Seismic heterogeneity of Mt Etna: structure and activity

Abstract

A dense seismic array maintained temporarily for 7 weeks provides an approach to deducing the 3-D heterogeneity of the structure of the upper crust beneath Mt Etna volcano, Sicily, Italy, from the inversion of P-and S-wave arrivals of local earthquakes. Independent data from a different source-array geometry using waves generated by distant shots at sea confirm a main lateral variation. A high-velocity body underlies part of the volcano. Its contrast with the surrounding thick sedimentary pile and its lo'cation extending from the present summit to the southeast suggests that it may have been built by the development and migration of past eruptive centres followed by caldera collapse. Local low-velocity anomalies near its sharp western edge may be associated with presently active features. These are: an extension of the region of the central craters from sea level to greater depth and a zone at 6 km depth, of possible proximity of magmatic material to sediments connected both to the upper central system and to greater depths. The structure under the western flank appears as highly heterogeneous.During the recording period, a sustained lava eruption of the Southeast Crater stopped and was followed by explosive activity at the central craters and a series of destructive earthquakes on the lower eastern flank in October 1984. No continuous migration occurred between these phases but they might be related through their locations with respect to structural heterogeneity. Seismic activity changed from a swarm of events just beneath the summit at sea level to a few isolated, much stronger events a few kilometres deeper and towards the edge of the central high-velocity zone and eventually to destructive single earthquakes further away under the lower slopes.

Insight into Mt. Etna (Italy) kinematics during the 2002–2003 eruption as inferred from seismic stress and strain tensors

“…The 3D relocation (mean gap = 102°) resulted in a reduction in the mean rms of ca. 24% with respect to the well-constrained hypocenters located using a 1D velocity model (mean erh = 0.3 km, mean erz = 0.5 km, mean rms = 0.17 s) derived from Hirn et al [1991]. The 3D hypocenters moved of 1.2 km, on average, if compared to the 1D locations.…”

Continuous dynamic response along a pre-existing structural discontinuity induced by the 2001 eruption at Mt. Etna

“…Figure 8 reports the location of about 350 events with M d ≥ 2.0. The locations were obtained using HYPOEL-LIPSE code (Lahr, 1989), which takes into account the difference in altitude of the seismic stations with a 1D velocity model derived from Hirn et al (1991). The accuracy of locations ranges between 0.2 and 1 km for the epicentral coordinates, and between 0.3 and 1.4 km for the focal depth (Patanè et al, 2003).…”

Intrusive Mechanisms at Mt. Etna Forerunning the July-August 2001 Eruption from Seismic and Ground Deformation Data

“…Earthquakes were located using HYPOELLIPSE code (LAHR, 1989) so as to allow for the difference in altitude of the seismic stations and to correctly detect the hypocentre spatial patterns in the volcanic cone. The 1-D velocity model used was derived by HIRN et al (1991), with sea level assumed as the reference (zero) elevation. We selected 232 events using the following thresholds: number of observations (N) ‡ 10, the horizontal 68% confidence limit in the least well-constrained direction (ERH) £ 1.0 km, the 68% confidence limit for depth (ERZ) £ 1.5 km, root-mean-square residual (RMS) £ 0.3 s, largest azimuthal separation in degrees between stations as seen from the epicenter (GAP) £ 180°.…”