The development of faults in rock fractured material is coupled with the propagation of microcracks and the generation of elastic waves, which can be detected by a suitable microseismic monitoring system. As a consequence, an accurate re-location of microseismic events can give some important indications on the presence of weakness surfaces and on the possible evolution of a monitored area.
Respect to the location of seismic events, the computa tion of the hypocenter of microseismic events requires an accurate knowledge of the velocity model, due to the different scale of the problem. In fact, the possible presence of an irregular topography (e.g mountain peak) and the spatial variability of the mass average characteristics in the subsurface require that a changing value of velocity in space can be assigned. In the present paper a new tool for heterogeneous multi-velocity model computation coupled with the location software NonLinLoc is described and applied to the case of the Matterhorn Peak (North Western Italian Alps), where a microseismic monitoring system was installed in the frame of the Interreg IIIA ALCOTRA "PERMAdataROC" project.
A comparison among results obtained for the re-location of a set of hammer strokes – which were used to test the correct working of the microseismic network – with a homogeneous, a heterogeneous bi-value and a heterogeneous multi-value velocity models is here presented and discussed. In particular, obtained results evidence the importance of a correct distribution of microseismic sensors in space and the improvement in location quality when a heterogeneous multi-velocity model is used.
