Abstract. Since 2004 a research project has been developed to
monitor subsurface deformation of Italian volcanoes using borehole
strainmeters and long-baseline tiltmeters. Six Sacks-Evertson dilatometers
were installed around Campi Flegrei caldera and Vesuvius during 2004–2005
(Scarpa et al., 2007), and in 2008 these instruments were supplemented by
two arrays of 28–280 m long water-tube tiltmeters in underground tunnels. Relevant strainmeter and tiltmeter data have been collected and analysed
from the instruments installed near Campi Flegrei caldera during the recent
unrest episodes. In the period 2004–2005 strain, tilt and GPS data from
Campi Flegrei indicate the onset of surface deformation that accompanied a
low rate of vertical displacement that continued to 2006, corresponding to
an increase of CO2 emission. This strain episode preceded caldera
microseismic activity by a few months, as was observed also during a
significant inflation episode in 1982. Other transient strain episodes
occurred in October 2006, which were accompanied by a swarm of VT
(Volcano-Tectonic) and LP (Long Period) events, in 2009, at the time of
renewed gas emission activity at Solfatara, and again in March 2010, several
minutes before a seismic swarm. The time scale of these transient strain
events ranges from some hours to several days, putting tight constraints on
the origin of ground uplifts at Campi Flegrei. Their location is compatible
with a source inferred from long term deformation signals, located about 4 km beneath Pozzuoli. A proposed mechanism for these aseismic strain episodes
is that they are associated with magma growth in reservoirs with occasional
pressure relief associated with the leakage of gas.
Supplemental Material: How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)?
