We analyzed the seismic data collected in the database of the Goma Volcano Observatory, for the period from 2002 to 2011. Based on the location of the various swarms of Long Period Earthquakes, migration of epicenters were assessed in order to estimate the weakness areas which are the ways for dyke intrusions at Nyiragongo and Nyamulagira volcanoes, the two very active volcanoes the Western Branch of the East African Rift in the Democratic Republic of the Congo. We found that the intrusions of dykes occur in two main perpendicular weak axes: the NE-SW axis generated by tensional forces from the East African Rift actions, and the NW-SE axis generated by divergent forces from the actions of magmas of both volcanoes.

A lava lake activity is observed at Nyamulagira volcano during this last decade. The training process of this lava lake began in 2012 by the release of gas fumes that was been continuously observed in the crater of the volcano. However no change in seismic activity was observed compared to the usual activity of the volcano until April 2014. On 22 June 2014, an activity of glow was observed by the Goma Volcano Observatory and the inhabitants of the city of Goma. On July 3rd 2014, the United States’s organization NASA (National Aeronautics and Space Administration) noted this situation by its satellite detection and published on his Web site the apparition of a new lava lake in the crater of Nyamulagira. Nyamulagira volcano (in its known history) logged again a lave lake from 1921 to 1938. Here are analyzed the seismic activity which preceded this new event at mount Nyamulagira. It was found that this event was been preceded by a significant swarm activity of Long Period earthquakes in April 2014, six hybrid earthquakes and volcanic tremors in June 2014. The April 2014 swarm of low frequency earthquakes lasted about four days and was been located in the North-Eastern part of the Nyamulagira crater (at the place where appeared the new lava lake) and was been interpreted as expressed by the precursor movements of the opening of the crater. The six hybrid earthquakes were been interpreted also as the events that led to a falling movement of the land masses and the opening of the crater. After the visibility of the lava lake in June 2014, the activity of LP events reduced, no swarm and hybrid events were been recorded from this period, but the number of Volcano-Tectonic events remained constant.