Volcanic tremors at etna: a model for hydraulic origin

Abstract

Spectral analysis of volcanic tremors at Etna reveals 2 characteristic features: (1) The escaping vapor and gas streams drive the magma in random turbulent motion, generating a seismic wave emission according toA ∼f ^N · exp (−M ·f ^K), whereA amplitude,f frequency, N, M, K parameters. (2) Sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages. Their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena. It is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity. Furthermore, positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra.