Damage mechanics preceding the September-October 1989 flank eruption at Mount Etna volcano inferred by seismic scaling exponents

Seismicity preceding the September-October 1989 flank eruption at Mt. Etna volcano has been analysed by means of the fractal two-point correlation dimension D(c) relative to epicentres distribution and the scaling exponent D inferred from the seismic b-value. Time evolution of D(c) and D preceding the eruption onset revealed: a general decrease of D(c) and increase of D (9-4 months prior the eruption onset), intermittent rates of D(c) increase and D decrease (4 to 1 month), steady high values of D(c) and low values of D (1 month) and sharp decreases of D(c) and D marking the eruption onset. Results allowed to constrain the increment of seismic damage by recognising negative (mechanical hardening) and positive (mechanical softening) feedback prior the. eruption onset. (C) 2002 Elsevier Science B.V. All rights reserved.