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Journal Article

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

Authors

Lindenfeld,  Michael
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Rümpker,  Georg
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Link,  Klemens
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Koehn,  Daniel
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

Batte,  Arthur
External Organizations;
Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum;
GEOFON, Deutsches GeoForschungsZentrum;

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Citation

Lindenfeld, M., Rümpker, G., Link, K., Koehn, D., Batte, A. (2012): Fluid-triggered earthquake swarms in the Rwenzori region, East African Rift—Evidence for rift initiation. - Tectonophysics, 566-567, 95-104.
https://doi.org/10.1016/j.tecto.2012.07.010


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_444894
Abstract
The Rwenzori Mountains are located within the Albertine Rift Valley in western Uganda. To monitor the microseismic activity in the area we have deployed a seismic network of up to 35 stations for a period of about 20 months. The analysis of the recordings revealed several earthquake clusters within a restricted area NE of the mountain block. The clusters form elongated pipes with 1–2 km diameter and vertical extensions of 3–5 km. Most of them are located in 5–16 km depths; however one cluster reaches down to 22 km. Each cluster is composed of a series of single earthquake swarms with durations between a few days and more than a week, interrupted by intervals of inactivity of up to several months. Some of the swarm events exhibit vertical migration tendencies with estimated velocities between 0.3 and 1 km/day. Local magnitudes range from ML = 0.5 to ML = 4.0 with b-values between 0.96 and 1.2. The source mechanisms of the swarm earthquakes are dominated by normal faulting with tension-axes orientations perpendicular to the rift axis. There are only few strike-slip events and no reverse mechanisms. From petrological considerations we presume that the earthquake swarms are triggered by fluids and gases which originate from a magmatic source below the crust. Melt and/or CO2 are guided along the intersection lines of two steep fault sets that were identified by shear-wave splitting analysis and fault mapping in the Rwenzori area. The existence of a magmatic source within the lithosphere is supported by the detection of a shear-wave velocity reduction in 55–80 km depth from receiver-function analysis and the location of mantle earthquakes at about 60 km. We interpret these observations as indication for an initial rifting process that may eventually lead to the complete detachment of the Rwenzori block from the surrounding rift flanks.