17 research outputs found
Coseismic and initial postseismic slip of the 2009 Mw 6.3 l’Aquila earthquake, Italy, from GPS measurements
Here we report the preliminary results of GPS data inversions for coseismic and initial afterslip distributions of the Mw 6.3 2009 April 6 L’Aquila earthquake. Coseismic displacements of continuous and survey-style GPS sites, show that the earthquake ruptured a planar SW-dipping normal fault with ∼0.6 m average slip and an estimated moment of 3.9 × 1018 Nm. Geodetic data agree with the seismological and geological information pointing out the Paganica fault, as the causative structure of the main shock. The position of the hypocentre relative to the coseismic slip distribution supports the seismological evidence of southeastward rupture directivity. These results also point out that the main coseismic asperity probably ended downdip of the Paganica village at a depth of few kilometres in agreement with the small (1–10 cm) observed surface breaks. Time-dependent post-seismic displacements have been modelled with an exponential function. The average value of the estimated characteristic times for near-field sites in the hanging-wall of the fault is 23.9 ± 5.4 d. The comparison between coseismic slip and post-seismic displacements for the first 60 d after the main shock, shows that afterslip occurred at the edges of the main coseismic asperity with a maximum estimated slip of ∼25 cm and an equivalent seismic moment of 6.5 × 1017 Nm. The activation of the Paganica fault, spatially intermediate between the previously recognized main active fault systems, suggests that strain accumulation in the central Apennines may be simultaneously active on distinct parallel fault systems.Published1539–15461.1. TTC - Monitoraggio sismico del territorio nazionale1.9. Rete GPS nazionaleJCR Journalrestricte
Contemporary crustal extension in the Umbria-Marche Apennines from regional CGPS networks and comparison between geodetic and seismic deformation
Here we report the results of the analysis of a GPS velocity field in the Umbria–Marche Apennines (central Italy) obtained from the integration of diverse geodetic networks. The velocity field obtained shows a high
degree of consistency both spatially and in terms of comparison with independent information, despite the limited time span of some GPS stations. Starting from the velocity field we derive a continuous strain rate field applying a spline interpolation technique which provide a smooth estimate of the deformation field. The main feature of the resulting strain rate field is a continuous high (N50 nanostrain/year) strain rate belt coincident with the area of largest historical and instrumental seismic release. The model directions of the
principal axes agree with geological and seismological information indicating NE–SW extension. We transform the strain rate field into geodetic moment rate using the Kostrov formula to evaluate the potential
seismic activity of the region and compare it with actual seismic release in the last 720 years from MwN5.5 earthquakes. This comparison highlights a large possible deficit in the seismic release with respect to the overall potential seismic activity, particularly concentrated in the northern part of the study area. This discrepancy can be resolved with either a large amount of seismicity to be released in the near future or significant aseismic slip and deformation.Published3-122T. Deformazione crostale attivaJCR Journalreserve
Contemporary crustal extension in the Umbria–Marche Apennines from regional CGPS networks and comparison between geodetic and seismic deformation
Here we report the results of the analysis of a GPS velocity field in the Umbria–Marche Apennines (central Italy) obtained from the integration of diverse geodetic networks. The velocity field obtained shows a high
degree of consistency both spatially and in terms of comparison with independent information, despite the limited time span of some GPS stations. Starting from the velocity field we derive a continuous strain rate field applying a spline interpolation technique which provide a smooth estimate of the deformation field. The main feature of the resulting strain rate field is a continuous high (N50 nanostrain/year) strain rate belt coincident with the area of largest historical and instrumental seismic release. The model directions of the
principal axes agree with geological and seismological information indicating NE–SW extension. We transform the strain rate field into geodetic moment rate using the Kostrov formula to evaluate the potential
seismic activity of the region and compare it with actual seismic release in the last 720 years from MwN5.5 earthquakes. This comparison highlights a large possible deficit in the seismic release with respect to the overall potential seismic activity, particularly concentrated in the northern part of the study area. This discrepancy can be resolved with either a large amount of seismicity to be released in the near future or significant aseismic slip and deformation.Published3-122T. Deformazione crostale attivaJCR Journalreserve
Il sistema di riferimento e la rete di ordine zero
In questi anni, le reti di stazioni permanenti finalizzate a servizi di posizionamento in tempo reale e
postprocessati sono in rapida espansione in Italia. Per ragioni amministrative i servizi di
posizionamento vengono progettati, implementati e gestiti alla scala spaziale delle Regioni. Si
ricorda che una rete di stazioni permanenti (RSP) materializza e distribuisce alla propria utenza un
sistema di riferimento (SR); per garantire che RSP locali distribuiscano il medesimo SR è
necessario che esse condivano un’infrastruttura comune, ovvero che siano inquadrate e monitorate
in una comune RSP di ordine zero, inoltre seguendo un protocollo comune di elaborazione dei dati.
Da un punto di vista teorico, la RSP globale di IGS e le linee guida IGS per la compensazione di
sottoreti locali costituiscono l’infrastruttura comune; da un punto di vista pratico, le stazioni IGS da
sole non possono costituire la rete di ordine zero perchè sono troppo rade e non omogeneamente
distribuite sul territorio nazionale. Inoltre IGS non si pone lo scopo di monitorare sottoreti locali,
mentre l’istituzione di una rete di ordine zero dovrebbe essere naturalmente accompagnata da una
sorta di organo di governo e controllo. Evidentemente, la scelta naturale è quella di istituire una
RSP di ordine zero a livello nazionale, in modo da soddisfare le priorità nazionali; tale RSP
dovrebbe essere inquadrata e monitorata in IGS, in modo da fornire il collegamento fra la rete
globale e i servizi locali di posizionamento; inoltre la RSP di ordine zero può costituire lo strumento
di controllo della consistenza fra servizi locali contigui. Per garantire tali scopi, la RSP di ordine
zero dovrà soddisfare numerosi requisiti di ordine scientifico e tecnico, che vanno dal disegno della
rete alle scelte di inquadramento.
Il presente documento si focalizza su tali argomenti: la situazione Italiana viene analizzata e un
primo test numerico viene descritto. Una rete test di circa 60 SP è stata selezionata in accordo a
criteri di buon disegno; i loro dati relativi a 3 mesi sono stati analizzati, al fine di valutare le
difficoltà intrinseche nelle operazioni di inquadramento. Inoltre, nell’ambito di una collaborazione
con l’Istituto Geografico Militare, è stato effettuato l’inquadramento della Rete Dinamica
Nazionale
Coseismic and initial postseismic slip of the 2009 Mw 6.3 l’Aquila earthquake, Italy, from GPS measurements
Here we report the preliminary results of GPS data inversions for coseismic and initial afterslip distributions of the Mw 6.3 2009 April 6 L’Aquila earthquake. Coseismic displacements of continuous and survey-style GPS sites, show that the earthquake ruptured a planar SW-dipping normal fault with ∼0.6 m average slip and an estimated moment of 3.9 × 1018 Nm. Geodetic data agree with the seismological and geological information pointing out the Paganica fault, as the causative structure of the main shock. The position of the hypocentre relative to the coseismic slip distribution supports the seismological evidence of southeastward rupture directivity. These results also point out that the main coseismic asperity probably ended downdip of the Paganica village at a depth of few kilometres in agreement with the small (1–10 cm) observed surface breaks. Time-dependent post-seismic displacements have been modelled with an exponential function. The average value of the estimated characteristic times for near-field sites in the hanging-wall of the fault is 23.9 ± 5.4 d. The comparison between coseismic slip and post-seismic displacements for the first 60 d after the main shock, shows that afterslip occurred at the edges of the main coseismic asperity with a maximum estimated slip of ∼25 cm and an equivalent seismic moment of 6.5 × 1017 Nm. The activation of the Paganica fault, spatially intermediate between the previously recognized main active fault systems, suggests that strain accumulation in the central Apennines may be simultaneously active on distinct parallel fault systems