An algorithm for the search of homogeneous strain-rate fields

The aim of this paper is to describe the theoretical fundamentals and the main features of a software suitably implemented to estimate the strain-rate tensor from continuous GPS data. Current softwares developed for geophysical applications generally estimate or compute bi-dimensional strain, since this is the most requested use. On the contrary, this software allows for a three-dimensional estimate of the strain-rate tensor. It accounts for all the significant GPS velocities and estimates the strain-rate components by the least squares method starting from the hypothesis of one homogeneous strain-rate field. An initial field has to be defined by at least 4 sites which pass the chi-squared test on the strain-rate homogeneity. The developed algorithm automatically searches for sites belonging to this initial homogeneous field, starting from the site nearest to the barycentre of the first 4 sites and proceeding until a user-defined limit distance. Each time a site is added, the homogeneity of the whole field is suitably tested by a number of statistic tests. In this work the algorithm has been also applied to some areas of geophysical interest

Current geodetic deformation in the South Africa region

We present a preliminary velocity field of the African continent derived from continuous GPS observations from 2004 to 2008. The aim of our work is to investigate the strain-rate pattern along the East Africa rift, in particular along the boundary of the two African plates (the Nubian and the Somalian) and in the South Africa region. We have processed GPS data in a time window spanning four years, i.e. from 2004 to 2008, involving IGS, TrigNet (a network of permanent GPS stations distributed throughout South Africa) and other sporadic sites. The GPS data have been processed by means of the Bernese software version 5.0 dividing the entire African network into two clusters. The combination of daily loosely constrained solutions provides the time series of about a hundred of permanent GPS sites mainly located in the African continent. Site velocities together with periodic signals, eventual steps, have been estimated simultaneously using the complete covariance matrices. Finally the velocity field has been expressed in the ITRF2005 reference frame. This investigation gives a preliminary idea of the velocity field and strain-rate pattern we can expect in the South-East Africa region, the observed deformations being barely measurable, below a few mm/year

Modeling ground deformations of Panarea volcano hydrothermal/geothermal system (Aeolian Islands, Italy) from GPS data.

Panarea volcano (Aeolian Islands, Italy) was considered extinct until November 3, 2002 when a submarine gas eruption began in the area of the islets of Lisca Bianca, Bottaro, Lisca Nera, Dattilo and Panarelli, about 2.5 km east of Panarea Island. The gas eruption decreased to a state of low degassing by July 2003. Before 2002 the activity of Panarea volcano was characterized by mild degassing of hydrothermal fluid. The compositions of the 2002 gases and their isotopic signatures suggested that the emissions originated from a hydrothermal/geothermal reservoir fed by magmatic fluids. We investigate crustal deformation of Panarea volcano using the GPS velocity field obtained by the combination of continuous and episodic site observations of the Panarea GPS network in the time span 1995-2007. We present a combined model of Okada sources which explains the GPS results acquired in the area after December 2002. The kinematics of Panarea volcano show two distinct active crustal domains characterized by different styles of horizontal deformation, supported also by volcanological and structural evidences. A subsidence in the order of several mm/yr is affecting the entire Panarea volcano and a shortening of 10-6 yr-1 has been estimated in the Islets area. Our model reveals that the degassing intensity and distribution are strongly influenced by geophysical-geochemical changes within the hydrothermal/geothermal system. These variations may be triggered by changes in the regional stress field as suggested by the geophysical and volcanological events that occurred on 2002 in the Southern Tyrrhenian area

A possible relationship between the Arctic Oscillation Index and atmosphere-triggered interannual long-wavelength

A host of geophysical processes contribute to temporal variations in the low-degree zonal harmonics of the Earth’s gravity field. The present paper focuses on atmosphere-based mass redistributions using global surface pressure data from the NOAA Climate Diagnostics Center for the period 1980-2002. We computed atmosphere-triggered temporal variations of the Earth’s low-degree zonal gravitational coefficients Jl (l = 2 : 4). Such atmosphere-triggered ΔJl(t) are compared with the Arctic Oscillation Index (AOI) and with the observed ΔJl(t) computed by the Italian Space Agency (ASI) so as to investigate a possible coupling. We show that there is a significant agreement between the AOI and atmosphere-triggered ΔJl(t), as well as a particularly interesting correlation between the winter ΔJl(t) series and the AOI active season series

GPS Positioning and Velocity Field in the Apennines Subduction Zone

A stable geodetic reference frame permits to relate one position to another and to compute a reliable deformation field from geodetic observations. In order to satisfy scientific requirements, the reference frame should be accurate, reliable and internally consistent over time with unambiguously specified datum definition (origin, scale, orientation and their respective time evolution). Current reference frame stability between successive frame realizations suggests that the agreement is at the level of 1 cm and 0.3 mm/yr respectively for absolute and time derivative translation and scale factors. They represent the current stability over time of the reference frame and set the sensitivity for geodetic measurements. Here we will present the results of a GPS deformation field in the Italian region obtained from all the available permanent GPS stations operated in Italy. The complex nature of the ongoing tectonic deformation along the Alpine-Apennines orogenic systems is now evident and GPS data have proven its capability to measure millimetre scale deformations

Placido Mossello. Progetti di decorazione

Placido Mossello (1835-1894) e la sua ditta specializzata in pittura a fresco, oli, tempere nonché in minor misura oggetti d’arredo, rappresentano l’apice di quella imprenditoria a cavallo tra la vena artistica e la maniera propria della seconda metà del XIX secolo. Le commesse, che alternano il servizio per la Real Casa alle esigenze delle famiglie nobili e alto borghesi, nelle due capitali, prima Torino e poi Firenze, e nelle residenze di villeggiatura, rendono conto dell’importanza assunta dalla ditta e della riconosciuta competenza tecnica di Mossello. Ai temi leggeri, con gusto per il panneggio, per l’ornamentazione a fiori, per i falsi sfondati prospettici, per i richiami all’antico che caratterizzano le commesse reali e private, egli alterna il gusto – a tratti sovraccarico – tipicamente ottocentesco per i temi devozionali, per l’iconografia agiografica dei santi, per il culto mariano, soggetti di maniera resi tuttavia con consumata perizia e aderenza alla religiosità dell’epoca. Con la sua attività, Placido apre a una fortunata progenie (di adozione) di decoratori che si esprimono nelle ditte e negli studi Fratelli Musso e Papotti, Carlo Musso, Giovanni Clemente e Paolo Musso, che per quasi un secolo rappresentano la forma più corrente di decorazione di interni, di plastica monumentale e financo di progettazione architettonica in ambito piemontese. Il presente volume, edito a chiusura della mostra Placido Mossello. Progetti di decorazione - allestita presso il Politecnico di Torino, DIST, Castello del Valentino, Manica Sud, da marzo a novembre 2023 - apre a una quadrilogia di esposizioni di disegni e fotografie, attinti dall’archivio Musso Clemente, conservato presso il DIST-APRi (Archivi Professionali e della Ricerca) e acquisito per donazione nel 1989

Strain rate relaxation of normal and thrust faults in Italy

n/

Static stress drop as determined from geodetic strain rates and statistical seismicity

Two critical items in the energetic budget of a seismic province are the strain rate, which is measured geodetically on the Earth’s surface, and the yearly number of earthquakes exceeding a given magnitude. Our study is based on one of the most complete and recent seismic catalogs of Italian earthquakes and on the strain rate map implied by a multi-year velocity solution for permanent GPS stations. For 36 homogeneous seismic zones, we used the appropriate Gutenberg Richter relation based on the seismicity catalog to estimate a seismic strain rate, which is the strain rate associated with the mechanical work due to a co-seismic displacement. The volume storing most of the elastic energy is associated with the long-term deformation of each seismic zone, and therefore, the seismic strain rate is inversely proportional to the static stress drop. The GPS-derived strain rate for each seismic zone limits the corresponding seismic strain rate, and an upper bound for the average stress drop is estimated. These results demonstrated that the implied regional static stress drop ranged from 0.1 to 5.7 MPa for catalog earthquakes in the moment magnitude range [4.5–7.3]. These results for stress drop are independent of the “a” and “b” regional parameters and heat flow but are very sensitive to the assumed maximum magnitude of a seismic province. The data do not rule out the hypothesis that the stress drop positively correlates with the time elapsed after the largest earthquake recorded in each seismic zone

The brittle-ductile transition as the switch of earthquakes: applications for seismic prediction

The brittle-ductile transition (BDT) separates the lower crust where deformation occurs in steady-state regime, from the upper crust where it is rather dominated by stick-slip. The fault hangingwall above BDT accumulates elastic energy during the interseismic period, without significant evidence of surface strain rate Faults activate in areas of high strain rate gradients along the segments with lower strain rates Fluid discharge varies as a function of the tectonic setting The phenomenology gives insights for the parameters to be monitored in earthquake forecastin