Geomechanical Interpretation of Local Seismicity During 2012 Tolbachik Volcano Eruption

Abstract

Local seismic activity during 2012 eruption of Tolbachik volcano is considered as a result of the injection of magma forming plane-oriented zones: dykes and sills with associated fractures. In order to identify these zones - the plane-oriented clusters of earthquakes were distinguished with the catalogs of Kamchatka Branch of Geophysical Survey RAS, their subsequent spatial-temporal analysis allows the following interpretation. 27.11.2012 Tolbachik volcano eruption was preceded by the injection of magma with the introduction of a series of dykes of west-north-west striking in the depth range -4 - +3 km abs. in the area to the southeast of the Plosky Tolbachik volcano structure. The indicated fractures dissection of a subhorizontal permeable zone at an altitude near zero lead to the formation of sills and a magma discharge injection dike (dip angle of 50°, dip azimuth 300 °) at 5.5 km from the epicenter of the initial magma injection. The presence of shallow clusters with dip angles less than 30 °, which does not belong to the activated shear fracture zone of Mohr’s diagram, indicates a possible existence of local melted magma chambers and (or) permeable stratiform reservoirs within the structure of Tolbachik volcanoes.