Earthquake Damage Inspection

Damage after the Yogyakarta earthquake

Checking your buildings for damage after an earthquake

See also:

• The risk of earthquakes in Bali and Indonesia
• Design of buildings to resist earthquakes
• Why houses fall down in earthquakes
• Dangerous developments in architectural design

History of Earthquakes in Bali

Well unfortunately earthquakes do happen, in fact we have them quite often. Most of them are small and we don't even feel them but now and then there are larger ones that might wake us up, or worse, demolish our house.

According to the US geological survey an earthquake in Bali in 2011 was a magnitude 6.1 situated 140 kilometres South West of Nusa Dua at a depth of 35 kilometres. Just for the record, the earthquake history in Bali area includes a severe earthquake on 14th July 1976 which killed 563 people and a moderate earthquake magnitude 6.5 on 28th September 1998 that killed 1.

An earthquake on the nearby island of Lombok on July 29th 2018 was a magnitude 6.4 which killed 14 people.

As we have discussed before the effect of earthquakes at a local level are highly unpredictable. In the 2011 earthmovement several buildings in localised areas were damaged while many others in close proximity were relatively unharmed, such is the quirkiness caused by the complex formation of the earth's crust and the resonance of vibrations that pass through it. All we can do is make buildings strong enough to withstand some pretty heavy duty shocks and vibrations.

I spoke to a good friend who ran his business from one of the buildings damaged in 2011, a row of shop houses (rukos) near the Dewa Ruci roundabout in Southern Bali. He reported that the building itself was sound with no cracks in the structure or walls. The damage was, in fact, roof tiles and concrete adornments being shaken off most notably a concrete facade along the top of the front walls which had cracked and pieces of which had broken away falling across the front of the building. This made it very dangerous for anyone trying to leave the building. It appeared the concrete structure of the building itself was well designed and properly built, the added adornments however, were not properly locked into the main structure and this was what caused the problems.

How To Inspect Your Buildings For Earthquake Damage

After an earthquake we should all take the time to take a look at our buildings and check for damage. Quite often damage is easy to spot.

1. First DO NOT enter the building, keep clear of it until you know it is safe. Walk around the outside of the building systematically checking each wall from top to bottom looking for cracks or signs of movement. Particularly inspect to see if there are serius cracks that might make the building unsafe. If your walls have stone cladding you might find parts that have fallen off.
2. Look at the roof and see if there are any tiles moved or missing.
3. Once you feel sure the outside is safe you can move inside and check all the walls and ceilings for cracks. Walk around the floors in each room and see if there are any cracks or gaps opened up between the floor tiles.
4. So much for the obvious but be careful, there may be damage that is not so easy to see particularly if your building has stone or other cladding that is hiding the structure beneath. Here are some ways you might look for clues.
5. Go around and check all the windows and doors and see if they still open and close properly. Movements in a house can often push the frames out of square, only a very small movement can result in a door or window sticking or the catches or locks not engaging properly. Cracked or broken window panes are also a give away
6. Earthquakes have a tendency to crack concrete particularly on the roof and even more particularly along the roof ridges where the ridge tiles are cemented in place. You might not notice damage for a while but these things can become obvious rather quickly when it rains. Go around the house and check the roof ridges for cracks (a pair of binoculars can help a lot).
7. Walk around the house and tap the floor tiles, earth movements can often “pop” the tiles releasing them from the cement underneath. They will sound hollow if they have lifted.
8. If your building has stone cladding tap the pieces of stone to see if they have lifted away from the concrete beneath and look for movement along the joints.
9. Swimming pools and fish ponds that have not been designed or built properly are particularly susceptible. You may find the water level is falling more than it used to suggesting there might be leakage somewhere.
10. Earth movement can also break pipes either underground or buried in walls, you might find damp patches or that your pump is running more than it used to.

Some Final Words Of Warning

In earthquakes most people are killed and injured from falling masonry. As was shown in the 2011event poorly made building facades (immediately above entrances) present a major danger. It is also noted that in Indonesia “infill” walls (these are the sections of walls that “fill in” the sides of the building between the reinforced concrete columns and beams) are usually not tied into the main structure of the building and can crack or even fall out while the main structure remains sound.

It is well to remember that roofs are not very strong, they are only designed to withstand wind and keep the rain out. If anything falls onto a roof, such as a wall, it may well fall straight through onto anyone in the room below. We came across one such case from the recent event where a lightweight steel roof frame was badly damaged by a parapet wall that fell over onto a roof.

If In Doubt Call An Engineer

If you do notice something that you area not sure about call a structural engineer to assess the building.

We can only expect more earthquakes as the Australia plate dives underneath the Sunda plate the Indonesia sits on. Of course what we need are more small earthquakes like the one in 2011, large enough to release the pent up energy in the earth's crust but not large enough to cause major damage or loss of life.

See also:

• The risk of earthquakes in Bali and Indonesia
• Design of buildings to resist earthquakes
• Why houses fall down in earthquakes
• Dangerous developments in architectural design