Regional earthquakes followed by delayed ground uplifts at Campi Flegrei Caldera, Italy: Arguments for a causal link
Introduction
Dynamic stresses associated with passing seismic waves generated by large earthquakes may trigger volcanic activity in the near- and in the far-field within days (Hill et al., 1995, Hill et al., 2002; Linde and Sacks, 1998). More recently it was shown that geological processes activated by passing seismic waves may become apparent beyond the commonly accepted time window of few days (Parsons, 2005, Jagla, 2011, Shelly et al., 2011, Watt et al., 2009, Johnson and Bürgmann, 2016). It is suggested that surface waves rather than body waves (Hill et al., 1995, Hill, 2012, Hill et al., 2002; Husen et al., 2004a, Husen et al., 2004b; Manga and Brodsky, 2006) are more efficient in promoting earthquake–volcano interactions. However, proposed models are still difficult to test due to the paucity of recorded triggered events (Prejean and Haney, 2014). As calderas are sensitive to incoming seismic energy (Hill et al., 1995; Husen et al., 2004a, Husen et al., 2004b) they are considered ideal natural laboratories to investigate earthquake–volcano interactions. Some magmatic systems underlying calderas periodically undergo rapid ground uplift phases (Acocella et al., 2015; Chiodini et al., 2012; Hurwitz et al., 2007, Hutnak et al., 2009, Todesco and Berrino, 2005) associated with intense local seismic activity and emission of volcanic gases marked by a strong magmatic component (Bodnar et al., 2007; Chiodini et al., 2012, Chiodini et al., 2003; Hurwitz et al., 2007, Hutnak et al., 2009, Todesco et al., 2014, Todesco and Berrino, 2005). Uplift phases (known at Campi Flegrei as bradyseismic episodes), generally followed by slow ground deflation (Del Gaudio et al., 2010), are thought to be driven by the rise of hydrothermal fluids or magmas (Battaglia et al., 2006, Bodnar et al., 2007, Chiodini et al., 2003; De Natale et al., 2006).
The Campi Flegrei caldera near Naples, Italy, is characterised by frequent bradyseismic episodes that may reach vertical ground displacement rates of about 1 m/yr (Del Gaudio et al., 2010). Most models relate bradyseismic episodes to the pressurization of the shallow hydrothermal system by injection of deep fluids (Battaglia et al., 2006, Bodnar et al., 2007, Chiodini et al., 2012, Hurwitz et al., 2007, Hutnak et al., 2009) while others invoke the intrusion of magma at shallow depths (Amoruso et al., 2014, Macedonio, 2014, Woo and Kilburn, 2010). Numerical modelling (Todesco and Berrino, 2005, Hurwitz et al., 2007, Hutnak et al., 2009, Chiodini et al., 2012) in agreement with measured fumarole gas signatures (Chiodini et al., 2003, Chiodini et al., 2012, Chiodini et al., 2016) suggests that CO2-rich fluids would be particularly efficient in generating the observed uplifts. Previous studies suggest that these fluids are released by a cooling magmatic body at ca. 6–7 km depth (Bodnar et al., 2007, Zollo et al., 2008) and accumulate beneath a low-permeability layer at ca. 3 km depth from which they are then episodically discharged.
In spite of longstanding scientific efforts, a consistent and predictive model accounting for different geological processes at Campi Flegrei is still lacking. By combining analysis of uplift time series, statistical studies and forward simulations of seismic waves, we show evidence for an association between regional earthquakes and bradyseismic episodes. We then develop a mechanistic explanation for a causal link between regional earthquakes and ground uplift that integrates several of the above-mentioned aspects into a single coherent model. Most notably, our mechanism is compatible with the two scenarios suggesting the release of CO2-rich brines or the intrusion of magma at shallow depths as the driving force of the bradyseismic episodes.
Section snippets
Observations
Since 1905 two distinct phases of ground deformation can be recognised at Campi Flegrei (Del Gaudio et al., 2010; De Martino et al., 2014): an overall deflation from 1905 to 1945 (not shown here) recorded by relatively sparse measurements (intervals of several years, refer to Del Gaudio et al. (2010) and De Martino et al. (2014) for the entire time sequence), and an overall inflation from 1945 to present (recorded by more frequent measurements after 1980).
To investigate potential
Data
Sparse observations are often too descriptive and not rigorous enough to establish a causative relationship between earthquakes and response of the Campi Flegrei to external forcing. To investigate the possible association between earthquakes and bradyseismic episodes we first compared the ground elevation dataset (Del Gaudio et al., 2010; De Martino et al., 2014) at Campi Flegrei with earthquake archives (Fig. 1c). For the construction of the surface elevation curve of Fig. 1c we combined two
Statistical analysis
To assess if the inferred association between earthquakes and bradyseismic episodes is statistically verifiable we carried out a binomial test to investigate the null hypothesis that uplift events are unrelated to earthquakes. To conduct the statistical study we considered both regional and teleseismic earthquakes. For the regional earthquakes we had to exclude fore- and after-shocks that may bias the statistical analysis. The excluding criteria for regional earthquakes is shown in Table 1. We
Numerical modelling
To identify the possible underlying mechanism for how incoming seismic energy may trigger delayed surface uplift we simulated body wave propagation through the impedance velocity structure of the Campi Flegrei (Vanorio et al., 2005, Zollo et al., 2008). The static model (Fig. 4) used for numerical seismic wave propagation modelling is based on an interpreted tomography (Vanorio et al., 2005) and a seismic reflection study (Zollo et al., 2008) and takes into account density variations (Petrillo
Discussion
The ground at Campi Flegrei undergoing bradyseism is constantly in motion with either uplift or deflation dominating the temporal evolution (Fig. 1). Continuous monitoring allows identification of single uplift events of highly variable magnitudes, but the precise timing of onset and peak uplift is naturally blurred by the superposition of events and can only be approximated by identifying acceleration and deceleration of ground motion. Typically, the bradyseismic events indicate a delay time
Conclusions
Comparing data sets of ground deformation at Campi Flegrei, Italy, with catalogues of regional and teleseismic earthquakes suggests an association between the dynamic stresses imposed by passing body (and not surface) waves released by regional earthquakes and delayed ground uplift at the Campi Flegrei. We argue that this association (supported by yet non-definitive binomial tests) represents a causal link, which can be explained by dynamic triggering of the magmatic-hydrothermal system. These
Acknowledgments
Donat Fäh is thanked for suggesting the ground motion classification of the earthquakes. Nima Riahi, Jean-Pierre Burg, and Stephen A. Miller for discussion of the paper. Andrea Parmigiani is thanked for extensive discussion on magmatic reservoirs. Matteo Lupi thanks SCCER-SoE and the Swiss National Science Foundation for financial support (grant n° PZ00P2_154815 and grant n° PYAPP2_166900). Finally, we thank the Editor, two anonymous Reviewers and Roland Bürgmann who provided constructive
References (54)
- et al.
Unrest episodes at Campi Flegrei: a reconstruction of vertical ground movements during 1905–2009
J. Volcanol. Geotherm. Res.
(2010) - et al.
Changes in CO2 diffuse degassing induced by the passing of seismic waves
J. Volcanol. Geotherm. Res.
(2016) The structure and interpretation of seismograms
Int. Geophys.
(2002)- et al.
Earthquake triggering of mud volcanoes
Mar. Pet. Geol.
(2009) - et al.
Sloshing of a bubbly magma reservoir as a mechanism of triggered eruptions
J. Volcanol. Geotherm. Res.
(2016) - et al.
Defining a 3D physical model for the hydrothermal circulation at Campi Flegrei caldera (Italy)
J. Volcanol. Geotherm. Res.
(2013) - et al.
Bubble migration and the initiation of volcanic eruptions
J. Volcanol. Geotherm. Res.
(1995) - et al.
Modeling the propagation of elastic waves using a modified finite-difference grid
Wave Motion
(2000) - et al.
Modeling hydrothermal fluid circulation and gravity signals at the Phlegraean Fields caldera
Earth Planet. Sci. Lett.
(2005) - et al.
The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone
Earth Planet. Sci. Lett.
(2009)
An overview of recent (1988 to 2014) caldera unrest: knowledge and perspectives
Rev. Geophys.
Dynamic strains at regional and teleseismic distances
Bull. Seismol. Soc. Am.
Clues to the cause of the 2011–2013 Campi Flegrei caldera unrest, Italy, from continuous GPS data
Geophys. Res. Lett.
Evidence for fluid migration as the source of deformation at Campi Flegrei caldera (Italy)
Geophys. Res. Lett.
Ground motion prediction equations derived from the Italian strong motion database
Bull. Earthq. Eng.
Quantitative model for magma degassing and ground deformation (bradyseism) at Campi Flegrei, Italy: implications for future eruptions
Geology
Magma degassing as a trigger of bradyseismic events: the case of Phlegrean Fields (Italy)
Geophys. Res. Lett.
Early signals of new volcanic unrest at Campi Flegrei caldera? Insights from geochemical data and physical simulations
Geology
Magmas near the critical degassing pressure drive volcanic unrest towards a critical state
Nat. Commun.
GPS time series at Campi Flegrei caldera (2000–2013)
Ann. Geophys.
The Campi Flegrei caldera: unrest mechanisms and hazards
Geol. Soc. (Lond.) Spec. Publ.
Hydrothermal processes related to movement of fluid from plastic into brittle rock in the magmatic-epithermal environment
Econ. Geol.
Surface-wave potential for triggering tectonic (nonvolcanic) tremor-corrected
Bull. Seismol. Soc. Am.
Response of Long Valley Caldera to the Landers, California, Earthquake
Geophys. Res. Lett.
Earthquake–volcano interactions
Phys. Today
Hydrothermal fluid flow and deformation in large calderas: inferences from numerical simulations
J. Geophys. Res.
Changes in geyser eruption behavior and remotely triggered seismicity in Yellowstone National Park produced by the 2002 M 7.9 Denali fault earthquake, Alaska
Geology
Cited by (12)
Small-magnitude earthquakes triggering fluid vents in a pressurised CO<inf>2</inf> system, Caprese Michelangelo (Central Italy)
2023, TectonophysicsCitation Excerpt :A short-term response of a given seepage feature after an earthquake (hours to few days) is a straightforward evidence of triggering. However, this condition is not mandatory, as in some cases the effects of the triggering (i.e., eruption, increased mud/fluid extrusion) may appear at surface several weeks or months after the passage of the seismic waves (Lupi et al., 2017b). A similar behaviour has been also documented for the Covivoli vents (see section 2.1.),
Upwards - Vertical extensions of masonry built heritage for sustainable and antifragile urban densification
2021, Journal of Building EngineeringCitation Excerpt :The construction work only lasted one year and 650 new properties were delivered to house the evacuated population. It is worth underlining that the bradyseism is a phenomenon strictly related to the volcanism, and the mechanisms producing the bradyseismic crises are still under study, with conflicting interpretations highly debated in the scientific community [e.g.: [27-30]]. There is no doubt that volcanic, bradyseismic, and seismic activities are closely connected.
Investigating earthquake triggering of fluid seepage systems by dynamic and static stresses
2020, Earth-Science ReviewsCitation Excerpt :A more recent study indicates a clear dependence of volcanic degassing on peak dynamic stress of just 5–25 kPa (Avouris et al., 2017). The latter stress values are also in agreement with the magnitude of seismic-related peak ground velocities that are supposed to have influenced the evolution of the Campi Flegrei caldera (Lupi et al., 2017a). In some cases, even small Earth tidal stress changes (1–4 kPa) have been proposed to influence volcanic eruptions and trigger earthquakes (e.g., Tanaka et al., 2006; Rubinstein et al., 2008), but the actual effect of such tiny stresses is controversial.
Mechanisms and patterns of magmatic fluid transport in cooling hydrous intrusions
2020, Earth and Planetary Science LettersTransient tectonic regimes imposed by megathrust earthquakes and the growth of NW-trending volcanic systems in the Southern Andes
2020, TectonophysicsCitation Excerpt :The transient strain may be induced by both body (Lupi et al., 2017a, 2013) and surface waves (Hill and Prejean, 2015; Lupi et al., 2017b). The activated geological processes may become apparent within days (Farías et al., 2014) or even years (Lupi et al., 2017a; Manga and Brodsky, 2006; Parsons, 2005; Sawi and Manga, 2018) after the main shock. Static stress triggering is broadly confined to fault rupture distances and takes place days to years after the main shock (Bonini et al., 2016; Toda et al., 2011).