The Council for Geoscience’s Eldrich Kgaswane confirmed that this event was indeed a tremor rather than an earthquake – but only by a whisker.
When the news was first reported by international seismic stations, they claimed that the magnitude of the quake registered at 4.6. According to Kgaswane, anything that registers as 4.0 or above can be considered an earthquake in South Africa.
#Tremor The council has confirmed the epicenter was recorded near Harmony Doornkop mine on the Westrand.
— EWN Reporter (@ewnreporter) March 1, 2019
However, local readings soon revised this figure to 3.8 – thus reducing it to a tremor. B
“There was a difference in the two figures because international readings don’t have our localized seismic network. They are using the global seismic network, so their nearest station will be based in Kimberley, hundreds of miles away from the scene in Johannesburg.”
“When the station is that far away from the epicentre, you’re likely to pick up a magnitude that’s over-determined. The closer the stations, the better the reading.”
Kgaswane also that a reading of over 4.0 may constitute an earthquake in South Africa, but that same benchmark wouldn’t apply in regions that experience quakes and tremors on a daily basis. In places like China and Japan, nothing under 5.0 would register as an earthquake.
Recall, on Friday’s tremor still had some way to go to beat the most devastating quakes this country has ever seen.