Active fault mapping in Karonga-Malawi after the December 19, 2009 Ms 6.2 seismic event

Abstract

The East African Rift System (EARS) has natural hazards – earthquakes, volcanic eruptions, and landslides along the faulted margins, and in response to ground shaking. Strong damaging earthquakes have been occurring in the region along the EARS throughout historical time, example being the 7.4 (Ms) of December 1910. The most recent damaging earthquake is the Karonga earthquake in Malawi, which occurred on 19th December, 2009 with a magnitude of 6.2 (Ms). The earthquake claimed four lives and destroyed over 5000 houses. In its effort to improve seismic hazard assessment in the region, Eastern and Southern Africa Seismological Working Group (ESARSWG) under the sponsorship of the International Program on Physical Sciences (IPPS) carried out a study on active fault mapping in the region.The fieldwork employed geological and geophysical techniques. The geophysical techniques employed are ground magnetic, seismic refraction and resistivity surveys but are reported elsewhere. This article gives findings from geological techniques. The geological techniques aimed primarily at mapping of active faults in the area in order to delineate presence or absence of fault segments. Results show that the Karonga fault (the Karonga fault here referred to as the fault that ruptured to the surface following the 6th–19th December 2009 earthquake events in the Karonga area) is about 9km long and dominated by dip slip faulting with dextral and insignificant sinistral components and it is made up of 3–4 segments of length 2–3km. The segments are characterized by both left and right steps.Although field mapping show only 9km of surface rupture, maximum vertical offset of about 43cm imply that the surface rupture was in little excess of 14km that corresponds with Mw=6.4. We recommend the use or integration of multidisciplinary techniques in order to better understand the fault history, mechanism and other behavior of the fault/s for better urban planning in the area.