Spectral energy distribution of Nevado del Ruiz Volcano seismicity near eruptive events

Volcano seismology is a key contributor for assessing the activity status of volcanoes and forecasting future eruptive behaviour. One measurement that may indicate a change in the volcanic behaviour is a temporal change in the spectral content, or frequency distribution, of seismic waveforms. Significant changes in frequency distribution have been observed at Soufrière Hills, Montserrat; Telica Volcano, Nicaragua; Redoubt Volcano, Alaska USA, and at other volcanoes prior to volcanic eruptions. Identification of such changes in spectral energy could indicate changes in volcanic activity, and hence be used in forecasting, as well as to investigate the physical processes behind eruptive processes. With the objective of identifying possible changes in the spectral energy distribution of the seismic sources of the Nevado del Ruiz Volcano (NRV) prior to eruptions, we analysed the spectral energy of volcano tectonic (VT), low frequency (LF) and hybrid seismic events during 2012, when the NRV had two Volcanic Explosivity Index (VEI) 2 eruptions on May 29^th and June 30^th. We analysed nearly 27,000 events and implemented a semi-automatic pre-processing pipeline in ObsPy for selecting the optimal stations and seismograms based on the signal-to-noise ratio and proximity to seismic clusters. Then, we cut the seismograms to isolate the seismic signals and bandpass-filtered the data before calculating metric such as dominant frequency, ratio of high to low spectral energy. In this work, we present preliminary results on the temporal changes in spectral energy of the seismic events at NRV and whether this could be linked, along with other geophysical measurements, with changes to eruptive behaviour.