Data analysis of the unsteadily accelerating GPS and seismic records at Campi Flegrei caldera from 2000 to 2020

Abstract

Ongoing resurgence affects Campi Flegrei caldera (Italy) via bradyseism, i.e. a series of ground deformation episodes accompanied by increases in shallow seismicity. In this study, we perform a mathematical analysis of the GPS and seismic data in the instrumental catalogs from 2000 to 2020, and a comparison of them to the preceding data from 1983 to 1999. We clearly identify and characterize two overlying trends, i.e. a decennial-like acceleration and cyclic oscillations with various periods. In particular, we show that all the signals have been accelerating since 2005, and 90–97% of their increase has occurred since 2011, 40–80% since 2018. Nevertheless, the seismic and ground deformation signals evolved differently—the seismic count increased faster than the GPS data since 2011, and even more so since 2015, growing faster than an exponential function The ground deformation has a linearized rate slope, i.e. acceleration, of 0.6 cm/yr2 and 0.3 cm/yr2 from 2000 to 2020, respectively for the vertical (RITE GPS) and the horizontal (ACAE GPS) components. In addition, all annual rates show alternating speed-ups and slow-downs, consistent between the signals. We find seven major rate maxima since 2000, one every 2.8–3.5 years, with secondary maxima at fractions of the intervals. A cycle with longer period of 6.5–9 years is also identified. Finally, we apply the probabilistic failure forecast method, a nonlinear regression that calculates the theoretical time limit of the signals going to infinity (interpreted here as a critical state potentially reached by the volcano), conditional on the continuation of the observed nonlinear accelerations. Since 2000, we perform a retrospective analysis of the temporal evolution of these forecasts which highlight the periods of more intense acceleration. The failure forecast method applied on the seismic count from 2001 to 2020 produces upper time limits of [0, 3, 11] years (corresponding to the 5th, 50th and 95th percentiles, respectively), significantly shorter than those based on the GPS data, e.g. [0, 6, 21] years. Such estimates, only valid under the model assumption of continuation of the ongoing decennial-like acceleration, warn to keep the guard up on the future evolution of Campi Flegrei caldera.

Investigating deformation and seismic data and their relationships during the ongoing unrest of Campi Flegrei caldera (Italy)

“…2 and 3) as well as the behavior of their annual rate (Figs. 4, 5 and 6), with speci c reference to the displacement rate, the seismic count rate and the strain release rate (Benioff strain) (see [39] for more details and a comparison with trends computed over the period 2000-2020). Particular focus has been given here to the analysis of the variations of the most recent period (i.e.…”

“…The temporal and spatial patterns of deformation and seismicity have been also investigated with speci c reference to the most recent uplift phase (2005-ongoing) and in comparison, with previous uplift episodes such as the 1982-84 crisis 19,37,39,40 . In particular, a temporal analysis of the datasets over the period 2000-2020 identi ed the existence of two distinct overlying trends: a decadal-like acceleration and cyclic oscillations with variable periods ranging from some years to a few months 39 .…”

“…The temporal and spatial patterns of deformation and seismicity have been also investigated with speci c reference to the most recent uplift phase (2005-ongoing) and in comparison, with previous uplift episodes such as the 1982-84 crisis 19,37,39,40 . In particular, a temporal analysis of the datasets over the period 2000-2020 identi ed the existence of two distinct overlying trends: a decadal-like acceleration and cyclic oscillations with variable periods ranging from some years to a few months 39 . Inspection of the distribution of seismic activity also highlighted how the ongoing seismicity is mostly located in correspondence of two main depth levels with signi cantly different mechanical and permeability properties 19,37,41 and on weaker pre-existing structures produced by a variety of processes such as dome resurgence, volcano-tectonic collapses, magma intrusions and migrations 18,40 .…”

“…The aim of this paper is to analyze the most recent accelerating trends of geophysical data of CFc and, particularly, the close relationships between deformation and seismic data in terms of temporal coupling between the associated trends, their rates and oscillation periods. The datasets used in the analysis are about 2.5-3 years longer with respect to those analyzed in previous similar studies 36,39 thus allowing a more accurate and robust characterization of the rapidly-evolving caldera dynamics. It is just worth mentioning here that more than 70% of seismic events recorded since 2000 have occurred in the last 3 years here investigated, and more than about 85% of the strain release occurred in the same period.…”

Coping Capacity, Adaptive Capacity, and Transformative Capacity Preliminary Characterization in a “Multi-Hazard” Resilience Perspective: The Soccavo District Case Study (City of Naples, Italy)

“…According to the Campi Flegrei National Civil Protection Plan (Piano Nazionale di Potezione Civile Campi Flegrei, [55]), together with many other western districts of Naples (i.e., Chiaiano, Arenella, Vomero, Chiaia, Posillipo, Fuorigrotta, Bagnoli, and Pianura), Soccavo is located within the Red Zone (i.e., high risk) that has to be rapidly evacuated if an eruption is approaching [56], considering that pyroclastic density currents have a destructive impact on exposed elements due to the high temperature and velocity [57][58][59]. The bradyseismic phenomenon, peculiar to the Campi Flegrei, consists of ground uplift and subsidence due to the variation of the volcano's magmatic and hydrothermal systems [60][61][62]. This, in turn, produces seismicity with epicentres mainly located around the area of maximum uplift (i.e., Rione Terra, the historical city center of Pozzuoli), but whose effects can also be perceived in the peripheral areas of the caldera [63].…”