Implication of Volcano-tectonic and Fluid Movements on Seismic Activity at the Paka Geothermal Prospect in Kenya.

Abstract

Seismic hydraulic diffusivity at the Paka geothermal prospect is investigated to examine the implications of fluid movements and volcano-tectonic activity on the seismic activity at the geothermal prospect. This is achieved by estimating the seismic hydraulic diffusivity from a source that originates from a point where the pore pressure propagates from for a distance (r) and time (t) from the single source that initiated the seismic swarms to each earthquake in the swarm. The seismic events located for the two years are mainly shallow seismic events that have magnitudes with a range of 0.29 ≥ MLv≤ 3.62 and at focal depths ranging from 0.8 km to 18.3km. This is due to their occurrence along the Kenyan arm of the East African Rift system where there is thinning of the crust as a result of the rifting and volcanic processes. The seismic events showed linearity with the major rift faults in the area. From the analysis of the seismic hydraulic diffusivity for the earthquake cluster located eastwards from the volcano has values that range from 7.5 *10-2 m2/s to 1.67 m2/s. The regions with high seismic hydraulic diffusivity values have a high pore pressure variation in comparison with the regions with lower seismic hydraulic diffusivity values. This is as a result of the dependence of pore pressure variation on the diffusion of fluids in the rock mass which causes the geothermal reservoir induced seismicity as pore pressure diffusion plays a role of triggering seismicity and also decreases the coefficient of friction. The faults and fractures where the pore pressure diffusion takes place are the zones of high permeability that act as conduits of convective heat transfer. The upflow zones in the study area lie in the regions that have high seismic hydraulic diffusivities. The focal mechanism solutions show that the faulting at the Paka geothermal prospect has; normal, normal strike-slip, reverse, reverse strike-slip, strike-slip reverse and strike-slip normal with nornal faulting being dominant. The strike directions from the inversion of the focal mechanism solutions are NW-SE, NE-SW and E-W strike directions on the faults; representing the regional tectonic stresses and local magmatic effects on the stresses. The tectonic regime at Paka is a normal faulting regime