Potential Earthquakes in Yangon Region

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Potential Seismicity of
Yangon Region (geological
Approach)
Article · July 2011
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May 26, 2011 16:27 AOGS-SE 9in x 6in b1146-ch12
Advances in Geosciences
Vol. 26: Solid Earth (2010)
Ed. Kenji Satake
c World Scientific Publishing Company
POTENTIAL SEISMICITY OF YANGON REGION
(GEOLOGICAL APPROACH)
HLA HLA AUNG
Member, Myanmar Earthquake Committee,
MES Building, Hlaing University Campus, Yangon, Myanmar
hhlaaung@gmail.com
Yangon sits on the southeast corner of Ayeyarwady Delta Basin, 35 km from
the west of Sagaing fault and on the southern spur of NNW–SSE trending Bago
anticlinal ridge. Yangon is mostly covered with alluvial deposits. Bago anticline
is threatening Yangon with seismic disturbances. This disturbance might not
be a significant one but the movement along Sagaing fault that was believed to
bring severe damage to buildings and loss of human lives in Bago and Yangon
in 1930 may have potential of causing a catastrophic earthquake in the future.
The prevailing geological structures, along with surface geological condition,
soil characteristics, and tectonic setting have made Yangon an earthquake
prone area. In this paper, an effort is made to examine Yangon region with
respect to geological knowledge, existing historical earthquake records, recent
investigation of seismic activity and seismotectonic of Yangon region to give
information on earthquake hazard for the region. Geological knowledge is very
important for analyzing geological site characteristics to consider for urban
development. To-date Yangon has annual increase in population and expanding
urban development. If an earthquake of magnitude 7.0 on Richter scale occurs
in Yangon, there would be higher damage to the buildings and more loss of
human lives.
1. Introduction
This paper is the first attempt to give relevant information about potential
seismicity of Yangon region from the point of view of geological knowledge.
Owing to spare population and traditional construction of buildings, no
historical earthquake records had shown a catastrophic earthquake in
Myanmar. A basic element to mitigate the effect of potential damaging
earthquakes is the geological understanding of built environment, which
involves potential earthquake source areas related to rupture mechanism
and surface geology. Geological aspects are also important for earthquake
139

140 H. H. Aung
zonation mapping, which can provide reliable and practical outcomes for
natural disaster planning projects for future earthquake, land-use planning,
and building code revision.
2. Location
Yangon is located between latitudes 16◦
45 N–17◦
4 N and longitudes 96
1 E–96 20 E, on the southeastern corner of the Ayeyarwady Delta basin,
at the mouth of three rivers: Yangon, Ngamoyeik and Bago rivers and
34 km from the sea in the coastal area. It has a tropical monsoon climate
with annual precipitation of 2366 mm. The average temperature is 27◦
C. It
has population of about six million people. Owing to the annual increase
in population, the size of the city has expanded several times than its
prewar size. Yangon’s pride: the Shwedagon Pagoda was built on the top
of Singuttara Hill, on the southern spur of Bago Yoma (Fig. 1). Town plan
map of Yangon is shown in Fig. 2.
16˚-
17˚-
18-
Fig. 1. Location and general geological map of the Ayeyarwady Delta Basin (adapted
from Geological Map,1:1,000,000).1

Potential Seismicity of Yangon Region 141
Fig. 2. Town plan map of Yangon City.
3. Tectonic Setting
Yangon region is tectonically located on the southern spur of the NNW–SSE
trending Bago anticlinal ridge, which lies immediately on the western site
of Sagaing Fault. Bago Yoma is a ridge of both geological and geomorphical
prominence ridge with 400 miles long and 40 miles wide and is composed of
Miocene rocks. Bago Yoma extends toward south into the gulf of Motamma
and might be connected to Alcock Rise.2
Yangon is 35 km in the west
of Sagaing fault. The Bago Yoma, Sagaing fault, and Central Andaman
spreading center are the most signiﬁcant structures of shear band of Sagaing
fault with 100 km width.3

142 H. H. Aung
4. Geology
Yangon area is underlain by alluvial deposits (Pliestocene to Recent), the
non-marine fluvialtile sediments of Irrawady formation (Pliocene), and hard,
massive sandstone of Pegu series (early–late Miocene). Alluvial deposits are
composed of gravel, clay, silts, sands and laterite, which lies upon the eroded
surface of Irrawaddy formation at 3–4.6 m above sea level. The central part
of Yangon area is occupied by the anticlinal ridge as a backbone, 30 m above
mean sea level and covered with sands, sand rock, soft sandstones, shale,
clays, and laterite of Irrawaddy formation. The hard compact sandstone
and shale of Pegu series can be found at the northwest corner of Hlawga
lake with NNW–SSE strike dipping to the east.4
Alluvial deposits are found
in the surrounding areas of the ridge (Fig. 3), whereas lateritic soils can be
found along the ridge (Fig. 4).
5. Structure
In the geological map (Fig. 2), two anticlines can be seen trending
NNW–SSE and are cut by NNE–SSW trending transverse fault. The
folds of Bago Anticlinorium plunge gradually to the south and finally
disappear under the deposits of Ayeyarwady delta.5
Eastern fold approaches
Bago whereas western fold extends south to Yangon and further south
into the Mottama basin. The structural trends here include Twante,
Kawhmu, Yangon, and Hlegu-Thanlyin trends. They are NNW–SSE
trending and are double-plunging anticlines, cut by transverse faults
trending NNE–SSW. Folds are aligned with axes parallel to the direction
of maximum extension and are arranged as en-echelon and oblique to
the main Sagaing fault zone (Fig. 5). These structures are the southern
most continuation of the Bago Yoma and are located quite close to
the Gulf of Mottama. Twante anticline is a symmetrical and double-
plunging anticline with gentle dip 7–15◦
on both flanks. It is made up of
Irrawaddian rocks and alluvium in places. Kawhmu anticline is an elongated,
asymmetrical and doubly plunging anticline with NNW–SSE strike. NNE–
SSW trending en-echelon tranverse faults cut the anticline into slices.
Sabagyisan anticline is a symmetrical anticline with dips 5–20◦
plunging
to NNW.
Miocene and Pliocene rocks are folded and quarternary pebbles and
terraces are uplifted. These deformation found in Yangon region should be

Fig. 3. Geological map of Yangon.6
considered due to the mobility of Bago anticline. Two terraces are found
near Yangon with 10 m thick of alluvial clays. They are situated 70 km
north from Yangon and raised 20 m above the sea level due to the uplifting
connected to the development of Bago anticline.

144 H. H. Aung
Fig. 4. Soil map of Yangon. (Source: Land Use Bureau of Yangon).
6. Seismicity Background
In 17 December 1927, a six-grade earthquake hit Yangon and caused certain
amount of damages. It was felt 15,000sq.km from Kyangin to Dedaye
along the western slope of Bago Yoma. In July 1930 Bago earthquake
with M = 7.3 aﬀected Yangon, vibration spread caused damage to the
buildings and 500 persons and 50 persons were killed in Bago and Yangon,
respectively.6
The last record of the earthquake that struck Yangon is 1978,
M = 5.7. In the recent seismicity map (Fig. 6) two signiﬁcant clusters of

Fig. 5. Structural trends in Yangon Region (derived from Oil map).1
epicenters draw our attention: one is along N–S trending Sagaing fault and
second one is along NNW–SSE trending Bago anticline. These distributions
of epicenters imply the tectonic movement along these structures, which
are tectonically active. The Yangon earthquake in 1927 probably originated
from the uplifting of Bago Yoma caused movement along the lines of
weakness below the deltaic alluvium and Bago earthquake in 1930 was
originated from the displacement on Sagaing fault. As seen in this seismic
intensity map, seismicity is high in the south of Yangon area, which

146 H. H. Aung
Fig. 6. Seismic intensity map of Myanmar region. (Source: NEIC).
indicates that the Andaman sea region is a zone of high seismicity zone
originated at shallow depth of less than 30 km. In seismic intensity map of
Modiﬁed Mercalli Scale (U.S.G.S. earthquake catalog 1970–1973) (Fig. 7)
and earthquake zonation map of Bago–Yangon region (Fig. 8), there are
three earthquake hazard zones according to their relevant magnitude, in
which Yangon falls in seismic zone VI whereas Bago falls in seismic zone
VIII.
Based on the lithology and the structure of the area, two areas are
divided in the micro-zonation map (Fig. 9). The area along fault and fold
covered with sand rock is a critical area and the area covered with loose
sand and alluvial deposits are the most critical area because such alluvial

Fig. 7. Seismic intensity map of Bago–Yangon region. (Source: USGS earthquake
catalog).
soil are the most vulnerable area for earthquake hazard. As earthquake can
trigger landslides, slope stability studies are very important for future urban
development. In Yangon area, most of the areas are ﬂat-lying lowland in the
deltaic region where slope gradient is gentle so that landslide can only be
taken account along the river bank (Fig. 10). To deﬁne which area in Yangon

148 H. H. Aung
Fig. 8. Seismic zone of Bago–Yangon.
has the highest risk is super-imposing the seismic hazard micro-zone map
on the slope stability map. For Yangon area, the most suitable area for
further urban development sits outside the most vulnerable seismic zone
and landslide-prone area.

Fig. 9. Microzonation map of Yangon Area.
7. Active Structures and Seismicity
The historical seismicity background along the Sagaing fault, shown in
Geology of Burma by Chibbher (1983), and recent seismic investigation3
show that Myanmar lies within the broad, which is seismically active
Sagaing transform belt between India and Indochina plate. A series
of pull-apart basins from Central Andaman Basin in the south to
Hukawng Basin in the northernmost part of Myanmar and other related

150 H. H. Aung
Fig. 10. Landslide hazard map of Yangon area.
structures such as NW–SE trending thrust faults, NW–SE and NNW–
SSE trending en-echelon folds, the basin bounding faults of ENE–WSW
trending normal faults, and N–S trending strike-slip faults are formed by
the NNW-oriented extension and ENE-oriented compressive deformations.
Within through-going deformation zone, the structures formed by these
deformations as Neogene is active and these active structures are capable
of generating future earthquakes and these are the potential source areas in
Myanmar.7

8. Conclusions
The aim of this brief paper is to give a proﬁle of seismic hazard in Yangon
region from a geological approach. Geo-morphologically speaking, Yangon
lies in a coastal area of Ayeyarwady delta region, at the mouth of three
rivers and mostly covered with alluvial deposits. Tectonically, it is located
on the southern extension of Bago anticline and 35 km from the west of
Sagaing fault. Structurally, spur of Bago anticlinal ridge passes through the
center of Yangon city as a backbone and extends to the south. There are
many en-echelon folds in Yangon region trending NNW–SSE and are cut by
NNE–SSW trending transverse faults. On the seismic aspect, Yangon falls
in seismic zone VI. The prevailing geological structures along with surface
geological condition, soil characteristics, and tectonic setting have made
Yangon an earthquake prone area. As the population increases in Yangon,
urban development has been taking place, at present, mostly on alluvial
deposits. Now there are many high-rise buildings in many parts of Yangon.
Damage potential to the buildings and loss of lives in a future earthquake
with magnitude of 6 or 7 on Richter scale in Yangon would be much larger
than that in 1927 and 1930.
References
1. F. Bender, Geology of Burma (Gebruder Borntraeger, Berlin Stittgart,
Germany, 1983).
2. J. R. Curray, J. Asia Earth Sci. XX (2005) 1–42.
3. C. Rangin, GIAC Conf. Yangon, Myanmar (1996–1999).
4. W. Naing, M. Sc. Thesis, Univ. of Yangon (1970), unpublished.
5. G. P. Gorshkov, Byull. Sovj. Seim. 12 (in Russ.) (1959).
6. H. L. Chhibber, The Geology of Burma (Macmillan and Co. Limited,
St. Martin’s Street, London, 1934).
7. H. H. Aung, Advance in Geosciences 13 (2009).

YANGON RIVER GEOMORPHOLOGY IDENTIFICATION AND ITS ENVIROMENTAL
IMAPACTS ANALSYSI BY OPTICAL AND RADAR SENSING TECHNIQUES
Aung Lwina
, Myint Myint Khaingb
a
Remote Sensing Department, Mandalay Technological University, Myanmar - aung.al2006@gmail.com
b
Remote Sensing Department, Mandalay Technological University, Myanmar - drmmkhaing@gmail.com
Working Group VIII/4: Water
KEY WORDS: Fluvial, Sedimentology, LULC, Hydrologic process, Environmental impacts
ABSTRACT:
The Yangon river, also known as the Rangoon river, is about 40 km long (25miles), and flows from southern Myanmar as an outlet
of the Irrawaddy (Ayeyarwady) river into the Ayeyarwady delta. The Yangon river drains the Pegu Mountains; both the Yangon and
the Pathein rivers enter the Ayeyarwady at the delta. Fluvial geomorphology is based primarily on rivers of manageable dimensions.
The emphasis is on geomorphology, sedimentology of Yangon river and techniques for their identification and management. Present
techniques such as remote sensing have made it easier to investigate and interpret in details analysis of river geomorphology. In this
paper, attempt has been made the complicated issues of geomorphology, sedimentation patterns and management of river system and
evolution studied. The analysis was carried out for the impact of land use/ land cover (LULC) changes on stream flow patterns. The
hydrologic response to intense, flood producing rainfall events bears the signatures of the geomorphic structure of the channel
network and of the characteristic slope lengths defining the drainage density of the basin. The interpretation of the hydrologic
response as the travel time distribution of a water particle randomly injected in a distributed manner across the landscape inspired
many geomorphic insights. In 2008, Cyclone Nargis was seriously damaged to mangrove area and its biodiversity system in and
around of Yangon river terraces. A combination of digital image processing techniques was employed for enhancement and
classification process. It is observed from the study that middle infra red band (0.77mm - 0.86mm) is highly suitable for mapping
mangroves. Two major classes of mangroves, dense and open mangroves were delineated from the digital data.
1. INTRODUCTION
1.1 Landforms formed by rivers
Running water in fixed channels is the most widespread agent
of land sculpturing working on earth's surface. Therefore, the
landforms created are more important than those formed by
other agents. Flow of water takes place in rivers under the
influence of gravitation. The type of flow can be laminar or
turbulent. `Laminar' flow is a flow in which the streamlines
remain parallel to the axis of the flow. In a `turbulent' flowing
river, a mixing of water by turbulent eddies takes place.
A river can erode when it transports material. The transport can
take place in different ways:
- in solution
- in suspension - these are the small particles carried in
suspension.
- in saltation - sand grains hop over the bottom, the
sand grain reaching the bottom gives an impulse to
another sand particle.
- shoving: coarse material rolls over the river bed.
Coarse material is often deposited as riffles and bars in the
riverbed, these bars are placed alternating in the left and right
side of the river and form bank bars. In braided channels with
criss crossing waterways, channel-bars and islands develop
between the water courses. Laboratory experiments have shown
that the cross section of a channel transporting the same volume
of water is dependent on the type of bed material. Fine material
gives a deeper bed, coarse material a flatter, broader river bed.
A river can have a straight, a sinuous, meandering, or
a braiding channel. A meandering river flows in sinuous curves.
Meanders are arbitrarily confined to a ratio of channel length
to valley length. The water in the meander moves as a
corkscrew, the so called helicoidal flow, that means that the
flow is downstream, but besides that a movement in
perpendicular direction occurs, formed by the centrifugal force
on the water in the bend. This type of flow causes erosion in the
outer(concave) side of the meander and deposition in the
inner(convex) side. The strongest erosion takes place a short
distance after the central part of the bend. This causes "point
bars" to develop on the inner side, and the meander to migrate
downstream. A meander tries to broaden and to move
downstream. When meanders attain extreme looping, a cutting
of the meander can be formed during avulsions. In the cut-off
part an oxbow-lake is formed. In aerial photographs old cut-off
meanders, meander scrolls or point bars etc. can be easily
distinguished.
The zone where the meanders are formed is called
"meander-belt". Sometimes a relation between the width of the
channel and the width of the meander belt exists, according to
different authors the relation varies between 1:12 and 1:18. A
'braiding' river is characterised by different criss-crossing
channel ways around alluvial islands. The growth of an island
begins as the deposition of a central bar starts. The bar grows
downstream and in height and forces the water to pass through
the flowing water channels.
1.2 Remote sensing techniques for landform Analysis
Remote sensing techniques have opened new vistas for
landform analysis (both static and dynamic aspects), coupled
with field verification surveys. Landforms can be directly and
best viewed using remotely sensed data, since relief forms are
well expressed on the surface of the earth and recorded in
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
XXII ISPRS Congress, 25 August – 01 September 2012, Melbourne, Australia
175

images. The combination of systems (DIGITAL IMAGE
PROCESSING, multi-date and multi-scale data analysis)
increases information generation capability and thematic map
generation facility. These modern techniques have contributed
tremendously towards terrain analysis, understanding of site
conditions, spatial distribution of features, and resources.
Analysis of remotely sensed data using standard
interpretation techniques is particularly useful in channel
change detection, identifying palaeo-channels, regional
landform distribution, as well as detection of shallow buried
channels and buried valleys under special conditions using
thermal IR and radar imagery. In radar imagery over extremely
dry sands of desert areas of Sahara in northern Sudan, buried
valleys at 1.5 meters depth below surficial cover have been
detected (SIR-A data, 1981). Dynamical aspects of
geomorphology, landslides etc. can also be monitored. Digital
enhancement techniques are useful for improved interpretation
of terrain features. The development of landforms depends on
the climatic regime, the operative processes of denudation and
sedimentation during and after their formation as well as their
intensity in time and space, and the rocks and materials (their
composition, nature, and structure) acted upon. Man-made or
anthropogenic causes also affect landform development.
The identification of landforms and geomorpholoical
domain on remotely sensed data is based on area association
(arid, mountainous, glacial, coastal, flood plain, tropical etc.),
association of features, landform shape and size, drainage
patterns/ dissection, relief, tone, texture, land use/land cover,
erosion and other patterns etc. leading to "convergence of
evidence" upon logical inductive and deductive reasoning.
Analytical "Keys" can also be developed for an area of study
based on field criteria and a priori knowledge of typical forms
as seen on images.
Remote sensing provides a regional, synoptic view and permits
recognition of large structural patterns and landforms over
contiguous geomorphic domains. It enables the location and
delineation of extent of identified features observed over large
areas. The repetitive coverage of terrain in multispectral
mode provided by satellite mounted sensors enables
comparison of scenes of the same location in different periods/
seasons. This is extremely valuable for monitoring change, as
well as extracting more information about significant earth
features from scenes by viewing under seasonal conditions
(temporal and spectral resolutions).
2. REGIONAL GEOLOGY AND TECTONICS
2.1 Study area and its existing conditions
The present study area covering the Yangon and its surrounding
region falls in 96° and 96° 15’E and 16° 45’and 17° N as
referred as map index of UTM Sheet No. 1969-01. The central
part of the Yangon comprises Miocene consolidated sediments
overlain by the Quaternary sands, silts and clay. Win Naing
(1972) stated the uppermost part of the Mingalardon Ridge as
the Irrawaddy Formation of Pliocene age. But, thinly laminated,
weathered shale exposed in Shwegondaing area during
excavation for motor road extension works in 2003 and
completely weathered sandstone during excavation for the
foundation of the Yanshin Centre at the Shwegondaing Junction
reveal that the lithological character is resemble to that
Miocene sediments exposed in the Taikkyi Taungnio area (Tint
Lwin Swe, 2002). Kyaw Htun (1996) explained that Thadugan
sandstone and Besapat alternations in the Thadugan area were
belonged to the Upper Pegu Group of Miocene age; namely, the
Kyaukkok and Obogone formations. In addition, some rock
exposed in the left and right abutments of Inyar Lake and
geological drilled data for water well at the junction of the
Inyar and the Damazete roads (Tint Lwin Swe, 1998) show that
the lithological type is especially similar to that of the
Thadugan.
The Quaternary sediments widely distributed at the
outskirt of the Yangon, consisting of thick, high plastic, stiff
clay underlain by sand and silt. Win Naing (1972) classified
generally the Quaternary sediments into valley-filled deposit
and the alluvium. The valley-filled deposit includes the
Pleistocene older alluvium of a particular type of terrace
deposit (Leicester, 1959 and Kyaw Htun, 1996) of
unconsolidated gravels, sands and silts and the alluvial is
younger age clayey deposit. The pattern and distribution of rock
basement and soil deposit are depicted in Figure (1).
Figure 1. Soil and rock distribution of the Yangon area
(Win Naing, 1972)
Tectonically, the Yangon is situated in the southern
part of the Central Lowland, which is one of three major
tectonic provinces of Myanmar. The Taungnio Range of the
Gyophyu catchments area of Taikkyi District, north of Yangon,
through the Thanlyin Ridge, south of Yangon forming a series
of isolated hill is probably resulted from the progressive
deformation (Ramsay, 1967) of the Upper Miocene rocks as the
eastern continuation of the subduction or stretching and
compression along the southern part of the Central Basin and
regional uplifting of the Pegu Yoma.
2.2 Yangon river in and around soil investigations
The different varieties of the individual soil characteristics are
Meadow and Meadow Alluvial Soil, Gley and Gley swampy
soils, Swampy soils, Lateritic soils, Yellow brown forest soils,
Dune forest & Beach sand, Mangrove forest soils and Saline
swampy meadow gley soils. The meadow soils which occur
near the river plains with occasional tidal floods are non-
carbonate. They usually contain large amount of salts. Meadow
176

Alluvial soils (fluvic Gleysols) can be found in the flood plains.
They have the texture of silty clay loam and they have the
neutral soil reaction and are rich in available plant nutrients.
nMeadow Gley soils (Gleysol) and Meadow swampy (Histic
Gleysol) occur in the regions of lower depressions where the
lands are inundated for more than 6 months in a year. The
texture of these soils is clayey to clay and usually having very
strong acid reaction, and contain large amount of iron.
Figure 2. Soil map of the Yangon area (copyright of Land use
division, Myanma Agriculture Service (Feb 11, 2002)
Dune forest and Beach sand can be found only at the
coastal line of Myanmar. The areas of their occurrence are
insignificant. The coastal line should be under wind and water
erosion control. Mangrove forest soils occur in very small area
along the coastal line of Myanmar, especially in the region of
Ayeyarwady Delta. These are marine flat lowlands, which are
affected by daily tides. Saline swampy meadow gley soils in
Ayeyarwady Delta and along the river bands of the Gulf of
Motama and the marine flat lowlands influenced by the tidal
sea water, which is always salty.
2.3 Typical Drainage Patterns
This area almost fluvial food plain, other is lower coastal plains
where there may be few surface drainage channels. In and
around Yangon river areas, the water table is often high;
relatively young and subjected to a minimum of dissection. A
high water table minimizes runoff and restrict system that may
from between floods.
Many major streams in level regions are constructional. They
build up their own flood plains and have little contact with the
underlying material of the area. Some major streams in level
areas, however, are engaged in eroding and are, therefore
destructional. Examples of such streams may be found in
coastal plains and in lakebeds.
Figure 3. Typical Tidal Flood Pattern in Myanmar
3. METHODOLOGY APPROACH
The methodology used in this study involved distinct steps of
digital processing of individual remote sensing data, multi-
sensor data integration, and visual interpretation of the
geomorphological products. The processing of remote sensing
images was done using ENVI 4.7 and Sufer version 10.7.972
software, following schemes for enhancements and integration
of optical and SAR images successfully used for Yangon river
geomorphology and terrain analysis. The corresponding
information was acquired on the terrain based on a ground
positioning system (GPS) campaign and used as ground control
points (GCPs). Since the area presents low relief and no digital
elevation model (DEM) was available, an ortho-rectification
scheme, assuming a flat terrain model.
4. RESULTS AND DISSUSION
4.1 Interpretation and terrain analysis from optical data
Long ago back from more than 10 years, AVNIR imagery
taken by Japan Advanced Earth Observation Satellite (ADEOS)
Figure 4. ADEOS/AVNIR 432 FCC Color Composite Image
acquisition at December 25, 1996
177

at December 25, 1996. In this imagery, we easily interpreted by
visually for land use land cover condition of Yangon river in
and around and City area.
Figure 5. Landsat 432 Color Composite Ortho-rectified Image
acquisition at Feb 25,2006
In Figure 5, Landsat Satellite acquired with ETM+ Sensor for
the study area. After composite of FCC 432 combination was
done and carefully analyzed for landuse landcover extended
and urban, sub-urban sprawled areas.
Figure 6. Landsat 432 Color Composite Ortho-rectified Image
acquisition at March 3,2009
In May 2 of 2008, Myanmar was seriously hit by Cyclone
Nargis and there was damaged to coastal mangrove areas and
its biodiversity system in and around of Yangon river terraces
(see figure 6).
4.2 Interpretation and terrain analysis from RADAR data
Figure 7. JERS 1 SAR Multi Temporal image of study area
In Figure 7, Japan Earth Observation Satellite was taken
Synthetic Aperture Radar (SAR) imagery for 3 different
seasons of around 1996. Coastal surveillance and
environmental monitoring has motivated the development of
automatized feature extraction tools using remote sensing data.
Target detection by Synthetic Aperture Radar (SAR) has been
extensively studied in recent years. In carefully interpretation
from SAR Imagery, river boundary and coast line field give
high radar backscattered energy due to their high surface for
roughness. Strong waves and tides (surfing in particular) make
seawater very rough which leads to very high radar
backscattered energy at places. Coastline is therefore masked at
places between land and water boundary.
Figure 8. SRTM data of Yangon river rings
178

In Figure 8, Shuttle Range Topographic Mission (SRTM) data
was prepared for shaded and relief map for terrain conditions.
This study area is almost flat and fluvial flood plains. The
product generated from SRTM data to topographic analysis is
important for descriptions of soil contacts and structural
features. The perspective of the relief, through the simulations
of different angles of illuminations, gave the shadow of the
relief, giving the impression of concavity and convexity,
allowing the identification of structural features, soil contacts,
erosion zones and other geomorphological features of the study
area.
4.3. Gemorphological Map generation
Figure 9. Geomorphological Map of Yangon river in and
around area.
The landform classification system is based on geomorphologic
principles, i.e., classification on the basis of landforms, and the
dominant processes in operation related to historical processes.
Additional factors, including land use and land cover, were also
used for classification. The final geomorphological map is
presented in Figure 9. Integration of both optical and radar data
was implied for geomorphic landform mapping, in details of
terrain conditions, manmade features and lanuse land cover
around Yangon river bed and around Coastal flood plain
terraces.
5. CONCLUSION
The contribution of TM band 4 was related to the
discrimination of dense mangrove forest from secondary
vegetation of the coastal plateaus, whose spectral response is
mixed with exposed soil produced by human activity and
disaster affected. The JERS-1 SAR data have contributed to the
enhancement of distinct coastal vegetation height, geometry,
water content, and degraded and regenerating mangrove
regions. The Multi temporal SAR product was fundamental in
providing consistent information about the geo-botany
(vegetation and coastal sedimentary environment relationship)
and emerged and submerged coastal geology that cannot be
accomplished from field investigations alone..
6. REFERENCES
References from Books:
Bushnell, T.M et al., 1955. Air Photo Analysis. Newyork, USA
p.p 12-13
Garde, R.J., 2005. River Morphology. New Age International
Publisher, India, p.p 71-72.
Lecture Notes, Geosciences Division, Indian Institute of
Remote Sensing, India, p.p 103-104.
References from Other Literature:
Aung Lwin, R. S Chatterjee and Myint Myint Khaing, 2010.
Analysis of Change Detection on Coastline using ERS SAR
tandem pair. Myanmar Engineering Society Annual
Conference, Yangon, Myanmar
Kyaw Htun. 1996. Sedimentology and Petrography of South-
Western Part of Thadugan, Shwe Pyi Tha Township, M. Phil.
Paper, Geology Department, Yangon University, Myanmar
Pedro Walfir M. Souza Filho and Waldir Renato Paradella
2005. Use of RADARSAT-1 fine mode andLandsat-5 TM
selective principal component analysis for geomorphological
mapping in a macrotidal mangrove coast in the Amazon Region
Can. J. Remote Sensing, Vol. 31, No. 3, pp. 214–224,
Tint Lwin Swe, 2004. Determination of Peak Ground
Acceleration for Yangon and Its Surrounding Areas. Staff
Report, Yangon Technological University, Myanmar.
Win Naing. 1972. The Hydrogeology of the Greater Rangoon,
M. Sc.Thesis, Geology Department, University of Rangoon.
Myanmar
7. ACKNOWLEDGED
The authors would like to thank the National Space
Development Agency of Japan (NASDA). In the case of JERS-
1 SAR data and ADEOS/AVNIR imagery were kindly provided
by the Ministry of International Trade and Industry of Japan
(MITI) and NASDA for research purposes.
Special thanks are extended to USGS, Google Earth and Global
Land Cover Facilities (GLCF) Teams for free provision of
Landsat 7 ETM+ Imagery and SRTM images. In many depth
are due to my colleagues from Remote Sensing Department,
Mandalay Technological University, Mandalay for their kind
patience and encouragement to finish this work.
179

Ceylon Journal of Science: Physical Sciences, 4(1), 47-59 (1997)
RELATIONSHIP BETWEEN SUBSURFACE GEOLOGY AND GROUND
SUBSIDENCE OF BANGKOK METROPOLIS, THAILAND
N.W.A.M.M.K.N. BANDARA*
Asian Institute of Technology, Bangkok, Thailand.
ABSTRACT
Bangkok city, the capital of Thailand which has many engineering and environmental problems
due to ground subsidence was selected as the main study object in this research study. The study
included data collection, bore hole logging and investigations on some important underground
geotechnical parameters to prepare thickness maps, static water level maps, ground elevation and
subsidence maps of Bangkok subsoil. Thickness of both fine grained compressible clay layers and
that of coarse grained non compressible sand layers are highly varying from place to place and they
are highly deformed. Area of eastern Bangkok is affected by the highest ground subsidence and this
area is underlain by the thickest portion of both first and second compressible clay layers. The lowest
static water levels of upper most aquifers is also overlain by this area. The uppermost two
compressible clay layers contribute more percentage for ground subsidence.
1. INTRODUCTION
General Situation
The study area is located within the latitudes 13° 29' 32" - 13° 57' 45" and the
longitudes 100° 24'- 100°45' Bangkok Metropolis covers an area about 1569 square
kilometers. The area is extremely flat and the relief is less than 0.5 m. The elevation is ranging
from 0 to 1.5 m while the average elevation is less than 1.0 m above mean sea level (Fig. 1).
The ground subsidence is the most serious threat to the development of Bangkok and
its suburbs. Ground water withdrawal from the deep well pumping is the main reason for this.
However, the current rate of ground water pumping cannot be reduced by a considerable
amount because of the high demand. In addition, the surcharge load of engineering structures,
weight of over layers and vibration due to traffic and pile driving are significant. Differential
settlement of the ground surface creates engineering, environmental and social problems.
However, flooding is the most disastrous result of ground subsidence because of the lower
ground elevations and smaller gradient of slopes. There are some places where the ground
elevation has gone down beyond the mean sea level.
*
* Current Address: Department of Geology, University of Peradeniya, Peradeniya.
47

it li li li J4 ii ii ir it it i» it I I II II II I I if I I I I n it rt n II n ri rr u n 1 1 1 1 n it 11 n II if 11 •• il
Fig. 1: Ground Elevation above Mean Sea Level
48

Bangkok and its suburbs are already developed but, the geology of greater Bangkok
has been largely ignored in land use planning and development. In addition, a proper land use
planning was not used in its development. Unplanned infrastructures and low land
reclamation in vulnerable areas are some examples.
The magnitude and the rate of subsidence are directly related to the change in effective
stress in the various compacting beds which is a result of piezometric level changes and the
thickness and compressibility of soil.
OBJECTIVES
Determination of the relationship between subsurface stratigraphy, ground water
withdrawal and ground subsidence.
2. GEOTECHNICAL CONSIDERATION OF GROUND SUBSIDENCE
Geology and Structure
The area is underlain by thick Quaternary and Tertiary deposits consisting of alluvial
and deltaic sediments. Subsoil within the uppermost 200 m consists of two types of
alternative layers, coarse grained sand with high permeability and low compressibility and
fined grained clay with low permeability and high compressibility. According to Brown et al.
(1951) and Sodsri (1978), three types of sediments underlain by the Bangkok plain.
I. Unconsolidated silt, sand, clay and gravel in the flood plain, stream channel or
terrace.
II. Beach and esturine clay, sand and gravel
IU. Residual layers of laterite or creator capping stabilised surfaces.
According to Nutalaya and Rau (1981), Quaternary and Tertiary sediments of the
Bangkok delta represent a complex sequence with a thickness of more than 2,000 m but, only
the uppermost 200m is explored. In the lower central plain, sedimentation was controlled
during the Tertiary and Quaternary times by a combination of tectonic movements both within
the plain and in the adjacent mountains. Further, they pointed out that the Bangkok basin had
been continuously filled with alternative layers of sand and clay throughout the Quaternary
time.
These sediments are underlain by a highly fractured and faulted basement rock
consisting of quartzite, gneisses and granitic gneisses. A series of active faults and structural
blocks occupied the basement.
Ground Water Consumption
Ground water is extracted from all the sand layers within the uppermost 200 m of
Bangkok subsoil. There are number of ground water monitoring stations installed to monitor
the ground water level after identifying the critical zones and areas of heavy ground water
49

development in the Bangkok area. It is estimated that, about 1.2-1.4 million cubic meters per
day of well water is pumped from ground water aquifers in the Bangkok Metropolitan region.
Due to the unplanned ground water consumption, a number of environmental problems have
arisen such as salt water encroachment, ground subsidence, ground water depletion etc.,.
Flooding
Flooding is one of serious hazards in Bangkok metropolis. The flood season in
Bangkok generally begins in September but rainstorms can cause immediate flooding at
almost any time between May and October. However, the most severe floods occur in October
when river draining from northern Thailand brings water to Bangkok. In the spring tidal
period, flooding is more severe as the high water level in the sea retards the river flow,
resulting the water level to rise in the flood plains. In addition, hundreds of canals which
receive runoff from the large sub urban area also flow in to the river. These canals have with
negligible gradients or are concave in some locations. Tidal action sends water back into the
canals during high tide periods. Water gates are designed to prevent flood water but when the
city is flooded and the river is at its highest state, this measure is not sufficient to prevent
flood. Since the gradient is extremely flat, the river flowing across the city called Chao
Phraya can not keep the water within its own when a certain gauging height is reached.
However, the Chao Phraya river can discharge 1,500 m3
/sec through the city without flooding
low lying areas.
Ground Subsidence in Bangkok
As mentioned elsewhere the ground subsidence is a serious problem in Bangkok area.
Sodarathit (1989) found that the average ground subsidence in the eastern part of Bangkok
metropolitan region was 5 - 10 cm per year and some parts of the area is below the mean sea
level. However, it is difficult to determine how much of the annual flood damage is due to the
ground subsidence.
Brand and Balasubramaniuum (1976) showed that the consolidation of the soft clay
contributes the major part of the subsidence. According to Nutalaya et al. (1989), the ground
subsidence of Bangkok area affects more than 4,500 km2
area.
Effect of Ground Subsidence in Bangkok
According to Nutaliya et al., (1989) differential settlement occurs when structures
located at different foundation depth cause cracking and bending of structures, floor slabs,
concrete walkways and steps, detachment of septic tanks and sidewalks or steps from
buildings. Sinking of benchmarks is another serious problem and hence, the benchmarks of
Bangkok area can not be used as reference datum. In addition, as a result of lowering of the
piezometric level, saline water replaces fresh water in the aquifers located next to the sea and
therefore, the amount of saline water content increases in the ground water. The deterioration
of ground water quality is also caused by the penetration of mineralized water from the higher
pore pressure area in the clay layers in to the sand layers.
50

When ground subsidence continues, the gradient of ground surface decreases and
therefore, drainage of flood water by gravity flow will be reduced and at the same time, water
accumulates in the centre area of subsidence bowl. As a sequence, septic tanks in the flooded
area will become water logged and the foul mass of night soils tearing with virulent bacteria
and water borne diseases will become a potential health hazard. Therefore, ground water of
Bangkok is now highly polluted and not suitable for consumption at all.
3. MECHANICS OF SOIL CONSOLIDATION AND GROUND SUBSIDENCE
The annual rate of subsidence varies greatly in direct response to seasonal pumping.
Subsidence at a given location will continue as long as declining water levels continue to
cause increased effective stress.
Das (1994), summarized the theoretical expressions related to ground settlement in
three ways that is deformation of soil particles, relocation of soil particles and expulsion of
water or air from void spaces. In general, the soil settlement caused by load is divided into
three categories, i.e. immediate settlement, primary consolidation settlement and secondary
Consolidation Settlement. However, primary consolidation settlement of soil is the most
relevant type since it is the result of a volume change in saturated cohesive soils due to
expulsion of water occupied by the void spaces.
Empirical expression for one dimensional primary consolidation of saturated cohesive
soils is as follows,
For normally consolidated soil
S = primary consolidation settlement
Cc = compression index (slope of the e-log p plot)
T - thickness of the Layer
e0 = initial void ratio at the initial volume
Po = initial average overburden pressure
Ap = increase of vertical pressure
Pc = maximum past pressure
Terzarghi and Peck (1967) described the mechanics of subsidence due to deep well
pumping. According to their interpretations subsidence or settlement can result from
consolidation of soil deposits due to deep well pumping because of the lowering of ground
water level or piezometric pressure. As a result, a descending water flow occurs from
compressible clay layers to aquifers. Force generated by this flow will compress the clay and
other compressible deposits.
(1)
Where,
51

They further introduced a relationship between water level changes and effective
stress(Ao) i.e.,
Aa = Yw(H-h) (2)
where,
H = current water table
h = original water table
yw = unit weight of water
According to Terzaghi and Peck (1967), if the clay strata are soft and thick, and if the
water level is lowered over a considerable distance, the settlement is likely to be occurred
over a large area. Further, the general pattern of subsidence can be expected to be
characteristics bowl shape, with the greatest subsidence at the centre of the well field.
Declining of piezometric pressure in a water bearing deposit imposes an increase in
effective stress in all the soil strata above it and in itself. Increased effective stress causes
consolidation and hence ground settlement.
Ground subsidence generally corresponds to the piezometric pressure fall. According
to Dowson (1963), in many areas, subsidence is directly proportional to the elevation of the
ground water level that is directly related to the quantity of water removed.
4. METHODOLOGY
The ground water well log data and records of ground water monitoring stations in
Bangkok were used to identify the subsurface geological charateristics. The thickness of sand
and clay layers were individually calculated for each station and transferred them as separate
layers based on their depths.
The static water level variation from point to point were estimated by studying the
static water level from many stations in the vicinity of Bangkok metropolis.
5. RESULTS AND DISCUSSIONS
Projected Ground Elevation in the Year 2005
From Fig. 2, more than 50% of the study area which is below the latitude 13°45' N
will be submerged by the sea if the current rate of subsidence is allowed to continue. The most
important zone of the city is situated within this limit.
52

H t m - - ,
" J , I U
MMI _ ' " IUUI .'.]»»'.»._,, ' l*Ji
u n 11 I I II II n ir li i» » II I I I I I I I I ii it i« I I n n r> ri n n ri ir ft 1111 •> 11 M n if 11 IT II I I II
Fig. 2: Projected Ground Elevation AMSL (m) in the Year 2005
Stratigraphy of the Study Area
The Chao Phraya basin comprises alternative layers of sand and clay. However,
during this study, these alternative layers were examined only up to 200 m depth from the
ground surface because of two reasons. First one is the depth of bore holes since most of them
penetrated up to the depth around 200 m while the other one is geotechnical importance of
uppermost subsoil within this range.
Five sand layers and another five clay layers could be identified within this limit and
the variation of subsoil characteristics of these strata and their depth range is shown in Table 1
and a N-S cross section over the study area is shown in Fig. 3.
53

From the Fig. 4, the rate of ground subsidence is varying from place to place.
According to the maps produced in this study, the highest ground subsidence rate takes place
in the area south to the Bangkok Metropolis where the first compressible clay layer has its
thickest section (Fig.5). This layer has the highest compressibility when compared to the other
lower lying compressible layers. In addition, as mentioned above, the static water levels of top
most two aquifers (Pra Phradaeng and Nonthaburi) are at their lowest level beneath the same
area (Fig. 6 and 7).
Furthermore, the rate of subsidence varies from place to place making depressions. In
addition to that, the rate increases towards the centre of each depression. Six major
depressions can be seen over the study area.
With the increasing of ground water withdrawal from sand layers, water contained in
compressible layers drains off from both top and bottom in to the overlaying and underlying
sand layers resulting a heavior. This is because of the hydraulic gradient developed due to the
ground water withdrawal.
Table 1: Description and the Depth Ranges of Soil Strata within the Upper-Most 200 m of Bangkok Sub Soil
Name of the Strata Soil Description Depth Range (m) Thickness (m)Name of the Strata Soil Description
Top of
Layer
Bottom
of Layer
Range Average
Bangkok Soft Clay Gray colored soft clay with
shell fragments
0 11-19 11-19 15
First Clay Layer Stiff to medium clay with
shell fragments
11-19 13-65 1-45 13
First Sand Layer Fine to coarse sand in
association with clay
patches.shell fragments
13-65 25-75 5-45 12
Second Clay Layer Clay with shell fragments 25-75 35-82 5-20 14
Second Sand Layer Fine to coarse sand with clay
layers
35-82 44-90 5-30 16
Third Clay Layer Silty clay with shell
fragments
44-90 60-102 5-40 17
Third Sand Layer Sand, fine to coarse with
clay layers and gravel
60-102 85-123 6-40 25
Fourth Clay Layer Hard clay with inter beds of
sand, shell fragments
85-123 98-157 5-25 19
Fourth Sand Layer Silt sand with shell
fragments
98-157 118-185 5-36 15
Fifth Clay Layer Clay, sandy with shell
fragments
118-185 124-210 5-68 14
Fifth Sand Layer Fine to coarse sand with thin
clay layers
124-210 - - -
54

M*: t . city h f m : I - M Uta-i
Fig.3: North-South Vertical Cross Section ofBangkok Metropolis
n II I I I I n I I ii ir I I I I •• it M I I I I I I •• if 1 1 I I fi FI ri rt if »i n if it »i •• « « I I • • • • " • • • •
Fig.4: Rate of Ground Subsidence in the Year 1996 (cm/yearj
55

II II Ii l l I I l l l l ir « • • • • i l il I I l< i l i l If I I • • II ri fi l i ll l l l « If M i l I I ll I I M l l l l l l If l i ll ll
Fig.5: Thickness of the Uppermost Clay Layer (m) •_
ll if II » l i I I l i ir I I if it II I I tt I I II l l if I I I I II II n ri fi » ri if fl l l if li • • I I I I I I • • I I i l if i l
' Fig.6: Static Water Level of the Pra Pradeang Aquifer in 1996 (meter below mean sea
56

6. CONCLUSIONS
1. Six compressible and five non-compressible layers were identified in the strata
within uppermost 200m depth (table 1). Basically, Bangkok metropolis consist of five
sand layers. The five sand layers are found at an approximate distance of 30m, 60m,
90m, 135m and 170m depth from the surface. Although these values will give some
idea of the sand layer locations, there can be high variations to the above figures
depending on the locality due to the presence of synclines, anticlines, connections of
layers etc. In some instances, sand lenses are found at various depth levels in the
Bangkok area. The first sand layer which is situated at a level of 20-40m takes almost
a planner and horizontal profile throughout the study area.
The Bangkok soft clay layer with an approximate thickness of 10-20m is the
top most layer. Other five layers are interbeded with sand layers.
2. The present highest subsidence rate takes place in the area of eastern Bangkok
where both the two top most compressible clay layers have their thickest sections.
3. The static water levels of all the top most aquifers are at their lowest, where the
rate of subsidence is highest.
4. Ground subsidence makes depressions throughout the area.
ACKNOWLEDGEMENTS
The author first expresses his profound gratitude and sincere appreciation to his
advisor Professor Prinya Nutalaya, for his persistent guidance, invaluable suggestions,
generous help and friendly discussions, all of which enabled the author to accomplish this
study.
Author also wishes to extend his sincere appreciation to Professor
A.S.Balasubramanium and Dr. Noppadol Phein Wej for their valuable guidance, suggestions.
A very special word of thanks goes to Dr. Vachi Ramnarong, Director of the
Mitigation of Ground Water Crisis and Land Subsidence in Bangkok Project (MGL),
Department of Mineral Resources, Thailand for providing valuable data related to this study
work.
REFERENCES
1. Research Report, Division of Geotechnical and Transportation Engineering, AIT,
Bangkok, Thailand, Vol. 2 (1978b).
2. Research Report no 82, Division of Geotechnical and Transportation Engineering and
Division of Water Resources Engineering, AIT, Bangkok, Thailand (1978 c).
3. Research Report No.91, Vol. 2, AIT, Bangkok, Thailand (1981).
4. A Report submitted to the Japan Internationa] Co-operation Agency by School of Civil
Engineering, AIT, Bangkok, Thailand (1993).
5. Brand, E. W. and Balasubramanium, A. S., Proceedings of the Second International
Symposium on Land Subsidence, Anaheim, California, pp. 365 - 374 (1976).
58

6. Das, B. M , Principles of Geotechnical Engineering, Third Edition, Ch. 8, pp. 253- 315
(1994).
7. Dawson, R.F., J. Surveying and Mapping Division, ASCE, V.89, No.SU2, pp 1-12
(1963).
8. Department of Mineral Resources and Ministry of Industry (DMR), 1992, Ministry of
Industry, Records of Groundwater Monitoring Wells in Bangkok and Adjacent
Provinces, Report No. 1, Bangkok, Thailand (1992).
9. Heley and Aldrich, Report of Haley andAldrich, Inc. (1969)
10. Metcalf and Eddy Inc., Report on Ground Water Monitoring, Well construction and
future programs, The Metropolitan Water Work Authority, Bangkok, Thailand (1972).
11. Nutalaya, P. and Rau, J.L., Episodes, Vol. 4, pp. 3-8 (1981).
12. Nutalaya, P., Yong, R.N., Chumnankit, T. and Buapeng, S., The Report Presented at the
Workshop on Bangkok Land Subsidence, 22-23 June (1989).
13. Rau, J. L., The Geology of Bangkok Metropolis and Adjacent Areas, ATT, Bangkok,
Thailand (1981).
14. Terzaghi, K., and Peck, R. B., Soil Mechanics in Engineering Practices, Wiley, New
York (1967).
15. Worayingyong, K., Preliminary Predictions of Subsidence in the Bangkok Area, M.Eng.
Thesis, AJT,Bangkok,Thailand (1975).
16. Nutalaya, P., Proc. of the Conference on the Geology of Thailand, Department of
Geological Sciences, Chiangmai University, Thailand (1973).
59

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