EARTHQUAKE SWARMS OF MT CAMEROON, WEST-AFRICA

Historical and recent instrumental studies of the central region of th e Cameroon Volcanic Line clearly indicate the occurrence of earthquake swarms of volcanic origin. Analyses of more than 3000 micro-earthquak es recorded between 1985 and 1992 show a well-defined seismic pattern characterised by single and swarm events with duration magnitudes betw een 2 and 3 at depths down to 20 km. On average, the earthquakes here occur at the rate of about 2 events every 3 days with occasional earth quake swarms, which greatly increase this number. The seismic swarms c omprising felt earthquakes are shown to be sometimes preceded by, simu ltaneous with, or followed by swarms from Bimbia and Equatorial Guinea . Mapped epicentres of some of these swarms correspond to regions of v olcanic gas emissions and are parallel to the fissures on Mt Cameroon and to the inferred direction of the underlying shear zone. The quiesc ent periods between swarms are seen to double each year since 1986. Th is observation was used to predict a major seismic swarm which occurre d in 1993. The data coupled with historical data, are used to infer th e involvement of a magma chamber in the generation of the earthquake s warms in the region. Since the installation of the network, no eruptio n has been observed on Mt Cameroon. This warrants more observation in order to study the seismicity that may precede, accompany or follow an eruption of the mountain. (C) 1997 Elsevier Science Limited.