ZONATION OF FAILURE PROBABILITY FORLANDSLIDES INDUCED BY EARTHQUAKE IN
KITAKYUSHU CITY USING GISSUN Junjie∗
MEE08166

Supervisor: Guangqi CHEN∗∗

ABSTRACT
We calculate failure probability of earthquake-induced landslides throughout Kitakyushu City basedon Monte Carlo simulation (minimizing the uncertainty of slope parameters) and Newmark stability
analysis (estimating factors of safety). Meanwhile, hazard maps of earthquake-induced landslides in
Kitakyushu city are produced according to the results of failure probability by using the geographicalinformation system (GIS) with different peak ground accelerations (PGAs) and seismic occurrence
periods at both conditions of m = 0 and m = 1 .
On the hazard maps, it is evident that the districts of Kokura Minami, Moji, Kokura Kita,
Yahata Higashi and Yahata Nishi in Kitakyushu City would suffer the disaster of landslide severely. In
the lower cases of PGA, the Southwest of Kokura Minami, the borders between Moji and Kokura Kita,
and the borders between Yahata Higashi and Yahata Nishi are the major areas impacted by extremely
serious hazard of earthquake-induced landslides. As PGA, seismic occurrence period or/and water
factor increases, critical hazard of landslide has an extensive area, covering Wakamatsu. Nevertheless,Tobata, the only one of fortunate district throughout Kitakyushu City, is in safety all the time.
Keywords: Landslide, Earthquake, Hazard map, Kitakyushu city, GIS.

1. INTRODUCTION
Landslide is a widespread hazard as well as a major geomorphic process affecting landscape evolution
in mountainous regions around the world (Aleotti 1999, Guzzetti 1999, Dai 2002, Roering 2005). The
hazard causes not only considerable financial losses but also major ecological and environmental
problems (Hovius 1997, Chigira 2006, Claessens 2007). Each year landslides cause more than 100,000
deaths and injuries, with damage costing more than 1 billion USD (Schuster 1996). In many countries,
the economic losses and casualties caused by the hazard of landslide are greater than commonly
recognized, and this kind of hazard generates a yearly loss of property larger than that from any othernatural disaster including earthquakes, floods and windstorms (Garcia-Rodriguez 2008).
Kitakyushu is a city located in Fukuoka Prefecture, Kyushu, Japan. The weather ofKitakyushu City is temperate and the rainfall is averagely 1,265 mm per year. The City, furthermore,is situated in a hill area. Thus, Kitakyushu City suffers the hazard of landslide induced by rainfall
critically. On March 20, 2005, a great earthquake with a magnitude of VII on the Richter scale hit
Fukuoka area. The earthquake induced very serious slope disasters in the around areas, including theKitakyushu City. It is necessary, therefore, to understand the potential disaster of earthquake-induced
landslides throughout Kitakyushu City. Unfortunately, it is the beginning yet to understand the issue of
hazard caused by landslides associated with earthquake although many scientists and engineers takemuch effort on the cases of rainfall.
∗

Assistant Research Fellow, Lanzhou Institute of Seismology, China Earthquake Administration, China.
Associate Professor, Department of Civil and Structural Engineering, Faculty of Engineering, Kyushu
University, Japan.
∗∗

1Zonation, which is an effective method to understand the hazard of landslides by macro
view, has been applied in many concerned mountain areas of the world. The authors assess thelandslide susceptibility induced by earthquake in Kitakyushu City using GIS, applying the Monte
Carlo simulation and Newmark stability analysis for theoretical computation of failure probability.
Here the former minimizes the uncertainty of strength parameters by applying huge numbers ofphysical parameters of geological slopes while the latter estimates the factors of safety ofearthquake-induced landslides, considering the influence of rainfall on the stability of slopes.

2. METHODOLOGY
2.1. Physical and Geometrical Parameters of Geological Slopes
According to a new geology map, there are mainly four types of soils in Kitakyushu City, which are
weathered respectively from granite, sedimentary rock, igneous rock and hydrogenous rock.
Through analyzing the frequency characteristics of three physical parameters, i.e. γ (unitweight), c (cohesion strength) and ϕ (internal friction angle), for the four types of soils, thedistribution functions for each parameter are obtained based on the laboratory data. On the other hand,
the geometrical parameters of landslides, θ (slope angle) and H (thickness of sliding layer), areaccepted as dependent to the logarithmic and normal distributions. After generating 3,000 random
numbers, furthermore, the corresponding statistical values of physical and geometrical parameters ofgeological slopes, 3,000 numbers for each one, are calculated by their distribution functions.
2.2. Factor of Safety and Failure Probability
The authors calculate the factors of safety for the estimation of theoretical failure probability ofearthquake-induced landslides by the equation (1) and equation (2), meanwhile considering theinfluence of rainfall on the stability of the landslides.

g  cm+ cos θ tan ϕm − sin θ a'γ H


(1)



γ 
g  cm+  1 − w  cos θ tan ϕ m − sin θ a '  γ sat H  γ sat 


(2)

Z=

Z=

Here equation (1) is applied to calculate factors of safety at the condition of only
earthquake whereas equation (2) is for coupling cases of earthquake and rainfall. As the PGA is zeroequation (1) and equation (2) would not be available to calculate the factor of safety. For those 0 gal
PGA cases, the traditional formula of Newmark stability analysis is applied, which has the following
form.

FS =

cm + (1 − m ) γ + mγ ' H cos θ tan ϕ m
(1 − m ) γ + mγ sat  H sin θ(3)As mentioned above, the authors apply Monte Carlo simulation and Newmark stability
analysis in the process to calculate factors of safety of earthquake-induced landslides. Furthermore, forcomputation of theoretical failure probability, the following definition is applied.

2

PF =

Numbers ( FS < 1)
3000

(4)

2.3. Meshes of Geology and Elevation Maps
For producing the hazard maps of earthquake-induced landslides, it is an essential step to divide
geology and elevation maps into small dimension meshes, each of which has a unique number and theinformation about the slope angle, soil types and areas.
A specifically meshed tool generates the meshes for geology and elevation maps in GIS,
where the dimension is 100m*100m for each one. The information of meshes such as slope angle, soil
types and areas are obtained by the spatial analysis approach of GIS. Based on these thoughts, themeshed work of maps is completed and some basic information associated with the meshed results isshown in Table 1.
Table 1 Basic information of meshed maps.
Numbers of
soils
1
2
3
4
None

MeshesNumbers
30,175
11,982
873
34
2,102

Soil types

Total

I
II
III
IV
Total

45,166Area
km2
40.144181.257
45.354183.020449.775

Percent (%)
8.925
40.30010.08440.691100.000

2.4. Zonation of Failure Probability for Landslides
Firstly, it is essential to calculate the actual failure probability for each mesh based on the meshed
information mentioned above. In this process, there could be always two cases to consider due to thenumbers of soils in one mesh as follows.
1) When the mesh has only has one kind of soil, a simple interpolating method is applied toobtain the actual value for failure probability. The method could be expressed as the following
equation,

PFi = PFj + ( PFk − PFj ) ⋅ ( i − j )(5)Where PFi is the failure probability of each mesh with actual slope angle of i , a real
number ; both PFj and PFk are theoretical failure probability associated with the actual slope angle,
in which j is the integer of i , and as a integer number also, k = j + 1 .
2) When more than one soils exist in the mesh (e.g. Table 1.), a weighted average of failure
probability is calculated for the mesh by the equation below.

PFiWA =

PFi1 ⋅ A1 + PFi2 ⋅ A2 + ⋅⋅⋅ + PFin ⋅ An
A1 + A2 + ⋅⋅⋅ + An

(6)

Where n is the numbers of different types of soils; PFin is the actual failure probability
for different types of soils in one mesh and An denotes the corresponding area.
Secondly, it is necessary to import the actual failure probability completely into each meshby the authors with a Fortran program. Then GIS could provide a color automatically for each mesh3

due to the level of probability value, and in this case, the color ranges from green to red, representing a
low-level and high-level of landslide failure respectively. This is the final step to produce hazard maps.

3. RESULTS AND DISCUSSION
3.1. Hazard Maps
Applying the zonation approach of earthquake-induced landslides mentioned above, we produces 28
hazard maps using GIS for different PGAs and seismic occurrence periods of years both at theconditions of m = 0 and m = 1 . The detailed information of those hazard maps throughout
Kitakyushu City could be found in Table 2.
Table 2 Hazard maps produced by this thesis.
Map
No. 1
No. 2
No. 3
No. 4
No. 5
No. 6
No. 7

PGA
(gal)
0
100
200
300
400
500
600

Map
No. 8
No. 9
No. 10No. 21
No. 22
No. 23
No. 24

PGA
(gal)
700
800
900
Per year
10 years
30 years
50 yearsm

Map

PGA (gal)

Map

PGA (gal)m0

No. 11
No. 12
No. 13
No. 14
No. 15
No. 16
No. 17

0
100
200
300
400
500
600

No. 18
No. 19No. 20No. 25
No. 26
No. 27
No. 28700
800
900
Per year
10 years
30 years
50 years

1

3.2. Failure Characteristics of Landslides
Some particular hazard maps of earthquake-induced landslides throughout Kitakyushu City are shownas Figures 1.~3. In order to reduce the pages, other maps are not displayed here. However, this has no
distinctly negative impacts on analysis results of failure possibility and distributional characteristics oflandslide disaster respectively caused by earthquake or coupling case of earthquake and rainfall.
The hazard maps of No. 1 and No. 11 draw the outline of the critical areas suffered byearthquake-induced landslides (Figure 1.). In the two cases, the PGAs are both 0 gal while water
factors are 0 and 1 respectively. As the PGA reaches 900 gal, those critical areas in hazard map of No.
20 become the severest, where the failure probability is the highest level as a whole (Figure 2.).
Meanwhile, hazard regions could be extensive. Some other areas without disaster at first begin tending
to bear a moderate-level or low-level failure possibility caused by earthquake or coupling condition ofearthquake and rainfall. These are the common characteristics of hazard maps for earthquake-induced
landslides in Kitakyushu City.
By the definition of calculation for failure probability with different periods of seismic
occurrence, it is easy to understand that these hazard maps with seismic occurrence period of years
may reduce the low-level features of failure probability, which appear visibly when PGA becomes
greater than 400 gal. One interesting example is the comparison between hazard maps of No. 20 and
No. 28. The latter has a higher maximum critical-level of failure probability, but it is much clearer than
the former that has many areas with the low-level probability of landslide failure.
On the hazard maps, it is generally evident that the districts of Kokura Minami, Moji,
Kokura Kita, Yahata Higashi and Yahata Nishi would suffer any disaster of landslide severely (Figures
1.~3.). In the lower cases of PGAs, the Southwest of Kokura Minami, the borders between Moji andKokura Kita, and the borders between Yahata Higashi and Yahata Nishi are the major areas impacted
by an extremely serious hazard of earthquake-induced landslides. As PGA, seismic occurrence period
or/and water factor increases, a critical hazard of landslide has an extensive area, covering Wakamatsu.
Nevertheless, Tobata, the only one of fortunate district in the City, is in safety all the time.

4

(a)

(b)
Figure 1 Hazard maps of No. 1 and No. 11.

(a)

(b)
Figure 2 Hazard maps of No. 15 and No. 20.

(a)(b)
Figure 3 Hazard map of No. 28 and districts of Kitakyushu City.

4. CONCLUSIONSFor the actual cases, the geological slopes are in the stable conditions because of the equilibrium
between soil strength and slope angle. As the external factors such as earthquake or rainfall are
involved into the equilibrium, the slope may fail. By this mechanism, it is better to understand that, for5

a certain case of geological slope, either greater PGA or shallower water table would make the slope
softer. Consequently, even the angle is lower; the slope would not be that stable all the same.
The districts of Kokura Minami, Moji, Kokura Kita, Yahata Higashi and Yahata Nishi
would suffer the disaster of landslide severely. In the lower cases of PGA, the Southwest of Kokura
Minami, the borders between Moji and Kokura Kita, and the borders between Yahata Higashi and
Yahata Nishi are the major areas impacted by an extremely serious hazard of earthquake-induced
landslides. As PGA, seismic occurrence period or/and water factor increases, a critical hazard oflandslide has an extensive area, covering Wakamatsu. Nevertheless, Tobata, the only one of fortunate
district in Kitakyushu City, is in safety all the time.
Those hazard maps with different periods of seismic occurrence may reduce the low-levelfeature of failure probability. The hazard map of seismic occurrence period within 50 years has ahigher maximum critical-level of failure probability whereas the map is much clearer than another at
the PGA of 900 gal that has many areas with moderate-level possibility of landslide failure. For thecases of m = 0 , a longer occurrence period of years has a greater area percent of failure probability inthe high-level hazard than a shorter one. This is more visible at the condition of m = 1 , corresponding
an obvious reduction of area percent with low-level probability of landslide failure.

AKNOWLEDGEMENT
I would like to express my sincere gratitude to Dr. Kouki ZEN and Ms. Makiko MISUMI from
Department of Civil and Structural Engineering, Faculty of Engineering of Kyushu University and theadviser Dr. Shin KOYAMA from IISEE, BRI, for their continuous support, valuable suggestion andguidance during my study.

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