The locations of magma chambers at Mt. Etna, Italy, mapped by b-values

We mapped b-values in three dimensions in a cube of the crust with approxim ately 20 km dimensions under Mt. Etna. The earthquake catalog used contains 450 events with M greater than or equal to 2.5 for 1990-1997.9. Comparison of b-values derived from samples of N=50 events, extracted from volumes wi th radii ranging from 2.5 to 6 km, showed statistically highly significant differences between b=1.5+/-0.3 in most of the crust and b=3.0+/-0.5 in two volumes with r less than or equal to 5 km, one located 2 km E of the summi t of Etna and at 10+/-3 km depth and the other one WSW of Etna at a depth o f about 3+/-2 km below sea level. We interpret these high b-value anomalies as an expression of two active magma chambers at those locations.