indonesia sumatra northern report
TRANSCRIPT
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pec a ar qua e epor ugus
Learning from Earthquakes
The Northern Sumatra Earthquake of March 28, 2005
tor s ote: eg nn ng w e
March issue and in each one sub-sequently, we presented six reports
y e many eams a o serve
the effects of the December 26,
2004, earthquake and tsunami in
coun r es aroun e n an cean.
This report adds information on
structural damage, largely from
shaking, on two islands west of
Sumatra in a subsequent large
earthquake in roughly the same
epicentral area as the December
qua e. u ca on o s repor s
supported by funds from the Na-tional Science Foundation through
s earn ng rom ar qua es
Program under grant # CMS-
0131895.
Within a few days of this earth-
quake, a team set out from Jakarta
o s u y e ear qua e amage on
the islands of Nias and Simeulue.
The team leader and author of this
report was Teddy Boen, consulting
eng neer n a ar aan sen or a v -sor, WSSI. Survey team members
on Nias were Teddy Boen, G. Hen-
ra, . rus, . o n, ames ong,
M. Agus, and B. Bernard. Survey
team members on Simeulue were
e y oen, . en ra, an .
Karsono.
n ro uc on
On Monday night March 28, 2005
at 11:09 pm local time, the Nias and
meu ue s an s were s a en y a
M8.7 earthquake with a depth of
30 km. The epicenter of the earth-
qua e was on t e reat umatran
fault, between the two islands at
2.074N, 97.013E (see Figure 1).
s s m rom unung to ,
the district capital of Nias, and 84 km
from Sinabang on Simeulue. In
unung to an e u a am,
many ouse s ops co apse an
e aroun , peop e w e t ey
were either sleeping or trying to runfrom the second and third oors. In
meu ue, some ouse s ops co -
apse , an a out peop e were
killed. There was a rush to exit
ouses an run to g er p aces e-
cause the people feared a tsunami
similar to that of December 26, 2004.
There was a local tsunami, but not
of the size or ferocity of the previous
one.
as s an s part o ort umatra
Province and Simeulue Island is partof Aceh Province. The population of
as s , an t at o meu ue
is 80,000. Most of the people on Nias
and Simeulue were already asleep,
or a out to e, w en t e eart qua e
occurre . g t a ter t e eart -
quake, electric power was cut offand telecommunication disrupted.
n unung to an e u a am,
as, t e amage was concentrate
in certain areas close to the beach.
n meu ue t e amage was a so
concentrate n areas c ose to t e
beach. Strong aftershocks (32 km
from Gunung Sitoli [M 6.0] and 41
km from Sinabang (M 5.5]) did not
cause any further damage to either
damaged or undamaged buildings.
Tectonic Effects
ur ng t e survey n meu ue as
well as in Nias Island, we observed
some subsidence in certain very
m te areas. ere were a so pop-
Figure 1.
Main shock and
a ers oc s
of the Nias/
Simeulue
ear qua e,
March 28, 2005
(USGS).
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up beaches in Nias and Simeulue,
caused by uplift (see Figure 2). Staffmembers of NGOs who worked in
several places across Simeulue re-
porte t at t ey a so o serve s m -
lar pop-up beaches all over the is-
land.
After the earthquake, a local tsunami
hit limited areas. In Nias, along the
roa enter ng ora e an n ora e
itself, the tsunami height was ap-
proximately 1.80 m, as can be seen
on t e wa o ouse n amaetan -
ha, approximately 1 km from Sorake
(see Figure 3). In Sorake, several
building foundations were scoured
by the tsunami, and some buildings
collapsed. The local tsunami wentn an up to m n amaetan -
a. rom t e amage, t appeare
that the ow force was not too
strong. n mue ue, traces o oca
tsunam cou e seen n a uan
Bajau primary school # 2 (see Fig-
ure 4). The tsunami height was ap-
prox mate y . m an no ev ence
of ow force could be seen.
Damage to Buildings
wo types o u ngs were a ect-ed: engineered and nonengineered.
In Nias and Simeulue, there are few
engineered buildings except for
district head ofces, hospitals, andsome other government buildings.
Engineered buildings consist mostly
o re n orce concrete com ne
with masonry walls. Almost 95% of
the buildings are nonengineered,
ma e o con ne masonry a -
burnt brick, concrete block, and
timber.
ng neere u ngs: Some en-
gineered buildings in Nias and Sim-
eu ue were amage ur ng t e
eart qua e, an some co apse .
There are two main reasons for this.
The reinforced concrete buildings
Figure 2.Pop up beach at Matanurung, East Simeulue.gure . oca sunam e g approx ma e y . m.
gure . amage y oca sunam n a uan a au
school, Simeulue. gure .District head ofce in Simeulue.
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were not designed for the seismicity
of the islands. We also found thatpoor qua ty o concrete an eta -
ng contr ute to t e co apses.
Even though Indonesia has a seis-
m c co e, t was not en orce n
e t er s an . t ona y, t e u -
ing permit system was not yet in
place.
For example, both district heads
ofces were damaged (see Figure
. e surmse t at n eac case,
the structure was analyzed as 2-D,
with the torsional effect overlooked.rom t e amage, t was ev ent
that the concrete quality was low
and the detailing was not in accor-
dance with requirements for earth-
quake-resistant construction (seegures an .
Nonengineered Buildings: Most of
t e u ngs were noneng neere
that collapsed in Gunung Sitoli in
Nias, Sinabang City in Simeulue,
and villages along the road from
na ang to a uan a au an rom
Gunung Sitoli to Teluk Dalam in Nias.
There are three main categories of
noneng neere u ngs: one or
two-story houses of burnt brick or
concrete block masonry with sand/cement mortar; two to our-story
shop houses of burnt brick or con-
crete block masonry with sand/
cement mortar; and 3) timber build-
ngs. n some areas, sea san sused for concrete mix and, of
course, results in poor quality
concrete.
The one or two-story buildings were
most y ouses, sc oo s, an com-
munity health centers. The roofs of
the houses mostly consist of gal-
van ze ron s eets or t atc ma e
of coconut tree leaves; other build-
ings use galvanized iron sheets.
ese masonry u ngs surv ve
t e s a ng w t out co apse,
though some had cracks in the
walls (see Figure 8).
Figure 7.Damage to district head ofce in Simeulue.Figure 6.Damage to district head ofce in Nias.
gures a an . oneng neere masonry ouses amage an co apse n as.
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e two to our-story s op ouse
buildings also use burnt bricks or
concrete block masonry with sand
an ort an cement mortar. e
roofs of these shop houses are
usually RC slabs. All the buildings
use pract ca co umns anbeams as connement. The term
practical is used because the
specs are not ase on any ca cu-
at ons an are a opte as a stan-
dard practice. The shop houses are
built according to prevailing practice
by contractors and foremen, without
structural analysis or drawings. In
neither Nias or Simeulue was the
u ng perm t system en orce ;
gure . m er ouses co apse n as ue o ac o
ma n enance.
gure . ra ona n genous ouse n as, no
amage .
Figures 11a and b.Traditional indigenous houses damaged due to lack of maintenance in Bawogosali Village, Teluk
Dalam, Nias.
Figure 12.
n genous ousebuilt during Dutch
occupation, slight-
y amage ue o
lack of mainten-
ance in Nias.
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t ere ore no structura c ec wasperformed to catch poor-quality
materials or poor workmanship.
Timber houses consist of a timber
frame and timber plank walls, and
ga van ze ron s eet or t atc
roofs. In spite of the closeness to
the epicenter of the earthquake, the
amage was not s gn cant n rea-
sona y u t t m er structures. ery
few one-story timber houses col-
lapsed during the earthquakes. The
damage that occurred resulted fromdeterioration of the poorly main-
tained columns (see Figure 9). In
a t on, some t m er co umns
were not anchored to the founda-
tion. There were no tie beams to
t e t e co umns toget er, so t e
columns moved in different direc-
tions during the earthquake. Some
t m er ouses were ean ng a ter
t e eart qua e ecause t e con-
nections were not appropriately
one.
Two types of indigenous nonengi-
neere u ngs st ex st on as.
rst, t e tra t ona ouses u t
some 200 years ago are earth-
quake-resistant and withstood the
s a ng see gure . en
these traditional buildings were
damaged, the main cause was
eterorat on ue to ac o ma n-
tenance (Figure 11). These types ofu ngs are not u t anymore e-
cause of the lack of expertise in this
generation, and because they are too
cost y to u . e ot er u ngs,
u t y t e utc some years
ago (Figure 12), are also earthquake-
resistant when properly maintained.
Causes of collapse: he main
causes of collapse in the two to four-
story s op ouses were poor mate-
rials and poor workmanship, exacer-
bated by the prevailing procedureso u ng n stages, epen ng on
the availability of funds. The long
intervals between the construction
o var ous e ements resu t n wea
o nts.
rst t e oun at on s u t w t t e
column-reinforcing bars already in
place. If additional funds are avail-
able, the columns are poured. The
size of the columns average 30 x 30
(40) cm with eight reinforcing bars
of diameter 12 mm and stirrups
usua y not proper y ent o mm
at an average distance of 20 cm.
Subsequently, the walls are built.
onstruct on o some u ngs stops
after the walls are completed. The
next stage is constructing the beams
an oor s a s or t e next story w t
splices for the upper-story columns.
Most buildings are in use as soon as
the rst story is completed. Only af-ter severa mont s or years, w en
more funds are available, do the
second-story columns and walls get
u t; t e process o construct ng t e
rst story is essentially repeated.
Some people continue the process
for the third and fourth stories. Col-
umn re n orcements an st rrups are
not sufcient if the structure works
as an open frame, particularly in the
ong tu na rect on.
In the damaged structures weoo e at, t e engt o t e co umn
splices for the upper oors con-
struction was generally insufcient,
an t e concret ng at t e sp ces
was very poor. s resu te n t e
shear failure of the columns, partic-
u ar y at t e o nts; t s was t e
main reason for the pancake or
soft-story collapse of shop houses,
particularly in Nias (Gunung Sitoli
and Teluk Dalam), that resulted in
most of the deaths (see Figures 13,
14 and 15).
For one-story conned masonry
houses, the construction is also
one n stages. rst t e oun at on
is built with column reinforcement
embedded. The column size is 12 x
cm w t our re n orc ng ars o
diameter 8 mm and stirrups of dia-
meter 6 mm at an average distance
Figure 13.Pancake type of collapse of shop houses
that killed many people in Teluk Dalam, Nias.gure . no er panca e co apse n unung
Sitoli, Nias.
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of 20 cm. If enough funds
are ava a e, t e co umns
are poured. At a later date,
he walls and the ring
eams are u t an , na y,
he roof is constructed.
e o serve severa s opouse u ngs t at were
built and supervised by the
owners, and did not suffer
amage. e earne t at
hey had been built contin-
uously, not in stages with
ong nterva s cause y
shortages of funds. The
workmanship and mate-
r a s use were aso o
better quality.
rospects for Change
n all areas in Indonesia, a good
eart qua e-res stant es gn eature
is available, namely reinforced con-
crete framing consisting of practical
columns and beams. However, in
many places in both Nias and Sim-
eulue, the columns and beams
were not constructed in accordance
w t preva ng pract ce on ava. n
spite of that, most did not collapse
in the M8.7 earthquake shaking.
uc masonry structures ave e-
come a new culture in Indonesia,
and from past earthquakes it has
ecome ev ent t at t ey are ap-
propriately resistant to the earth-
quake forces identied in the Indo-
nesian seismic hazard map. This new
cu ture s assoc ate w t soc a sta-
tus: as t e r econom c con t on m-
proves, people tend to build masonry
houses at least partly because they
are a sign of status.
The reconstruction period is a good
opportun ty to ntro uce t e u ng
permit system and to start enforcing
the seismic code. Ofcials must start
ma ng qua ty contro part o t e cu -ture in order to improve the perfor-
mance of buildings in earthquakes.
gure .
Cracks onroad in Lasara,
Gunung Sitoli,
as, cause
by lateral
spreading.
Infrastructure Damage
ost o t e amage to n rastruc-
ture occurred to bridges, and there
were ssures along the roads pro-
uce y su s ence an atera
sprea ng. any r ges n ot
Simeulue and Nias were displaced
rom t e r supports rom cm
to cm. any r ge a utments
settled during the earthquake,
thereby damaging bridge ap-
proaches. The differential settle-
ment was jointly caused by lurch-ing, liquefaction, and uneven com-
pact on, part cu ar y c ose to t e
abutments (see Figures 16 and 17).
e ma n e ectr c power generat ng
plant in Gunung Sitoli in Nias was
damaged by the shaking (Figure 18).
rans ormers were s g t y over-
turned (Figure 19) and some gen-
erator foundations settled. But the
ca e networ n t e c ty as we as
along the road from Gunung Sitoli
to Teluk Dalam was not affected,
an a ter t e power p ant was re-
pa re , e ectrc power resume . n
Teluk Dalam, the cable network
was practically intact. The power-
generat ng p ant n meu ue was
not damaged, but some cable
network to Lasikin was damaged
an too a ew ays to restore.
gures a an . oneng neere masonry
shop houses damaged and collapsed due to
ea co umns n agun r , unung o , as.
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Figure 17a.Movement of end support, bridge in Kelapa
Street, Gunung Sitoli, Nias.
Figure 17b.Settlement of bridge approach in Teupah
Barat, Simeulue.
Figures 19a and b. Transformers overturned at power generating plant in Gunung Sitoli, Nias.
gures a an . Power generating plant in Gunung Sitoli, Nias.
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Figure 21a.
e orme e y
ue o s ear
failure of columnjoints, Simeulue.
gure .
Shear failure of
the column joint,
meu ue.
e water pur cat on p ant n u-
nung Sitoli, Nias, was not dam-
aged, but the piping network was
srupte y t e tsunam see
Figure 20). Distribution was done
by water tank trucks. In Sinabang,
Figure 20.
Damage to drink-
ng wa er p pes
y oca sunam
in Lagundri,
Hiliamaetaniha,
as.
Simeulue, the water puri-
cat on p ant was not act -
vated prior to the earth-
quake because of a change
n t e p p ng system ue to
the widening of the main
road. After the earthquake, water
purication was provided by a
erman , an water was
e vere y tan truc s.
One part of the newly constructed
jetty at Gunung Sitoli, Nias, sank
into the sea, most probably be-cause the piles were not driven
own to t e ar ayer. part rom
that portion, the remaining jetty was
still intact, which was fortunate in it-
se ecause o ow p es a een
used. These should not, in fact, be
used for undersea structures be-
cause t e t c ness o t e concrete
cover is not sufcient to protect the
reinforcing bars from corrosion. In
meu ue, many o t e same type
of piles supporting the jetty were
sheared at the connection betweent e p e ea an t e p es, ecause
the upper parts of the columns were
already deteriorated and weakened
(see Figure 21).
Airport runways at Gunung Sitoli
in Nias and Lasikin in Sinabang
were not amage ; a rp anes were
able to land and take off right after
the earthquake. At Lasikin Airport,
some u ngs co apse , name y
the terminal building (Figure 22), a
storage building, and some airportsta res ent a ouses.
Figure 22. Collapsed Lasikin Airport Terminal
u ng, meu ue.