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ACTIVE FAULT IN THE UPPER REGION OF CIMANUK RIVER RELATED TO ITS
IMPLICATION OF LANDSLIDE RISK ZONES
Nana Sulaksana1,Ludya Hermayanti
2,Puguh Setiyanto
3, Ildrem Syafri
1 and Murni Sulastri
1,
1Padjadjaran University, Jatinangor 45363, West Java, Indonesia
Email: [email protected] 2Training Centre of Mineral and Coal, Energy and Mineral Resources Education and Training Agency , Indonesia
Email: [email protected] 3Training Centre of geology, Energy and Mineral Resources Education and Training Agency , Indonesia
Email: [email protected]
KEY WORDS: Active Fault, Cimanuk Downstream, Straightness Landslide
ABSTRACT: According to the Department of Water Management Center of West Java, there are 40 rivers flowing
in the area of West Java. The development of Jatigede Reservoir in the area of Upper Region of Cimanuk
Watershed raises some concerns because the reservoir area passed Baribis fault, which formed minor faults in the
upper of Cimanuk Watershed. Faults can cause geological disasters such as landslides. It is necessary to make
prevention and minimize the possible impact of disaster. The purpose of this study is to obtain information about
the fault occurrences in upper region of Cimanuk Watershed that will affect landslide risk zones in the area. The
aim of the research is to obtain information about the existence of faults that control the occurrences of landslide
potential in the upper region of Cimanuk Watershed. Research area include of Sumedang Regency and Garut
Regency, covering some districts such as Tomo District, Paseh District, Situraja District, Pasanggrahan District,
Darmaraja District, and Wado District (Sumedang Regency), and Limbangan District (Garut Regency).
Geographically, the study area is located between 107o 45’ 46.95” - 108
o 10’ 43.04” East Longitude and 7
o 2’
35.84” - 6o 44’ 15.64” South Latitude.
1. BACKGROUND
Research methods done in this study include of geological mapping through collection of strike/dip data, joints, and
taking some pictures for documentary data. Besides that, statistical test is done to prove lineaments data and fault
indication through studio analysis. Then collection of landslide zones data in the research area is used to get soil
movement result through Weight of Evidence (WoE) method to determine how far the soil movement. Last method
is the arrangement of final report and making landslide zonation map based on WoE results.
Downstream part of Cimanuk Watershed is controlled by Baribis minor-faults located in the research area. Based
on laboratory analysis through DEM lineaments, river lineaments indicated the direction of these lineaments are
Northwest-Southeast, Smf, and occurrences of field data such as joint & offset which indicate the fault forming in
this area classified in sinisterly strike-slip fault and trending Northwest-Southeast. It is also classified based on the
distance of the river. The calculation result of WoE 0.7706878 shows the river lineaments parameter occurs soil
movement in the downstream part of Cimanuk Watershed.
1.1 Purpose and Objective
The purpose of this research is to obtain information about the fault occurrences in the downstream part of Cimanuk
Watershed that will affect landslide risk zones in the area. The aim of the study was to obtain information such as:
1. To determine the river lineaments of Downstream part of Cimanuk Watershed affected by the presence of
faults.
2. To determine Cimanuk landslide risk zones in the downstream region which are affected by the faults.
1.2 Usefulness of Research
The results of the research which describe the landslide risk zonation can be used as references of development
planning in the study area. It will also minimize the impact of geological disaster as a result of the faults.
1.3 Location and Time of Research
Administratively, research area include of Sumedang Regency and Garut Regency, covering some districts such as
Tomo District, Paseh District, Situraja District, Pasanggrahan District, Darmaraja District, and Wado District
(Sumedang Regency), and Limbangan District (Garut Regency). Geographically, the study area is located between
107o 45’ 46.95” - 108
o 10’ 43.04” East Longitude and 7
o 2’ 35.84” - 6
o 44’ 15.64” South Latitude as shown in
Figure 2.
Figure 2. Study Area
2. LITERATURE REVIEW
Cimanuk Watershed is located in Sumedang Regency and Garut Regency, include of some districts such as Tomo
District, Paseh District, Situraja District, Pasanggrahan District, Darmaraja District, and Wado District (Sumedang
Regency), and Limbangan District (Garut Regency).
2.1 Physiography
Based on Van Bemmelen (1970), research area is divided into five physiographic zones of West Java which has
trending of east - west according to the longitudinal direction of Java (Figure 2.1). Five physiographic zones are
(Figure 3):
Figure 3. Distribution of Physiographic Zone in West Java (Van Bemmelen, 1949; Sulaksana 2013)
1. Coastal Plain Zone of Jakarta
Jakarta coastal plain zone of north limit stretching from Serang until the eastern part of Cirebon to the
northern part of Java Sea, while the south limit stretching from Zone of Bogor around Purwakarta with a
width of approximately 40 km consist of alluvial deposition (river and coastal) and Quarternary volcanic
sediments (lava and pyroclastic).
2. Zone of Bogor
Zone of Bogor is stretching from western part of Rangkasbitung through Bogor, Purwakarta, Subang,
Sumedang and ends at Bumiayu with a width of approximately 40 km. Bogor zone is an anticlinorium of
Neogen-aged layers which have strongly folded and intruded intensively. It causes the deposition of
hornblende, pyroxene andesite and diorite.
3. Zone of Bandung
Zone of Bandung is located in south of Bogor Zone, stretching from the western part of Palabuhan Ratu Bay
through the valley toward Sukabumi, Cianjur, Bandung, Garut, and Citanduy Valley.
4. Southern Mountain Zone of West Java
Southern Mountain Zone of West Java is a plateau with a peak in the southern part of Bandung and located in
Palabuhan Ratu until Nusakambangan Island, southern part of Segara Anakan with a width less than 50 km,
Alluvial plains of north Java
Alluvial plains of north Java
Dome And Mountains In The
Central Zone Of Depression
Dome And Mountains In The Central Zone Of Depression
Bogor Zona
Bogor Zona
The zone Bandung and central
depression
The zone Bandung and central depression
Pengunungan Selatan Zona
Vulcanik kuarter
Vulcanik kuarter
Pengunungan Selatan Zona
narrowed to a few kilometers to the eastern part. Entire South Mountain is Java geanticline which experienced
a period of shrinkage sloping southward into the Indian Ocean.
5. Mountains Zone of Bayah
Mountain zone of Bayah is located on the southern coast of West Java which is bordered with Bandung Zone
and South Mountain Zone. This zone is also characterized by the faulted structures of geanticline after the
Tertiary period. Geological structures of the study area cannot be separated from the regional tectonic pattern
of the Java island, which have 3 geotectonic evolutions such as in the age of Cretaceous, Tertiary Era and the
boundary between Tertiary Era – Quaternary Era (Martodjojo, 1984).
2.2 Regional Stratigraphy
Based on the regional geology map of Arjawinangun area (Djuri, 1995), Bandung (Silitonga, 1973), Garut (Bachri,
1992) and Tasikmalaya (Djuri, 1995), stratigraphy in the study area contains lithological formation (youngest –
oldest) described in the such as:
Alluvium: Clay, Silt, gravel, pebbles, especially sediment deposited in Holocene river.
Result of the Young-Lava Mountain: Young lava flows of Mt. Ciremai which contain characteristic of
andesitic and young lava flows of Mt. Tampomas which contain characteristic of basalt in the western part
of study area.
Results of Unrefined Materials of Young Mountain: Breccia, andesitic-lava and basalt, sand, tuffaceous,
lapilli derived from Mt. Tampomas (in the sheet map of Bandung and Mt. Ciremai, actually these lithology
formed plains or low hills with yellowish gray and reddish-colored soil.
Result of Old Mountain-Lava: Old flow which has characteristic of andesitic with Hornblende minerals as
major minerals, shows the flow structure and firstly taken in Tarikolot Village.
Tuff-Pumice: tuffaceous sand, lapilli, bombs, lava, and pieces of solid andesite-basalt which have angle
with lots of bombs and pieces, derived from Mt. Tangkubanparahu (“A” Eruption, Van Bemmelen, 1934)
and Mt.Tampomas.
Results of the Old Volcano-Breccia: Volcanic breccia, mudflow deposition. The components consist of
igneous rock such as andesite and basalt. Exposed in the southern and eastern part of map sheet.
Deep Sediment Deposition (0-10) tuffaceous clay, sandstone, conglomerate and breccia, black-colored
clay, contain remains of plants (lignite).
Result of Unrefined Old Volcano: Mudflow volcanic breccia, andesitic and basaltic lava, tuffaceous
breccia, coarse sandstone, tuffaceous clay, greywacke sandstone.
Tuffaceous Sandstone, Clay, Conglomerate: Tuffaceous sandstone, tuffaceous silt, clay, conglomerate,
tuffaceous breccia contains pumice. These materials revealed in very wide weak-wavy plain of northern
part of map.
Citalang Formation: light brown-colored tuffaceous sandstone, tuffaceous clay, conglomerate, in some
locations found hard lenses of calcareous sandstones.
Member of Claystone of Subang Formation: Claystone contains dark grey-colored of Carl limestone layer.
In different locations also found the inset of green-colored glauconitic sandstone.
Upper Member of Halang Formation: tuff sandstone, clay, conglomerate, while sandstone is a major part.
Under Member of Halang Formation: Andesitic-basaltic volcanic breccia, beside that found also tuf, clay,
conglomerate, and morphological form of questa.
Member of Cinambo Formation Shale: shale with lamination of sandstone and limestone, tuffaceous
sandstone with thickness of 400-500m.
Sandstone Member of Cinambo Formation: greywacke, calcareous sandstone, tuff, clay, silt, greywacke
has characters of thick layers with black-colored inset of solid shale and clay. Sedimentary structures
developed in this formation are composite layers and trace structures which show rock debris deposited by
turbidity current.
2.3 Regional structure of Java
According to Van Bemmelen (1949) Zone of Bogor has experienced two tectonic periods such as Intra-Miocene
Period and Pliocene – Pleistocene Period. The tectonic period led to forming regional compression with trending of
north-south. According to Van Bemmelen (1949) study area is a series of anticlinorium which has trending of east –
west and naturally experience strongly folding. There are faults which cause shifting of the anticline and syncline
axis.
Intra-Miocene tectonics resulted formation of geanticline in Java Island, also form the fold and faults structures in
Paleogene and Neogene rocks. General direction of axis fold is east - west and strike-slip fault zone has trending of
southwest-northeast and northwest-southeast.
Pliocene – Pleistocene tectonics is a continuation of the previous tectonic period. In this period occurred volcanism
dominantly result volcanic sediments. Beside that the forming of folding and faulting occurred which is caused by
southern force that leads declining Bandung Zone. This strong pressure causes folding and reverse fault structures
in the northern part of Bogor, extends from Sumedang to Mount Ceremai. This fault known as Baribis Fault.
During this period a process of folding and faults caused by the subsidence of the north zone of Bogor, which led to
strong pressure disturbance on the Bogor zone. Relative folds east-west trending fault that faulted by horizontal
dextral whereas normal faults trending north-west there are two trends - southeast and southwest - northeast, while
the reverse fault which is in the south-west trending north-northeast. Situmorang (1976), states that the general
structure of the northwest trending Java is southeast. From the interpretation of gravity data of tectonic fault
Wrench concept has been developed by Moody and Hill (1956) was created by the Java tectonic patterns
Situmorang et al. (1976).
From the description above, tectonic elements that try to be revealed, among others:
1. System sharpness are meridian oriented east - west, and northwest - southeast, and south-west - north-east
caused by the north-south compression force which has an azimuth of N 140 E. This is because the Asian
plate collision with the Indian Ocean plate.
2. Wrench, first-order, second and third follow primary crease pattern in which only a few creases around Jakarta
as a second order. Furthermore, the forces acting trending south-west - north-east.
2.4 Regional Geological History
Van Bemmelen (1949) suggested in the early Oligocene, Bogor Zone is a deep ocean basin, which is characterized
by the deposition of flinch and marine sediments with inserts volcanic rocks, which became known as Pemali
Formation. After the evolution of non-volcanic lane ends, followed by volcanic activities are accompanied by
symptoms of decline, thus forming several underwater volcanoes on Early Miocene, which produces sediment,
andesitic and basaltic. In the Middle Miocene volcanic activity is reduced and replaced with the deposition of clay,
marl and limestone reefs in the marine environment indicates. In Bogor zone at that time, it’s formed the precipitate
formation and Formation Cidadap Halang. The lithology of the southern part consists of breccia and tuffaceous
sandstone lithology while the northern part is dominated by mudstone and marl. End of the Middle Miocene formed
geanticline southern hill country, which was followed by the launch of the peak towards the northern part of the
basin. End of Upper Miocene volcanism shifted to Bandung and Bogor southern zone which produces sediment
breccia beetle, this indicates that subduction zone has shifted towards more to the southern than ever. During the
Middle Miocene volcanic activity, sediment of Bandung and Bogor zone experienced strong erosion. Meanwhile
Jakarta Coastal Plain continued to decline characterized by clay and marl deposition known as the Kaliwangu
Formation of Pliocene old. In the Late Miocene, it can be said that the basin has been turned into a shallow Bogor.
It is characterized by sandstone unit with cross-maze sedimentary structures and fossil mollusks. On it was
deposited volcanic Pliocene - Pleistocene, where the activity is evident in the transition zone lines of Bandung and
Bogor zone.
2.5 Active Fault
According to Keller and Pinter (1996) definition of active faults are faults that never moves during the period of
10,000 years ago and potentially active faults are fault sever engaged in a period of 2 million years ago. While no
active faults are occur, it means that fault have not or never engaged in a period of 2 million years ago. Fault is a
geological phenomenon which is common in the earth's crust. Fault is defined as an area of fracture is accompanied
by a shift in the relative (displacement) of the block to the block of rock (Billing, 1959).
2.6 Morphotectonic
Morphotectonic is a geomorphological conditions in the area of research, which is controlled by tectonic that
happened in the past, because it has a dimension of space morphology and tectonics have time dimension (Suhemi,
2009). Tectonic landforms would describe most of the topography in the region (Figure 4) Basic information given
DEM and used in processing are the coordinates of points on the earth's surface DEM, namely: Topographic
mapping, civil engineering, hydrographic mapping, mining engineering, simulation and visualization of the ground,
military engineering DEM data shows that the study area has a morphology "hills and plains" as shown in the three-
dimensional images of the DEM (Figure 4).Morphotectonic can also be seen on the image (Sukiyah, 1993). It has
been observed that the alignment pattern analysis using aerial photos could explain the deformation conditions in an
area. Alignment patterns intersect and be an indication that the area susceptible to deformation process. Alignment
pattern contained in an area, either straightness of the ridge and the river can be an indication of active tectonic
control.
Figure 4. Dimensional DEM of Study Area
2.7 Tectonic Structure Patterns Java
From the various studies that have been conducted by Martodjojo (1994) and updated by Satyana (2007), basically
in Java consists of a four-way alignment structure includes Meratus Pattern (Northeast - Southwestern), Sunda
Pattern (North - South), Java Pattern (West-East), and the patterns of Sumatra (Northwest – Southeast) (Satyana,
2007).
• Pattern Meratus (Northeast - Southwestern)
Meratus patterns have the northeast - southwest (NE - SW), which includes the Cimandiri fault in West Java
that can be followed to the Northeast to Eastern boundary of the Olives Basin and Billiton Basin (Martodjojo,
1994). Faults contained in Meratus pattern is known start in Cretaceous to Paleocene (Supartoyo, 2007).
• Pattern Sunda (North - South)
The dominant pattern of the second structure described by the faults trending, north - south pattern called
Sunda (Martodjojo, 1994). This direction is represented by faults that bounding Asri Basin, Sunda Basin and
Arjuna Basin. Sunda pattern is generally has stretch patterned.
• Patterns Java (West - East)
The third direction is of the pattern is west - east and generally dominant in mainland Java, here in after called
"Java Patterns" (Martodjojo, 1994). In West Java, this pattern is represented by a fault - as Baribis reverse
fault, and the fault zone in Bogor (Van Bemmelen, 1949; Martodjojo, 1994).
• Pattern Sumatra (Northwest - Southeast)
The fourth direction is northwest - southeast of the main structure of Sumatra while in West Java and Central
Java is now no longer visible, because eroded by erosion (Supartoyo, 2007).
This structure can be indicated as the azimuth structure located in the study area. The dominancy of structural
trends in Java can be seen in (Figure 5).
Figure 5. Major Structure Trend in Java Island (Satyana, A., 2007)
2.6 Landslide
Landslide is a slope-forming material movement caused by shear failure, in addition to one or more areas of
landslides (Varnes, 1957).
2.6. 1 Type landslide
According to its kind landslides grouped into 6 (six) types, namely translational slides, avalanches rotation, the
movement of the block, to rock, soil creep, and the flow of material destruction (Varnes, 1978). In Indonesia alone
avalanches are common types are translational slides and avalanches rotation. Here is a description of the six types
of avalanches:
• Avalanches Translations
Translational slides as shown in Figure 6 are the movement of soil and rock in the future sliding plane that can
be flat or curve sloping.
Figure 6. Translational Landslide
• Avalanches Rotation
Avalanches rotation as shown in Figure 7 is the movement of soil and rock period in curved sliding plane.
Figure 7. Rotational Landslide
• Aligned Movement
Aligned movement as shown in Figure 8 is the displacement of rock that moves on sliding plane is flat.
Avalanches are also called translational slides rock form.
Figure 8. Block Movement
• The ruins of Stone
Rock slides occur when large amounts of rock or other material moves down by means of free fall. Generally
occur on steep slopes to hang, especially in coastal areas.
Authentic Slope
The land mass
moved
Authentic Slope
The land mass
moved
Origin position
The Moving block
Figure 9. Rock Slide
• Soil creep
Soil creep (Figure 10) is a type of slow-moving landslides. With this type of soil in the form of coarse and fine.
Type landslide soil creep is almost unrecognizable.
Figure 10. Soil Creep
• Flow of Rework Material
As shown in Figure 11, the type of landslide occurs when the ground moves past driven by water. The flow of
this land can be killed quite a lot. According to the Broms (1975) landslide also classified based on the material
depth avalanche, landslide classification is as follows:
Figure 11. The Flow of Rework Material
2.6.2 The cause of landslide
Landslide-prone slopes caused by the influencing factors, which include internal factors are factors derived from
slope body itself and external factors that are coming from outside (Zulfiadi, 2011). External factors that trigger
landslides, among others: seismicity, climate (rainfall), vegetation, morphology, rock / soil and the local situation
(Anwar and Kesumadharma, 1991; Hirnawan 1994), soil moisture levels, the presence of seepage, and geological
activity such as fracture (especially those that are still active), fractures and earthquake (Sukandar, 1991; Zulfiadi,
2011).
a. Earthquake or Vibration
b. Weather / Climate
c. Load imbalance in peak and Foot Slope
d. Vegetation / Plants Nature
e. Face Rising Groundwater
Origin position
rock falls
road most of
covered by a
material folds
bedrock in
the
basement
landslide materials come
from upper slope and fill the
sloping area
Karnawati (2001) also mentions that the geological conditions that include rock types, faults, stocky, and the degree
of weathering, physical environmental factors that influence the occurrence of landslides, in addition to the factors
of slope, texture and permeability of the soil, and climate.
2.7 Weight of Evidence (WoE)
Weight of Evidence (WoE) method is included in the bivariate statistical method that it is a model based on
Bayesian probability framework shown in a series of GIS environment (Mezughi et al, 2011; Yukni, 2014). In this
method, weights are calculated based on the presence or absence of ground movement events in the area of
research, such as the formula that has been delivered in Bonham - Carter et al (1994) as follows:
........................................ (1)
Where P is the probability, B is the presence and absence ground motion prediction factor, and S is the presence
and absence of ground movement events. Positive weights (W+) and negative weights (W-) indicates a correlation
between the presence of positive and negative predictive variables respectively and landslide. Calculation of W +
and W- in GIS is done by combining the incidence of ground motion parameters lineament classes, resulting in four
possible combinations of the frequency expressed as the number of pixels (Npix1 Npix2 Npix3 Npix4), as shown in
the following table (Mezughi et al, 2011):
Based on the equation (1) above, the formula can be written WoE in the number of pixels as follows:
........................................ (2)
Where Npix1 is the number of pixels on the ground motion events lineament class, is the number of pixels Npix2
ground motion events that are not present or attendance at class lineament, Npix3 is the number of pixels in the
class lineament without incident ground motion, and Npix4 is the number of pixels in which the incidence of
ground motion and parameters lineament none at all.
3. METHODS & MATERIAL
The data needed to analyze the active faults in the region and their implications for downstream Cimanuk landslide
prone zones are: geological data, such earth map scale of 1: 25000, regional geological map, straightness map of
Cimanuk downstream watershed area, topographic map scale 1: 25000, Data ground movement.
3.1 Subject and Object Research
In this study will be used as the subject is the measurement and analysis of river straightness and Cimanuk
Downstream Region morphometry. While the object of this study includes the morphology of the study area which
refers to the topographic map (Bakosurtanal) and satellite imagery.
3.2 Population and Sample
Population is the generalization region consisting of objects and subjects that have certain qualities and
characteristics defined by the researchers to learn and then drawn conclusions.
3.2.1 Operational Variables
The data used is the data field and the data studio, which of them is obtained from ASTERGDEM, topographic
maps, Volcanology and Disaster Mitigation, and field observation data. Data obtained from the studio include:
alignment ridge ASTER DEM, ASTER DEM alignment of the valley, alignment of the river, SMF
Data obtained from the results of field observations include:
1. Strike / dip stocky data
2. Ground motion data
3.3. Analysis Method
Statistical analysis was performed to determine the presence of active faults in the study area and to get the results
with a certain confidence level. These statistical tests include:
o Test normality of data distribution
o Test different (t-test)
Distribution normality test is required to determine whether the data obtained from the results of measurements and
observations derived from the normal distribution or population distribution is not normal. Different test (t-test) was
performed to see the comparison between samples free, whether significantly different or the same. There are two t-
test formula that can be used to test the hypothesis that two independent samples comparative Separated Variance
and Polled Variance. Formula (3) as separated variance and formula (4) as polled variance.
........................................ (3)
........................................ (4)
Based on the above formula, and then the following instructions in selecting the t-test formula:
1. If n1 = n2 and homogeneous variance σ1 = σ2, then it can be used t-test polled and separated variance. To find
t table used dk = n1 + n2 - 2.
2. When n1 ≠ n2, variant homogen σ1 = σ2 can be used t-test with polled variance. To find t table used dk = n1 +
n2 - 2.
3. If n1 = n2, the variance was not homogeneous σ1 ≠ σ2 can be separated and polled variance, knowing t table
used df = n1 - 1 or dk = n2 - 2.
4. When n1 ≠ n2, not homogeneous variances σ1 ≠ σ2 separated variance formula can be used. To find the
difference between the t table used df = n1 - 1 and dk = n2 - 1, divided by 2 and then added with t minim
price.
If t count < t table then accept H0 which means not significantly different or not. There is an average difference
between the two independent samples, but if t count ≥ t table then reject Ho which means significantly different or
the average difference between the two independent samples.
The next stage is to test the spatial analysis to determine the relationship between the incidences of soil movement
with the presence of active faults. Analysis of the spatial test to determine the effect of alignment parameters and
the flow of the river is done using the WoE method (Weight of Evidence), this method using Arc GIS software. In
the data processing steps taken are as follows, To measure the distance from the alignment by combining the flow
of the river and straightness. The distance of a point on the straightness can be obtained with the function of
Euclidean Distance. Further classifications per 100 meter distance, i.e. 100, 200, 300 and so on up to > 1000.
Classify distance to straightness. The classification is divided into 11 (eleven) class with manual start of the value
of 0-100, 100-200, and so on up to > 1000 meters. Classification process will set the new value of the value range
of 0-100 meters rated 1, 100- 200 value 2 and so on determining the incidence of landslides on each straightness
class. This process will illustrate how much of a landslide in each class alignment, for example in class lineament 1
(distance 0-100m) there are 8 occurrences of landslides, the lineament class 2 (within 200-300 meters) there are two
occurrences of landslides, and so on.
WoE to calculate AUC values obtained (Area Under the Curve). AUC values were used to test whether the
alignment parameters have influence to be reckoned against the occurrence of landslides.
4. RESULTS AND DISCUSSION
Area of research and field observations is located in the District of Wado and Darmaraja located in Sumedang. In a
study conducted by collecting data in the form of data strike / dip bedding rock, the data stocky, photos and data
from laboratory analysis and use of data to ground movements of Volcanology and Disaster Mitigation (PVMBG)
in the study area as a supporter.
4.1 Data alignment DEM (Digital Elevation Model)
Straightness interpretation of DEM conducted to determine the type of geological structure, the alignment of the
structure is the result of geological structures in a region and expressed in the form of ridges, depression zone. The
appearance of straightness in the study area can be derived from DEM as shown in Figure 13. Alignment
topography interpretation data of the drainage pattern (Figure 13) is useful to determine the geological structure that
develops as a result of tectonic and know the author in the field of rock lithology. The result can be provided from
the interpretation of the drainage pattern of the river lineament azimuth values obtained by the value of the
alignment length.
Figure 13. River Alignment Interpretation
4.2 Data Smf
Smf value is a reflection of the balance between the forces of erosion that cut along the curve of the mountain face
and tectonic style which produces mountain face. This is related to a series of active fault zones (Keller, 1996).
Active mountain face will show a straight profile with a lower value Smf, and mountain face an inactive or less
active profile characterized by irregular or more eroded, with high values of Smf (Wells et al., 1988). According to
Keller and Pinter (1996) division Smf value associated with a value from 1.0 to 1.6 tectonically active, reflecting
the value of 1.4 to 3.0 is still tectonically active, and a value of 1.8 to greater than 5 reflects tectonic not active. Smf
calculations in the area of research conducted as many as 10 locations, as shown in Figure 14. Analysis data of Smf
value calculation results in ten locationsobtained as follows:
Figure 14. Smf Map in the Study Area
Lineament of Cimanuk River Hilir District
4.3 Land Movement Data
Based on field data and the data obtained from the distribution point PVMBG ground motion events for Cimanuk
downstream basin spread in the study area. The point of this landslide covers most areas in Garut and Sumedang
District as shown on the following map landslide distribution point Figure 15.
4.4 Data Stump
In addition to the direction of alignment and the calculation of the value of Smf, fault occurrences in Lower River
Region Cimanuk can be observed also on the presence of muscular shear zones (shear fracture) and offset rocks.
The burly data obtained from the four points of the study site (Figure 16).
5. DISCUSSION
Data obtained from the analysis of studio data and field data, which then these data are statistically tested against,
and the statistical tests include tests of normality, homogeneous and different test and regression correlation test to
determine the activity of growing structures in the study area. The geological structure seen through the DEM,
topographic maps, Smf, ground movement data and a review of morphology, cracks, and avalanches in the area of
research that is caused by the fault which is supported by the stout and rock offset. Geological structure can be seen
with the DEM data, which is then performed on the image alignment withdrawal ASTERG DEM (Advanced
Spaceborne Thermal Emission and Reflection Global Digital Elevation Map). The withdrawal form straightness of
the ridge and valley and it can predict the existence of geological structures. Withdrawal topographic lineament was
also carried out on the river segment to calculate the azimuth of the river. Analysis data is done by using statistical
test.
5.1 Straightness Analysis DEM
The existence of faults in the Lower River Cimanuk Region can be observed from the appearance of DEM. It can
be seen that in the study area the straightness representing the geological structures in the area. Based on the
straightness of the alignment analysis with DEM and then analyzed in a diagram that includes valley and ridge
Rosette as shown in Figure 17 below. From this diagram ridge formed for alignment and valley straightness can be
seen that the frequency dominance fault lineament trending direction is Northwest-Southeast, and it can be
concluded that the direction of sharpness is Southwestern Sea-east.
Figure 17. Rosette Diagram of Valley (A) and Ridge (B) Alignment Analysis
5.2 Straightness Analysis Topography
River lineament analysis using topographic maps in the study area are described in the rosette diagram (Figure 18)
shows that the dominant direction of the alignment itself is in the northwest - southeast. From the diagram it can be
concluded that the emphasis directed towards Northeast - Southwestern.
Figure 18. Rosette Diagram of River Alignment Analysis
5.3 Analysis Smf
Smf value analysis conducted in ten locations assessment, of the ten locations between the values obtained from the
calculation of the Smf value taken at ten locations. Smf value calculation are as many as ten of data calculations,
the four are worth between 1.0 to 1.6, which means that associated with active tectonics, and four other calculation
data is also worth <3.0 this reflects the persistence of the effect of active tectonics, this is in accordance with the
classification Keller and Pinter. From these calculations it can be concluded that most of the watershed Cimanuk
Downstream area influenced by active tectonic processes.
5.4 Morphology Research Area
The existences of visible fracture morphology in the local area also supported by laboratory data such as
straightness DEM, burly in the field of data streams and segment results and offset is the product formed as a result
of tectonic processes that take place. Geomorphological observations in the field indicate that the study area can be
divided into three morphology, namely by morphology plains, hills morphology rather steep ramps and hills. The
morphology of the study area can be seen from the shape of the mountains, and depression zones as shown in
Figure 19.
Figure 19. Morphology of Study Area
5.5 Analysis Stump
The fourth point of data collection in the field stocky have been analyzed and obtained illustration result of the
direction of alignment stocky and primary emphasis on the study area. The data on the location of the first
observations can indicate the type of muscular and tensile shear zones (Figure 20), which is located on the lithology
sandstone, mudstone in the first observe locations are offset rocks, which indicate the direction of movement. The
four measurements obtained stocky sharpness Southwestern direction - Northeast areas of broken directional
northwest - southeast. Based on the analysis of muscular using software obtained σ dip approaching the central
point is that indicated cesarean σ3 indicate normal fault location (Figure 21).
5.6 Offset Rock
From the four locations of field data collection point for measuring muscular, predominantly indicate the direction
of sharpness Southwestern - Northeast, it is concluded that the direction of sharpness trending Northwest -
Southeast. In addition to getting the data stout, in the field also get the offset data show the direction of movement
of the rock. The offset is in sandstone and clay lithology offset trending toward the Northeast-Southwest, it is show
that the offset movement and muscular rupture plane direction (Figure 22).
Figure 22. Photo of Offset in Study Area
5.7 Zoning landslide
The data obtained from the field (Figure 23) and the existing literature of the research area shows that the area is
prone to landslides, with the type of translational and rotational. Landslides in the study area are affected by the
presence of faults control of the research sites.From the distance of the alignment classification is divided into 11
(eleven) classes ranging from 0-100 meters distance up to 1000 meters and the distribution as shown in Figure
24.From the analysis conducted to measure the distance to the river channel alignment distribution of distance
values obtained are very low, with the calculation of the value of the landslide WoE straightness obtained AUC
value of 0.7706878, the AUC values of this magnitude indicates that the alignment parameter is indicative of a fault
affecting the occurrence of landslides in the watershed Cimanuk Downstream section (Figure 25). The region is in
the process of construction of Jatigede reservoirs. So the water can flow through the area, and power plants will be
located in the region around the border district of Garut - Sumedang. The government's plan is great for the
construction of the reservoir, but the region has complex geological structure (Figure 25)
Figure 23. Photo of Landslide Location in Tuff Unit
Figure 24. Euclidian Distance Lineament Map
Figure 25. AUC Calculation Graphic
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