| Abstract |
The East African Rift System (EARS) within Kenya has been previously studied for its potential for geothermal energy production. EARS, an active continental rift zone, contains a number of active and inactive volcanoes that may be potential sites for geothermal energy production. The University of Texas at El Paso and the Kenyan Geothermal Development Company (GDC) collaborated to monitor several volcanic centers by deploying 14 seismic stations around the Menengai Caldera and nine stations at the volcanic centers: Silali, Paka, and Korosi. We perform double-difference relocations to obtain high precision earthquake locations, and identify three major seismic swarms located in two volcanic systems. Two of them occur at the center of Menengai, one with a pipe-like shape and one on the northwestern flank with a circular pattern of seismicity. A third swarm is located at the center of Paka volcano and shows a pipe-like pattern of seismicity at the summit of the crater. Korosi volcano shows no seismic activity during this study. We also estimate the stress conditions of the swarms using Gutenberg-Richter b-value analyses to interpret the variation in stresses accompanying the migration of fluids and the tectonic stress state. One seismic swarm in Menengai occurred at the center of the caldera with an increase of b-value (b=1.24) and another swarm on the northwestern flank has a lower b-value (b=1.76), which we interpret as being due to magmatic fluid flow generating high temperature and pore pressure. For the third swarm at Silali volcano, the b-value is also lower (b=0.83) and attributed also to the regional tectonic stress conditions. We further use focal mechanisms to approximate the orientation of stress and whether faulting is modulated by local stresses. We find that P-axis strikes NE-SW for two seismic swarms beneath the Menengai and Paka volcano. To further resolve the geometries and locations of the magmatic reservoirs at the four volcanic centers, we develop a 3-D high-resolution S-wave velocity model, which delineates the locations and shapes of the sources of the magmatic reservoirs as well as the stress perturbations due to these processes. The tomography model extends throughout the four volcanic systems, and we identify four magma chambers at approximately 6 km in depth, consistent with the seismicity results. We conclude that active fluid movement under Menengai and Paka indicated by seismicity and low S-wave velocity suggest potential for geothermal production at these sites. |