Đặc điểm phát triển địa hình trong mối liên quan với địa động lực hiện đại đới đứt gãy sông hồng bản tóm tắt tiếng anh

MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF MINING AND GEOLOGY
***




HOANG TUAN CHUNG






RESEARCH ON SUITABLE SURFACE MINING
TECHNOLOGY FOR SMALL-SCALE MINES
IN VIETNAM


Major: Surface Mining Engineering
Code: 62.53.05.01



ABSTRACT OF THESIS
OF DOCTORATE IN ENGINEERING

1
VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY
INSTITUTE OF GEOLOGICAL SCIENCES
***




NGO VAN LIEM






CHARACTERISTICS OF LANDFORM EVOLUTION IN
RELATION TO RECENT GEODYNAMICS ALONG THE
RED RIVER FAULT ZONE


Major: Geomorphology and Paleogeography
Code: 62.44.72.01



ABSTRACT OF DOCTORATE THESIS

HANOI - 2011




2
Research finished at Institute of Geological Sciences
Vietnam Academy of Science and Technology


Supervisors:
1. Acc. Prof. Dr. Phan Trong Trinh,
Institute of Geological Sciences
2. Dr. Vy Quoc Hai,
Institute of Geological Sciences




Examiner 1: Asc. Prof. Dr. Dang Van Bao
Vietnam National University, Hanoi

Examiner 2: Asc. Prof. Dr. Ta Trong Thang
Hanoi University of Science - VNU

Examiner 3: Asc. Prof. Dr. Ha Van Hai
Hanoi University of Mining and Geology

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……/……/ 2011.





This thesis can be found at Vietnam National Library
or Library of Institute of Geological Sciences
PREFACE
1. Neccessary requirements of research
The Red River Fault Zone (RRFZ) plays an important role in
tectonic framework of Asia and the fault zone drew special concern
of Vietnamese scientists as well as foreigners. However, in this
work, it was concentrated on study of geological structures and
tectonics, not mentioned to the roles and significances of
geomorphology. Besides, this study still has some debates; shortage
or existence of contrary figures about a number of horizontal and
vertical motions of landforms in Pliocene-Quaternary period.
Regional landform clearly depicts marks of recent faults but
seismicity is fairly low in recent years… Thus, research on character
of landform evolution in relation to regional recent geodynamics is
necessary and imperative, aiming to supplement and support each
other. Research on characteristics of landform evolution allows us to
estimate the rate of landform displacements during a long period but
it contains some limitations itself. Research on quantity of recent
tectonic movement gives us estimation with higher confidence but
time span is not long enough. Thus, research on character of

landform evolution is supplemented and verified through study
results about recent geodynamics. Inversely, study results of recent
geodynamics are lightened by study results of landform evolution in
a long time period. With this in mind, it allows us to exactly assess
and predict about landform evolution and recent geodynamic
processes as well as its consequence (especially, earthquake hazards)
in the future. The situation mentioned above is the reason for
choosing this thesis: “Characteristics of landform evolution in
relation to recent geodynamics along the Red River Fault Zone”.
1
2. Purposes of thesis: clarifying the relation between characteristics
of landform evolution with active tectonics and recent geodynamics
RRFZ from Pliocene to Recent.
3. Thesis missions: (1) Research on geomorphological
characteristics of RRFZ; (2) Research on characters of active
tectonics and endogenic recent geodynamics from Pliocene to Recent
period; (3) Analysis of the relation between recent landform
characteristics with geodynamic regime from Pliocene to Recent
period and related earthquake hazards.
4. Objectives and Scope of Research:
+ Objectives: Are landforms which were formed or displaced by
endogenic geodynamic processes from Pliocene to Recent period.
+ Scope: - Temporal span: From Pliocene (N
2
) to Recent. – Spatial
scope: is a part of RRFZ and surroundings from Lao Cai to Viet Tri,
from 103
0
13’E to 105
0

43’E and 21
0
12’E to 22
0
52’E.
5.
The new contribution of the thesis
- Defined 3 stages of landform evolution from Pliocene to Recent
period with increasing trend of vertical motion and decreasing trend
of horiziontal motion. Rate of vertical motion (uplift) ranging from
~0.12 ÷ ~0.3mm/yr in Pliocene to ~0.7 ÷ ~1.2mm/yr in Late
Quaternary; rate of horizontal motion decreases from ~1.8mm/yr in
Early-Middle Pleistocene to less than 1mm/yr in recent time.
- Vertical motion creates 9 topographic surfaces; horizontal motion
creates fault segments, among them, it can be defined their location
and dimension of 5 main segments which have possibility to generate
maximum earthquake with magnitude from 6.3 to 7.0 in Richter
scale.
2
6. Scientific and Practical Significances: Scientific Significances:
The thesis contributes to completing argument base for studying
relation between landform evolution process with active tectonics
and recent geodynamics, especially in applying new techniques in
research and semi-quantitative and quantitative methods, in
analyzing and assessing. The study results also contribute to
clarifying acting character and zoning role of RRF in recent time.
Practical Significances: The thesis contribute to explain the reason
and regime of a variety of geo-hazards, especially in assessing
maximum earthquake in detail as well as PGA which affects to
facilities in the area, severing for territory planning.

7. Documentation: Thesis was built basing on database collected by
myself during participation in 9 scientific projects from 2006 to date;
within 15 published articles on journals and workshop proceedings in
Vietnam and overseas; from 5 field-trips from the year 2006 to
present. Besides, I also refer uncountable amount of related works.
8. The outline of thesis: Apart from Preface, Conclusion and
Refercence cited sections, this thesis consists of 4 chapters, displayed
in 146 typed pages including 51 figures, 7 tables and 10 inlustration
pictures.
9. Acknowledgement: Thesis was completed at Division of
Geodynamics - Institute of Geological Sciences under supervision of
Asc. Prof. Dr. Phan Trong Trinh and Dr. Vy Quoc Hai. I am really
appreciate their whole-hearted instruction during studying and
completing this thesis. Besides, in progress of the thesis, I have
always received guidance and favorable conditions from Institute of
Geological Science’s directors and colleages at Division of
Geodynamics, Institute of Geological Science as well as other
3
scientists. Moreover, I have been encouraged by my family and
friends and supported by the NAFOSTED project with code
105.06.36.09. From the bottom of my heart, I want to send my
thankfulness to all people with valuable help for this thesis.

CHAPTER 1
OVERVIEW OF RESEARCH SITUATION AND METHODS
1.1. RELATED CONCEPTS
1.1.1. Recent Geodynamics: Arccording to Kuzmin (2009) “Recent
Geodynamics is a part of general geodynamics, which studies
motions in the Earth’s interior and the factors responsible for them,
when the time of action of the latter is commensurable with the

duration of the observation process”. Arcording to Chu Van Ngoi
(2007) “Recent geodynamics refers to geological processs occuring
in recent time or occurred in human history”. Thus, concepts about
recent geodynamics all emphases on two problems: Earth’s motion
(endogenic, exogenic, anthropongenic) and duration of motion in
recent time observed by humanbeings. Basically, I acknowledge this
point of view, but in this thesis, my concern is only about endogenic
recent geodynamics of the Earth’s crust.
1.1.2. Active tectonics: The terms active tectonics refers to those
tectonic processes that produce deformation the Earth’s crust on a
time scale of significance to human society (E.A. Keller and N.
Pinter, 2002). The time period may span from decades to hundreds
years – the time period for which we plan the lifetimes of building
and important facilities such as dams and power plants. However, in
order to study and predict tectonic events over this time period, we
must study these processes over a much longer time scale - at least
4
several thousands years to several tens of thousands years, because
characteristics of seismogenic fault has long recurrence intervals.
Some ideas stated that suitable time span to study active tectonics is
several million years. In my opinion, knowledge of tectonic process
in several milion years is necessary to fully understand about
landforms evolution, active tectonics and recent geodynamics as well
as geo-risk reduction, especially earthquake hazard.
1.2. RESEARCH SITUATION
1.2.1. Overseas: RRFZ attracs many scientists all over the world.
Published works concentrateed on explaining two models about
collision processes between Indian –Eurasian and its consequences in
relation to RRF: (1)- Model of (England & Houseman, 1985, 1986,
1993) suggested that deformation initiated by collision between

Eurasian plate and Indian-Australian plate mainly focused on
collided zone, exhumation (if existed) along RRF is not significant.
(2)- Model of (Tapponnier, Peltzer & nnk, 1986, 1988, 1990, 2001;
Amijo & nnk, 1989) considered Indian-Australian plate as a rigid
plate, whereas Eurasian plate is deformed through ductile-plastic
regime, a part of deformation occured along collided zone, and a part
of deformation occured aling strike-slip faults, in which there is righ-
lateral strike-slip along RRF causing South China block extruded
eastwards. In general, there studies suggested that extrusion
hypothesis, confirmed ductile-deformed Ailao Shan shear zone with
left-lateral strike-slip regime in Oligo-Miocene, a number of
displacement can reach to hundreds kilometers. These studies also
confirmed that RRF is an active fault or recent fault with righ-lateral
strike-slip regime.
5
1.2.2. Domestic: It can be divided into 5 main subsidiary topics: (1)
Geological - tectonics; (2) Neotectonics and Tectonic
geomorphology; (3) Satellite geodesy in geodynamics; (4) Sediment
comparision and (5) Geological and geomorphological hazards.
In brief, because of its importance in Asian tectonic
framework, RRFZ attracts many scientists worldwide with various
research fields. The results of these works are important, contributed
to explaination and clarification of problems about geology,
tectonics, geomorphology and related natural hazards in the region.
However, the role and significance of regional geomorphology is not
adequately mentioned as well as there is an existence of contrary
ideas.
1.3. RESEARCH METHODOLOGY: Based on methodology of
Geomorphology: Research considering landforms as having
generating, development which obeys logical evolution and as a

result of the interaction between endogenic and exogenic processes
occurring on the surface. In the bilateral relation, the role of
endogenic forces is active which causes landform difference:
uplifting in mountain and depressing in trough and caynon ,
whereas, exogenic processes always have trend to descrease the
difference and make complication of landforms on structure
framework created by endogenic processes. In this thesis, I
concentrate on study and analysis of characteristicss of landform
from Pliocene to Recent, especially landform formed by processes of
endogenic geodynamics in Quaternary.
1.4. RESEARCH METHODS: In this thesis, there are 6 main
methods were applied, as listed below: (1) Geological-
geomorphological methods: Analysis of morphostructure; analysis of
6
landform offsets; morphometry; analysis of pediment and stream
length gradient. (2) GIS methods; (3) Geodetic (GPS) methods; (4)
Paleo-seismologic methods; (5) Seismotectonic methods (assessment
of maximum earthquake and PGA) (6) Modelling methods.

CHAPTER 2: GEOMORPHOLOGICAL CHARACTER
ALONG RED RIVER FAULT ZONE
2.1. OVERVIEW OF LANDFORMS AND FORMING FACTORS
2.1.1. Characteristics of pre-Pliocene tectonics-geology:
Characteristics of geology in pre-Pliocene period of RRFZ consists
of four high grade metamorphosed belts, including: Xuelong Shan,
Diancang Shan, Ailao Shan (in Yunnan, China) and Con Voi
metamorphic belt (in Viet Nam) which were exhumuted as
metamorphosed belts with 10-20km in width. Tectonic activities
depict left-lateral strike-slip regime with the total amount of
displacement reaching to 700 ± 200km. In the study area, geological

structures are rather complex with rocks aging from Proterozoi to
Cenozoic and a number of active shear zones distributed along fault
zone. Cenozoic sediments distribute mainly along troughs along Red
river and Chay river valleys. Besides, it can be observed these
sediments along inter-mountainous troughs and valleys of main
subsidiary rivers and streams of the two-rivers-system.
2.1.2. Regional landforms characteristics: Analysis of regional
morphometry shows us characteristics as boudler nature which
displays the consistence between elevation contour and and the old
geological structures; substage nature displays the interaction
between Neotectonic motions with cycle nature and symetric nature
with the key role is not uniform uplifting and depressing upon
7
different geological structures and faults. The characteristics depict
general tectonic framework of the region.
2.1.3. Overview of climate characteristics: Climate conditions in
the study area have huge difference with various differences of
topography. Climate characteristics are inportant factors affecting
geological structures and topography which are depiected by thick
weathering layers, strong erosion and washing-out processes,… This
causes more complex landforms in tectonic framework generated by
endogenic processes.
2.2. CHARACTERISTICS OF MORPHOMETRY
2.2.1. Characteristics of topographic level: Character of
topographic levelling of the study area is quite clear. Along with
dividing into different topographic levels in the same area, there is
also different number of levels among areas. The division of
topographic levels depicts exactly uplifting and depressing in the
region: NW and northern part is more active than southern and
eastern ones.

2.2.2. Characteristics of vertical dissection: Study area are
subdivided into 8 levels of vertical dissection, corresponding to 4
levels of activity: weak (with dissection ranging from 0-50 m/km
2
to
50-100 m/km
2
), average (from 100-150 m/km
2
to 150-200 m/km
2
),
strong (from 200-250 m/km
2
to 250-350 m/km
2
) and very strong
(from 350-500 m/km
2
to above 500 m/km
2
). Characteristics of
vertical dissection in the study area depicts clearly Neotectonic
structures about their geometry and uplifting and depressing
characteristics.
2.2.3. Characteristics of horizontal dissection: Character of
horizontal dissection also clearly depicts geodynamic regime in the
8
area as strongly fractured at high density of rivers. Most of the area
has density ranging from 2.5 km/km

2
to above 3km/km
2
, area with
density above 3km/km
2
mainly occurs along large river valleys, area
with density less than 2km/km
2
mainly occur along watersheds and
at areas of plains and mountains.
2.2.4. Slope characterictics: Most of study area is high mountain,
their slope is so high, slope mostly ranging from 10
o
to 30
o
.
However, slope has also difference, that is consistent with
topography and tectonic structures; area with low slope distributes as
narrow bands at two river sides and in plateaux or valleys along
rivers depicting regional topographic textures.
2.3. CHARACTERISTICSS OF MORPHOSTRUCTURE: Study
area can be divided into 10 types of morphostructure with 22 sub-
types. Three genesis groups include: tectonics, petrologic tectonics
and erosional tectonics. Based on uplifting-depressing nature, it can
be divided into two groups: (1) Neotectonic uplifted morphostructure
and (2) relative depressed morphostructure and Neotectonic
subsidence.
2.3.1. Neotectonic uplifted morphostructure: including three
genesis types as tectonics, petrologic tectonics and erosional

tectonics.
Morphotectonics: including 2 types: (1) morphostructure with step-
like host, typically at eastern flank of Fansipan mountain and (2)
morphostructure with host distributed along left strand of the Red
river, typically as Con voi metamorphic belt.
Tectonic-petrologic morphostructure: including 6 types of typical
morphostructure: (1) Boulder mountain belt developed upon igneous
rocks (mainly Paleogen granite), strongly uplifted in N-Q; (2)
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Boulder-folded mountain blocks mainly developed on Mezozoic
intrusive and extrusive rock; (3) folded-boulder host mainly
developed on Proterozoic metamorphosed rocks; (4) Folded-bounder
mountain belt developed on Paleozoic sediments; (5) Arch-bounder
mountain developed on Proterozoic ignous and metamorphosed
rocks; (6) Plateaux and uplift mountain block developed on
cacbonate rock and interbed terrigenous rocks.
Morphostructure of tectonic erosion: including low mountain or
hill, chain of hills or trough-like inter-mountaion with small area,
with or without deposition; low uplifting rate, mainly occuring in
fracturing zones or faults or at the edge of uplifted moutain blocks.
The texture includes two types: (1) low mountain belt developed on
Paleozoic-Mezozoic sediments and (2) low hill an/or mountain
developed ununiform structure.
2.3.2. Relative depressed morphostructure and Neotectonic
subsidence
The Red river valley graben : Extending along NW-SE direction,
with 3km in width and located in vincinity of subsidiary faults of
RRFZ, there is development of terrace and alluvial flat. However,
there is geometrically difference: widened areas (Lao Cai city, Yen
Bai…) are subsided with base mainly consist of Neogene and

Quaternary sediments; narrowed area is eroded exposing bed rock.
Notably, along valleys in the study area, there are troughs, including:
Lao Cai, Bao Ha, Yen Bai and Phong Chau troughs.
The Chay river valley vale: Extending along NW-SE direction, from
Ban Phiet to SW Thac Ba lake. This is ancient river valley developed
in fractured zone of CRF. Along fractured zone, there are some
locations of Neogene deposition in Neotectonic troughs. Recent
10
topography displayes as a trough extending with hill topography and
chain of hills, somewhere there are small streams running along and
sediments is deposited with varoius genesis: alluvi – proluvi, alluvi –
deluvi , proluvi - swam, typically as Bao Yen trough.
Tectonic - erosion valley: Along RRFZ, apart from the Red river and
Chay river valleys, there is a geo-basin and trough system with
different scales: Muong Hoa, Xuan Giao - Vo Lao, Nghia Lo troughs
… (mainly distributed at righ strand of the Red river), they are also
limited by subsidiary fault of RRFZ. Most of the troughs formed in
Quaternary, especially Nghia Lo trough formed earlier (N
2
).
2.4. CHARACTERISTICS OF LANDFORM GENESIS TYPES:
Study area is divided into 32 landforms with 4 types genesis and age.
2.4.1. Landform types of Tecto-genesis: In the study area,
landforms generated by active tectonics normally distribute as
narrow bands, sharply display with NW-SE direction along large
tectonic faults.
2.4.2. Landform types of synthetically erosion
2.4.2.1. Landform types of synthetically erosion aging pre-
Pliocene: The group consists of surface with elevation above 600m,
with 2 types of erosional peneplain and incompletely erosional

pediplain.
2.4.2.2. Landform types of synthetically erosion aging from
Pliocene to Recent: The landform type consists of topographic levels
with elevation ranging less than 500-600m and slope surfaces,
margin of topographic levels at different elevations and most of them
are assumed to be in Quaternary.
Pediments: including: (1) erosional pediment - uncompletely
erosional pediment, elevation 400-600m, early Pliocene in age; (2)
11
planation surface at elevation 200-300m, Middle Pliocene in age and
(3) Segmented valley pediment making low slope hills, 3-8
o
, late
Pliocene in age.
Slope surfaces includes 5 types: (1) synthetic erosion slope; (2)
gravitational erosion slope. (3) corrasion – erosion slope along tiny
streams; (4) corrasion-erosion slope and (5) washing out – deluvi
deposition slope.
2.4.3. Landform type of Karst: The collection of karst summit
surfaces, valleys and slope. Karst landform mainly distribute at the
area of Bac Ha and Muong Khuong where geologic foundation
consists of limestone belonging to Ha Giang and Chang Pung
formations and distributing as narrow area at area of Thon Dao, Ban
Tung, Ban Phung, Van Ban, Nui Tham,
2.4.4. Flow-generated landform
2.4.4.1. Alluvi landforms: Study area consists of 2 types of alluvial
flat, including alluvial low flat at elevation from 0.5 to 2m Late
Holocen in age and alluvial high flat at elevation 2.5-6m whose
materials consist of sand, clay and grit, brown and red-brown in
color belonging to Phung Nguyen formation, Early-Middle Holocen.

2.4.4.2. Terrace surfaces: Along large rivers and stream from Lao
Cai to Viet Tri, it can be obeserved that there are 4 terrace levels
with different elevation and age: (1) Erosional-depositional terrace
surface level I, elevation 7-14m, age Q
1
3
; (2Erosional-depositional
terrace surface level II, elevation 15-25m, age Q
1
2-3
; (3) Erosional-
depositional terrace surface level III, elevation 35-55m, age Q
1
2
and
(4) Erosional-depositional terrace surface level IV, elevation 70-
90m, age Q
1
1
.

12
2.5. HISTORY OF LANDFORM EVOLUTION
2.5.1. Overview of pre-Pliocene tectonic and landform evolution:
In Cenozoic era, pre-Pliocene period, RRFZ undergone ductile
deformation, left-lateral strike-slip faulting with various evidences
about geothermal and geochronology. The total amount of left-lateral
strike-slip offset in topography in this period is about 700 ± 200 km
and landform developed with weak uplifting rate (0.03mm/yr).
2.5.2. History of regionally landform evolution from Pliocene to

Recent: In Pliocene to Recent period, it can be observed that there
are three stages of landforms evolution: (1) Pliocene stage, landforms
started with right-lateral strike-slip displacement and decisively
uplift, marked by three elevation levels of topography at 400-600m
aging N
2
1
, at 200-300m aging N
2
2
and valley pediments segmented
into mounds and hills aging N
2
3
; (2) Stage from Early Pleistocene to
Late-Midlle Pleistocene: landform is displaced right-laterally but
with lower rate in comparison with previous stage. Landform is
uplifted with average rate, marked by three levels of of river terrace:
terrace level IV, terrace level III and terrace level II; (3) Stage from
Late Pleistocene to Recent: landform evolution is controlled by righ-
lateral strike-slip faulting regime but weaker than previous stages;
uplifting reaches to maximum, marked by depositional terrace level I
and two generation of alluvial flat and low alluvial flat.

CHAPTER 3: ACTIVE TECTONICS AND RECENT
GEODYNAMICS ALONG RED RIVER FAULT ZONE
3.1. ACTIVE TECTONICS
3.1.1. Recording of active tectonic from Pliocene to Recent:
RRFZ is still active in Recent time. Collected evidence are recent
13

shear zones and offsets in weathering layers of Neogene formations
which have orientation coninding with trending of RRFZ (300-330
o
),
width ranging from severals centimeters at Yen Bai bridge to ten
centimeters, even hundreds meters at Lao Cai new residual area.
Dislpayed in landforms are offsets of river, terrace surface and
sediment formations aging from Pleistocene to Holocene as
mentioned in Section 3.1.3.2.
3.1.2. Amount and rate of vertical motion from Pliocene to
Recent: Based on elevation and age of applanation surfaces, river
terraces and alluvial flats (dealing with rate of regional erosion),
average uplift rate of landforms in the region in Pliocene ranging
from 0.11-0.24mm/yr, in period from late Early Pleistocene to Late -
Middle Pleistocene, uplift rate is about from 0.17-0.30mm/yr and in
from the end of late Pleistocen to Recent average uplift rate is about
0.70mm/yr to 1.25mm/yr.
3.1.3. Young strike-slip displacement
3.1.3.1. Kinematics of main seismic fault segments: In the study
area, RRFZ is sub-divided into two main faults as CRF and RRF.
RRF runs along SW edge of Con Voi metamorphic belt. The fault is
displayed by two subsidiary faults running along righ and left strands
of the Red river.
They do not extend continuously but segmented
into some discrete units
. In specific areas, left strand fault of the
Red river is displayed more clearly than righ strand fault, vice versa.
Notably, along the fault it can be defined 3 main segments: (1) SH1
fault starts at NW Lao Cai city, runs along the Red river and extends
continously ~14.5 km length; (2) SH2 fault

extends 12km long from
Pho Lu to Cam Duong
as righ-lateral strike-slip fault and (3) SH3
fault extends ~18km length from Khe Giua lake (Yen Hop
14
commune, Van Yen district) to the end of Minh Tien commune (Tran
Yen) and it is the boundary dividing level IV terrace and level III
terrace. CRF runs along the NE of Con Voi metamorphic belt,
extends as a straight line from Lao Cai to Viet Tri, but not
continuously. Along the fault, it is showed that it is a strike-slip fault,
including two main fault segment: (1) SC1 fault extends continously
~17,7 km length, runs in a narrow valley at Luc Yen district, with
quite symetric topography and no vertical motion observed at fault
surface; (2) SC3 fault runs along SW edge of Thac Ba lake, extends
~51,4km length from north of Bao Ai commune, through Cam An to
Mong Son, Tan Huong, Dai Dong, to Que Lam, Tay Coc and
ended at the center of Ngoc Quang commune.
3.1.3.2. Amount and rate of displacement
Amount of displacement: It can be defined that offsets of subsidiary
rivers and river terraces reach to more than 100m to ~1300m in the
study area. Typically, offset of Ngoi Thap stream is ~1330m,
topographic offset between level III and level II terraces in the area
of Yen Hop and Xuan Ai communes is ~142m, offset of streams and
and Quaternary sediments in the area of Mau Dong-Mau A ranging
from ~130m to ~240m and in the area along SC1 fault ranging from
~250m to ~370m, offset của Quaternary sediments at subsidiary
stream (NW of Trinh Tuong, Bat Xat) is about more than 150m.
Rate of righ lateral displacement: Through methods of determing the
total amount of offsets and age of terrace surface and subsidiary
stream - river and Quaternary sediments where there are faults

crosscuting, it can be determined that slip rate of fault segment
locating at righ strand of the Red river from ~1.1 - 1.7mm/yr, left
15
strand of the Red river from ~1.2 - 1.8mm/yr and on CRF from ~1.4
- 1.7mm/yr.
3.2. RECENT GEODYNAMICS
3.2.1. Seismicity: Historical earthquakes were recorded in some area
such as Ha Noi in the year 1278 and 1283 and events in Luc Yen in
1953 (M=4,7) and 1954 (M=5,4) with focal depth less than 25km
and focal mechanisms display strike-slip regime.
3.2.2. Recent tectonic movement along RRFZ: To study recent
movement along RRFZ, GPS technology was used.
GPS network and data: GPS network used in this thesis including 5
stations evenly distributed along two strands of RRFZ. The stations
are located in 4 provinces: Thai Nguyen, Tuyen Quang, Yen Bai and
Phu Tho. GPS data including 40 data files (RINEX) surveyed in
2000 in a cooperative project between Viet Nam and France and 51
data file (origin) of survey campaign in February, 2010 of a
NAFOSTED project, code 105.06.36.09.
Data processing and results: Data was processed and estimated
(absolute and relative movement) through BERNESE software (ver.
5.0). The result shows that study area is now moving southeastward
with rate ~32mm/yr in IGS05 reference frame and relative motion
between strands of fault is relatively weak with motion rate less than
1mm/yr (about from 0.6 ÷ 0.8 ± 0.3mm/yr).

16
CHAPTER 4: THE RELATION BETWEEN CHARACTERS
OF LANDFORM EVOLUTION AND RECENT
GEODYNAMICS AND SEISMIC HAZARD ALONG RRFZ

4.1. DEPICTION OF VERTICAL MOTION IN LANDFORMS
4.1.1. Depiction of youth uplift motion in landform: Evidence of
recent uplifting is depicted on regional recent landform along RRFZ
section Lao Cai - Viet Tri, that is existence of planation surfaces at
elevation less than 600m, river terrace levels (4 levels of river
terrace) and alluvial flat along Red river valley, Chay river whose
age is said to be from Pliocene to Recent. Radiating fluvial system
depicts local uplifted blocks such as Con Voi, Nui Sat, Doi Chieu-
Doi Bai belts Specially, in the area it can be observed that there is
“penetration” recent topographic levels and river terraces of fluvial
flows (penetration valley) at Chin Trang Ho stream, “capture” of
Ngoi Thap stream with Ngoi Tu stream.
4.1.2. Depiction of relative depression: Depressing motion
(relative) in the area can be observed through troughs along Red
river valley (Lao Cai, Bao Ha, Yen Bai and Phong Chau troughs),
Chay river valley (Bao Yen trough ) and inter-mountain troughs such
as Muong Hoa, Van Ban, Nghia Lo, Along the troughs it can be
seen that there is convergent of fluvial system (concentric fluvial
system). Otherwise, the existence of river terrace and alluvial flat
system depicts uplifting (absolute) and depression (relative) of
landform in the areas.
4.2. THE RELATION BETWEEN LANDFORM AND
HORIZONTAL MOTION: In researching along RRFZ from Lao Cai
to Viet Tri, it can be observed that there is uncontinuosly recent fault
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system that distributes along righ strand left strand of the Red river
as well as along Chay river valley. Characteristics of the faults and
their displacements were reported in Chapter 3, Section 3.1.3. In this
section, I concentrate on analysis of some typical locations which

depict most clearly the relation between displacement characteristics
of active tectonics and their magnifestion on landform (landform
offsets).
Locations which are chosen to study in detail are areas belong
to communes Yen Hop, Xuan Ai and Hoang Thang của distric Van
Yen, Yen Bai province. In this area, righ strand of the Red river have
two fault segments, with the main fault SH3. The fault crosscuts area
of Xuan Ai-Hoang Thang and can be clearly observed offset of Ngoi
Thap stream when it cuts through the fault with the total amount of
the offset is 1330m.
Particularly, to the NE and apart from SH3 fault about 1km,
there is a subsidiary fault of RRF, but its length is shorter than SH3
(about 7km vs. 18km of SH3 fault), recent activity of the fault is
depiected very clearly on landform. The fault is the boundary
between terrace surface level III and level II in the area. Along the
fault, it can be observed an offset system of landform surface at two
fault strands.
Detailed sutdies at areas along the fault use trategy: fixing
location of left strand of fault and displacing part of landform at the
remaining strand with inversely sense of righ lateral displacement of
fault and with the amount of displacement so that landform between
two fault strands has consistence with each other. If in area along the
fault there is system of offsets which has the same amount of
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displacement (inverse sense to slip sense of fault), the amount of
offset includes displacement of the fault.
First, the strategy is applied at Tan Xuan village, Yen Hop
commune, Van Yen distric (part located nearly centre of fault).
There, when landform is offsetted at righ strand of the fault with the
amount of ~142m, there is almost completely coinciding of

landforms at two sides of the fault.
The same way is doned for surrouding areas, the results show
that the amount of displacement is about ~142m. From here, the
strategy is applied for landform along overall fault with inverse
offset ~142m, it is showed that landform between the two fault
strands is mostly consistent. This is evidence (detail, visual) for righ-
lateral strike-slip offset of the fault which is depicted clearly on
regional landform.
Apart from righ-lateral strike-slip offsets of landform as
presented above, along RRFZ section Lao Cai - Viet Tri, offsets can
be obseved at many different locations with various scale and
amount, such as at Ban Qua (Bat Xat), at subsidiary stream of 3km
NW Trinh Tuong, along righ and left strands of the Red river (as
center area of Mau Dong commune to Mau A town or area along
Chay river fault, especially at area along SC1 fault , it can be
defined that offset of subsidiary river is hundreds meters to about
1300m.
In particular, at righ strand of the Red river, area from Mau
Dong commune to Mau A town has 3 subsidiary streams flowing
into the Red river as Ngoi Vai, Ngoi Quach and Ngoi A. Through
field works and topographic map, it is showed that Quaternary
sediment layers and and Ngoi Vai stream is offsetted with ~180m;
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Ngoi A stream offsetted ~240m. Ngoi Quach stream locating in the
middle of Ngoi Vai and Ngoi A, it also showed that Quaternary
sediment layers is offsetted ~130m. The offsets are consistent with
righ-lateral strike-slip nature of Pliocene-Quaternary faults cutting
through the area.
Through observation, analysis and surveys at subsidiary
streams of Chay river at communes north of Bao Yen distric, Yen

Bai province, it can be seen that there is a system of offsets of stream
and Quaternary sediment layers along these streams ranging from ~
250 to ~370m, which is consistent with righ-lateral strike-slip faults
in Pliocene-Quaternary period (SC1) crosscuting the area.
In brief, The evidence proves that landform along RRFZ
depicts clearly recent geodynamicc regime in the region, that is
ununiformly uplifting trend which is dislayed through the occurence
of levels of planation surface and generations of river terraces at
different elevation. Horizontal motion with righ-lateral strike-slip
regime which can be clearly observed in landform is offset of
subsidiary rivers and streams, of terrace surfaces with different
amount and distributed widely in the study area.
4.3. THE RELATION BETWEEN VERTICAL MOTION AND
STRIKE-SLIP DISPLACEMENT ALONG RRF: As results about
characteristics of uplifting and landform strike-sliping of RRFZ
mentioned above, it can be seen that two types of motion alway have
close relation, but their advantages are not the same at diffrent
periods. In Pliocene to Recent period, highly uplifting occures
gradually in overall area nut not uniform between areas (uplifting
rate at the north of the study area-in Lao Cai is higher than the rate in
the south and the rate at the west of Hoang Lien Son mountain is
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higher than the east - Con Voi metamorphic belt); in contrast to trend
of uplifting (increasingly), righ-lateral strike-slip activity decreased.
4.4. THE RELATION BETWEEN LANDFORM EVOLUTION
AND SEISMIC CHARACTERISTICS: Offsets along faults can be
obeyed two regime: (1) There is gradually displacement of two fault
strands with low friction or in other words, fault is not locked at the
two ends and no energy is accumulated, so there is no potential to
suddenly occur displacement which generates earthquakes. (2) There

is gradually displacement of two fault strands with high friction, fault
is locked and in deformation process enegy is accumulated. When
accummulated energy is too high which exceeds strength of
Earth’crust, rapturing occures causing sudden displacement and
releasing energy and resulting in earthquakes. In another way,
earthquakes cause ground shaking which changes landform surface.
Sometime shaking resulting from earthquakes (strong) causes great
destruction of landform and lefts severe consequence, especially in
high density-population cites or important infrastructure such as
hydropower plants or nuclear plants, Thus, research on the relation
between motions changing landforms and seismicity is very
important and greatly significant in science and in practice.
4.4.1. Maximum earthquake assessment: Maximum earthquake
was estimated through seismotectonic method based on fault length,
fault area and seismic moment for 5 main acitve fault segment
including SH1, SH2, SH3, SC1 and SC2. The result shows that along
RRFZ section Lao Cai - Viet Tri and surrounding area, it has
potential to generate maximum earthquake with magnitude from 6.3
to 7.0 in Richter scale.
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4.4.2. PGA assessment: Peak ground acceleration when earthquake
occured was also estimated for 5 main fault segment with Thac Ba
dam. The results showed that SC3 fault apart from the damp ~2 km
is the most influent one to the Thac Ba damp. When maximum
earthquake occur on this fault, it can generate PGA 0.344g at the
dam body corresponding to 337 cm/s
2
; PGA with 10000 years cycle
is 0.339g corresponding to 332 cm/s
2

; horizontal PGA corresponding
to maximum designed earthquake (cycle 950 years) is 0.271g
corresponding to 265 cm/s
2
; effective base acceleration with cycle
475 years is 0.214g corresponding to 210 cm/s
2
; and effective base
acceleration with cycle 145 years is 0.176g corresponding to 173
cm/s
2
.
4.4.3. Deformation and Coulomb stress change model with
occurrence of maximum earthquake: Coulomb stress change
model was calculated at all 5 fault segments corresponding to various
depth, from topographic surface to 30km depth with vertically
calculated separation 5km. In the model, it is showed that areas
experienced extensive and compressive stress at different levels. The
remaining areas have no stress change. The highest increased
Coulomb stress area is the most dangerous area because it has high
potential of earthquake generation and its strength decreases sharply,
especially regarding to concrete damps. In Coulomb stress change
model on topographic surface, when maximum earthquake occures,
fault segments: SC3, SC1 and SH3 cause quite large stress changed
in surrounding areas. In which, because Thac Ba hydropower dam
located quite closely to SC3 fault (~2km), the dam locates in area of
compressive stress increasing; thus, it is very dangerous if eathquake
occurs on SC3 fault.
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Corresponding to Coulomb stress change models,

displacement vector field are also estimated from topographic
surface to 30km depth. The models display spatial distribution about
direction and magnitude of lateral displacement along the fault zone.
CONCLUSION
Research on characteristics of landform evolution and recent
geodynamics along RRFZ section Lao Cai-Viet Tri, it can be
inferred some main conclusions as the followings:
1. Landforms characteristics along RRFZ section Lao Cai -
Viet Tri is nature of boulder, levelling and symmetry. The
characteristics depict exactly recent geodynamic regime of the study
region.
2. In the study area, it can be divided into 10 types of
morphostructure with 22 sub-types. Based on their genesis, it
consists of three groups: tectonics, petrologic tectonics and tectonic
erosion. Based on uplifting-depressing nature, it includes 2 groups:
Neotectonic uplifted morphostructure and relative depressed
morphostructure- Neotectonic subsidence.
3. Study area are subdivided into 32 landforms with 4 different
genesis types, including type of tectonic-genesis landform; type of
landform with synthetic erosion genesis; type of landform with
dissolving-washing genesis; and type of landforms affecting by water
flows.
4. From Pliocene to Recent period, RRFZ section Lao Cai -
Viet Tri undergone three stages of landform evolution with 9 active
uplifting phases and inserting by 9 phases of relative stabilizing of
regional landform, demonstrated through existence of 3 plantation
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