A preliminary analysis of icequakes at the Ruiz volcano glacier - Colombia

The Ruiz volcano glacier is located in the central region of Colombia at the equatorial zone but by its height it has perpetual snow. In 1985 this volcano had a catastrophic eruption that produced a lahar by glacier melting; this lahar buried the Armero town. From this event a seismological network was installed. Since the beginning of the seismological network of Ruiz volcano, the icequakes have been registering by the nearest station to glacier. It is clear the relationship between this kind of seismicity and the meteorological conditions; the most quantity of the icequakes is registered very early at the morning and during the dry seasons. The origin and the location of these icequakes were not possible to determine because of the geometric network and of its instrumentation (short period sensor of vertical component). Since 2007 the network has been using broad band sensors and 3-component short period seismometers. We characterized the source of the icequakes from the new database in order to understand the main origin of this seismicity. This study consisted in both spectral and polarization analysis. The results show a near relation between this seismicity and shallow process related to the cryogenic phenomena, the natural motion of the glacier and the volcanic heat release.