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 approximately 20 km dimensions under Mt. Etna. The earthquake catalog used contains 450 events with M≥2.5 for 1990-1997.9. Comparison of b-values derived from samples of N=50 events, extracted from volumes with 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≤5 km, one located 2 km E of the summit of Etna and at 10±3 km depth and the other one WSW of Etna at a depth of 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.

We interpret the two anomalies of high b -values we mapped beneath Mt. Etna as expressions of magma chambers. One is centered about 2 km E of the sulmnit at 12+/-3 km depth, the
other WSW of the summit at approximately 5 +/-2 km depth. These depths are relative to 1.6 km above sea level, the mean elevation of the seismograph network. This means that our data support the previously published estimates of magma
chambers based on crustal deformation data.