The Bilila-Mtakataka fault in Malawi: An active, 100-km long, normal fault segment in thick seismogenic crust

Some parts of the east African rift system have deeper earthquakes (30-40 km), a larger effective elastic thickness (similar to 35 km), and wider half grabens (similar to 50 km) than are typical in other regions of continental extension. One such region is the southern part of the western branch of the east African rift in Malawi. In this region we describe a normal fault scarp that is up to 15 m high and continuous over a distance of more than 100 km. It represents the latest increment of slip, perhaps in a single earthquake, on a fault (the Bilila-Mtakataka fault) with a total offset of about 1000 m. It is the longest continuous normal fault segment that we know of on the continents, and it supports the suggestion that the thickness of the seismogenic layer is the fundamental control on the scale of geological structures that form within it. A consequence of this association is the possibility of very large (M(w) 8.0), though infrequent, normal faulting earthquakes in east Africa.