Classification of Volcanic Earthquakes Observed at Nyamulagira and Nyiragongo Volcanoes Reference on Frequency Analyses and its Implication in Volcano Monitoring

Identification of the types of seismic signals is the basic of the seismo-volcano analysis, because it allows to have information on the magmatic activity prevailing in the crater. Modern analysis for this work identifies the frequency observed in the evaluation of the signals that can lead to a proper classification following groups arranged in specific spectral bands. This frequency analysis was applied to seismic data that preceded the eruption of Nyamulagira Volcano of 6 November 2011 and the persisted lava lake within Nyiragongo Volcano. The data analyzed covered a period of two years, from January 2010 until November 2011. The work consisted to analyze the frequency content of the signals and to deduce the type of the signals reference to the general classification made by Lahr et al. [1], Miller et al. [2] and White et al. [3]. The work resulted on a classification ranging signals into 5 groups including: (1) Earthquakes whose frequency band row from 10 Hz and over, which were identified as volcano-tectonic earthquakes or A-Types, (2) Earthquakes whose frequency band  row between 3 and 10 Hz identified as Hybrid earthquakes or B-Type earthquakes, (3) Earthquakes whose frequency band row between 1 and 3 Hz identified as Long Periods earthquakes or C-type earthquakes, (4) ) Earthquakes whose frequency band row between 0.25 and 1Hz identified as Very Long Period, VLP earthquakes and (5) Continuous signals marking the same values as the Long Period earthquakes identified as volcanic tremors.It was eventually found that swarms of Long period and hybrid earthquakes are those related to magmatic intrusions, and thus can lead to volcanic eruptions. At other hand, there are only VLP and A-type earthquakes which are observed in the period of persisted Lava Lake. This classification can be used in the monitoring of the volcanoes.