A 4.5-magnitude earthquake on Sunday night struck central Uganda’s Nakasongola District, sending tremors felt hundreds of kilometres away across the west, east, and northern regions.
Scientists from Makerere University’s College of Natural Sciences told this publication that while aftershocks are possible and could cause damage, the earthquake felt was not a strong one. According to scientists, this magnitude of 4.5 is classified as a light earthquake (4.0-4.9). At this level, the quake is strong enough to be felt across many regions but may not cause damage. But strong quakes (6.0-6.9) can damage buildings, and major or great quakes (7+) often cause widespread destruction, according to information from the University of Alaska Earthquake Centre.
Local authorities in Nakasongola and nearby areas have not yet reported any (significant) damage caused by the 4.5-magnitude earthquake.
‘Earthquakes are elastic waves that propagate within the Earth and are caused when stress that is stored within the Earth is released,’ Dr Arthur Godfrey Batte (PhD), a seismologist at the Makerere University College of Natural Sciences (Conas), said.
‘These earthquakes originate at some point within the Earth known as the Earth’s hypocenter. In this case, the hypocenter was in Nakasongola. Just like any wave, these elastic waves travel at a distance proportional to their energy,’ Mr Batte added.
The hypocentre is the exact point inside the Earth where an earthquake rupture begins, and seismic waves first start to generate. The seismologist further explained that the strength of the earthquake weakens as the distance increases.
‘It was felt in Kampala because this wave travelled like any other wave away from the hypocentre. In other words, it spreads outwards from the hypocenter, and that’s why it was felt in other areas,’ he added. Dr Hillary Mwongyera (PhD), another seismologist at Conas, said this particular earthquake is important because it ‘happened in Nakasongola, an area which sits on a suture zone -boundary between two geographical terrains.’ A suture zone, according to scientists, is the deep, scarred boundary where two landmasses have collided and welded together over millions of years. The suture zones fuse different types of crust together, and the contact is highly fractured and structurally weak, making it prone to significant stress buildup and release in the form of quakes, according to the scientists.
On the possibility of aftershocks, Dr Batte said he can’t rule it out. But he said it will be weaker. ‘On the issue of the aftershock, I understand the magnitude of this earthquake was about 4.5,’ he said. ‘This implies that yes, an earthquake of that magnitude can have aftershocks, but of a smaller magnitude, for example, 3.5 or 3.0, that may not last long but can cause significant damage,’ he said. EarthScope Consortium, a global geophysical research and education body under the US National Science Foundation, states that large earthquakes are usually followed by hundreds and even thousands of smaller earthquakes. ‘These aftershocks, according to scientists, can cause damage or collapse structures that were already weakened by the first earthquake.