Abstract
A network of tiltmeters has been operational on Vulcano Island for numerous years. At present, the network comprises five functioning borehole stations, four of which are installed at 8-10 m and allow recording very stable, high precision signals with very low noise. We report observations over the last 12 years that illustrate impulsive variations linked to seismicity and long-term (several years) trends in the signals. We suggest a relationship between tilt changes correlated to the strongest regional seismic events and site acceleration; long-term tilt variations analyzed in combination with other ground deformation data seem to represent evidence of a contraction of the La Fossa cone. We also analyzed how the tilt device has the capability to detect possible magma migrations; we considered previous studies that have imaged spatially well-defined levels of magma accumulation beneath La Fossa, and Vulcanello; we concluded that the Vulcano tilt network should be capable of detecting the upward migration of small magma volumes. Finally, we show that no evidence of changes are visible on tilt signals during anomalous degassing episodes (linked to a building up input of magmatic fluids) at the La Fossa thereby evidencing that no magma migration occurred during such events.
Highlights
The island of Vulcano is a composite volcanic edifice located in the south-central sector of the Aeolian Archipelago (Tyrrhenian Sea, Italy)
Data reported in this paper cover the period 1994-2005. During these last 12 years the tilt network has recorded: impulsive variations linked to the strongest seismic events located in a radius of about 30 km from Vulcano and longterm signals outside the seasonal noise; no rapid variations correleted to magma migration have ever been evidenced; in particular we focused our observation on tilt signals recorded during the last anomalous degassing episode occurring at the end of the 2005
We previously showed how the Vulcano Island tilt network is able to record very stable, high precision signals; tilt data of the last 4 months of 2005 seem to evidence no changes that may lead to suppose magma migration; an evaluation of the volumes of a magma migration that the tilt network may detect is an important parameter for the discussion
Summary
The island of Vulcano is a composite volcanic edifice located in the south-central sector of the Aeolian Archipelago (Tyrrhenian Sea, Italy). N-S and NE-SW striking normal faults are visible on Vulcano; they are tension fractures associated with the main NW-SE shear zone and the primary volcanic structures Ground deformation at Vulcano is monitored geodetically by GPS, EDM and levelling campaigns and by continuous tilt and GPS EDM and levelling measurements began at the end of 1970s and since 1997 the EDM lines. In the late 1980s, continuous ground deformation monitoring using a few tilt stations was initiated. From 1994, the tilt network was improved and expanded to yield a good areal coverage of Vulcano and higher quality data acquisition. Since 2004, the network has operated with five functioning stations that allow a high signal to noise ratio to be achieved
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