Breaking up the hanging wall of a rift-border fault: The 2009 Karonga earthquakes, Malawi

[1] The southern East African Rift has an unusually large seismogenic thickness (35–40 km), which is responsible for wide tilted basins and extremely long faults with the potential for M7-8 normal-faulting earthquakes. From 6–19 December 2009, a shallow earthquake sequence (four of Mw > 5.5) hit the Karonga region of northern Lake Malawi. The location is 50 km west of the rift-bounding Livingstone Fault, within the hanging-wall. We used seismology and InSAR to obtain source parameters and combined this with information on rift structure from geomorphology and seismic profiles. The deformation is consistent with rupture of a shallow, west-dipping fault, with no evidence for the involvement of magmatic fluids. Although the Livingstone Fault dominates local geomorphology, the Karonga earthquakes demonstrate that the hanging-wall block is actively breaking up, reflecting temporal and spatial migration of activity or the release of stresses within it.