We define the geometric and kinematic characteristics of the fault activated during the Mw = 6.3, 6 April 2009 L'Aquila earthquake, from the modeling of Envisat and COSMO‐SkyMed (the first ever X‐band interferogram inverted for a coseismic dislocation study) DInSAR interferograms. Our best‐fit solution for the main shock is represented by a normal fault ∼16 km long and ∼12 km wide, with a small right‐lateral component, dipping 47°SW with a maximum slip of ∼90 cm. Although the seismic dislocation probably ended at 1 km depth, the updip projection of the fault plane corresponds to the northern segment of the mapped Paganica–S. Demetrio fault, where alignment of surface breaks was observed in the field. The absence of this fault in existing seismic source catalogues suggests that an improved approach, involving detailed surface and subsurface geological and geophysical investigations, is needed for a better assessment of the seismic hazard at the local scale.

We use InSAR and body‐wave seismology to determine independent source parameters for the 6th April 2009 Mw 6.3 L'Aquila earthquake and confirm that the earthquake ruptured a SW‐dipping normal fault with ∼0.6–0.8 m slip. The causative Paganica fault had been neglected relative to other nearby range‐frontal faults, partly because it has a subdued geomorphological expression in comparison with these faults. The L'Aquila earthquake occurred in an area with a marked seismic deficit relative to geodetically determined strain accumulation. We use our source model to calculate stress changes on nearby faults produced by the L'Aquila earthquake and we find that several of these faults have been brought closer to failure.

[1] We determine geodetic strain in peninsular Italy by the GPS reoccupation of the first order triangulation network of Italy installed from 1860. The uncertainties in the original measurements (about 3 ppm), and the time span between the two observations, imply that tectonic signals larger than about 0.03 ppm/yr are resolvable. Along the Apenninic belt, where the largest earthquakes are concentrated, the geodetic deformation has a clear and consistent strain pattern between adjacent regions, well above the uncertainties, and shows a pervasive NE-SW extension. Along the Tyrrhenian and Adriatic coasts the geodetic signal is not homogeneous and is comparable with the uncertainty in the original measurements. Seismic deformation, calculated over the same time interval, agrees well with estimated extensional direction, but the magnitudes of geodetic and seismic strain differ suggesting that, in part of the Apennines, significant strain accumulation over the past 130 years may not have been released in earthquakes.

S U M M A RYWe propose a dislocation model for the two normal faulting earthquakes that struck the central Apennines (Umbria^Marche, Italy) on 1997 September 26 at 00:33 (M w 5.7) and 09:40 GMT (M w 6.0). We ¢t coseismic horizontal and vertical displacements resulting from GPS measurements at several monuments of the IGMI (Istituto Geogra¢co Militare Italiano) by means of a dislocation model in an elastic, homogeneous, isotropic half-space. Our best-¢tting model consists of two normal faults whose mechanisms and seismic moments have been taken from CMT solutions; it is consistent with other seismological and geophysical observations. The ¢rst fault, which is 6 km long and 7 km wide, ruptured during the 00:33 event with a unilateral rupture towards the SE and an average slip of 27 cm. The second fault is 12 km long and 10 km wide, and ruptured during the 09:40 event with a nearly unilateral rupture towards the NW. Slip distribution on this second fault is non-uniform and is concentrated in its SE portion (maximum slip is 65 cm), where rupture initiated. The 00:33 fault is deeper than the 09:40 one: the top of the ¢rst rupture is deeper than 1.7 km; the top of the second is 0.6 km deep. In order to interpret the observed epicentral subsidence we have also considered the contributions of two further moderate-magnitude earthquakes that occurred on 1997 October 3 (M w 5.2) and 6 (M w 5.4), immediately before the GPS survey, and were located very close to the 09:40 event of September 26. We compare the pattern of vertical displacements resulting from our forward modelling of GPS data with that derived from SAR interferograms: the ¢t to SAR data is very good, con¢rming the reliability of the proposed dislocation model.

The paper presents an unprecedented description of the climatology of ionospheric irregularities over the Arctic derived from the longest Global Navigation Satellite Systems data series ever collected for this specific aim. Two TEC and scintillation receivers are working at Ny-Ålesund (Svalbard, NO), the first of which has been installed in late September 2003. They sample the L1 and L2 signals at 50 Hz from all the GPS satellites in view. The receivers monitor an area of about 600 km radius that includes the auroral and cusp/cap regions in the European longitudinal sector. The length of the data series and the privileged site of observation allow describing the Arctic ionosphere along about two solar cycles, from the descending phase of cycle 23 to almost the end of cycle 24. Our analysis results into a detailed assessment of the long-term behaviour of the ionosphere under solar maximum and solar minimum conditions, including several periods of perturbed ionospheric weather caused by unfavourable helio-geophysical conditions. Since November 2015, a multi-constellation GNSS receiver has been deployed in Ny-Ålesund, providing the opportunity to perform the ionospheric climatology from Galileo signals. The results offer realistic features of the high latitude ionosphere that can substantially contribute to the necessary improvements of forecasting models, providing a broad spectrum of ionospheric reactions to different space weather conditions.