Abstract
One of the most effective approaches to identifying possible precursors of eruptions is the analysis of seismicity patterns recorded at volcanoes. Accurate locations of the seismicity and the estimate of source mechanisms can resolve fault systems and track fluid migrations through volcanoes. We analysed the six main swarms recorded at Campi Flegrei since 2000, using them as a proxy of the processes involved in the long-term-unrest of this densely populated caldera. We re-located the earthquakes comprised in these swarms and estimated the focal mechanisms, which appear in agreement with the fault systems of the caldera and with tomographic images. The focal mechanisms are in agreement with the tensional stress induced by the caldera uplift. Most of the swarms and remaining seismicity delineate a highly fractured volume extending vertically below the Solfatara/Pisciarelli vents, where gases find preferential paths to the surface triggering earthquakes. The main swarms are located below this volume where the presence of a rigid caprock is still debated. We interpreted the current unrest in term of a gradual increment in the activity of a wide hydrothermal system whose most evident manifestation is the enlargement of the fumarolic-field of Pisciarelli and the increment of the earthquakes occurrence rate.
Highlights
We investigated the swarm seismicity recorded at Campi Flegrei in the last 20 years to obtain information on faults, stress regimes and fluid movements that are mainly involved during the current uplift phase and to draw considerations on the possible preferential routes for fluids and magma movements towards the surface
The focal mechanism, which are consistent with normal, high-angle or nearly vertical faults, obtained for all the analysed earthquakes well fit with the uplift of the central part of the caldera in the analysed period
Until 2014, a correlation between the main swarms and peaks in the geochemical signal ( CO2/CH4 recorded within Solfatara crater) has been reported by Chiodini et al.[38], finding a delay of ~ 200 days
Summary
One of the most effective approaches to identifying possible precursors of eruptions is the analysis of seismicity patterns recorded at volcanoes. We re-located the earthquakes comprised in these swarms and estimated the focal mechanisms, which appear in agreement with the fault systems of the caldera and with tomographic images. In 2000, when the last phase of subsidence stopped, a swarm of hybrid events was recorded in the area South of Solfatara at a depth of almost 3 km. During the last bradiseismic crisis, in 1982–84, more than 16,000 earthquakes accompanied an uplift of almost 1.8 m In this period, seismic swarms have been identified which correlate in space and time with possible fluid injection from a deep hot s ource[15]. The fluids moved from a volume located 3–4 km below Pozzuoli toward a shallower aseismic volume below Solfatara, identified as the ground deformation source, reaching the area of the last eruption (Mt. Nuovo, 1538) at the end of the crisis[15]. In the recent eruptive history of Campi Flegrei, stress changes, due to topographic, bathymetric
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