Estimates of fluid pressure and tectonic stress in hydrothermal/volcanic areas:a methodological approach

An analytical approach to estimate the relative contribution of the fluid pressure and tectonic stress in hydrothermal/ volcanic areas is proposed assuming a Coulomb criterion of failure. The analytical procedure requires the coefficient of internal friction, cohesion, rock density, and thickness of overburden to be known from geological data. In addition, the orientation of the principal stress axes and the stress ratio must be determined from the inversion of fault-slip or seismic data (focal mechanisms). At first, the stress magnitude is calculated assuming that faulting occurs in 'dry' conditions (fluid pressure=0). In a second step, the fluid pressure is introduced performing a grid search over the orientation of 1) fault planes that slip by shear failure or 2) cracks that open under different values of fluid pressure and calculating the consistency with the observed fault planes (i.e. strike and dip of faults, cracks, nodal planes from focal mechanisms). The analytical method is applied using fault-slip data from the Solfatara volcano (Campi Flegrei, Italy) and seismic data (focal mechanisms) from the Vesuvius volcano (Italy). In these areas, the fluid pressure required to activate faults (shear fractures) and cracks (open fractures) is calculated. At Solfatara, the ratio between the fluid pressure and the vertical stress ?is very low for faults ( ?=0.16) and relatively high for cracks ( ?=0.5). At Vesuvius, ?=0.6. Limits and uncertainties of the method are also discussed

La Rete Sismica Mobile dell'Osservatorio Vesuviano

La RETE SISMICA MOBILE (=RM) è un'unità costituita da stazioni sismiche adatte ad una rapida installazione ed in grado sia di acquisire il segnale sismico localmente che di trasmetterlo via radio ad un sito centrale. La RM viene impiegata per interventi di emergenza a seguito di forti terremoti o durante crisi sismiche che possono precedere ed accompagnare le fasi eruttive dei vulcani, anche ad integrazione delle stazioni delle Reti Fisse di sorveglianza per migliorare la qualità delle localizzazioni e per una migliore definizione del meccanismo di liberazione dell'energia sismica. Gli interventi possono anche essere focalizzati allo studio della sismicità di una determinata area sismogenetica (tettonica o vulcanica) in periodi non di crisi. Altro peculiare impiego delle stazioni sismiche della RM è lo studio della struttura della crosta terrestre mediante prospezioni sismiche profonde

Integrated methodologies for 3D deformation analysis at Ischia Island (Italy): state of the art, prospectives and modelling.

Ischia Island, located SW of Naples (Italy), has been characterized by both explosive and effusive activity with the last eruption occurred in 1302. Subsequent dynamics, characterized by seismic activity with the strongest events occurred in 1881 and 1883 and a diffuse hydrothermal phenomena, shows a significant subsidence in the S and NW sectors. The presence of the active volcanoes in a very densely area needs continuous monitoring of the dynamics related to the pre-eruptive processes. Ground deformation studies are an important precursor because are linked to magma overpressure and migration. In particular, the geodetic monitoring system is mainly based on GPS and Precise levelling techniques. Here, we present a study of the surface deformation occurring in the island based on Differential Synthetic Aperture Radar Interferometry (DInSAR) referred to as Small BAseline Subset (SBAS) technique. Levelling surveys carried out between 1990 and 2003 on the Mt Epomeo resurgent block record negative dislocations on the northern and southern flanks with a maximum subsidence rate of 1.27 cm/yr. This deformation is not associated with cooling, crystallization or lateral drainage of magma and cannot be explained by a pressure point or prorate ellipsoid source. The data show that between 1990 and 2003 Mt Epomeo has been affected by a subsidence with two maxima located on its northern and southern sectors. Then, the 1992–2003 time interval and SAR data acquired by the European Remote Sensing (ERS) satellites from ascending and descending orbits have been used, thus allowing us to discriminate the vertical and east–west components of the displacements. A validation of the DInSAR results has been carried out first by comparing the vertical deformations estimated from the SAR data with those measured from the spirit levelling network that is present in the area. The deformation is due to the closure of cracks associated with ENE–WSW to E–W preexisting faults along which degassing processes occur. We propose that the recorded dislocations reflect a decrease in the fluid pressure within these cracks

SISCam 2.0

The Seismotectonic Information System of the Campania Region is aimed to improve the knowledge of the geodynamic processes affecting this seismically active, highly populated region. The Information System is oriented to the production of scientific and technical information for seismotectonic applications

Programma "Geotraversa Europea": Settembre 1986

In the tex

Sorveglianza Sismica Vesuvio: 01 Gennaio - 04 Giugno 1998

In the tex

M.Etna: crisi sismica del 19/06/88. Detezione e localizzazione mediante rete sismica digitale

In the tex

APPLICAZIONE DI TECNICHE DI COLLASSAMENTO IPOCENTRALE A DUE SEQUENZE SISMICHE DI BASSA ENERGIA NELL’APPENNINO MERIDIONALE

In this study we analyse two recent low energy (Mdmax = 4.1) seismic sequences (1990-1997) that affected the northern sector (Sannio-Benevento area) of the Southern Apennines chain. We applied the Best Estimate Method to earthquake locations in order to constrain the position and geometry of the seismogenic structures. The most striking features of the obtained fault geometries indicate that earthquakes of the 1990 Benevento sequence align along a NW-SE striking structure, while the earthquakes of the 1997 Sannio sequence outline a NNE-SSW striking structure. The southernmost NW-SE structure dips towards the NE, is characterized by a conjugate fault arrangement and overlies the fault responsible for a larger historical earthquake (Iomax = XI MCS, 1688 earthquake). Available focal mechanisms from earthquakes that occurred on the recognized NW-SE and NE-SW faults are consistent with dip-slip normal solutions. This suggests the occurrence of coexisting NW-SE and NE-SW extension in the Southern Apennines

Shallow heterogeneities and seismic activity of Mt. Vesuvius

In the tex

L'anisotropia sismica all'Etna: problematiche connesse e relazioni col campo di stress

In the tex