The seismicity of East Africa, the Gulf of Aden and the Arabian and Red Seas

abstract Maps of earthquake epicenters are presented for East Africa, the Gulf of Aden and the Arabian and Red Seas for the period January 1955 to March 1964. Many of these epicenters were located with an accuracy of about 10 km; errors of 100 km or more were common in previous studies. Several tectonic features can be resolved with the new epicenters. In the Gulf of Aden and in the Arabian Sea, the epicenters are confined to narrow linear segments. A large fracture zone that intersects the mid-oceanic ridge near 58°E is clearly delineated with the new epicenters. In the Gulf of Aden regions of high seismic activity are found where NNE-SSW trending faults intersect the median ridge. The seismic activity in the Red Sea is less than that in the Gulf of Aden and the Arabian Sea. A large number of the earthquakes in East Africa are associated with various branches of the rift system. However, many well-recorded earthquakes were not located along the rift valleys. The large areal extent of seismic activity in East Africa differs from the narrow linear pattern of activity that is associated with the mid-oceanic ridge.