Recent seismicity and tomographic modeling of the Mount Etna plumbing system

The monitoring of seismic activity in eastern Sicily (southern Italy) has b een recently improved, in the framework of the Poseidon Project, to investi gate both tectonics and volcanic processes of Mount Etna. This effort has p roduced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of t he recent seismicity, encompassing the 1995 eruption, diffuse eruptions bet ween 1995 and 1997, a further magma intrusion started in 1997, and an incre ase of volcanic activity in July 1998. We inverted P wave arrival times fro m 307 selected local earthquakes to obtain a three-dimensional velocity mod el of the volcano; With a. Simultaneous inversion for hypocenters and veloc ity parameters. The new tomographic images permit us to define the structur e beneath the volcano from the surface down to 18 km depth. The main struct ural feature revealed by our inversion is a high-velocity body located bene ath the central craters whose lateral extent increases from similar to 6 km between 18 and 9 km depth to similar to 12 km between 9 and 3 km depth. Ne ar the surface the fast anomaly branches in two separate high-V-p regions, which are located below the summit craters sad the eastern flank (Valle del Bove), respectively. The high-velocity features are interpreted as high-de nsity cumulates of solidified magma that intruded the shallow crust. We hyp othesize that magma ascends the crust within the relatively small high-velo city conduit (below 9 km depth) and is stored at depth shallower than 9 km within the broad high-velocity region, as also suggested by petrological da ta. A sharp increase of seismicity in 1997, with earthquakes occurring at t he border of the high-velocity body, suggests that Mount; Etna sustained re cent episodes of intrusions, which possibly herald future eruptions;. No la rge low-velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust, while a broad low-velocity anomaly in the uppermost mantle, revealed by regional seismic data, possibly indicates the magma source region at depth. Earthquake occurrence from the deep source t o the shallow intrusive area helps to trace the magma migration and the fee ding of the volcanic system.