Studies of crustal structure, seismic precursors to volcanic eruptions and earthquake hazard in the eastern provinces of the Democratic Republic of Congo

Abstract

In recent decades, civil wars in the eastern provinces of the Democratic Republic of Congo have caused massive social disruptions, which have been exacerbated by volcanic and earthquake disasters. Seismic data were gathered and analysed as part of an effort to monitor the volcanoes and quantitatively assess the earthquake hazard. This information can be used to regulate the settlement of displaced people and to 'build back better'. In order to investigate volcanic processes in the Virunga area, a local seismic velocity model was derived and used to relocate earthquake hypocenters. It was found that swarm-type seismicity, composed mainly of long-period earthquakes, preceded both the 2004 and 2006 eruptions of Nyamuragira. A steady increase in seismicity was observed to commence ten or eleven months prior to the eruption, which is attributed to the movement of magma in a deep conduit. In the last stage (1 or 2 months) before the eruption, the hypocenters of long-period earthquakes became shallower. Seismic hazard maps were prepared for the DRC using a 90-year catalogue compiled for homogeneous Mw magnitudes, various published attenuation relations, and the EZ-Frisk software package. The highest levels of seismic hazard were found in the Lake Tanganyika Rift seismic zone, where peak ground accelerations (PGA) in excess of 0.32 g, 0.22 g and 0.16 g are expected to occur with 2%, 5% and 10% chance of exceedance in 50 years, respectively.