3-D Modelling of Campi Flegrei Ground Deformations: Role of Caldera Boundary Discontinuities

Campi Flegrei is a caldera complex located west of Naples, Italy. The last eruption occurred in 1538, although the volcano has produced unrest episodes since then, involving rapid and large ground movements (up to 2 m vertical in two years), accompanied by intense seismic activity. Surface ground displacements detected by various techniques (mainly InSAR and levelling) for the 1970 to 1996 period can be modelled by a shallow point source in an elastic half-space, however the source depth is not compatible with seismic and drill hole observations, which suggest a magma chamber just below 4 km depth. This apparent paradox has been explained by the presence of boundary fractures marking the caldera collapse. We present here the first full 3-D modelling for the unrest of 1982–1985 including the effect of caldera bordering fractures and the topography. To model the presence of topography and of the complex caldera rim discontinuities, we used a mixed boundary elements method. The a priori caldera geometry is determined initially from gravimetric modelling results and refined by inversion. The presence of the caldera discontinuities allows a fit to the 1982–1985 levelling data as good as, or better than, in the continuous half-space case, with quite a different source depth which fits the actual magma chamber position as seen from seismic waves. These results show the importance of volcanic structures, and mainly of caldera collapses, in ground deformation episodes.     

Ground deformation modeling of flank dynamics prior to the 2002 eruption of Mt. Etna

On 22 September 2002, 1 month before the beginning of the flank eruption on the NE Rift, an M-3.7 earthquake struck the northeastern part of Mt. Etna, on the westernmost part of the Pernicana fault. In order to investigate the ground deformation pattern associated with this event, a multi-disciplinary approach is presented here. Just after the earthquake, specific GPS surveys were carried out on two small sub-networks, aimed at monitoring the eastern part of the Pernicana fault, and some baselines belonging to the northeastern EDM monitoring network of Mt. Etna were measured. The leveling route on the northeastern flank of the volcano was also surveyed. Furthermore, an investigation using SAR interferometry was performed and also the continuous tilt data recorded at a high precision sensor close to the epicenter were analyzed to constrain the coseismic deformation. The results of the geodetic surveys show a ground deformation pattern that affects the entire northeastern flank of the volcano, clearly shaped by the Pernicana fault, but too strong and wide to be related only to an M-3.7 earthquake. Leveling and DInSAR data highlight a local strong subsidence, up to 7 cm, close to the Pernicana fault. Significant displacements, up to 2 cm, were also detected on the upper part of the NE Rift and in the summit craters area, while the displacements decrease at lower altitude, suggesting that the dislocation did not continue further eastward. Three-dimensional GPS data inversions have been attempted in order to model the ground deformation source and its relationship with the volcano plumbing system. The model has also been constrained by vertical displacements measured by the leveling survey and by the deformation map obtained by SAR interferometry.     

Power Laws Governing Historical Earthquakes in the Apennine Chain (Southern Italy)

Rank-ordering analysis is applied to the intertimes between seismic events recorded in the Apennine belt between 40–42° N and 14–16° E from the 15th century onwards. It shows a power law capable of governing the intertimes between 1529 and 368 months and another power law which approximates a random simulation, for the intertimes shorter than 368 months. Only the first power law allows the computation of the return period of major events. Earthquakes with the same energy that are aligned according to different power laws imply the presence of two different populations, indicating, in turn, that the physics of seismic phenomena in the region examined is not straightforward, that the stress is probably not unidirectional and that it acts on a non-isotropic medium. The most probable estimated intertime value for the next event is found to be equal to 60 ± 20 years.     

Recent terrestrial and satellite observations to model deformations at Colli Albani volcano (central Italy)

The Colli Albani volcanic complex (Rome, Italy) has been dominated by episodic eruptions commencing around 561?ka and ending with the most recent activity of the Albano maar phase (<70?ka). Earthquakes of moderate intensity, gas emissions and significant ground deformations are the recent evidences of a residual activity. Former geodetic data from leveling surveys, GPS stations and InSAR observations tracked ongoing significant uplift of the order of few mm/year near the Colli Albani western flank. Different uplift rates were detected by each technique in different time spans, suggesting also the possibility of sporadic recharge of the hydrothermal system. The renewed high precision leveling data from IGMI survey carried out in 1997/1999 and the last leveling survey carried out in 2006 show that the uplift along the route is currently significant at an average rate of ~3?mm/year. Radar interferograms from ALOS satellite show uplift rate of ~6?mm/year, southwest of the central sector of the leveling route. We have undertaken a joint inversion of the various geodetic data (vertical rates from leveling surveys, GPS site velocities and InSAR observations acquired by ALOS satellite) using a nonlinear inversion technique to estimate the parameters of a point-pressure source, possibly capable of explaining the ongoing deformation at Colli Albani volcano.     

The roots of Mt. Vesuvius deduced from gravity anomalies

Summary The structures of the Somma-Vesuvius volcanic complex are modelled on the basis of the interpretation of gravity anomalies obtained from data available in the literature and acquired along a new profile along the coastline from Naples to Castellammare di Stabia. In order to highlight the contribution of shallow crustal structures, the residual anomalies were considered. A marked gravity low was recognised in the eastern sector of Vesuvius. Furthermore data interpretation was carried out along two profiles centred on the low gravity region in question: a first profile crossing the Vesuvius crater in direction WNW-ESE, and a second one in NNE-SSW direction. The 2 ? D model obtained reveals a crustal structure characterised by sediments of 2.3 Mg/m³ density, overlying bedrock with a density of 2.6 Mg/m³. Near the volcanic system the model becomes more complex due to the presence of light sediments with a density of 2.1 Mg/m³ overlying a body with a density of 2.4 Mg/m³ which extends into depth. The latter is thought to be closely related to the zone of magma ascent developed along the volcanic axis. Along the coast the volcanic component is reduced and the model shows that the layer with a density of 2.3 Mg/m³ ranges in thickness from 0 to about 3500 m. An additional body between 1500 and 3000 m with a density of 2.4 Mg/m³ was considered in order to account for the slight rise in the residual anomaly in the area in the vicinity of Mt. Vesuvius. The analysis of the gravity anomaly pattern coincides with the complex system of faults and fractures intersecting the carbonate basement and the volcanic area in question, which developed as a consequence of extensional processes at the continental edge of the Italian Peninsula due to the opening of the Tyrrhenian basin. This extensional tectonics has created favourable conditions for the collapse of the south-western slope of Mt. Vesuvius and the development of eruptive vents and cracks on its flanks. Received May 18, 2000; revised version accepted March 6, 2001     

Contribution to knowledge regarding the sources of earthquakes on the island of Ischia (Southern Italy)

Natural Hazards - This paper analyses data regarding the seismicity and ground deformations of the island of Ischia. The goal is to describe these phenomena as a space–time process, exploring...