Cape Town's shaky ground: what you need to know about the earthquake and tremors

28 September 2020 - 14:17
Cape Town was hit by a 2.5 magnitude earthquake on Saturday night, the SA Council of Geoscience confirmed.
Cape Town was hit by a 2.5 magnitude earthquake on Saturday night, the SA Council of Geoscience confirmed.
Image: 123rf/ Jerry Rainey

Cape Town felt the earth shake when an earthquake struck on Saturday and tremors were felt on Saturday night and Sunday morning.

Here is what you need to know.

First quake and tremor

According to executive manager of the Council for Geoscience (CGS), David Khoza, a strong magnitude 6.2 earthquake struck about 1,600km offshore of SA on Saturday.

Shortly after that, a tremor happened at 8.41pm and registered a preliminary 2.5 on the local magnitude scale, as recorded by the SA Seismographic Network.

The CGS said the 6.2 magnitude earthquake was not related to the tremor felt in Cape Town and surrounding areas in the Western Cape.

“Many reports have been received from residents in Cape Town who experienced a tremor during this time. It does not seem to be related to the earthquake at 7.10pm off the coast of SA.

“There has been no tsunami warning issued by the Indian Ocean Warning System, and it is on this basis the CGS wants to assure the public there is no eminent threat to the affected area, and no cause for panic.” it read.

Second tremor

The CGS on Sunday confirmed another earth tremor was felt at 9.12am.

The tremor was felt near Durbanville and the epicentre was “five or six kilometres north of Durbanville”.

According to the CGS, there is a possibility Sunday's tremor could have been linked to the tremor on Saturday.

Sunday’s shift, measuring 2.3, was slightly weaker than the one recorded on Saturday, measuring 2.5. 

“These events might be related as they seem to occur in the same area.”

No damage 

Cape Town authorities said no damage was caused by the tremors and urged the public to report any potential problems.

“The Disaster Risk Management Centre is not in a position to provide comment on the apparent seismic event until it has been confirmed by the CGS. We can, however, confirm the tremor did not appear to cause any damage to infrastructure or public safety.”

Earthquake vs tremor 

An earthquake is a seismic activity registering around a magnitude higher than 4.0. A tremor is a seismic activity that is less than a magnitude of 4.0. 

On a global scale, CGS said, SA is considered a stable region because it is located away from boundaries between tectonic plates, and therefore its activity rate is lower than in seismically active regions like California and Japan.

“This means that while earthquakes are comparatively rare, they can still happen from time to time, and sometimes this manifests itself as earthquake swarms,”  the council said on its website.

Earthquake swarms are events where a local area experiences sequences of many earthquakes in a relatively short time. Earthquake swarms occur regularly throughout the world and in SA. An earthquake swarm occurred in the Sutherland area in early 1952, with no significant activity recorded since.