Publication Date:
2017-04-04
Description:
We report a laboratory and microstructural study of a suite of deformation experiments in which basalt from
Mount Etna volcano is deformed and fractured at an effective confining pressure representative of conditions
under a volcanic edifice (40 MPa). Particular attention was paid to the formation of a fracture and damage
zone with which to stimulate coupled hydro-mechanical interactions that create the various types of
seismicity recorded on volcanic edifices, and which usually precede eruption. Location of AE events through
time shows the formation of a fault plane during which waveforms exhibit the typical high frequency
characteristics of volcano-tectonic (VT) earthquakes. We found that these VT earthquakes were particularly
pronounced when generated using dry samples, compared to samples saturated with a pore fluid (water). VT
events generated during deformation of water saturated sample are characterised by a distinctive high
frequency onset and a longer, low frequency coda exhibiting properties often seen in the field as hybrid
events. We present evidence that hybrid events are, in fact, the common type of volcanic seismic event with
either VT or low frequency (LF) events representing end members, and whose proportion depend on pore
fluid being present in the rock type being deformed, as well as how close the rock is to failure. We find a
notable trend of reducing instances of hybrid events leading up to the failure stage in our experiments,
suggesting that during this stage, the pore fluid present in the rock moves sufficiently quickly to provide a
resonance, seen as a LF coda. Our data supports recent modeling and field studies that postulate that hybrid
events generated in volcanic areas are likely to be generated through the interaction of hydrothermal fluids
moving through a combination of pre-existing microcrack networks and larger faults, such as those we observe in forensic (post-test) examination.
Description:
Published
Description:
315-323
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
reserved
Keywords:
volcano-tectonics, acoustic emission, rock physics, seismology, hazard
;
04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
;
05. General::05.02. Data dissemination::05.02.02. Seismological data
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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