Abstract:
Magadi area is located in the southern part of the Kenyan rift, an active
continental rift that is part of the East African Rift system. Local seismic activity
monitored previously around Lake Magadi revealed an earthquake cluster caused
by swarm activity in the rift centre at shallow depths, which was probably
triggered by magma movements. There was need for a follow-up to locate any
body at depth with sufficient density contrast that may represent magmatic
intrusions. Gravity measurements were carried out in 58 established stations and
data from 52 other stations merged from existing coverage of previous
measurements. Necessary corrections were applied to the gravity data and a
Bouguer contour map prepared. Euler deconvolution technique was used to image
depth to the causative bodies along selected profiles on the Bouguer anomaly
map. Two dimensional gravity forward models of the subsurface structure were
generated by using Euler depth solutions in the start models. Among others, a
unique body of density of 3.20 gcm-3 was modelled on the northern region near
little Magadi at a depth of approximately 0.4 km. The location of the body
coincides with the area where earthquake swarm occurs. Such a body of high
density contrasts may be caused by mafic intrusions into the crust. Discontinuities
in Euler solution cluster along the profiles indicated buried faults in the volcanic rift
infill. The high seismicity may hence be associated to magma intrusions.
