An Augmented Reality Application for the Community Learning about the Risk of Earthquake in a Multi-storey Building Area

Abstract

The earthquake comes with great risks, especially in urban areas where many multi-storey buildings exist. These risks have not been understood well yet by the people of the urban area. Socialization, simulation, and learning media need to be provided continuously to improve people awareness on the importance of knowledge about the earthquake risks. An interesting learning media is not only contain informations but also a 3D animation and an interaction with the user. For a more immersive interaction, this application is equipped with augmented reality technology that gives more real visual representation like the actual condition. The evaluation result shows that 82% respondent appreciates this application, at first common users do not know the risk of earthquakes on multi-storey building, with this application users can understand the importance of earthquake risk in buildings.

Full text

EMITTER International Journal of Engineering Technology
Vol. 5, No. 2, December 2017
ISSN: 2443-1168
Copyright © 2017 EMITTER International Journal of Engineering Technology - Published by EEPIS
192
An Augmented Reality Application for the Community
Learning about the Risk of Earthquake in a Multi-storey
Building Area
M. Unggul Pamenang, Achmad Basuki, Riyanto Sigit
Postgraduate Applied Engineering of Technology
Division of Information and Computer Engineering, Department of Information and
Computer Engineering, Electronic Engineering Polytechnic Institute in Surabaya
EEPIS Campus, Jalan Raya ITS, Sukolilo 60111, Indonesia
E-mail: unggul@pasca.student.pens.ac.id,{basuki, riyanto}@pens.ac.id
Abstract
Area surrounding tower is a danger area when earthquake attack. It
has an enermous risk. People in this area have to know the risk for
their safety. Socialization, simulation, and learning media need to be
provided continuously to improve people awareness on the
importance of knowledge about the earthquake risks. The media that
can reach all society is a mobile application. An application that
contains earthquake information in the surrounding area of tower is
the solution to this problem. Earthquake learning application that is
able to explain level of risk in detail and easy to understand. For more
immersive interactions, we propose the augmented reality on mobile
application to visualize the simulation of earthquake effect on the
tower. The augmented reality provides the conditions with 3D
modeling. So, users have experience to feel the level of damage and
safe distance in the tower area. The evaluation result shows that 84%
respondent appreciates this application. First common users do not
know the risk of earthquakes on the surrounding area of the tower,
and they understand the importance of earthquake risk in buildings
after use this application.
Keywords: Augmented reality, earthquake in tower, earthquake
learning, mobile application, 3D modeling, and
simulation of disaster.
1. INTRODUCTION
Indonesia is in the ring of fire that is potentially affected by earthquakes.
On the other hand, there has many tower as city development. The
earthquakes in the surrounding tower had a great impact as in the Padang
(2009). This earthquake caused a large number of casualties because buried

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
193
under the ruins of the building. It may occur again in other areas. To reduce
this impact, it needs to socialize and simulate special natural disasters in urban
area or regional areas that have many towers such as office, school etc.
Figure 1. Padang earthquake 2009 (left) and simulation of earthquake in Ponpes
Ashshidiqiyah 2, Batuceper Tangerang (right) [13]
Simulated natural disaster earthquakes need to be done periodically and
continuously. BMKG (Meteorology Agency in Indonesia) and BNPB (Disaster
Management Agency in Indonesia) has made efforts to socialize and simulate
earthquakes to the public. The simulation of the earthquake made as real as
the earthquake environment [13], so the students immediately scattered out
when the earthquake was simulated. This simulation use the firecracker
explosion to capture the atmosphere and have more tense effect to the
students. Students tried to gather in the field. Some students and teachers who
were simulated became victims also dressed up with the number of injured
and artificial blood, while surviving students simulated how to evacuate the
wounded and die. The simulation carried out by BMKG has not covered all the
elements of society [13].
In the other hands, the uses of technology, especially mobile applications,
as media reach the wider range. The use of mobile simulations for natural
disasters is an alternative method to provide knowledge about natural
disasters themselves, their impact and characteristics. It is a key to select
media for learning of disaster impact. This also applies to the simulation of
earthquakes in the area surrounding the multi-story building.
Currently, mobile apps provide more interactive features such as
augmented reality, virtual reality and kinesthetic sensors. Augmented reality
uses camera sensors and combines both the real world and the virtual world.
This technology generates 3D objects that interact with the user. Users can see
3D objects and feel as if they appear in the real world. The use of AR technology
to simulate the earthquake disaster in the area around the high rise building
offers an interactive and immersive learning media. This application not only
provides information about earthquakes and their impacts in the area around
high rise buildings, but also presents an interactive module that allows users
to feel the impact of earthquakes on high rise buildings while looking for a safe
place.

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
194
2. RELATED WORKS
Johannes Leebmann, et al [1] explains to Search and Rescue team about
how to perform a rescue action in a building where an earthquake happened.
With the help of ARS (augmented reality system), the real object and the
virtual is integrated, and the scale of the virtual is adjusted on the same size as
the real one. ARS is developed for rescuing individuals who are trapped in the
ruin of the building. In this journal the augmented reality concept is used as
learning media about the effect of the earthquake on the multi-storey building.
Restu Faizah, et al [2] The effect of the earthquake on multi-storey
building and with dynamic response analysis. Dynamic response analysis will
help planners as consideration inputs. The research is analyzing the
gravitation forces mode 1 on the 2D structure.
Rony Ardiansyah, [3] The magnitude of an earthquake on hipocentre is
measured by Richter scale will cause the amount of vibration and different
effects on the different surface areas on the earth (epicentre). This different
interpretation is introduced by an Italian scholar, Guiseppe Mercalli in 1902,
known as Modified Mercally Intensity Scale (MMI). The total of effect scale is
12 unit that is adjusted with the effect of the earthquake. The commonly used
scale is Richter scale which use the result of seismograph measurement to
explain and compare the strength and the wide of the earthquake.
Jusuf J. S. Pah, et al [4] this research analyze the structure of high
buildings. Every sample is tested on four earthquake accelerogram, those are
El-Centro, Kobe, Chi-chi Taiwan, and Japan to identify the shaking mode. To
identify the maximum height of the deformed high building in mode 1 while
responding to the earthquake. And also to identify the maximum height of the
shifted wall ensuring mode 1 deformation of high structured building while
responding to the earthquake.
Naosuke Yamashita, et al [5] This research estimates safe zone and
danger zone in a room with learning application using augmented reality on
android smartphone. Vuforia [6] is a tutorial book to make augmented reality
applications on android smartphone using Vuforia and Unity 3D. This book is
very useful for the production of this application. Yi-Shiuan, et al [7] this
research is educative advanture game which the player encouraged to run
away from earthquakes. This game can be used to enhance the user’s
knowledge on escaping from earthquakes and looking for safe shelters.
Autodeks [8] is tutorial book about 3ds Max 2011 that is useful to make
building model and building animation when strucked by earthquakes. W.
Kim, et al [9] this research develops an augmented reality application in
supporting damage and safety assessement. Irfan Subakti [10] Insap Santoso
[11] is a book about human interaction and computer with the purpose to
identify knowledges on how to desaign a visual appearance and writing in
order to make a more enjoyable application for the user. Giving a result before
and after using the application.
Kurniawan Teguh Martono [12] this research discusses the development
of augmented reality on various field such as military, health, education, and

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
195
others. By using augmented reality technology the users are expected to
experience a direct interaction.
3. ORIGINALITY
This study produces learning media to recognize the impact of
earthquakes on towers through mobile devices. Application from this learning
media not only contains graphical and textual information, but also an
interactive module that lets users feel in the true environment. This
application use AR technology and interaction in gaming technology to
produce immersive effects. In the use this application used visualization object
3D tower and 3D character. Users can know whether they are in secure
position or not using moving character that provided in this application. The
safety positioning use data trends method like already done in the research
about earthquake effect to damage of high buildings. The determination safe
positioning use approach of data trend that already done in the research about
earthquake effect to damage of tower. The mobile application usage able to
reach wider communities, thus socialization and simulation process in order
to acquaint the impact of earthquake nearby the tower will be more
convenient to be carried out by the society.
4. SYSTEM DESIGN
System design of this research is shown in figure 2. There are three main
processes in this system that is: Damage Calculation, Visualization and
Simulation (Game-Interaction).
Figure 2. System Design

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
196
4.1 Damage Calculation
There are three steps to calculate the damage on surrounding area of the tower
when earthquake stroke it: specify the strength of earthquake, calculate the building
damage and calculate the minimum distance to reach safe area. Strength of
earthquake is in Richter scale. The damage is calculated using the strength of
earthquake to generate the intensity and its impact on the building. The
distance of safe area is calculated by referring on the damage. This research
use reference data that show the effect of earthquake on the tower using
Richter scale [3][4][5]. These studies provide two tables. Table 1 shows the
effect of earthquake on the epicenter area [3]. Table 2 shows the effect of
earthquake on the damage of tower [4][5].
Table 1. Strength effect of earthquake [3]
Kekuatan Keterangan Rata-Rata Intensitas Dekat
Episentrum
0 – 1,9 - 700.000 Recorded, but unfelt
2 – 2,9 - 300.000 Recorded, but unfelt
3 – 3,9 MINOR 40.000 Felt by few people
4 – 4,9 LIGHT 6.200 Felt by many people
5 – 5,9 MODERATE 800 Slightly damaging
6 – 6,9 STRONG 120 Damaging
7 – 7,9 MAJOR 18 Highly damaging
8 – 8,9 GREAT 1 in 10 – 20 years Destroying
Table 2 is the reference for building the animation of damage on the
tower. This research uses 3DSmax to create animation with 8th floor tower and
plugin “FractureVoronoi_v1.1” to create the damage on building randomly in
accordance with the specific scale of characteristics of earthquake as shown
on figure 3. This animation presents the broken and cracked parts that fall
down when the strength of earthquake is given. This animation also use to
rigid body that has been provided in 3dsmax for calculating density, so the
create building can be set weight or density. And then on the base is made
shifted left and right so it generate effect swaying building

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
197
Table 2. Effect of strength earthquake on tower damage.
Scale Damage outside of building Animation
4 Nothing The building can only shake
5 Nothing The building can only shake
6 Minor damage in the glass The building rocked and experienced
broken glass on the eighth floor
7 Minor damage to parts of glass
and cracked walls
The swaying building was great causing
broken glass on the sixth to eighth floor
and the wall cracked on the seventh
floor
8 Large damage to the glass and
wall
The building rocked so violently that
the glass broke on the fifth and eighth
floor and the wall was badly cracked on
the sixth to eighth floor
9 The enormous damage caused
the building to collapse
The incredible swaying building
resulted in a foundation failure so the
building collapsed
Figure 3. Accelerator earthquake [4]
Calculation of the distance of safe area can be set with earthquake data
rocks from El Centro and Chi-chi Taiwan as shown on table 3 and table 4. We
use correlation values from each parameter from the horizontal and vertical
deviation. This earthquake data was taken because it has the characteristics of
simple equations to determine the correlation. This is important considering
the use of mobile applications to be heavy when using complex calculations
and high-level. Table 3 shows the earthquake load on El Centro America in
figure 3 with a maximum shift of close to 5000 mm / second2. And the
earthquake in Chi-chi Taiwan in figure 3 with maximum shift of nearly 2000
mm / second2.
Table 3 and table 4 show the horizontal and vertical deviation on each
floor during earthquake stroke it. The animation use these tables to create the
change of deviation on each frame in according to the Richter scale. Table 3
uses 7 Richter, and table 4 uses 7.3 Richter.

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
198
Table 3. Maximum displacement of buildings in earthquake El Centro [4]
R
Scale Floor
1 2 3 4 5 6 7 8 9
7 Y(m) 4 8 12 16 20 24 28 32 36
X(m) 0.08 0.24 0.41 0.58 0.73 0.87 0.98 1.06 1.12
Table 4. Maximum displacement of buildings in earthquake Chi-chi Taiwan [4]
R
Scale Floor
1 2 3 4 5 6 7 8 9
7.3 Y(m) 4 8 12 16 20 24 28 32 36
X(mm)
0.11 0.28 0.61 0.55 1.35 4.05 6.51 7.76 7.85
After getting the value of the shift, we can calculate the highest horizontal
difference of the horizontal side using the maximum deviation table as shown
in table 5 [5]. Table 5 shows the maximum deviation on each floor based on
the Ricther scale.
Table 5. Maximum deviation
R Scale Floor
1 2 3 4 5 6 7 8
4 Y(m) 4 8 12 16 20 24 28 32
X(m) 0.05 0.06 0.08 0.1 0.12 0.13 0.15 0.17
5 Y(m) 4 8 12 16 20 24 28 32
X(m) 0.05 0.07 0.1 0.12 0.15 0.2 0.26 0.32
6
Y(m) 4 8 12 16 20 24 28 32
X(m) 0.055 0.092 0.13 0.18 0.26 0.32 0.39 0.45
7 Y(m) 4 8 12 16 20 24 28 32
X(m) 0.094 0.14 0.22 0.32 0.42 0.55 0.66 0.75
8 Y(m) 4 8 12 16 20 24 28 32
X(m) 0.11 0.19 0.305 0.503 0.74 0.98 1.2 1.4
9 Y(m) 4 8 12 16 20 24 28 32
X(m) 0.24 0.38 0.5 0.89 1.2 1.6 1.9 2.2
The maximum distance to reach safe area have two parameters; stiffness
of glasses and walls, and the slope of building. These parameters cause the
different effect of damage when earthquake stroke it. The slope value on the
each floor is calculated by gradient equation (1).
∇ = 
 (1)
Next result of the derived gradient as perpendicular is written by equation (2).
∇̇ = − 
∇ (2)
We use the median of the gradient derivative.

=∑∇̇
 (3)
Then the minimum value of the gradient derivative is written by equation (4).
 = ∑∇̇
 (4)

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
199
The quarter value is average of the median result and the minimum value.
 = 

 (5)
The angle of the quarter value is written by equation (6).
 = 90 −  (6)
The last calculation is the distance to reach safe area,
 =  ∙ sin( 
.) (7)
This distance is compared by the distance between person and tower to
show that it is safe or not. So, the user will move to other place and the system
will show the current condition comparing with the distance to safe area. Then,
user feel this system as the real condition by mobile application. The AR
system visualize the damage and user move to reach safe area bya simulation.
We calculate the distance using euclidean distance theory on 3 dimensions,
using the following formula
(, )= (− )+(− )+(− ) (8)
4.2 Modeling
This research uses 8th floor tower with uniform rectangular model. The
height of each floor is 4m so the total height of the building is 32m as shown in
figure 4. The regular building construction withstand when it was affected by
earthquakes because there is not the soft floor. Almost all of the destroyed
buildings have collapsed when the floor is softer the the above parts.
(a) (b)
Figure 4. Building modeling: (a) framework, (b) the end result
This application is learning application, so this application provide
information and material about impact of earthquake on around area tower.
This application just work in smart phone android. Figure 5 show menu and
information provided by this application such as learning application. Material
learning start from introduction about earthquake and characteristics, up to
the impact caused including damage to tower.

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
200
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
Figure 5. Information and media learning has provided

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
201
4.3 Marker
The key of augmented reality is the marker. This research uses marker in
the form of an image of Postgraduate Building of Electronic Engineering
Polytechnic Institute in Surabaya. After calibration is done, we try to use
smartphone camera to detect whether the marker made is working properly.
In order to fit the purpose, we use the original building that we capture online
and capture the marker results as shown in Figure 6. The number of star shows
the rating or success rate of marker detection.
Figure 6. Marker : (a) Marker 1, (b) Marker 2, (c) Marker 3, (d) Marker 4, (e) Marker
5, (f) Marker 6, (g) Marker 7, (h) Marker 8, (i) Marker 9, (j) Marker 10
5. EXPERIMENT AND ANALYSIS
Experiments do to know performance from learning application the
impact of earthquake in area around tower through several stages. Start
testing from checking running application with good in all the parts until
testing maximum deviation for to show safe distance.
5.1 Running Application
This application work on all device mobile with operating system
Android. System calibrate with printing marker, and implement on printing
marker or direct at the front of building for example the front of Pascasarjana
Building, PENS as shown in figure 7. Implementation like this make users feel
the simulation as if it were in the virtual world

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
202
Figure 7. Running Application
5.2 Analysis of building damage
We determine the deviation on each floor based on the strength of
earthquake stroke and data from table 3 and 4. We test animation to measure
the change shift on each frame and on each scale of 3D modelling of tower.
Every scale is taken one frame that has rate of change the highest shift. The
value of the highest shift produce maximum deviation as shown on figure 8.
Figure 8. Diagram of maximum deviation
0 0.5 1 1.5 2 2.5
1
2
3
4
5
6
7
8
Friction (Meter)
Floor
Maximum Deviation
Scale 9
Scale 8
Scale 7
Scale 6
Scale 5
Scale 4

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
203
Table 6 shows the implementation result for calculating the distance to
reach safe area and animation the damage of tower with entered Richter scale.
User know the damage of tower from result animation and information the
safe distance based on the determined seismic strength.
Table 6. Safe distance and building damage
Scale Safe Distance of
Building Area Result Damage Outside The Building
4 1.75 m
Nothing
5 2.51 m
Nothing
6 3.45 m
Minor damage to the glass

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
204
7 5.70 m
Minor damage to parts of glass
and cracked walls
8 11.02 m
Large damage to the glass and
wall
9 17.58 m
The enormous damage caused the
building to collapse
5.3 Analysis Marker
Table 8 explains that on marker on some trial experiments from small
rating until large rating as shown table 7. For the small object, we need small
the distance to identify the marker perfectly. Some marker are not perfectly
identified caused by the large distance from the marker to user for example on
experiment 4, 6 and 8. The other factor to make marker is not identified is
object complexity. This system need complex marker to identify the tower.

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
205
Table 7. Marker
No
Marker Distance
Result Accuracy
1
3.5 m Appear perfect 0.0045
m/pixel
2
8.4 m Appear perfect
0.023
m/pixel
11.4 m Appear perfect
3
2.4 m Appear perfect 0.01 m/pixel
4
0.5 m Appear perfect
0.0084
m/pixel
1 m Appear perfect
1.8 m Do not appear
5
1.8 m Appear perfect
0.0047
m/pixel
2 m Appear perfect
3.9 m Appears
imperfect
6
0.5 m Appear perfect
0.0097
m/pixel
1.7 m Appear perfect
1.8 m Do not appear
7
24.3 m Appear perfect
0.021
m/pixel
25.8 m Appear perfect
28.8 m Appear perfect

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
206
8
0.5 m Appear perfect
0.003
m/pixel
1 m Appears
imperfect
9
1 m Appear perfect
0.003
m/pixel
4.5 m Appear perfect
6.6 m Appears
imperfect
10
0.5 m Appear perfect
0.0042
m/pixel
1 m Do not appear
5.4 Users Evaluation
We implement this system for 20 respondents with various background
to check the user responses. The questionnaire is asking about the interactive
factor and the learning material. Table 8 shows the result of user evaluation
for using the system. This system has easy navigation (80% user agree).
Presentation of information is enough or fairly good (70% user consider
good), but not completely written. It needs improvement to make user know
about impact of earth quake. The other function of this system is good such as
aesthetic and cognitive substance. Overall function of this system can
implement by user to simulate the effect of earthquake on the surrounding
area of tower. The overall result from table 8 shows that 84% of respondents
think that the earthquake application is up to the standard of interactive
multimedia application.
Table 8. Users Evaluation
No
Criteria Result
1. Navigation Easiness 80% Agree
2. Informational Presentation 70% Good
3. Arts and Aesthetic 90% Very Appealing
4. Cognitive Substance 80% Good
5. Overall Function 100% Very Good
6. CONCLUSION
Based on the above experiment, it can be concluded that the 8th floor
tower if exposed to earthquakes with large-scale magnitude then the greater
the damage to buildings and secure areas around the building. At the marker
retrieval is not always a high rating resulting in better recognition, because of

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
207
marker retrieval is not from the 2D field, but directly from the object in real
time without an intermediate print. The results of the user evaluation show an
average of 84% of respect with this application, with this learning application
users already understand the importance of earthquake risks in high rise
buildings.
REFERENCES
[1] Johannes Lebmann, An Augmented Reality System For Earthquake
Disaster Response, The International Archives of the Photogrammetry,
Remote Sensing and Spatial Information Science, Vol. 34, part XXX.
[2] Restu Faizah, Widodo, Analisis Gaya Gempa Rencana Pada Struktur
Bertingkat Banyak Dengan Metode Dinamik Respon Spektra
(Analysis Earthquake Style Plan in Multi-storey Structure using
Dynamic Spectral Response Method), Konferensi Nasional Teknik Sipil
7, 2013.
[3] Rony Ardiansyah, Sistem Pengukuran Kekuatan Gempa (Korelasi
Skala) Richter dengan Modified Mercally Intencity Scala
(Measurement of seismic strength system (Scale Correlation)
Richter with Modified Mercally Intencity Scala).
[4] Jusuf J. S. Pah, I Made Udiana, and Deddy I. Matarohi, Evaluasi Batasan
Tinggi Maksimum Bangunan Tingkat Tinggi Beraturan Untuk
Penerapan Metode Statik Ekuivalen (Evaluation of Tower Maximum
High Limits Regularly For the Application of Equivalent Static
Methods), Jurnal Teknik Sipil, Vol. III, No. 2, 2014.
[5] Naosuke Yamashita, Hirokazu Taki, and Masato Soga, A Learning
Support Environment for Earthquake Disaster with A Simulation of
Furniture Falling by Mobile AR, Information Technology Based Higher
Education and Training (ITHET), 2012.
[6] Vuforia, Augmented Reality on Android, Qualcomm, 2012.
[7] Yi-Shiuan Chou, Huei-Tse Hou, et al, Running Tommy©: Developing a
Digital Adventure Game Based on Situated Learning to Promote
Learners' Concepts of Earthquake Escape, IEEE International
Conference On Digital Game And Intelligent Toy Enhanced Learning, 2012.
[8] Autodesk, Tutorial Autodesk 3ds Max 2011, Autodesk, 2010
[9] Sáfár Attila, Balonyi Ádám, and Kováts Róbert, Surface Models View
Design with 3DS MAX Software, IEEE 9th International Conference on
Computational Cybernetics, 2013.
[10] Irfan Subakti, Interaksi Manusia dan Komputer (Human and
Computer Interaction), Jurusan Teknik Informatika Falkutas Teknologi
Informasi Institut Teknologi Sepuluh November Surabaya, 2006.

Volume 5, No. 2, December 2017
EMITTER International Journal of Engineering Technology, ISSN: 2443-1168
208
[11] Insap Santoso, Interaksi Manusia dan Komputer (edisi 2) (Human
and Computer Interaction (Edition 2)), Andi Offset, 2010.
[12] Kurniawan Teguh Martono, Augmented Reality sebagai Metafora Baru
dalam Teknologi Interaksi Manusia dan Komputer (Augmented
Reality as a New Metaphor in Human and Computer Interaction
Technology), Jurnal Sistem Komputer, Vol. 1, No 2, 2011.
[13] Vera Framawati, Semarakan HKBN 2017, LPBI NU Gerakan 1,5 Juta
Pelajar Dan Santri Siaga Bencana (Semarakan HKBN 2017, LPBI NU
Movement 1.5 Million Students And Santri Disaster Preparedness),
https://wartapriangan.com/2017/04/27/semarakan-hkbn-2017-
lpbi-nu-gerakkan-1-5-juta-pelajar-dan-santri-siaga-bencana/
(Accessible date 14 July 2017).