POSTERUPTIVE SEISMIC ACTIVITY OF MOUNT-CAMEROON (CAMEROON), WEST-AFRICA - A STATISTICAL-ANALYSIS

Recent seismological studies of the Cameroon Volcanic Line show that M t. Cameroon is the most active centre, so a permanent seismic network of six seismographs was set up in its region between 1984 and 1986. Th e network was reinforced with temporary stations up till 1987, and the local seismicity was studied. Here we emphasise a statistical analysi s of seismic events recorded by the permanent seismic stations, Four s warms lasting 9 to 14 months are identified at intervals of 2-3 years. Most earthquakes are felt (intensity and magnitude, respectively, les s than VI MM and 5) during the first three swarms and a few during rep ose periods. The main focal regions are the northwest and southeast fl anks, the Bimbia and Bioko regions in the South of the volcano, Hypoce ntres are distributed from the surface to 60 km depth indicating crust al and subcrustal activities. The subcrustal events are observed only in the southeast flank, they are the most regular earthquakes with a m onthly frequency of 9 to 15 events. They are characteristic earthquake s with magnitude 2.8 +/- 0.1. Between 1984 and 1992, their yearly mean time interval between successive events range from 50 to 86 hours. Fo r that period their occurrence can be modelled as a stationary renewal process with a 3-day period. But the analysis of variance shows possi ble significant differences among yearly means. A Weibull's distributi on confirms that the time intervals between successive deep events are not independent, and in 1993 a swarm of deep earthquakes is recorded, hence a non-loglinear magnitude/frequency relation. The deep seismici ty is thought to be associated with a zone of weakness (perhaps a magm atic conduit) and may have some close relationship with the magmatic a ctivity. (C) 1997 Elsevier Science B.V.