10th Asian Regional Conference of IAEG (2015)

Control morphology to the landslide Induced Earthquake:
Case Study Padang Pariaman, Sumatra
Sumaryono1,2, Yunara Dasa Triana1, Sri Hidayati1, Donny R. Wahyudi2,
Dicky Muslim2, and Nana Sulaksana2
1

Geological Agency, Indonesia
Department of Geological Engineering, Padjadjaran University, Indonesia

2

Abstract
The September 30, 2009, Padang earthquake has induced huge landslide in Padang Pariaman Regency, West
Sumatera, Indonesia. Earthquake induce landslide occasionally occurred in tephra with a thick pumice deposit. The
thickness and characteristic tephra contents of pumice, slope, presence of clay layer to the sliding surface are themain factors controlling landslide occurrences. Other factors are morphology and tectonics conditions. The present
lithology and morphology play important factors controlling of landslide occurrences within this area. This study
aimed to identify the level of tectonic activity in Padang Pariaman, West Sumatra by morphotectonic index analysis
such as ; the stream-gradient index(SL), drainage basin asymmetry (Af), valley floor width–valley height ratio (Vf),drainage density (Dd), and mountain-front sinuosity (Smf). Geomorphic aspects were analyzed by using
geomorphological index to identify the tectonic activity of the study area. The lineament of stream segments will becompared with the azimuth of joint and azimuth of landslide crown using statistical test to determine the relationshipbetween these variables. Based on morphometric measurements it’s known that the study area has an active tectonic
activity level and the river channel give significant parameter to the landslide occurrences. In this paper we will
describe landslide triggered by earthquake in the Padang Pariaman, West Sumatra from morpho-tectonics of view.
Keywords: landslide, geomorphology, tectonics, river channel.

1.

zone may become important trigger of landslide
occurrences within this area.
West Sumatra September 30, 2009 earthquakewith magnitude scale 7.6 Mw had triggered landslides
at approximately 154 sites caused 244 people killed
and dozens of houses buried. Landslide occurred
within 52 miles (+ 84 km) radius from the epicenter ofthe earthquake, mostly affected the whole of West
Sumatra Province area. In Pariaman and Agamregencies especially Tandikat and Damarbancah area
were severely damaged. Geologically, this area iscomposed mostly of pyroclastic deposits and theselandslides occurred in strongly weathered volcanic
terrain. Despite earthquake mostly induced landslides
in West Sumatra area, but there are some factors
which have important role, namely morphology andtectonical conditions. In this paper describe
controlling factor of Padang Pariaman landslide frommorphology and tectonics point of view.

Introduction

According to Heath (1988) and Varnes (1996), thefactors controlling landslide occurrences must
consider the conditions of geomorphological / slope,geological, soil or rock, hydrogeological and land use.
Keefer (2000) showed that the geotechnicalparameters as friction angle and cohesion cannot
explain the distribution and density of landslides. He
also showed that landslide caused by earthquakes
more correlated with the characteristics of engineering
geology and geomorphology than geotechnicalparameters. Lin (2008) showed 88 percent ofearthquake-induced landslides due to Chi Chi
earthquake do not relate directly with river channel.
Wang, (2010), based on laboratory test using ringshear apparatus, the result indicates that the pumicelayer from landslide location at Pariaman is verystrong even in the saturated condition and the slope
can remain stable during rainfall. Faris (2014), theresult from cyclic triaxial show that pumice layer
posible to failure without increasing water pore
presure, in dry condition, small earthquake with PGA
of 0.05 g would only probably excites minor landslide.
the high probability of catastrophic landslide that
could happen in the area even if earthquake with PGA
as small as approximately 0.15 g occurred during
rainfall result Warmada (2012) conclude the highdegree of weathering which possibly overprinted byalteration in Padang Pariaman district produces large
amount of clay minerals, especially smectite and illite.
The presence of smectite and/or illite in the weathered2.

Methodology

Field survey was conducted in Pariaman District
to identify the dimension and stratigraphy as well as
to map the distribution of landslides. In order to makeclear the characteristic of the landslide, topography
analysis using IFSAR were carried out. GIS Analysis
is performed to assist the morphometric and slope
analysis. The flowchart of the methodology toanalysis factor controlling landslide is shown in Fig.1.

1

10th Asian Regional Conference of IAEG (2015)

Satellite
Image
IFSAR

Landslide
distribution,
dimensionand slope

Field
Investigation

Geologicalcondition andstratigraphy,
landslide
distribution ,dimension and
slope

GIS
Analysis

flowsliding characteristic at gentle slope (Fig. 3a) and
Tephra deposit consist pumice layer overlying theclay (Fig 4b). The SEM and XRD analysis found outthat clay minerals, especially halloysite (Table 2 andFig 5) formed due to tephra alteration. It is strongly
controlling factor of landslide occurrences within thisarea.

Controlmorphology
to thelandslideoccurrence

Table 1 Landslide occurrences at 5° intervalMorphometric,
Distancelandslide to
the river andlineament

Fig. 1. Research Methodology

Slope (o) Number ofLandslide>30 – 35
22

Slope
(o)
>5 – 10

Number ofLandslide
4

>10 –
15
>15 –
20
>20-2517>35 – 404

33

>40 – 453

40

>45 – 501

>25-3029>50 – 55

1

3. Regional Geology
Geologial condition of research area based on
volcanostratigraphy shows the landslide at West
Sumatra landslide occurred dominantly on Tephra
Malalak (Pribadi, 2007). Tephra deposit from
Tandikat which consists of pumice lapilli, ranging
from 2 – 10 cm in diameter, slightly consolidated.
Landslide predominantly occurs in this rock type due
to unconsolidated, very loose structure, easy collapse
and eroded, pores are larger and has high permeability.
Several landslide and rockfall occurred at andesite ofManinjau lake caldera. The elongated form of thecaldera could indicate a prolonged period of eruption
during right lateral displacement on the Great
Sumateran Fault, also the tephra Malalak to overlie
the Maninjau volcanic rock.
Fig 3 Landslide distribution and morphologicallineaments in research area.

tephraclay

Fig 4 (a) The main scarp of the Tandikat flowslide,the slope angle was about 35 degree; (b) clay layer
underlie pumice layer from tephra Malalak

Fig 2. Geological condition of research area based on
volcanostratigraphy (Pribadi, 2007)
4. Analysis and Result
4.1.

Tabel 2 Mineralogical contents of sliding surface oflandslide.

Landslide distribution

Ref.
Code
00-0291487
01-0832465
00-0411486

GIS Analysis and field survey in Pariaman District
found 154 landslide sites due to West Sumatra
earthquake on September 30, 2009 (Table 1 and Fig 3).
Landslide concentrated at Manggur Gadang rivers andaround the lineaments (fault), and occurred on theslopes of 15o - 45o (Table1). Field survey found out
2

Score
21
34
27

Compound
Name
Metahalloysite

Displacement [°2Th.]
0.000

Scale
Factor0.380

Silicon dioxide$-alphaAnorthite,ordered

0.000

1.047

Chemical
FormulaAl2 Si2 O5
(OH)4
SiO2

0.000

0.718

Ca Al2 Si2 O8

10th Asian Regional Conference of IAEG (2015)

Halloysite

(a)

(b)

Fig.5 SEM analysis on the sliding surface
4.2.

Distance of landslide to the river

Based on GIS analysis show that, most ofearthquake trigered landslide in Pariaman connect
directly with river channel, mostly landslide occurredon the distance 0-100 m (Table 3). Based on 65 %landslide that random seleceted from GIS, show that
49 landslide occurred on the range 0-100 to the river
channel. The meaning is the landslide also controlled
by cutting slope by rivers erotion other than lithology
and stratigraphy.

(c)Fig. 6 Rosette diagram river (a) river segmen at
Manggur Gadang, (b) Azimuth fault/linieament at
Manggur Gadang River (c) azimuth landslide crownat Manggur Gadang. All of diagram show relativelly
parallel.

Table 3 Distance landslide to the river
Distancelandslide to
the river

Landslide
Area

LandslideOccurrences

0-100

10611449

100-20068082

24

200-30053247

11

300-40029642

12

400-500

19111

2

500-6009843

3

4.3 Correlation between landslide crown azimuth
and river segment

Fig. 6 Correlation between azimuth of landslide withriver segments

Due to part to topografic site effect, most ofearthquake trigered landslide in Chi-Chi earthquake
not connect directly with river channel (Lin, 2008). In
Pariaman case the landslide connect with riversegment and the landslide material reach the river,
especially Manggur Gadang river. The measurementof landslide crown azimuth with the river segment at
Pariaman showed that 97% the direction of thelandslide crown azimuth correlated with the directionof the river segment and majority of landslides reachthe river (Fig. 6 and 7). It suggests that landslidecondition is controlled by slope cutting due to erosion
and local tectonic in this area as well as morphology
or morphometric aspects. It can be concluded that thetectonic possibly has an influence in landslide
occurrence in this area.

4.4. Morphometric indices
The study area also had an experienced on land
earthquake on January 20 to 25, 2003, with a 3.3
magnitude scale and have caused 80 houses damaged
at this area, but no landslide occurrences at that time.
Landslide area due to West Sumatra earthquake was
located parallel on drainage pattern or river channel.
The flow pattern was developed in a longitudinalslope conditions with a rather steep, and it is possibly
controlled by geological structures. Geomorphic
indices is useful to identify tectonic parameters,
include the stream gradient index (SL), drainage basin
asymmetry (Af), Valley floor width-valley heightratio (Vf) and mountain front sinuosity (Keller and3

10th Asian Regional Conference of IAEG (2015)

Pinter, 1996). Most of these obtained- indices are used
to identify river basins in Naras, Manggur Gadang and
Manggur Kecil Sub Watershed.

4.4.2 Drainage basin asymmetry (AF)The asymmetry factor (AF) of catchments wasused to detect possible tectonic tilting at the scale of
the whole range. The AF is defined as (Keller andPinter, 2002):
AF = AR/AT× 100(2)
where AR is the area of the basin to the right (facing
downstream) of the trunk stream, and AT is the total
area of the drainage basin. Values of AF above or
below 50 indicate that the basin is asymmetric (Table
5). Af is close to 50, if there is no or little tilting
perpendicular to the direction of the master stream. Af
is significantly greater or smaller than 50 under theeffects of active tectonics or strong lithologic control.
Af values were grouped into three classes: 1 (AF≥65
or AF<35); 2: (35≤Af<43 or 57≤Af<65), and 3(43≤Af<57) (El Hamdouni et al., 2007).
4.4.3 Drainage density (Dd)In tectonic studies, drainage density is influenced
by the number of fractures in the watershed, thegreater the flux density in a watershed is estimatedmore and more cracks in the watershed. This index isdefined as:(3)
Dd = L/A
Where L, is total length of the stream in the watershed
and A is total area of the watershed

Fig.7. Location measurement of Morphometricindices at Naras, Manggur Gadang and Manggur
Kecil Sub Watersheed, Pariaman District
4.4.1 Stream length gradient index (SL)The SL index can be used to evaluate relative
tectonic activity (Keller and Pinter, 2002). Although
an area on soft rocks with high SL values indicatesrecent tectonic activity, anomalously low values of SL
may also represent such activity when rivers andstreams flow through strike-slip faults. SL indices aredefined as:
SL = (ΔH/ΔL) ×L(1)

Table 5Drainage
Manggur
GadangManggur
Kecil
Naras

L (m)

SL

645

∆L
(m)
12210

15040

794,4963

215

13170

15740

256,9552

3

204

2229

4296

393,1736

4

230

1617

5227

743,4818

5

165

1288

2594

332,3059

6

180

975,7

3643

672,0713∆H (m)

1
2

At

AF

L

A

Dd

75,78

97,72

77,5481

165,7

97,72

1,69

32,29

49,36

65,41734

104,5

49,36

2,12

90,11

121,2

74,34818

229,9

121,2

1,90

The Vf is defined as the ratio of the width of thevalley floor to its average height (Bull and McFadden,1977) and defined as:
Vf = 2Vfw / Eld + Erd − 2Esc

(4)

where, Vf is the ratio of valley floor width to valley
height, Vfw is the width of the valley floor, Eld is theelevation of the divide on the left side of the valley,
Erd is the elevation on the right side and Esc is theaverage elevation of the valley floor.
This index differentiates between valleys with awide floor relative to the height of valley walls with a
U-shape compared to narrow, steep valleys with a Vshape. Valleys with a U-shape generally have highvalues of Vf, whereas V-shaped valleys with relatively
low values. Because uplift is associated with incision,
the index is thought to be a surrogate for active
tectonics where low values of Vf are associated withhigher rates of uplift and incision.

SL ValueNo.

Ar

4.4.4 Ratio of valley floor width to valley heightratio (Vf)where; ΔH is change in altitude, ΔL is length of areach, and L is the horizontal length from thewatershed divide to midpoint of the reach. We
calculated SL along rivers using a digital elevation
model which is extracted from a digitized 1:25000
topographic map and using GIS to perform its averagevalue for each sub-basin. The values were classified
into three categories: 1 (SL≥500), 2 (300≤SL<500)
and 3 (SL<300) (El Hamdouni et al., 2007). The resultof the classification is shown in Table 8.
Table 4

AF and Dd Value4

10th Asian Regional Conference of IAEG (2015)

Table 6 Vf values

2C

128

70

87

212

1,630573248

EldEsc

70

55

73

195

1,09375

Vw

ErdEsc

3C

No.

Esc

Vf

4C

423

81

89

159

4,976470588

1A

36,51

79

66

664

0,503586207

5C

148

134

110

121

1,213114754

2A

93

61

49

797

1,690909091

6C

321

81

104

76

3,47027027

3A

62

26

83

561

1,137614679

7C

107

50

135

18

1,156756757

4A

34

66

61

482

0,535433071

8C

311

69

117

14

3,344086022

5A

89

68

90

408

1,126582278

11C

53

87

79

375

0,638554217

6A

162

122

71

357

1,678756477

12C

61

79

118

318

0,61928934

7A

67

78

23

297

1,326732673

8A

84

41

36

268

2,181818182

9A

85

45

26

227

2,394366197

10A

49

40

49

843

1,101123596

11A

57

29

55

1277

1,357142857

12A

58

40

31

1182

1,633802817

13A

78

56

40

1153

1,625

14A

98

87

26

1174

1,734513274

15A

57

47

82

1096

0,88372093

16A

28

39

100

1165

0,402877698

17A

214

201

141

1107

1,251461988

18A

160

83

58

960

2,269503546

19A

228

149

247

1069

1,151515152

20A

42

25

48

1330

1,150684932

21A

137

85

76

940

1,701863354

22A

112

113

74

689

1,197860963

23A

77

70

98

912

0,916666667

24A

45

56

54

697

0,818181818

25A

68

86

45

567

1,038167939

26A

55

90

97

607

0,588235294

27A

115

66

47

466

2,03539823

28A

110

77

72

393

1,476510067

1B

61

50

57

509

1,140186916

2B

37

104

88

457

0,385416667

3B

50

77

28

568

0,952380952

4.4.6 Evaluation of relative tectonic activity

4B

29

22

30

433

1,115384615

5B

54

128

118

875

0,43902439

6B

67

122

113

520

0,570212766

7B

37

88

85

902

0,427745665

8B

31

106

126

944

0,267241379

9B

65

36

93

468

1,007751938

10B

13

42

24

356

0,393939394

11B

31

30

33

140

0,984126984

12B

45

70

123

193

0,466321244

13B

32

29

58

270

0,735632184

14B

13

58

64

281

0,213114754

1C

43

59

47

237

0,811320755

Morpho-tectonics parameters are used to evaluate
relative tectonic activity in a wider area. The averageof the four measured geomorphic indices is used in
the study area in order to define the degree of active
tectonic. The values of the index are divided into fourclasses as follow 1—very high (1.0≤Iat<1.5); 2—high(1.5≤Iat<2.0); 3—moderate (2.0≤Iat<2.5); and 4—low(Iat> 2.5) (El Hamdouni et al., 2007).
The four class morphometric index for each subwatershed is shown in Table 8. The calculatedgeomorphic indexes in this work suggest that
Manggur Gadang and Manggung Kecil aretectonically active, with the recent uplift concentrated
in the north, east, southeast and southwest. The
asymmetry factor (AF) of this area shows a value
above and below 50. It means that the drainage basin

4.4.5 Mountain-front sinuosity (Smf)
Mountain-front sinuosity (Smf) is the nodal planeof active faults along the mountain front. It has asimple landscape compared to the slopes in areas
dominated by erosion (slopes formed in periods oftectonic stability). Mountain front sinuosity (Smf) was
defined by Bull and McFadden (1977) as:
Smf =Lmf/Ls(5)

Where Lmf, is total length mountain front and Ls is
straight line in front of mountain front.
Smf value for active tectonic zones in arid areas,
typically between 1.2 and 1.6, while value for slightly
active or inactive tectonic area tend to fall in theranges 1.8 – 3.4 or 2 – 7 (Bull and McFadden, 1977).
El Hamdouni divide Smf into three classes: 1(Smf<1.1), 2 (1.1≤J<1.5), and 3 (Smf≥1.5) (El
Hamdouni et all, 2007).
Table 7 Smf value from different watershed

5

No.

Lmf

Ls

Smf

1

13,17

6,844

1,924313

2

10,25

6,517

1,57281

3

12,3

6,942

1,771824

4

4,252

2,882

1,475364

5

2,905

2,648

1,097054

10th Asian Regional Conference of IAEG (2015)is asymmetry due to tilting on the drainage basin.
When AF = 50, the drainage basin is perfectly
symmetric, while values greater or less than 50 belong
to asymmetric basins. The SL index shows values
ranging 332-794, and the great values indicate that thestream has a steep gradient profile. It suggested that
there is an uplifting. Smf index along the area has
values < 2 indicating erosion did not occur much.
Moreover, most of the Vf and Smf value obtained for
Manggur Gadang, Manggur Kecil and Naras sub
watershed are low (0.213 to 4.976 for Vf and 1.09 to
1.92 for Smf). Table 1 and 2, which may indicate anarea weakly active tectonism. According to Wells etal (1988) active fronts will show straight profiles withlower values of Smf, and inactive or less active fronts
are marked by irregular or more eroded profiles, withhigher Smf values. The high values drainage density
and low values of Vf ratio indicate that the area havemore fractures and associated with higher rates ofincision and uplift. The Smf index is a measure ofincision and not uplift; but in an equilibrium state,incision and uplift are nearly matched. Calculation of
the index is carried out at a prescribed distance
upstream from the mountain front (Silva et al., 2003).

Faris, F dan Wang, F., 2014 Stochastic analysis of
rainfall effect on earthquake induced shallow
landslide of Tandikat, West Sumatra, Indonesia.
Journal of Geoenvironmental Disasters. 2014,
1:12, h. 1-13
Heath, W. dan Saroso, B.S. 1988. Natural Slope
Problems Related to Roads in Java Indonesia.
Proc.of the 2nd Int. Conf. On Geomechanics inTropical Soils, Singapore, pp.259-266.
Keefer (2000) Statistical analysis of an earthquakeinduced landslide distribution – the 1989 Loma
Prieta, California event, Engineering Geology
58(3-4): 231-249
Keller, E.A., Pinter, N., 1996. Active Tectonics.
Earthquakes, Uplift, and Landscape.Prentice
Hall, New Jersey. 362 pp.
Lin, G. W., Chen H., Hovius. Et al, 2008. Effects ofearthquake and cyclone sequencing onlandsliding and fluvial sediment transfer in a
mountain catchment, Earth Surface Proceses
and Landforms, 33, 1354 – 1373,
doi:10,1002/esp 1716.
Pribadi A, Mulyadi E, Pratomo I, Eruption Ignimbrite
Mechanism of Maninjau Caldera, West
Sumatra, Indonesian Journal on Geoscience,Vol. 2 No. 1 Maret 2007: 31-41 (in Bahasa
Indonesia)

Table 8 Tectonic activity of each Sub Watershed
Sub
Watershed
Manggur
GadangManggur
Kecil
Naras

Class

Lat

Tectonic
Activity

SL

AF

Smf

Vf

1

1

3

3

2

Medium

1

1

2

2

1,5

High

3

1

3

3

2,5

Low

Silva, P.G., Goy, J.L., Zazo, C., Bardají, T., 2003.
Fault-generated mountain fronts in southeast
Spain: geomorphologic assessment of tectonic
and seismic activity. Geomorphology 50, 203–
225
Varnes, D.J. 1978. Slope Movement Types andProcesses. Special Report 176; Landslides;
Analysis and Control, Eds : R.L. Schuster dan
R.J. Krizek, Transport Research Board,
National Research Council, Washington , D.C.
pp.11-33.

Conclusion
The landslides occurring in Pariaman District
were triggered by combination, 30 September 2009
Padang earthquake and rainfall. This landslide locatedat medium tectonic activity. The stratigraphy under
the tephra, slope, presence of clay layer (halloysite
contents) to the sliding surface are the main factors
controlling landslide occurrences. Geomorphology
conditions and control lineaments around Manggur
Gadang are important parameter to the landslide
occurrences in this area.

Wang Fawu, Muhammad Wafid A.N and Zhang
Fanyu, 2010 Tandikek and Malalak flowslides
triggered by 2009.9.30 M7.6 Sumatra
earthquake during rainfall in Indonesia
Geoscience Rept. Shimane Univ., 29, p.1-10

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Bull and McFadden. 1977. Tectonic Geomorphology
North And South Of The Garlock Fault,
California.
Geosciences
Department
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El Hamdouni, R., Irigay, C., Fernandes, T., Chacon, J.,
Keller, E. A., 2007.Assessment of Relative
Active Tectonics, Southwest Border of Sierra
Nevada (Southern Spain). Geomorphology, 96,
150-173.

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