On Sunday night, January 10th 2016, slight tremors hit areas around Mt. Kenya. The Daily Nation reported tremors jostling sleeping residents in Meru, Tharaka Nithi, and Embu counties. Of course, as a geologist I got curious. I mean, we are used to hearing about tremors within the Great Rift Valley (in areas like Eldoret and Nakuru) but Meru? A region rooted within the relatively stable Mozambique Mobile Belt? That raised a few eyebrows – well at least my eyebrows.
So before we go any further, it would be scientific to note that within the rich plantations of these areas lies Mt. Kenya, the second highest (volcanic) mountain in Africa. For purposes of this ‘investigation’ it would also be appropriate to note that Meru County is about 300 kilometers east of The Rift Valley. Are you wondering what investigation I am talking about? Well, I am searching for the source tremor; the focus/hypocenter and epicenter. Since such events do not happen every day, I think it merits investigation. Bear with us San Andreans!
Now, having stumbled over two very interesting reports with a colleague of mine (Cheers Naima!), this ‘micro-mini’ event could be one of two possibilities; either the rift has ‘learnt’ to really stretch its activities this far east or Mt. Kenya – considered to be extinct for over 3 million years – is waking up. Hey! Don’t make that face, I am a scientist and scientists are allowed to consider all causes possible right? (I should add the random possibility of Meru experiencing a pre-Alien attack – yes, no, maybe?)
Now, geologist Brian Howard Baker did quite a lot on the geology of Mt. Kenya area in 1967 and highlighted a few interesting things including:-
The Mt. Kenya suite of rocks is divided into a.) volcanics of the main eruptive episode that erupted from the main vent that is now plugged by nepheline syenites deposits and b.) volcanics of the satellite vents and fissures on the side of the main crater.
The satellite vents were derived from a different magma chamber.
In simple terms, Baker proved to us that the possibility of eruption via the vents surrounding the main vent since they get their ‘juice’ from a different ‘jug’.
And guess what else is possible? Extinct volcanoes (eg. Mount Vesuvius) have erupted even after being declared extinct! Are you thinking what I am thinking?
According to Elizabeth Shah (1986), a seismologist who studied 388 earthquakes on the seismicity of Kenya, seismic activity around the Mt. Kenya region is not a new thing. She managed to point out, from local data a N-S linear trend of epicenters to the North of the area (at around 2.5°N). Though her claim to the tentative correlation of recent volcanism with the local seismic activity matches that of Baker, her discussion on Meru area’s seismic activity with respect to the Kenyan dome traces the second possible source of these tremors. Could the Kenya dome, the great plume situated at the base of the Rift Valley and the source of all local events in Olkaria’s geothermal area, also be the source of tremors in areas within its NE flanks? Areas such as the Meru region?
Having information and conclusions from such reports is a worthy start, but we cannot assume the need for primary data especially on matters seismic. We hope the experts will trace the epicenter of this ‘micro-mini’ event and at least quench the thirst of curious scientists like myself. And while we wait, we can try a few basic things. Reports of the event noted the following:
Tremors were reported
No damages were reported
People jolted in their beds as they slept
From these few points Mercalli allows us to state that the tremor was a level IV, a number that translates to a general magnitude of about 3 to 3.5 on the Richter scale! Tracing the source is all that’s left now!
Shah, E., 1986. Seismicity of Kenya