Inflating Source Imaging and Stress/Strain Field Analysis at Campi Flegrei Caldera: The 2009–2013 Unrest Episode

Giuseppe Solaro,Pietro Tizzani,Raffaele Castaldo

doi:10.3390/rs13122298

Abstract

In this study, we analyze the 2009–2013 uplift phenomenon at Campi Flegrei (CF) caldera in terms of temporal and spatial variations in the stress/strain field due to the effect of an inflating source. We start by performing a 3D stationary finite element (FE) modeling of X-band COSMO-SkyMed DInSAR and GPS mean velocities to retrieve the geometry and location of the deformation source. The modeling results suggest that the best-fit source is a three-axis oblate spheroid ~3 km deep, which is mostly elongated in the NE–SW direction. Furthermore, we verify the reliability of model results by calculating the total horizontal derivative (THD) of the modeled vertical velocity component; the findings emphasize that the THD maxima overlap with the projection of source boundaries at the surface. Then, we generate a 3D time-dependent FE model, comparing the spatial and temporal distribution of the shear stress and volumetric strain with the seismic swarms beneath the caldera. We found that low values of shear stress are observed corresponding with the shallow hydrothermal system where low-magnitude earthquakes occur, whereas high values of shear stress are found at depths of about 3 km, where high-magnitude earthquakes nucleate. Finally, the volumetric strain analysis highlights that the seismicity occurs mainly at the border between compression and dilatation modeled regions, and some seismic events occur within compression regions.

Highlights

The Campi Flegrei (CF) volcanic area is a collapsed caldera with a well-documented and long history of ground inflation and deflation
We considered on average DInSAR velocity uncertainty equal to 0.003 m/year [26]; for global positioning system (GPS) data, the uncertainty is equal to 0.001 m/year for northward and eastward velocities and 0.003 m/year for vertical velocity [11]
The DInSAR and GPS observed deformation velocity patterns can be explained by the action of an oblate-like spheroid source, slightly ENE–WSW oriented and represented by a filled hydrostatic pressurized source at ~3 km deep

Summary

Introduction

The Campi Flegrei (CF) volcanic area is a collapsed caldera with a well-documented and long history of ground inflation and deflation (bradyseismic activity). In the last 15 ka, ground deformations at long (resurgence) and short timescales have affected the inner caldera region [1,2,3,4]. Since 1905, ground-based topographic leveling networks, recently integrated with a global positioning system (GPS) monitoring network and satellite data, have recorded the unrest episodes of the Neapolitan Yellow Tuff (NYT) caldera. The pattern of recent uplifts was almost radially symmetric with decreasing deformation velocity values moving from the Pozzuoli harbor towards the borders of the NYT caldera (Figure 1) [12,13,14]

Objectives

Results

Discussion

Conclusion