Source and dynamics of a volcanic caldera unrest: Campi Flegrei, 1983–84

Abstract

Despite their importance for eruption forecasting the causes of seismic rupture processes during caldera unrest are still poorly reconstructed from seismic images. Seismic source locations and waveform attenuation analyses of earthquakes in the Campi Flegrei area (Southern Italy) during the 1983–1984 unrest have revealed a 4–4.5 km deep NW-SE striking aseismic zone of high attenuation offshore Pozzuoli. The lateral features and the principal axis of the attenuation anomaly correspond to the main source of ground uplift during the unrest. Seismic swarms correlate in space and time with fluid injections from a deep hot source, inferred to represent geochemical and temperature variations at Solfatara. These swarms struck a high-attenuation 3–4 km deep reservoir of supercritical fluids under Pozzuoli and migrated towards a shallower aseismic deformation source under Solfatara. The reservoir became aseismic for two months just after the main seismic swarm (April 1, 1984) due to a SE-to-NW directed input from the high-attenuation domain, possibly a dyke emplacement. The unrest ended after fluids migrated from Pozzuoli to the location of the last caldera eruption (Mt. Nuovo, 1538 AD). The results show that the high attenuation domain controls the largest monitored seismic, deformation, and geochemical unrest at the caldera.

Reservoir Structure and Hydraulic Properties of the Campi Flegrei Geothermal System Inferred by Audiomagnetotelluric, Geochemical, and Seismicity Study

“…The general distribution of the 1983–1984 seismicity is highly asymmetric compared to the observed ground deformation pattern, which is more concentrated in the Solfatara area, to the east of the maximum of the vertical ground displacement observed in the Pozzuoli area (D'Auria et al, ; De Siena et al, ). In Figure we observe that the highest values of the Benioff's strain release are located just beneath Solfatara, at depths between 2 and 3 km.…”

Insight Into Campi Flegrei Caldera Unrest Through Seismic Tremor Measurements at Pisciarelli Fumarolic Field

“…Starting from 2004, changes in seismicity (Chiodini et al, ; D'Auria et al, ; Saccorotti et al, ), deformation (Troise et al, ; Trasatti et al, ; D'Auria et al, ; De Martino et al, ; Giudicepietro et al, ; Iannaccone et al, ), and degassing activity (Cardellini et al, ; Chiodini et al, ; Chiodini et al, ; Tamburello et al, ) became evident in the Campi Flegrei caldera. These changes were the subject of scientific investigations that resulted in a remarkable production of articles over the recent years (Amoruso et al, ; De Siena et al, ; Di Luccio et al, ; Giudicepietro et al, ; Kilburn et al, ; Zaccarelli & Bianco, ; Zollo et al, ). In December 2012, the civil protection authorities raised the alert of the caldera from green level (base) to the current yellow level (attention) as consequence of a further increase in the deformation rate, seismicity and degassing (Chiodini et al, ).…”

Ambient Seismic Noise Image of the Structurally Controlled Heat and Fluid Feeder Pathway at Campi Flegrei Caldera

“…Thousands of microearthquakes associated with strong ground deformation (e.g., Bellucci et al, ) and variations in geochemical gas composition (Chiodini et al, ) spread across Campi Flegrei caldera in 1983–1984. The seismic unrest stopped at the end of 1984 due to the opening of an ∼2‐km‐deep fluid reservoir, expressed as a low‐velocity and high‐attenuation anomaly under Pozzuoli town (Figure , P ; De Siena et al, ; Vanorio et al, ). This reservoir intersected the structurally defined area of cumulative uplift between 1251 and 1536 CE (Bellucci et al, ; Di Vito et al, ) preceding the Monte Nuovo eruption (Figure , M ).…”

“…This reservoir intersected the structurally defined area of cumulative uplift between 1251 and 1536 CE (Bellucci et al, ; Di Vito et al, ) preceding the Monte Nuovo eruption (Figure , M ). It was also affected by daylong seismic injections from depth throughout the 1983–1984 unrest (Figure , the gray polyhedron defines the injections' extent using the aperture of the corresponding seismic swarms, from De Siena et al, ). The injections were due to an input of likely magma and magmatic fluids (Amoruso et al, ) from an offshore 4‐km‐deep magmatic reservoir, marked by high deformation and high seismic attenuation anomaly (De Siena et al, ) and still active in 2011–2013 (Amoruso et al, ; Figure , the asterisk marks the center of the deformation ellipsoid).…”

“…It was also affected by daylong seismic injections from depth throughout the 1983–1984 unrest (Figure , the gray polyhedron defines the injections' extent using the aperture of the corresponding seismic swarms, from De Siena et al, ). The injections were due to an input of likely magma and magmatic fluids (Amoruso et al, ) from an offshore 4‐km‐deep magmatic reservoir, marked by high deformation and high seismic attenuation anomaly (De Siena et al, ) and still active in 2011–2013 (Amoruso et al, ; Figure , the asterisk marks the center of the deformation ellipsoid). An injection on 1 April 1984 marked a drastic change in the fluid reservoir, making it subject to 2 months of aseismic slip; after this aseismic period, hundreds of microearthquakes spread from the reservoir crossing the structural faults bounding the region of the 1538 CE Monte Nuovo eruption (D'Auria et al, ; De Siena et al, ).…”