical geohazards
Conclusions and recommendations
List of published works related to the thesis
References

Acknowledgement
The thesis was completed at Division of Tectonics, Institute of
Geological Sciences under the supervision of Dr. Tran Van Thang and
Dr. Associate professor Tran Thanh Hai. The author would like to
express his deep gratitude for the guidance of scientists inside and
outside the Institute of Geological Sciences, of the family and friends,
leadership board of Institute of Geological Sciences who dedicated study
guidance through the whole study, research and thesis writing.

CHAPTER 1. OVERVIEW OF THE PAST STUDIES AND
STUDY METHODS
1.1. Overview of the past studies
The Lai Chau - Dien Bien fault zone plays an important role in the
northwest Vietnam geotectonic map. Furthermore, in recent years many
disasters: earthquakes, landslides, mud-flows, etc. closely related to
modern activities of the fault zone cause serious human life and property
consequences to the people in the region. Therefore, the Lai Chau - Dien
Bien fault zone had been interested in the early past years and especially
in the present time has more promoted research including the following
issues:
Studies of development scale and history are of Dovjikov A.E
(1960 - 1964); Tran Van Tri (1977, 2009); Van Duc Chuong (1979-
2002); Tran Thanh Hai (2002, 2004, 2006).
Studies of active period are of Wemmer K. et al. (1999); Charusiri
(2006); Te-Hsien Lin (2009).
Studies of slipping and movement mechanism and rate of different
development stages and the role of the Lai Chau - Dien Bien fault in
the regional tectonics are of Nguyen Trong Yem et al. (1996); Tran Van
Thang (2001- 2003); Zuchiewicz W. et al. (2004); Nguyen Van Hung
(2001); Van Duc Tung (2006-2009).

Studies of composition are of Pham Tich Xuan, Nguyen Trong
Yem (1999); Koszowska E. (2005, 2007, 2009); Tran Tuan Anh (2005);
Tran Trong Hoa (2008).
Studies of modern activity and its relationship with geohazards are
of Nguyen Dinh Xuyen (2004); Nguyen Ngoc Thuy (2005); Cao Đinh
Trieu (2000- 2003); Tran Trong Hue (2002, 2003).
Conclusion: Overall so far there has been no integrated work on the
formation and development of the Lai Chau - Dien Bien fault zone
throughout its development history. The division, the deformation phases
and deformation ages, mode and mechanism of deformation according to
the criteria of plate tectonics, especially for the development stages
before the Cenozoic have not been in detail and fully studied.
1.2. Study methodology and methods
1.2.1. Methodology
As it had been known that folding deformation (plastic deformation)
and fault deformation (brittle deformation) are two main types of
deformation due to tectonic movement. In areas where the continental
crust was formed and consolidated, tectonic movement has intraplate
nature and occur mainly along major fault zones which act as the
boundary dividing the architectural blocks of different sizes. Research of
deformation characteristics-the marks of tectonic activity phases in the
fault zones allows to reconstruct the sequence and characteristics of
intraplate tectonic development of the study area.
1.2.2. Study methods
Combination of the following methods have been used: 1 -
Method
of analysis of geological structures; 2 - Method of three conjugate
fracture systems, fracture belt, method of geodynamic structure,
structural dynamic method; 3 - Method of analysis of the absolute age-
LA ICPMS U-Pb, method of spore-pollen; 4-Method of analysis of

geomorphological factors; 5 - Method of analysis of strutural partten; 6-
Remote sensing analysis.
In addition, the results of group of study methods such as group of
gas geochemical methods; group of geophysical methods; repeated
accurate geodetic measurements have been used.

CHAPTER 2. CHARACTERISTICS OF TECTONICAL
STRUCTURE OF THE LAI CHAU - DIEN BIEN FAULT ZONE
2.1. General characteristics
The study area, which includes the Lai Chau - Dien Bien fault, is in
the west of north-west Vietnam, and belongs to the north edge of
Indochina geological block, and is separated with South China
geological block by Ailaoshan suture zone in the north, and with
Sibumasu geological block by Jinghong - Nan - Sra Kaeo in the west.
2.2. Tectono-stratigraphy Assemblage
2.2.1. Criteria of division of Tectono-stratigraphy Assemblage
According to defened of Hutchison (1992
2.2.2.Tectono-stratigraphy Assemblage 1: Passive continental edge
Neoproterozoi (NP) is Nam Co formation.
2.2.3. Tectono-stratigraphy Assemblage 2: Passive continental
edge, late to early-middle Paleozoic (PZ
1-2
), is Ben Khe, Bo Hieng, Nam
Cuoi, Tay Trang, Nam Pia and Ban Pap formations.
2.2.4. Tectono-stratigraphy Assemblage 3: Active continental
edge, middle Paleozoic (PZ
2
) is Huoi Tong complex.
2.2.5. Tectono-stratigraphy Assemblage 4: Shallow marine-
intermediate continental edge, late Paleozoic (PZ

3
) is Bac Son, Ban Diec,
Pa Sa formations.
2.2.6. Tectono-stratigraphic Assemblage 5: Active continental
edge, late Paleozoic-early Mesozoic (PZ
3
-MZ
1
), is Da river, Si Phay, Na
Vang, Cam Thuy, Yen Duyet, Vien Nam, Co Noi, Tan Lac, Dong Giao,
Muong Trai, Lai Chau, Nam Mu, Dien Bien formations.
2.2.7. Tectono-stratigraphic Assemblage 6: post-mountainous
Mesozoic (MZ) is Suoi Bang, Nam Po, Nam Ma, Yen Chau formations.
2.2.8. Tectono-stratigraphic Assemblage 7: intraplate intrusive,
early Cenozoic is Ye Yen Sun, Pu Sam Cap complex; intraplate rift, late
Cenozoic is effusive basalt and Mio-Pliocene sediments.
2.2.9. Loose modern formations
2.3. Characteristics of deformation phases
2.3.1. Criteria of recognition and classification of deformation
phases

- Deformation characteristics and deformation products
- Deformation state: ductile, ductile-brittle, brittle
- Superimposed and penetrated relationship, Pumperly law
- Tectonic stress field
- Effected tectono-stratigraphy assemblages
- Deformation age
2.3.2. Characteristics of deformation phases of the Lai Chau -
Dien Bien fault
2.3.2.1. First deformation phase (B.1)

The first deformation phase occurred in the plastic deformation
state, which marked the appearance of the Lai Chau - Dien Bien fault
zone. The products of this deformation phase is sub-longitudinal shear
zone, along with foliation surfaces which are parasite-axis cleavages
which coincide with the axis of accompanied small folds. The
geodynamic signs were recorded such as boudinage structure, ductile
lineation, the axes of sandstone of micro folds, the structure of mylonite
and ultramylonite, mineral-orientation tremolite, right slipping
porphyroblast, quartz-fish and S-C' structure which express right strike-
slip mechanism (Figure 2.1 and Table 2.1).
Along with the axial cleavages in this deformation phase are folds
from open-shape to narrow with close-to-vertical shaft axis with sub-
longitudinal direction. Axes of the folds are gentle and range from 5-15
0

with dipping both to the north and south. The first deformation phase
developed in most formations, except the formations of intraplate
Cenozoic tectono-stratigraphic assemblages.
Deformation phase age (B.1):
- This deformation phase marked the beginning of the Lai Chau -
Dien Bien fault zone appearance. The
40
Ar/
39
Ar method used for
determining quartz-fish and mylonite (simultaneous deformation) which
reflects right strike-slip mechanism inside the shear zone had identified
the absolute age of this phase as 198-158 million years. U-Pb isotopic
age of zircon in Dien Bien granite complex in the northeastern of Dien
Bien city and Muong Tung is 230 million years old. It is probably that

initially those two samples were in a unified magmatic block of Dien
Bien complex, but later were moved by the Lai Chau - Dien Bien fault
by right strike-slip mechanism.
- The surface layers of T
3
n-r sb Suoi Bang formation which is
corresponding to 220-210 million years had been cut by foliation
surfaces of the zone shear show that the relative age of the fault zone
rocks is younger than Suoi Bang formation.
Therefore, the formation of the Lai Chau - Dien Bien fault zone
was completely in the intraplate Indochina block after a powerful strike
of Southeast Asia in the Permian-Triassic. This fault zone does not play
a role of boundary between Indochina and Sibumasu blocks.
2.3.2.2. The second deformation phase (B.2)
The second deformation phase also was a ductile deformation.
Product of this phase is also shear zone with sub-longitudinal direction
developed over the first deformation phase. Similarly, the second
deformation phase also formed the foliation surfaces in most rocks of the
Nam Po formation (J
1-2
np) to the older rocks distributed along the shear
zone. In some places it is also observed veins of bright color granite
applite which cut through foliation surfaces of the first deformation
phase (B.1) and was simultaneously deformed. This shear zone has right
strike-slip mechanism (Figure 2.1 and Table 2.1.)
Age of the deformation phase (B.2):
Samples were taken from bright color granite applite have mostly
felsite composition. Field relations: this is a vein of applite granite,
which was simultaneously deformed along foliation surfaces of the first
deformation phase in Lai Chau formation and which simultaneously

deformed in the Lai Chau - Dien Bien fault zone.
Results: Analysis by LA-ICPMS method for the two samples VN-
M4 and VN-M6 in Huoi Leng area gave the age of crystallization of the
stone is (113.8 ± 2.3 million years) and (109.3 ± 1.6 million years).
Interpretation: sample VN-M4 has 10 zircon grains and VN-M6 has
9 zircon grains in the first group are on the discordant line at lower
crossing point with concordant line which gave value (113.8 ± 2.3
million years) and (109.3 ± 1.6 million years). Lower crossing point is
the age of crystallization of the granite applite vein of simultaneous
deformation so the age of crystallization of the two samples is the age of
the Lai Chau - Dien Bien fault zone in this deformation phase. Along
with the results of K-Ar and Ar-Ar analysis along the Lai Chau - Dien
Bien fault zone and in the Vietnam middle region, the student has an
opinion that the second deformation phase occurred in the range of 135-
80 million years.
2.3.2.3. The third deformation phase (B.3)
The third deformation phase took place in the ductile to the brittle-
ductile. The products of this deformation phase are overthrust
reverse/reverse fault zones, with the gentle slip surfaces (20-30
0
), in
many areas Ban Pap formation limestone rocks are observed overly
foliation surfaces of the deformation phase (B.1) and (B.2) with vertical
bedding, the folds have bedding axes less than 30
0
developed in Lai
Chau formation, granite vessels had been folded, which in some places
dragged off into the boudinages, reverse faults. The development of the
fault system also came with the development of system folds with axes
nearly parallel to the fault surface. At the River crossing it is also

observed the interference of folds of the first and the third deformation
phases. The third deformation phase affected all tectono-strategraphic
assemblages in the region, but did not effect on tectono-strategraphic
assemblages of the late Cenozoic intraplate rift (Figure 2.1; Table 2.1).
Age of the third deformation phase (B.3):
Samples were taken from bright color granite have mostly felsite
composition. Field relations: this is a vein of granite before deformation,
which intruded into foliation surfaces (B.1) and (B.2) in Lai Chau
formation and crystallized, and then deformed into folds in the Lai Chau
- Dien Bien fault zone.
Results: Analysis by LA-ICPMS method for the two samples VN-
M2 and VN-M6 in Muong Muon and Huoi Leng areas gave the age of
crystallization (35.05 ± 0.46 million years) and (33.7 ± 0.79 million
years).
Interpretation: VN-M2 sample had 9 zircon grains and VN-M6 had
3 zircon grains numbering A192, A202 and A203 are located on
discordant straight line at lower crossing with concordant line gave value
(35.05 ± 0.46) million years and (33.7 ± 0.79) million years. The
intersection under sample VN-M6, VN-M2 is a vein of granite which
crystallized before the deformation, so the age of crystallization should
also give the maximum age of the Lai Chau - Dien Bien fault zone in the
third deformation phase. Along with deformation phase, the folds have
axial faces perpendicular on the Red river zone. The student proposes
that this tectonic phase took place in a short time since (33-28) million
years.
2.3.2.4. The fourth deformation phase (B.4)
This is a brittle deformation development phase superimposed on
the structures of older deformation phases. The products of this
deformation phase is characterized by a system of gentle slopping to
horizontal scratches developed on steep to vertical slipping surfaces with

right strike-slip mechanism which concentrated in the Lai Chau - Dien
Bien fault zone in the sub-longitudinal direction. The movement and
slipping mechanism must also be observed under the petrographic
orientation composition samples. In the area of Nam Sao and Nam Cay
villages, Ban Pap complex limestone overlies onto Lai Chau complex in
the third overthrust deformation phase and then destroyed and cut by the
Lai Chau - Dien Bien fault zone in the fourth deformation phase with
leaving some tectonic remaining bodies in the west wing. The fourth
deformation phase developed on all types of tectono-petrographic
assemblages of Neoproterozoic passive continental margin to intraplate
Cenozoic, except tectono-petrographic assemblage of late Cenozoic
intraplate rift. Stress field of this deformation phase is characterized by
the normal strike-slip with the sub-latitudinal axis of maximum
compression. Under the influence of this tectonic stress field the Lai
Chau - Dien Bien fault zone experienced with right strike-slip (Figure
2.1 and Table 2.1).
The fourth deformation phase age (B.4):
The products of the third deformation phase such as boudinages
were formed from veins of granite with crystallization age of 33-35
million years which have been cut through to leave cleavages, overlying
faces of Ban Pap formation limestone on the foliation surface of Lai
Chau complex in deformation phase (B.3) which was cut by the Lai
Chau - Dien Bien fault with leaving some tectonic remaining structures
in the west wing. The student proposes that the fourth deformation phase
has age of about (28-5.3) million years.
2.3.2.5. The fifth deformation phase (B.5)
This is the youngest brittle deformation phase had been discovered,
which left a clear sign in the Lai Chau - Dien Bien fault zone. The
products of this deformation phase are fault destruction, systems of
fractures, and fractured and crushed zones, tectonic silts, cleavage

surfaces, different shapes of structure, subsidence holes, Quaternary
trenches.
The left strike-slip mechanism J the normal left strike-slip
mechanism of the Lai Chau - Dien Bien fault zone in this phase is clearly
expressed via slip surfaces-cleavages, structure shape “pull apart” in
Chan Nua and is rather clear in the orientation samples taken from Mio-
Pliocene formation in River crossing where the above-mentioned fault
cut through. The normal part of the fault zone is relatively expressed
through slip surfaces containing cleavages and the formation of series of
subsidized holes and Quaternary trenches along the fault zone (Figure
2.1; Table 2.1).
The deformation phase age:
The age of the fifth deformation phase is determined to be 5.3
million years based on that it cut through tectonic structures of the
previous deformation phases (especially through Mio-Pliocene
formations), Chan Nua Quaternary tectonic structure, Quaternary
formation valleys along the fault, effusive basalt olivine around Dien
Bien basin.
CHAPTER 3. SEGMENTARY CHARACTERISTICS OF THE LAI
CHAU - DIEN BIEN FAULT ZONE IN THE MODERN PERIOD
The Lai Chau - Dien Bien fault zone has sub-longitudinal direction
which is gently changing to northerneast-southernwest in the south-west
region. This is north-west part of the Lai Chau - Luong Pha Bang - Phet
Cha Bun fault zone and has a length in Vietnam territory of about
150km.
To have scientific basis for dividing the fault into segments it needs
to determine the special features of the fault zone and their changes
along its development line.
3.1. General characteristics
3.1. 1. Geomorphological characteristics

The Lai Chau - Dien Bien fault zone is a low strip with elevation
below 1000 meters which serves as slopes and bottoms of a series of
river valleys and streams: Nam Na, Nam Lay, Nam Muon, Nam Muc,
Nam Ron from the Vietnam - China at north to the border of Vietnam -
Laos in the south, between the mountains 1500 - 2000m high in the east
and 1000 - 1700m in the west. Average width of the zone from 7 - 8km.
The central strip has width of more than 100 kilometers and
elevation of 200 - 300m and slope angle of 10 - 15
0
, including isolated
valleys (Pa Tan, Chan Nua, Lai Chau, Na Pheo, Huoi Chan, Muong Pon,
Dien Bien).
The eastern strip has slope ranging from 30 - 45
0
, with many high
steep cliffs of hundreds of meters height and of several tens kilometers
long and neighbouring on Ta Phinh-Huoi Long plateau which is
stretching from Pa Tan to Muong Pon.
The western strip slope ranges from 20 - 25
0
, poor level terraces,
more gentle in the south, in some places separated into small mountains
along the fault zone.
3.1.2. Characteristics of young geological formations
The center of the fault zone destroyed and cut Lai Chau, Suoi Bang,
Nam Po complexes. In the north there are Phu Sam Cap and Ye Yen
complex of Paleogene age. Lai Chau formations have been penetrated by
granite massifs in some places such as Chung Chai, Muong Tung, Huoi
Leng, Cong Troi, Sa Long, Muong Muon of radioisotope age 33-35
million years. Within the fault zone it has been observed olivine basalt

rock with the absolute age of 4.4 to 5.8 million years distributed in the
valley of Dien Bien Phu and Co Chay mountain pass; Mio-Pliocene
sediment rocks in the area River crossing in the north of old Lai Chau
town. Besides, there are also the distribution of Quaternary formations in
the valley along the zone (Pa Tan, Chan Nua, Lai Chau, Na Pheo,
Muong Muon, Huoi Chan, Muong Pon, Dien Bien).
3.1.3. Structural characteristics
On the map of modern architecture, the Lai Chau - Dien Bien fault
zone includes the main fault zone developed along the central and
secondary faults developed on both the East and West wings which had
formed 7-8km wide zone. From Huoi Chan the fault divided into 2
branches: a main branch and a tributary. Along the main fault there are
some "pull apart" valleys (Chan Nua) and rift type (Pa Tan, Lai Chau,
Na Pheo, Muong Muon, Huoi Chan, Muong Pon, Dien Bien Phu)
developed.
The west strip is the tributary short faults between 10 - 20km long,
while the east strip is of 15 - 20km to 50 - 60km long. The combination
of faults in the Lai Chau - Dien Bien fault zone had created a relatively
clear "feather" architecture, especially the southern part of the zone.
3.1.4. Characteristics of dynamic zone
According to the study of geomorphology, geology and tectonic
physics, the dynamic Lai Chau - Dien Bien fault zone is narrowed in the
middle, expanded at both ends. The average width of 7 - 8 km, the
narrowest is 6km in the south of Lai Chau town, the widest is about
25km in the area of Dien Bien Phu (partly in Laos).
3.1.5. Characteristics of fault surface
At the outcrop in Nam Sao, Chieng Chan, old Lai Chau, old Muong
Lay, Cong Troi mountain pass, Hang Lia, Pu Ca and especially Pa Tan
villages it is clearly observed the slipping surface of the Lai Chau - Dien
Bien fault, which is represented by position of the system of the main

fractures, the foliation surfaces and the bedding of the veins. Besides, the
fault surface is also determined by the facets and side walls, by the sliding
surfaces containing tectonic scratches in the outcrop in the fault zone.
The fault surface of the fault zone is shown on the geophysical
sections: gravity line in old Muong Lay, Nam Cay - Lai Chau, Lai Ha -
Muong Mun, Na Pheo-Si Pha Phin, Nam Ty-Deo Co Chay; geomagnetic
field in Pa Tan, Chan Nua, Cong Troi, Na Pheo, Muong Muon, Huoi Chan,
Ban Linh, Ban Thin Toc areas; the VLF field in Dien Bien city and adjacent
areas. The Dien Bien - Lai Chau fault zone is met in all the sections with
slipping surface steeply dipping into west. The main destruction zone has a
width from 800 - 1000m and in some places 2000m.
Based on analysis of 18 physical tectonic cross sections perpendicular
to the fault zone, fault slip surface of the fault zone has been identified as
steep slope of (75-80
0
) into the west and northwest.
Additional evidence of that fault slip surface is the position of
hypocenter of earthquake occurred on the 19th of February 2001 in Thin
Toc village near Dien Bien valley with Ms = 5.3 on the Richter scale, etc.
3.1.6. Slipping mechanism
The slipping mechanism of the Lai Chau - Dien Bien fault zone in
the modern period had been determined to be normal left-lateral strike-
slip, which means including both left-lateral and normal dip-slip
movement:
- The left-lateral strike-slip component is determined by the
scratches on the surface of the fault slip surface; by left-lateral strike-slip
of marked strata, slipping of the minerals, veins, cracks under the
microscope; by left deviation of the structural partten in Chan Nua "pull-
apart" depression with 1200m amplitude, Huoi Leng with 1700m
amplitude, Thin Toc with 5500m amplitude; by systematical shift of

system of rivers and streams across the fault in areas in Lai Chau black
stone company such as Chan Nua, Lai Chau, Na Pheo, Nam Muc; by
structure of epicenter of earthquake on the 19th of February 2001 in Thin
Toc village; by tectonic stress field of the modern and last tectonic stages
by repeated GPS measurements of Lai Chau in three measurement
cycles.
- The normal dip-slip component is determined by the difference in
elevations and the preservation of the terraces and flood plains between
east and west wings in Nam Sao and Lai Chau area; normal dip-slip
movement of strata is marked at the river crossing, north of Cong Troi
mountainous pass; slipping surface of the fault contains normal
scratches; by the tectonic facets dipping into west in Chan Nua and
Muong Pon on different architectural shapes; by the formation of a series
of Quaternary depressions such as Pa Tan, Chan Nua, Lai Chau, Na
Pheo, Muong Muon, Huoi Chan, Muong Pon, Dien Bien; by the
meandering rivers in the subsiding zones in Pa Tan, Lai Chau; by the
streams in the east wing are much shorter and steeper than in the west
wing in Lai Chau due to large amplitude upward movement to 300-500m
in the east wing; by the Mio-Pliocene sediments in the river crossing and
basalt eruption at Dien Bien valley, Co Chay mountainous pass; by the
modern tectonic field.
3.1.7. Amplitude and velocity movement
The left-lateral strike-slip rate of the Lai Chau - Dien Bien fault
zone in Quaternary is determined by the meandering of Nam Na river in
Chan Nua and Da river in river crossing area in north of old Lai Chau
town (magnitude 1200 - 2000m) to be from 0.55 to 0.66 mm/year. In Na
Pheo area the maximum amplitude of about 3000m that is about 1.66
mm/year. In Nam Ty area, the rivers and streams have not only been
impacted by the left-lateral strike-slip mechanism, but also the whole
area had been impacted as reflected by a greater left-lateral strike-slip.

Therefore, the left-lateral strike-slip rate of the fault part with northeast -
southwest direction would be much higher.
The strata marked with left-lateral strike-slip in the Mio-Pliocene
formation recently were discovered in the river crossing with slip
amplitude of about 25cm on one slipping surface. If calculation carried
out for many slipping surfaces of the same direction then the slip
amplitude may much greater.
Mio-Pliocene sediments in the river crossing-north of old Lai Chau
town, at the same time in the Dien Bien valley at borehole 3D near the
General De Castries tunnel at a depth of about 150m basalt with K-Ar
age from 4.4 to 5.8 million years is met. Unconformably lying on this
weathered formation is loose Quaternary formation with age from
middle Pleistocene - Holocene with a thickness of about 140m and as by
geophysical data of about 200 m in the south, according to tellurium
magnetic data of 600 - 700m. Thus, the average rate of subsidence of
Dien Bien valley from the middle Pleistocene to present about 0.25
mm/year (according to tellurium data around 1mm/year). The trench has
width of about 1.5 km and it can be estimated the rate of horizontal rift
of over 1-2mm/year. Similar picture is also observed in Chan Nua
Quaternary "pull apart" depression.
3.1.8. Signs of modern activity
The modern activity of the Lai Chau - Dien Bien fault zone is rather
clearly expressed through different signs:
The Quaternary valleys in from Na Pheo to Nam Ty are kidney-
shaped with a much smaller sizes compared to the valleys of Lai Chau in
Chan Nua - Cong Troi mountainous pass, Pa Tan trenches in from Ma
Lu Thang to Chan Nua "pull apart" depression.
Mercury geochemical anomalies in from Na Pheo to the Thin Toc
are more than 2 times higher than the north, the springs of hot and
mineral water in Muong Muon, Huoi Chan, Muong Pon, Pe Luong, U Ba

in from Cong Troi mountainous pass to Thin Toc village show that the
south part is more active than the north.
Modern rather active activity of the Lai Chau - Dien Bien fault is
also expressed quite clearly by geothermal anomalies in the survey
routes: Lai Chau; Na Pheo, Ban Linh, Nam Ty.
In recent years many mud flows occurred in the east wing, in the
area of old Lai Chau town to old Muong Lay. Mud flows have destroyed
many houses, land and human lives, which forced Muong Lay town to
be relocated to Na Pheo.
Many earthquakes having magnitude 5.0÷5.5 level on Richter scale,
mainly concentrated in three important epicenter positions: Chan Nua,
Huoi Leng, Thin Toc and Dien Bien Phu city with a higher frequency.
3.2. Segmentary characteristics of the Lai Chau - Dien Bien
fault zone
Based on the results of detailed studies of geological,
geomorphological features along the length of the Lai Chau - Dien Bien
fault zone and based on six criteria: 1 - horizontal deviation across the
fault; 2 - the shape slip direction change; 3 - characteristics of
development of branches; 4 - morphology of the fault (slipping surface,
slipping mechanism rate for the period N
2
- Q); 5 - level of expression of
earthquakes; 6 - characteristics of different endogenic and exogenous
processes, such as cracking, landslides, hot water - mineral water, gas
geochemical anomalies, etc., it allows the author divide the Lai Chau -
Dien Bien fault zone on the territory of Vietnam into three segments with
the different features and activity extent, including:
3.2.1. The first segment: Ma Lu Thang - Chan Nua
This segment begins from Ma Lu Thang border gate in Vietnam-
China border through Pa Tan and finishes at the Chan Nua "pull apart"

depression, with length of about 50 km, characterized by the sub-
longitudinal and with the normal left-lateral strike-slip mechanism with
large normal slip component which is expressed by the formation of Pa
Tan depression and Chan Nua "pull apart" depression. Chan Nua
depression is a tip where the first segment ends and the second segment
starts, where an earthquake occurred on the 4th February 2001 with the
normal left-lateral strike-slip mechanism and Ms = 4.5 on the Richter
scale and the depth was 15km. Earthquake activity along the segment is
not clear.
The left-lateral strike-slip component is determined by the feature of
the river meandering of the Nam Na river and by the shape of Chan Nua
Quaternary "pull apart" architecture with amplitude 1000 - 1200 m. It
can evaluate the left-lateral strike-slip rate in the Quaternary in this
segment from 0.55 to 0.66 mm/year (Table 3.2, 3.3).
3.2.2. The second segment: Chan Nua - Cong Troi
This segment is about 35km long, with the sub-longitudinal
direction, which is expressed in the form of valleys-trenches with a width
of 1 - 2 km, which were created by the horizontal deviation of the fault to
the left to be formed Chan Nua "pull apart" structure in the northern tip
and a compressed Huoi Leng "horse tail" in the southern tip. This
segment has rather specific and typical active expression with increasing
seismic activity, especially at two the ends and in old Lai Chau town
where it intersects with the upstream Da River fault.
The second segment has normal slip component expressed through
the formation of the Quaternary Lai Chau trenches, as well as study
results of tectonic stress field. The left-lateral strike-slip component in
the Quaternary is determined by the feature of the river meandering of
Nam Na and Da rivers, by the shapes of Chan Nua Quaternary "pull
apart" architecture and "horse tail" types in Cong Troi-Huoi Leng area.
The analysis of tectonic fractures, with a magnitude of 1,200 - 2,000m it

can evaluate the left-lateral strike-slip rate of this segment from 0.66 to
1.11mm/year (Table 3.2; 3.3).
3.2.3. The third segment: Huoi Leng-Thin Toc (Laos)
This segment has a length of about 70km starting from Huoi Leng
through Na Pheo, Muong Muon and to Huoi Chan and with sub-
longitudinal direction. From Huoi Chan the Lai Chau - Dien Bien fault
developed into branches, main branch turning to north east - south west
running through the Nam Ty, then to Thin Toc (Laos). Tributaries from
Huoi Chan through Muong Pon, Co Chay mountainous pass and the
Dien Bien valley with sub-longitudinal direction.
The width of the branch destruction zone is about 800 - 1000m as a
result of geological survey and the route magnetic field 7. In the field, in
Ban Nam Ty it is observed foliation zone and then crushed into small
pieces and silts which overlap developed over 1-2km width with steep
sloping to the west northwest, where the structures are navigated by the
fault direction from Huoi Chan to Nam Ty.
Huoi Chan - Dien Bien Phu secondary fault destruction zone has
width 200 - 350 detected by the VLF anomalies, with a length of about
40km. Tectonic fracture study results show that of the fault slip surface
slopes into west with a quite steep angle (70 - 80
o
) and had formed
Quaternary trench-form valleys with sub-longitudinal direction.
The regional structure of Na Pheo area is characterized by
combinations of trench-form rift type and normal left-lateral strike-slip
of continuous alternate type. Nam Muc bridge area has a similar picture,
but was transformed by system of small northeast - southwest faults. The
modern movement with some tendency of the streams flowing into the
Nam Muon with a total amplitude of up to 2500 - 3000 meters, the left-
lateral strike-slip rate has a value of 1.38 to 1.66 mm/year (Table 3.2,

3.3).
Architectural shape of Nam Ty area (near Vietnam - Laos border)
has a typical spine branch by compression architecture. Amplitude of
horizontal slip in this area is more 3000m, the speed of the left-lateral
strike-slip of the Lai Chau - Dien Bien fault zone in this area is greater
than 1.38 to 1.66 mm/year.
Earthquake activity of this segment is quite strong with magnitude
from 5.1 to 5.5 on the Richter scale. Left-lateral strike-slip mechanism is
expressed through the structure of epicenter position of earthquake on
the 19th of February 2001 with Ms = 5.3 on the Richter scale.

CHAPTER 4. GEOTECTONIC DEVELOPMENT HISTORY OF
THE LAI CHAU - DIEN BIEN FAULT ZONE
4.1. Early Jurassic period - Cretaceous
After the collision in Indosinian period, the study area in the
Indochina plate was unified with South China plate to form a unified
continental block. The force from the collision of North China plate with
the original Eurasian plate in the north and the continuous accumulative
compression of the sub-plates Sibumasu and Simao from west to
Indochina had impacted the study area to form the first deformation
phase. This is part of the Yen Son tectonic event (Yanshanian), marking
the appearance of the Lai Chau - Dien Bien fault zone at the beginning of
this period about 198 million years ago (early Early Jurassic).
Consecutive collision were the result of the movement of the Lhasa,
West Burma and Sikuleh plates from southwest which collided and
mixed with the original Eurasian plate about late Jurassic - Cretaceous
that marked the start of the second deformation phase to form new shear
zone having sub-longitudinal direction normal right-lateral strike-slip
mechanism to develop over the first deformation phase. The second
deformation phase occurring in between (80 - 135 million years) have

been recorded along the Lai Chau - Dien Bien fault zone with the result
K-Ar isotopic age and U-Pb isotopes (91-113 million years).
4.2. Cenozoic and modern period
During the whole Cenozoic tectonic movement, the study area is
controlled directly by the interaction between the major plates: the
Pacific plate in the east, the India - Australian plate in the south and west
and Europe - Asia plate in the north. Because of the three mentioned
plates that made the study area experience with periods of tectonic
activity under the influence of the stress fields with the compression
direction changing in accordance with this relation.
- The first stage in the development of reverse tectonic stress field
of east-west compression force on the area to create the folds with nearly
horizontal axes developed along the Lai Chau - Dien Bien fault in the
range of 33 to 28 million years. This resource originated from the
simultaneous impact of the Pacific plate attracting from the east and the
collision of the Indian continent from the west.
- The second stage developed in normal tectonic stress field due to
the overwhelming northeast - southwest compression force on the region
corresponding to left-lateral strike-slip phase of the Red river fault zone,
making the Lai Chau - Dien Bien fault zone have right-lateral strike-slip
about 28 to 5.3 million years. This force source was due to the
simultaneous impact of the Pacific plate attracting from the northeast and
the collision of Indo-Australia plate in southwest.
- The third phase had normal tectonic stress field with the main
compression of north-south direction, due to the simultaneous impact of
the Indo - Australian plate with Europe - Asia continent through
attracting south Indonesia strip and partially direct effect of the collision
of Indian and European - Asian continents at the northwest of the area
which made the Lai Chau - Dien Bien fault zone experience the left-
lateral slip about 5.3 to 0 million years.

CHAPTER 5. THE RELATIONSHIP OF MODERN ACTIVITY
OF THE LAI CHAU - DIEN BIEN FAULT ZONE WITH
TYPICAL GEOHAZARDS
5.1. Present status of geohazards
5.1.1. Earthquake
In recent years, the study area frequently and repeatedly experiences
with earthquakes with different levels.
In the 29th and 30th of March 1993 there were two consecutive
earthquakes in the Lai Chau with magnitude Ms = 5.0 (I
0
= 6 ÷ 7) with
epicenter of 13km. After the main shock, it was also recorded nearly four
hundred aftershocks magnitude Ms = 1 ÷ 3.5 for three consecutive
months.
Especially recently, on the 19th of February 2001 an earthquake
with Ms = 5.3 on the Richter scale with an epicenter of 12km occurred in
the area of Thin Toc village, 15km west of Dien Bien town. In Dien Bien
town area most houses were cracked, some houses were seriously
damaged including collapse and cracks with wall opening 3 - 10cm and 3
- 7m long such as Independent Hill area, Pa reservoir dam. Estimated
losses worth hundreds of billion dongs and four wounded. After the
major earthquake to end of the 5th of March 2001 nearly 200 aftershocks
were recorded.
In early March 2001, in Chan Nua area an earthquake Ms = 4.7 on
the Richter scale again occurred. Most recent on the 29th of December
2002 an earthquake with Ms = 3.4 on the Richter scale occurred in Nam
Ty A area.
5.1.2. Landslides
Landslides were recorded over the entire length of national road 12,

but mainly in area of old Muong Lay town then in Cong Troi area.
Landslides in Muong Lay town and Cong Troi areas often happen,
repeat from time to time, large landslide on the slope s of more than 25
0

in products of tectonic destruction. Almost every year landslides are
recorded with high density.
Along Huoi Lo stream many large landslides are observed in
tectonic destruction zone with hundreds of meters wide, short and steep
streams, high topographic differentiation, the east wing is currently
rising to create steep slopes which are favorable conditions for landslide
occurrence. Huoi Phan stream also has similar picture.
5.1.3. Mudflows
Mudflows happen along the length of national road 12, but mostly
in the old Muong Lay town.
From 1990 until now there were four earthquakes (1990, 1991,
1994 and 1996) which has caused enormous losses of life and property,
and the psychological fear among the population in the area. Mudflow on
the 27th of June 1990 devastated Lai Chau town, caused many people
deaths, hundreds of buildings and houses were washed away. Mudflow
on the 23rd July 1994 in Huoi Lo destroyed 18 houses, 11 people dead,
20 wounded. Mudflow in Muong Lay on the 17th of August 1996 has
broken most of the irrigation system and bridges in Muong Lay town,
caused many people dead and wounded.
5.2. Relationship between the Lai Chau - Dien Bien fault zone
activity and typical geohazards: earthquake, landslide, mudflow
5.2.1. Relationship between the Lai Chau - Dien Bien fault zone
activity and earthquake
The first segment has normal left-lateral strike-slip mechanism with
small slip amplitude and rate along with the absence of mineral and hot

water, earthquake activity is only concentrated at Chan Nua with
magnitude not exceeding 5.0 degrees on Richter scale. This shows weak
seismic activity which creates sparsely earthquake only in between
segments 1 and 2.
Segment 2 also has normal left-lateral strike-slip mechanism but
with a larger slip amplitude and rate with the absence of mineral and hot
water, gas geochemical and geothermal anomalies are rather high,
earthquake activity is distributed fairly evenly over the length with 8
earthquakes of magnitude Ms> 4.5 on the Richter scale, which shows
that tectonic activity is concentrated in Chan Nua, old Lai Chau town
and Huoi Leng.
Segment 3 is the most active left-lateral strike-slip mechanism with
greatest slip amplitude and rate in comparison with the two above-
mentioned segments, the appearance of mineral water and hot water in
many areas, especially in area around Dien Bien depression and Thin
Toc village, large gas geochemistrical and geothermal anomalies, active
earthquake with 35 earthquakes. All of this show that tectonic activity is
very active and concentrated Thin Toc village and Dien Bien depression
and reflects great differences in the frequency of earthquake appearance,
magnitude, number of earthquakes in comparison with segments 1 and 2.
5.2.2. Relationship between the Lai Chau - Dien Bien fault zone
activity and landslide
Along segment 1, landslides are in many places, but mainly in area
around Nam Cay village in north of Chan Nua with high density, inside
the area which the Lai Chau - Dien Bien fault destruction zone cut
through with tectonic characteristics of brittle destruction (small rock
pieces and particles). This band of landslides is near the position of
segment 1 which has greatest slip rate, in upper road slope, high
landslide density and frequency.
Along segment 2, landslides are distributed in many places, but

were located within destruction zone width from 1000 - 2000m width,
where rocks have been destroyed into loose small pieces and particles,
limestone and metamorphic rocks were broken and distributed in
disorder. With the large normal component due to strong tectonic rise
and tectonic fault running closely to east slope it had created huge energy
level to create conditions favorable for landslide development. The most
powerful area is Muong Lay with very large intensity and frequency and
scale. Huoi Leng area was formed in the normal slip-compressive
mechanism had created reverse structure of "horse tail" made the terrain
in this area unusually high, so large and very large landslides often
occurred in the this area.
Segment 3 has direction changing from the sub-longitude to the
northeast - southwest. Landslides occur most powerfully in the Cong
Troi and Na Pheo area. Besides, landslides also occur scattered in some
places in the intersection of the Lai Chau - Dien Bien fault zone and
minor northeast - southwest faults. In Cong Troi area landslides usually
occur because of Huoi Leng node. This segment had large left-lateral
strike-slip and small normal slip so the terrain differences are not large,
destruction zone has width of 800 - 1000m, magnitude and rate are far
greater than the first two segments which can create large landslides, but
it is separated by small faults so the activity much decreases and weaker
than segment 2.
5.2.3. Relationship between the Lai Chau - Dien Bien fault zone
activity and mudflow
Mudflows occur scattered and not concentrated, and it is extremely
serious in old Muong Lay area. This area is located on the second
segment, where landslide phenomena occur frequently and continuously
and a source of great material for mudflows is available. Due to strong
tectonic destruction, topography is much differentiated, the east wing
much raised with large slope from 30 to 45

0
which generates large terrain
energy which led to the high risk of mudflows. The two most typical
mudflows in in Huoi Lo were on the 23rd of July 1994 and the 17th of
August 1996. Mudflows also occur in Sa Long area, but in smaller area
and lower frequency than on segment 3.

CONCLUSIONS

1. The Lai Chau - Dien Bien fault zone derived from early-middle
Jurassic (198-158 million years) in the early phase of Yen Son tectonic
activity and the activity of the fault zone is dominated by intraplate
tectonics. Since its formation to the present the activity of the fault zone
has experienced five tectonic deformation phases.
2. In its development history, the Lai Chau - Dien Bien fault zone
has experienced five deformation phases characterized by different
mechanisms: plastic, brittle-plastic and brittle. The first and second
phases are characterized by plastic deformation, the third phase is
characterized by brittle-plastic deformation, the fourth and fifth phases
are characterized by brittle deformation.
3. The Lai Chau - Dien Bien fault zone is a deep fault zone, with
width of destruction zone reached 800 - 2000m and the impact zone of 5
- 10 km, with a length of about 150 km on the territory of Vietnam.
Slipping surface of the main Lai Chau - Dien Bien fault zone dips to
west and west-northwest with steep slope angle.
4. Modern active of the Lai Chau - Dien Bien fault zone has clear
segmentary nature. The research results have allowed to divide into three
segments in the territory of Vietnam. In segment 1 Ma Lu Thang - Chan
Nua has length 50km, slip mechanism was defined as normal left-lateral