Main geophysical features related to the Virunga zone, Western rift, and their volcanological implications

Abstract

Listen

Translate article

The Virunga volcanic complex in the Western rift vahey of Africa is the most important volcanic structure within the East African rift system. It includes eight main volcanic edifices: Muhavura, Gahinga, Sabinyo, Visoke, Karisimbi, Mikeno, Nyiragongo, and Nyamuragira (fig. 1, Hamaguchi et al., this volume). During the last decade, seismic, magneto-telluric, gravity, geodetic, and levelling studies have been conducted in this area, particularly near the Nyiragongo and Nyamuragira volcanoes. Some of the survey periods included eruptive episodes of the Nyamuragira volcano (e.g., Hamaguchi et al., this volume; Wafula et al., this volume). The results derived from the observational data can be summarized as follows: (1) The spatial distribution of the epicenters of the current seismic activity is usually confined to NE-SW oriented faults and fissures transecting the Nyiragongo and Nyamuragira fields. The earthquakes shown in Figure 1 are of A type (e.g., Wafula et al., this volume). Their foci are mainly in the depth range of 8-13 km beneath Nyamuragira and 14-16 km beneath Nyiragongo (Tanaka, 1983). The vertical distribution of earthquakes associated with eruptive episodes of Nya-