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The 2009 Mw6.0 Karonga, Malawi earthquake caused by partial rupture of a blind fault: Evidence from aeromagnetic data

The 2009 Mw6.0 Karonga, Malawi earthquake caused by partial rupture of a blind fault: Evidence from aeromagnetic data

Name:
Folarin Kolawole

Department:
Geology

Abstract:
The 2009 Karonga, Malawi earthquake caused a 14-18 km long surface rupture along a single W-dipping fault on the hinge zone of the E-dipping half graben that form the North Basin of the Malawi Rift. This part of the rift is underlain by the NW-trending Precambrian Mughese Shear Zone (MSZ). We used aeromagnetic and electrical resistivity data to elucidate the relationship between surface rupture locations and pre-existing basement structures. Although several magnetic lineaments are visible in the basement, mapped surface ruptures align with a single 37 km-long magnetic anomaly oriented 148°-162° and dips 40°SW, a segment of which coincides with geoelectrical disturbance (‘electrical mélange’) caused by near-surface soil liquefaction and sand dike. Fault geometries, regional kinematics and spatial distribution of seismicity suggest that extension in the Karonga area is accommodated by active break-up of the hinge zone of Malawi Rift’s North Basin through transtension and reactivation of faults that originally exploited a segment of the MSZ. This study presents for the first time, electrical signatures of an earthquake rupture zone and the application of aeromagnetic geophysical data to the study of earthquake causative faults.