VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY INSTITUTE OF GEOLOGICAL SCIENCES MINISTRY OF EDUCATION AND TRAINING *** HANOI UNIVERSITY OF MINING AND GEOLOGY *** - NGO VAN LIEM HOANG TUAN CHUNG CHARACTERISTICS OF LANDFORM EVOLUTION IN RELATION TO RECENT GEODYNAMICS ALONG THE RESEARCH ON SUITABLE SURFACE MINING RED RIVER FAULT ZONE TECHNOLOGY FOR SMALL-SCALE MINES IN VIETNAM Major: Geomorphology and Paleogeography Code: 62.44.72.01 Major: Surface Mining Engineering Code: 62.53.05.01 ABSTRACT OF DOCTORATE THESIS ABSTRACT OF THESIS OF DOCTORATE IN ENGINEERING HANOI - 2011 Research finished at Institute of Geological Sciences Vietnam Academy of Science and Technology Supervisors: Acc Prof Dr Phan Trong Trinh, Institute of Geological Sciences 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 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” Purposes of thesis: clarifying the relation between characteristics of landform evolution with active tectonics and recent geodynamics RRFZ from Pliocene to Recent 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 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 (N2) to Recent – Spatial scope: is a part of RRFZ and surroundings from Lao Cai to Viet Tri, from 103013’E to 105043’E and 21012’E to 22052’E The new contribution of the thesis - Defined 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 topographic surfaces; horizontal motion creates fault segments, among them, it can be defined their location and dimension of main segments which have possibility to generate maximum earthquake with magnitude from 6.3 to 7.0 in Richter scale 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 Documentation: Thesis was built basing on database collected by myself during participation in scientific projects from 2006 to date; within 15 published articles on journals and workshop proceedings in Vietnam and overseas; from field-trips from the year 2006 to present Besides, I also refer uncountable amount of related works The outline of thesis: Apart from Preface, Conclusion and Refercence cited sections, this thesis consists of chapters, displayed in 146 typed pages including 51 figures, tables and 10 inlustration pictures 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 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 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 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 righlateral 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 1.2.2 Domestic: It can be divided into 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 main methods were applied, as listed below: (1) Geological- geomorphological methods: Analysis of morphostructure; analysis of 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 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 levels of vertical dissection, corresponding to levels of activity: weak (with dissection ranging from 0-50 m/km2 to 50-100 m/km2), average (from 100-150 m/km2 to 150-200 m/km2), strong (from 200-250 m/km2 to 250-350 m/km2) and very strong (from 350-500 m/km2 to above 500 m/km2) 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 planation surface at elevation 200-300m, Middle Pliocene in age and (3) Segmented valley pediment making low slope hills, 3-8o, late Pliocene in age Slope surfaces includes 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 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 terrace levels with different elevation and age: (1) Erosional-depositional terrace surface level I, elevation 7-14m, age Q13; (2Erosional-depositional terrace surface level II, elevation 15-25m, age Q12-3; (3) Erosionaldepositional terrace surface level III, elevation 35-55m, age Q12 and (4) Erosional-depositional terrace surface level IV, elevation 7090m, age Q11 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 N21, at 200-300m aging N22 and valley pediments segmented into mounds and hills aging N23; (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 righlateral 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 (300-330o), 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 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 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 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 stations evenly distributed along two strands of RRFZ The stations are located in 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 ChieuDoi 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 17 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 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 18 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 righlateral 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 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; 19 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 20 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 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 21 4.4.2 PGA assessment: Peak ground acceleration when earthquake occured was also estimated for 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/s2 ; PGA with 10000 years cycle is 0.339g corresponding to 332 cm/s2 ; horizontal PGA corresponding to maximum designed earthquake (cycle 950 years) is 0.271g corresponding to 265 cm/s2 ; effective base acceleration with cycle 475 years is 0.214g corresponding to 210 cm/s2 ; and effective base acceleration with cycle 145 years is 0.176g corresponding to 173 cm/s2 4.4.3 Deformation and Coulomb stress change model with occurrence of maximum earthquake: Coulomb stress change model was calculated at all 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 22 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: 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 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 groups: Neotectonic uplifted morphostructure and relative depressed morphostructure- Neotectonic subsidence Study area are subdivided into 32 landforms with 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 From Pliocene to Recent period, RRFZ section Lao Cai Viet Tri undergone three stages of landform evolution with active uplifting phases and inserting by phases of relative stabilizing of regional landform, demonstrated through existence of plantation 23 surface levels and river terrace generation and types of alluvial flat with different elevation and age Study area is undergoing uplifting with none-uniform uplifting nature Average rate of uplifting of regional landform in Pliocene is ~0.11-0.24mm/yr; from late Early Pleistocene to late Middle Pleistocene is ~0.17-0.30mm/yr and from the end of late Pleistocen to Recent is ~0.70-1.25 mm/yr Faults is not continously active but segmented into highly potential seismogenic segments: SH1, SH2, SH3, SC1 and SC2 with various evidence of topographic displacement, those are offsets of rivers, streams, river terrace level and fault slip surface, slicken sides in recent sediment and weathering layers, vice versa These displayed righ-lateral strike-slip regime The total amount of river and terrace offset ranges from ~100m to ~1300m, displacement rate estimated at different segments ranging from ~1.1mm/yr to ~1.8mm/yr In recent, RRFZ at SE part of Vietnam teritory displaces with rate less than 1mm/yr Regional upliftting and strike-slip displacement have close relationship with each other In Pliocene to Recent, uplifting has been increasing and righ-lateral strike-slip displacement lowering Seismicity in the area has a close relation with manifestation of recent tectonics and geodynamics The area in this study has potential to generate maximum earthquake with magnitude ranging from 6.3 to 7.0 in Richter scale Earthquake can cause landforms offseted and strongly affect to cities and important infrastructure adequately located fault zone such as Thac Ba lake, Lao Cai, Yen Bai and Viet Tri cities and as well as Ha Noi capital 24 BIBLIOGRAPHY Ngo Van Liem, Phan Trong Trinh, Hoang Quang Vinh (2006) The active faults and the maximum earthquakes of the Red River fault zone in Lao Cai-Yen Bai area; Journal of Sciences of the Earth-VAST; 21(2), pp 110-120 Ngo Van Liem, Phan Trong Trinh, Nguyen Tuan Anh, Hoang Quang Vinh (2008) Application of GPS to the determination ò present day tectonic moverment and deformation of ground surface and construction works Vietnam Geotechnical Jounarl, No 2, pp 21-32, 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Télédétection, V7, N1÷4 Phan Trong Trinh, Bui Van Thom, Nguyen Hong Phuong, Hoang Quang Vinh, Ngo Van Liem et al (2008) The role active Neotectonics to geohazards at the Central Vietnam Journal of Sciences of the Earth-VAST, No 30(4)PC, pp.396-407 Hanoi 25 Phan Trong Trinh, Ngo Van Liem, Nguyen Van Huong, Hoang Quang Vinh (2008); Schema of actual tectonic movement in Vietnam Eastern Sea and surrounding area; Proceedings: First National Scientific Symposium on Marine Geology; pp.100-107, Ha Long 10 Phan Trong Trinh, Bui Van Thom, Hoang Quang Vinh, Ngo Van Liem et al (2008) The role active tectonics to geohazards at the Central Vietnam and adjacent – searegion Proceedings: First National Scientific Symposium on Marine Geology; pp.154-164; Ha Long 11 Hoang Quang Vinh, Phan Trong Trinh, Nguyen Van Huong, Ngo Van Liem and Le Minh Tung (2006) Remote sensing and GIS for seismic risk assessment in Hoa Binh hydropower dam; GIS Ideas Workshop, November 9-11, 2006, Ho Chi Minh, Vietnam 12 Hoang Quang Vinh, Ngo Van Liem, Nguyen Van Huong, Le Minh Tung, Phan Trong Trinh (2006) Seismic hazard assessment in Hoa Binh hydropower dam; Provention Consortium – ADPC Workshop, Innovative intiatives in disater reduction; 6-7 December 2006, Bangkok, Thailand; P161-169 13 Hoang Quang Vinh, Phan Trong Trinh, Nguyen Van Huong and Ngo Van Liem (2009) Assessment of seismic hazard in the Hịa Bình hydropower dam Journal of GEOLOGY, No 34/2009, Series B 14 Nguyen Vi Dan, Ngo Van Liem, Bui Thi Le Hoan (2005) Intial study on recurrence of flash flood in Ha Tinh province; Jounal of Science (Vietnam National University, Hanoi); No5AP, pp 2934 15 Nguyen Vi Dan, Nguyen Hieu, Ngo Van Liem (2006) Intial landslide warning in the Northern middle of Vietnam by using geomorphologuc method Proceedings: Second National Geography Workshop; pp 11-19; Hanoi 26 ... area; Journal of Sciences of the Earth-VAST; 21(2), pp 110-120 Ngo Van Liem, Phan Trong Trinh, Nguyen Tuan Anh, Hoang Quang Vinh (2008) Application of GPS to the determination ò present day tectonic... Phan Trong Trinh, Mai Thanh Tan, Ngo Van Liem et al (2007) Apport de la télédétection l’étude des faillies actives et des risques simiques au nord du Vietnam Télédétection, V7, N1÷4 Phan Trong. .. Bai and Viet Tri cities and as well as Ha Noi capital 24 BIBLIOGRAPHY Ngo Van Liem, Phan Trong Trinh, Hoang Quang Vinh (2006) The active faults and the maximum earthquakes of the Red River fault