PRELIMINARY ASSESSMENT AND GEOLOGICAL EVIDENCE FOR THE SEISMOGENIC POTENTIAL OF SOUTHERNMOST PORTION OF THE EAST AFRICAN RIFT, MOZAMBIQUE

The Southern East African Rift (EAR) in Mozambique is the most poorly characterized and mapped major onshore plate boundary on the planet. Although the EAR is well documented north of the Mozambique border, a 20 year war in Mozambique made it an extremely difficult place to conduct neotectonic investigations. Recent fieldwork in Mozambique, coupled with satellite and airphoto mapping facilitates a preliminary sense of the seismogenic potential of this active extensional system. In southern Mozambique, the rift splits from a discrete symmetric graben in the north of the country near the border of Malawi into a series of sub-parallel symmetric and asymmetric grabens that are seismically active and with long-axis of the rift roughly North-South. Earthquake catalogs shows earthquakes ranging in magnitude from 2.5 to 7.0 with an Mw 7.0 earthquake occurring in 2006 along a near-vertical normal fault. These grabens vary from 30 to 100 km long, with graben floor widths from 8 to 15 km wide, and rift flanks varying from 30 to 80 m above the graben floors due to normal faulting. Fieldwork in two of the largest EAR grabens in Mozambique, the Funhalouro and Banamama rifts show that these rifts are active. Sedimentary rocks along the southern EAR are limestone, mudstone, and sandstone and Plio-Pleistocene or younger in age and volcanic rocks are noticeably absent compared to areas further north in the EAR. Holocene sediments are faulted in both grabens and near Lake Banamama, which is the southernmost rift lake in Africa. Lake Banamama possibly stores both sedimentary climate records in the lake basin as well as paleoseismic records. Samples dating geomorphic surfaces, and thus earthquake activity, were obtained during recent fieldwork and will provide insight into the dynamics of the poorly-characterized southernmost portion of the EAR.