Didn't feel any tremors in Cape Town? Here's why

Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences explains the effects of earthquakes.

On Saturday, an earthquake with a magnitude of 6.2 occurred off the south coast of South Africa. While that magnitude is considered a big earthquake, people who felt tremors in Cape Town actually experienced a smaller event. It was only a magnitude of 2.5.

Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences, says it is unlikely Cape Town experienced the effects of the big earthquake. Rather it was the result of a smaller event that occurred just North of Durbanville in the Western Cape. He adds that there was an hour-and 15-minute discrepancy between the events.

The 6.2 magnitude event just basically happened a little earlier. Because it was so far away, over 1600 km south of South Africa along the African plate module, it was highly unlikely that we felt that event. We are attributing it to the smaller event that happening just North of Durbanville.
Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences

While the tremors were a shock to many people, Dr Khoza says that the Western Cape is not unfamiliar with seismic events. He says that there have been a number of big events in the past that caused damage. As to those who feel the tremors and those who don't, Dr Khoza says that it all depends on geology.

You could be sitting 20 km away from the epicentre and you might not feel anything, and someone sitting on the other side, 20 km away from the epicentre will feel the tremors. And that purely depends on the rocks over which propagate.
Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences

So if they are propagating over soft sand, for example, even if a shallow earthquake could cause quite significant damage. But if they are propagating over very hard rock, you might not feel as much as the other person on the other side.
Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences

Dr Khoza says that they constantly monitor fault lines in across the country and that the Western Cape has a number of fault networks. He adds the monitor both natural events and manmade ones such as mining-induced earthquakes.

For those who are worried about the big earthquake of the coast, causing a tsunami, Dr Khoza says there is no need for immediate concern.

In this case, the Indian Ocean Tsunami Warning Centre, of which we participate in, did not issue any tsunami warnings for this earthquake.
Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences

I must make it clear, at this point, we can not predict earthquakes. So to say that it is more likely to happen in the future, we don't know, because we can not predict, all we are doing is monitoring the current events. When they happen we observe then and we try to issue alerts as and when they come through.
Dr David Khoza, Executive manager of Applied Geosciences at the Council for Geosciences

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