By P. Selvarani
ALERT: With increased seismic activity in the region following a series of major earthquakes in recent years, Malaysian Meteorological Department senior director Dr Mohd Rosaidi Che Abas tells P. Selvarani how these temblors affect Malaysians. He stresses, however, that they do not mean that the end of the world is nearQuestion: Was the 8.6 magnitude earthquake which struck off the coast of Aceh on Wednesday in any way related to the massive earthquake which hit Japan in March last year?
Answer: Not really because they are on different tectonic plates. The subduction zone where the two plates meet — the Indo-Australian plate and Eurasian plate (where Sumatra and Malaysia sit) — can see earthquakes occurring at any time and the magnitude can reach 9.0 or more. It can be anywhere along the fault line.
Question: When does an earthquake trigger a tsunami?
Answer: The earthquake last Wednesday occurred far from the subduction zone, about 100km away. So, the mechanism was more of a “strike slip” meaning that the movement of the seabed was horizontal. The earthquake that hit Aceh in 2004 occurred along the subduction zone where there was vertical movement of the seabed. We call this reverse faulting. That is why the Aceh 2004 earthquake generated a very big tsunami due to the vertical movement of the seabed, compared with the recent earthquake.
Question: But a tsunami warning was still issued on Wednesday.
Answer: Yes, but it was a minimal tsunami. It was observed that the maximum (height of waves) at the coastal areas of Sumatra was only one metre.
Question: Although we are not in the Pacific Ring of Fire, is there a possibility of a major earthquake occurring in Malaysia, considering our proximity to Indonesia?
Answer: In Malaysia, so far we have experienced only weak earthquakes in the Bukit Tinggi area, from 2007 until 2009. There are some fault lines in peninsular Malaysia, for example the Bukit Tinggi fault as a result of the strong earthquakes which occurred starting from the 2004 earthquake in Aceh, followed by several big earthquakes in the Sumatra subduction zone. But it triggers a weak earthquake. But we don’t foresee anything more than a magnitude of 5 on the Richter scale.
Question: So any earthquake that occurs in Malaysia will not exceed 5 on the Richter scale?
Answer: Not in peninsular Malaysia. But in Sabah, it is different as there are some active fault lines. In 1976, there was a 5.8 magnitude earthquake in Lahad Datu. It occurred in the centre of the town and caused some structural damage. So, in Sabah, earthquakes that occur there can reach a magnitude of up to 6.0, but in peninsular Malaysia, it won’t be more than 5.
Question: How much damage can a 5 magnitude earthquake cause?
Answer: If it occurs in a densely populated area where there are high-rise buildings, it may damage the buildings.
Question: How bad would the damage be?
Answer: If the epicentre of the quake is just below a very dense area where there are many high-rise buildings, it could cause some buildings to collapse if they are not structurally sound.
Question: In view of this, should the authorities, our developers and those in the construction industry now think of building earthquake-proof structures?
Answer: Actually, we are already doing this. We have a committee to look into this. It is under the Institution of Engineers Malaysia. They are drafting the guidelines for earthquake-proof building designs for the country.
Question: What exactly is the committee looking at?
Answer: Certain factors we should consider in the construction of buildings ….especially critical buildings such as dams, bridges, LRT and monorail networks and other major structures.
Question: When a major earthquake occurs in Sumatra, we feel the tremors here, especially in the northern states, why is it that only those in high-rise buildings feel the tremors?
Answer: Firstly, it depends on the epicentre of the earthquake. For example, if the epicentre is north of Sumatra, Penang will be more affected by the tremors. If the epicentre is near Padang (west Sumatra), then Selangor and Kuala Lumpur will experience stronger tremors, depending on how deep the earthquake is. A taller building will sway more compared with a low-rise structure.
Question: With all these major earthquakes occurring everywhere, how will Malaysia be affected? Is is true that the tectonic plates are moving closer towards Malaysia?
Answer: Actually, the movement of the tectonic plates towards our country is not so significant because the plate from the Indian Ocean will actually move down underneath Sumatra. The movement is very minimal, so we don’t worry too much about that.
Since the plate from the Indian Ocean is continuously moving, it will continuously develop energy along the subduction zone. For example, Wednesday’s Aceh earthquake was followed by more than 50 aftershocks because the surrounding of the epicentre was under stress and the energy was released.
But we are worried that there is a segment where the energy has not been released yet and due to the recent earthquake, there is additional pressure (on that segment) now. Maybe that segment is a very strong bed of rock and it has to wait for more energy to accumulate and when it releases that energy, it will be a much bigger earthquake.
Question: And when is that likely to happen?
Answer: We don’t know when. It can occur at anytime…now or in years to come. Most of the scientists now worry about the Padang one because (the) Padang (earthquake) is already due. Last Wednesday’s earthquake may also increase the energy at the Padang fault line and may speed up the occurrence of an earthquake there.
We are worried because Padang is closer to us. The recent Aceh earthquake was quite far, about 800km from Penang. But if the Padang one occurs, it’s only about 300km from Kuala Lumpur. If it has the same magnitude of 8.5, the tremors will be strongly felt here.
Question: Could that also trigger a tsunami?
Answer: Yes, depending on the depth. If it’s shallow (less than 100km in depth), it may trigger a tsunami. But the waves may go towards the north (of Sumatra) and because we are blocked by Sumatra Island, the impact on us may be very minimal.
Question: When Wednesday’s quake occurred, the Pacific Tsunami Warning Centre estimated the arrival of tsunami waves in George Town at 9.11pm and Port Dickson at 1.43am. Aren’t states such as Negri Sembilan, Malacca and Johor safe from tsunamis because we are shielded by Sumatra?
Answer: From our analysis, they (the tsunami waves) travelled only until Selangor. The high-risk area is from Perlis down to Selangor. From Malacca to Johor, Pahang, Kelantan and Terengganu are considered low-risk areas.
Question: If an earthquake occurs on the Philippines side or close to the Sulu Sea, then is there a risk for these states?
Answer: Malacca, no. Johor very minimum. For Pahang it is also not so dangerous, but for Sabah, yes.
Question: So we are in no danger of a major earthquake, but we could be at risk of a major tsunami?
Answer: Yes, right now, we believe our buildings will not be damaged by earthquakes.
Question: Why did the MMD only issue a tsunami advisory and not a tsunami warning although the PTWC issued a tsunami alert following last Wednesday’s earthquake?
Answer: We use the PTWC as a guide but we do our own analysis. That’s why although India and Thailand evacuated their people after the tsunami alert was issued, we did not.
The advisory alert is to advise people to stay away from the beach. Warning means we have to evacuate people. From our analysis, we estimated that the waves will reach Malaysian shores about three to four hours later. So, we have time to give the warning. Also from our database, we estimated the maximum height of the waves will be about 0.76 metres. So we did not worry too much. That’s why we issued the advisory for the public to stay away from coastal areas. And when we confirmed there were no waves coming in, we terminated the warning. We did not have to ask people to evacuate.
Question: How effective is our tsunami alert system?
Answer: Now we are able to disseminate information and early warning within 10 minutes (of the earthquake happening). Since this year, we have reduced it to 10 minutes compared with 12 minutes last year and 15 minutes after the 2004 Aceh earthquake. We keep reducing the time. We have tsunami sirens at 23 locations now, but that siren will be activated only if evacuation is needed.
Question: Why are earthquakes now bigger and more intense? We rarely heard of these occurrences in the past as we do now.
Answer: I suppose because there is more awareness now. And compared with the last 30 years or so, we did not have many high-rise buildings. So when an earthquake occurred in Sumatera, we did not feel the tremors here.
Question: One of the reasons earthquakes occur is because of man-made activities such as the building of dams and drilling for oil in the ocean bed. How big a part do these activities play?
Answer: They may produce induced earthquakes. For example, when we built the Kenyir dam, there were a series of earthquakes, but it was only temporary. When the ground settled, it stopped. But it does not always happen. It depends on the underground structure and whether there is a fault line nearby. For example, Bakun (dam) now….no induced earthquakes or seismic activity have been reported there so far.
Question: It was reported that after Wednesday’s earthquake, tremors that were felt in Penang were between 5 and 6 on the Modified Mercalli Intensity scale (MMI). What does that mean?
Answer: That is the measure of intensity of the tremors at the location where you are. It depends very much on the location you are at. If you live in a high-rise building, the intensity of the tremors will be more. But a scale of 5 to 6 will not cause major structural damage. Maybe the wall of the building may crack a bit. But if the reading was 7 and above, it may cause some structural damage.
Question: Are all these earthquakes and tsunamis part of climate change?
Answer: No, because earthquakes have been occurring for millions of years.
Question: People are wondering whether these are signs that the world is coming to an end, as predicted by the Mayans?
Answer: No, these are just normal natural disasters which occur from time to time. They have occurred for millions of years and will keep on occurring. It’s just that we have become more aware of these disasters now.
Question: So how should we prepare ourselves when faced with such disasters?
Answer: If you experience an earthquake or feel the tremors, don’t panic. Find shelter under a strong structure, wait until the tremors stop and then go out and wait for advice from the authorities. For tsunami, heed our early warning advice. The best is to listen to the authorities.