Risk Returns

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Earthquake risk reduction in Indonesia

Krishna S. Pribadi and Wayan Sengara, Center for Disaster Mitigation, Institut Teknologi Bandung, Indonesia

ndonesia, an archipelago of more than 13,000 islands

spreading 5,000 kilometres from its western to its eastern

tips along the equator, is located where three global

tectonic plates (Indo-Australian, Eurasian and Pacific) meet.

Accordingly, high seismic and volcanic activity can be found

along the plates’ boundaries. Strong earthquakes are generated

along the subduction zones which are located in the sea trenches

west of Sumatra, south of Java, Bali and Nusa Tenggara islands,

as well as north of Sulawesi and Papua, exemplified by the

recent devastating earthquakes (Aceh Mw 9.2 in 2004, Nias Mw

8.6 in 2005, West Java Mw 7.0 and West Sumatra Mw 7.6, both

in 2009). Sumatra island is divided into two parts by the Great

Sumatra strike-slip fault, which consists of 19 segments. Other

inland faults can also be found on Java (which was responsible

for the killer Mw 6.3 Yogyakarta earthquake in 2006), Sulawesi

(the Palu-Koro fault) and Papua. Indonesian seismicity is well

represented in a map of main shocks (M>5.0), collected from

1900 to 2009 by the Indonesian Team for Revision of Indonesian

Seismic Hazard Maps.

Due to its high earthquake hazard potential and its physical and socio-

economical vulnerabilities, Indonesia is categorized among countries

with the highest risk from earthquake. In terms of mortality due to

earthquake, Indonesia shares with China and India the highest earth-

quake mortality index out of the top ten countries (8.5 on a scale of 1

to 10).

Earthquake risk in Indonesia is increased significantly by its

collateral hazards, in particular tsunamis and landslides. Data from

the OFDA/CRED International Disaster Database (EMDAT-CRED)

shows that almost 200,000 people were killed by earthquakes and

tsunamis from 1900-2011.

Earthquake damage to buildings in Indonesia

commonly results from problems with building quality,

regardless of the types of the buildings. Poor design

of buildings, caused by non-compliance to building

codes, often contributes to poor performance under

earthquake loading. Lack of detailing in the structural

drawing and building specifications leads to improvi-

sation by construction workers, resulting in structural

irregularities which may cause force concentrations and

disruptions in load transfer elements.

A 2005 study in Aceh shows that much building and

infrastructure damage was caused by strong seismic

motion causing soil liquefactions, lateral spreads, slope

failures, and settlements.

Soil erosion and foundation

failures which caused the damage to most single- and

two-storey buildings close to shorelines were due to high

tsunami wave force. Another study, on the reconnais-

sance survey and preliminary assessment of building

and infrastructure damage related to geotechnical earth-

quake engineering aspects, was conducted after the West

Java and West Sumatra earthquakes in 2006 and 2009.

Many instances of building and infrastructure damage in

both provinces were caused by relatively strong shaking

causing liquefactions and lateral spreads in some areas,

ground settlements and slope failures.

Traditionally, earthquake mitigation measures in

the form of local knowledge have been practised by

many indigenous people in the different islands in the

earthquake and tsunami-prone areas, such as the tradi-

tional construction of communal houses in areas of

West Sumatra,

the traditional architecture of the local

people in Nias island, the tsunami legends of the local

people in Simeulue island (which prompt them to move

to high ground when a strong earthquake occurs), and

the traditional rituals which serve to keep alive collec-

tive awareness of earthquake risk when the people of

Siberut island in West Sumatera build a new house.

However, the formal policy related to structural miti-

gation of earthquake risk began to appear only when the

Government of Indonesia established its first seismic

building code in 1970. In the years that followed, new

codes were developed and implemented.

Seismic monitoring system

Earthquake activities in Indonesia have been scientifi-

cally monitored since 1898 when the Dutch Colonial

administration installed a Ewing mechanical seismo-

graph for the first time. Since then, various types of

2037

Indonesian seismicity (main-shock)

Map showing that Indonesia is located in a highly seismic active zone

Source: Irsyam et al., 2010