Earthquakes are not funny, in fact it would be true to say
that they are quite serious.
As many people know most parts of Indonesia are susceptible
to earthquakes. “The ring of fire” does not refer
to a particularly hot curry the night before but to the high
level of activity underfoot that results in volcanoes and
earthquakes. A joint between the Indo Australia and Eurasia
tectonic plates runs right along the western and southern
edges of the Indonesian archipelago only a few kilometres
offshore. Moving an average of 6 cms a year this boundary
has been very active in recent years and caused the major
earthquake and tsunami that devastated Aceh and, more recently,
the major earthquake in Yogyakarta.
Could such an earthquake occur in Bali? Well unfortunately
yes it could. In fact damaging earthquakes have occurred in
the East Java Bali region 15 times in the last century the
last one being in 1979.
Now before you go off to find your brown trousers there are
a few things to know about earthquakes to get things into
perspective. Firstly there are some places in the world such
as Tokyo that have earthquakes every day. The people live
with it on a daily basis. Secondly large earthquakes are very
rare and you are more likely to get injured on the way to
the airport than by a major earthquake. Finally most people
are killed not by the earthquake but by falling masonry and
if buildings are properly designed and well built most will
survive an earthquake.
In the aftermath of the recent earthquake in Southern Java
I went to Yogyakarta to asses the damage and examined many
buildings affected by the earthquake. In some areas buildings
were left in relatively good condition while in others almost
every house was flattened. All in all 400,000 houses were
either seriously damaged or totally destroyed in the province.
It is rather sobering to sit and talk to hard working people
who, because they didn’t understand or couldn’t
afford the basics of housing construction, are still living
under tarpaulins amongst piles of shattered bricks. It is
even more heartbreaking to hear the stories of the many people
who escaped from their houses only to be killed or seriously
injured by walls falling on them in the narrow streets.
Five basic factors can be blamed for most of the house failures
in Yogya:
1. The absence of reinforced concrete columns and beams in
the building structures.
2. The practice of reducing cement content in building mortar
to save money (mortar should be 2 parts of sand to 1 of cement,
in some cases 10 parts of sand to 1 of cement had been used!)
3. The use of weak, low temperature red bricks to build structural
walls.
4. Heavy tiled roofs on weak wall structures.
5. Poor foundations.
It was very noticeable that houses that were well built with
integral reinforced concrete columns and beams survived with
surprisingly little damage. The Yogya earthquake was not only
strong (6.5 on the Richter scale) but it was also long, 50
seconds, which is a very long time for a building to withstand.
50 seconds is also a terrifyingly long time for victims surrounded
by falling buildings, just try timing it and you’ll
see what I mean.
In an earthquake ground movement varies enormously including
up and down fractures, sideways fractures, the ground moving
apart leaving open voids or moving together so the land rises
up. Some people in Yogya reported seeing waves rippling through
the paddy fields like waves on the sea.
Earthquake resistance of houses was a subject discussed by
building experts at Gajah Mada University in the aftermath
of the earthquake. Traditional buildings, particularly made
from bamboo or wood, are better able to withstand earthquakes
than modern “brittle” buildings made from concrete.
Houses built with wood or bamboo frames tend to withstand
earthquakes with relative ease because the main structure
of such houses is locked together and not rigid. These buildings
absorb the ground movement by swaying and flexing and so are
far less likely to fall.
The point was proven in Yogya where I found a house fully
intact in the centre of an area where barely a wall was left
standing. It was a very old timber and bamboo house with a
tiled roof. Hardly a tile was out of place.
Concrete buildings should have a well designed structure of
reinforced concrete beams and columns to provide stability.
Raft construction where the building is built on a single
reinforced concrete slab is another technique which allows
the building to “float” as a solid single unit
on moving ground.
The Japanese deal with so many earthquakes they have developed
some interesting techniques.
Many multistory office buildings in Japan are built with steel
girder framed structures mounted on coil springs that absorb
earthquake vibrations. I suppose this is why the Japanese
always have that inscrutable look. They are either wondering
when the next tremour will be or “how on earth do those
coil springs work?”
But what about Bali?
Well Bali is a place that has more personal wealth than other
parts of Indonesia. As a result most houses and hotels here
tend to be well built with properly designed and constructed
reinforced concrete structures.
Many villas have Alang Alang roofs which are light and of
a construction that can sway without disintegrating.
So what do you do if an earthquake strikes? The Yogya experience
says:
Get out of the house and away from walls or other structures.
You are likely to have around 10 seconds to get out. If you
can’t get out of the house get under something as solid
as possible such as a heavy table leaning against a structural
wall. Find something that will deflect falling masonry rather
than try to withstand it.
With a bit of thought at the building design stage and good
supervision during construction living in an earthquake zone
need not be a cause for serious concern.
“Did you feel the earth move my dear?”
“I hope not!”
Phil Wilson
Phil Wilson a project director for Focus Indonesia and a partner
of MrFixit property maintenance services. Opinions expressed
are those of Phil Wilson. If you have any questions or comments
related to property maintenance he can be contacted at the
office on 0361 288 789 or through the website at www.mrfixitbali.com
Copyright@2007 Fixed Abode
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