Earthquake hazard in Africa : perspectives on the Nubia-Somalia boundary : news and view

A wide plate boundary zone between the Nubia and Somalia plates extends through eastern and southern Africa, from the Red Sea-Gulf of Aden region to the mid-oceanic Southwest Indian Ridge. The observed pattern of earthquake activity divides it into seismic belts surrounding relatively stable aseismic blocks. In eastern Africa, the Ukerewe Nyanza plate and the Rovuma plate are separately distinguishable, but in southernAfrica and the adjacent Southwest Indian Ocean, the separation of the Transgariep and Lwandle blocks remains to be demonstrated. Because of the slow rates of plate motion along the wide Nubia-Somalia plate boundary and the correspondingly long recurrence times of major events, the quantitative assessment of earthquake hazard requires a new method of estimating maximum magnitudes in the seismic belts, based on the principle of seismic moment conservation. Application of this method requires that the rates and directions of motion of the major plates and the boundary zone blocks be known with sub-mm/yr accuracy. A proposed new project to extend the network of spacegeodetic observatory sites inAfrica and establish a unified continental reference frame would determine these motions and thus contribute to a long-term African international strategy for natural disaster reduction.