Interaction between active faults and migration of fluids

The aim of the research project is to investigate the influence that fluids and their migration can have on the seismicity of active faults. The study area is the Fentale-Dofan magmatic segment of the Main Ethiopian Rift (MER). It is an area of active rifting processes with widespread seismicity and hydrothermal manifestations. The seismic database used here was collected during the EAGLE project from October 2001 to February 2003. Initially, the events were relocated with a linear location method using Hypoinverse software and a simple 1D velocity model. This allows me to understand the overall distribution of seismicity. Then, a non-linear location method was performed, using NonLinLoc software with an 2D velocity model of the area. This produced an earthquake distribution more grouped that shows a pattern parallel to the rift. Then, the cross correlation analysis was performed. It reveals the presence of families of similar earthquakes in the clusters into the rift but not on the border fault. The occurrence of these families corresponds to an increase in the seismic rate. The differential times for the events with high cross correlation coefficients were used to improve the earthquake location using the HypoDD software. While the earthquakes in the rift are characterized by the presence of swarms, locally high b-value, small release of seismic moment, alignment of events along high angle normal faults, a similar pattern is absent or not as clear in the earthquakes on the border fault. In conclusion, it is possible to assume that the earthquakes in the rift show clear characteristics attributable to the fluid-fault interaction process. Instead, these characteristics are less clear on the western border faults, where it is more likely a tectonic dominated process. In the end, a map of hydrothermal deposits was. No clear correlation between the seismicity and the hydrothermal deposits is observed. Then I can conclude that the fluid induced earthquakes in the rift are caused by a different fluid circulation compared to the one that generates the hydrothermal deposits.