Fluid-triggered earthquake swarms in the Rwenzori region, East African Rift—Evidence for rift initiation

摘要: The Rwenzori Mountains are located within the Albertine Rift Valley in western Uganda. To monitor microseismic activity area we have deployed a seismic network of up to 35 stations for period about 20 months. analysis recordings revealed several earthquake clusters restricted NE mountain block. form elongated pipes with 1–2 km diameter and vertical extensions 3–5 km. Most them 5–16 depths; however one cluster reaches down 22 Each is composed series single swarms durations between few days more than week, interrupted by intervals inactivity Some swarm events exhibit migration tendencies estimated velocities 0.3 1 km/day. Local magnitudes range from ML = 0.5 4.0 b-values 0.96 1.2. source mechanisms earthquakes dominated normal faulting tension-axes orientations perpendicular rift axis. There only strike-slip no reverse mechanisms. From petrological considerations presume that triggered fluids gases which originate magmatic below crust. Melt and/or CO2 guided along intersection lines two steep fault sets were identified shear-wave splitting mapping area. existence lithosphere supported detection velocity reduction 55–80 depth receiver-function location mantle at 60 We interpret these observations as indication an initial rifting process may eventually lead complete detachment block surrounding flanks.