Time evolution of medium and long-period ground tilting at Campi Flegrei caldera

Enza De Lauro,Simona Petrosino,Mariarosaria Falanga,Ida Aquino,Ciro Ricco

doi:10.5194/adgeo-52-9-2020

Enza De Lauro, Simona Petrosino + Show 3 more

Open Access

https://doi.org/10.5194/adgeo-52-9-2020

Copy DOI

Abstract

Abstract. We analyse tiltmeter time series recorded from April 2015 to March 2019 at three borehole instruments installed at Campi Flegrei caldera (Italy). We evaluate the crustal response in terms of ground tilting to external excitations of medium/long-period tidal constituents by applying a polarization analysis. The azimuths of the tilt vectors show well-defined polarization directions and the ground tilting planes oscillate with the periodicity of the corresponding tidal constituents. For two of the three tiltmeters, the average ground oscillation pattern related to the monthly Mm and fortnightly Mf constituents show seasonal variations, which can be ascribed to rainfall-induced tilting. In addition, for the same two instruments, a clear seasonal amplitude modulation of the diurnal S1 constituent appears in the time series, revealing the occurrence of site thermoelastic effects. The results indicate that the tidal tilting is mainly controlled by the local stress field distribution and rheology; in addition, seasonal exogenous factors like rainfalls play a role in modulating the ground deformation.

Highlights

Geophysical signals are a superposition of many effects related to different sources, which act over several time scales, from seconds/hours up to seasonal/annual
Recent studies have highlighted that earth tides modulate the occurrence of long-period volcanic earthquakes (De Lauro et al, 2012) and volcano-tectonic seismicity (Petrosino et al, 2018) at Campi Flegrei, evidencing that exogenous phenomena play a role in the dynamics of the area
Recent studies of the ground tilt at Campi Flegrei highlighted that the medium responds to a complex mixing of endogenous and exogenous sources (Petrosino et al 2018; De Lauro et al, 2018; Ricco et al, 2019)

Summary

Introduction

Geophysical signals are a superposition of many effects related to different sources, which act over several time scales, from seconds/hours up to seasonal/annual. The physical process at the origin of ground deformation related to water infiltration is explained in terms of the theory of poroelasticity (Wang, 2000; Wang and Kumpel 2003) According to this model, the tilt amplitude is proportional to the pore pressure gradient and depends on the rock poroelastic parameters. The magnitude of the tilt and the orientation of the tilting plane can put constraints on the source location and help in identifying the hydrologically active structures Interesting results are those of Lesparre et al (2017), who modelled the observed rainfall-induced tilt considering different possible processes associated with water infiltration and pressure changes on fracture walls. Depending on the site, seasonality modulates the amplitude of the tilt induced by the diurnal S1 constituent indicating the occurrence of thermoelastic effects

The Tiltmeter Network at Campi Flegrei

Data analysis

Findings

Discussion and conclusions