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We investigated whether the joint inversion of geodetic and stress direction data can constrain long-term fault slip rates in the central Apennines, and ultimately how extension is partitioned among fault slip and bulk lithosphere permanent strain Geodetic velocities are collected in the fault interseismic stage with steady secular deformation;thus, long-term estimates can be derived with a model of elastically unloading seismogenic faults within a viscously deforming lithosphere As the average spacing of permanent Global Navigation Satellite Systems (GNSS) stations is similar to the average length of seismogenic faults (25?35 km), if not larger, we decided to merge permanent and temporary GNSS measurements, resulting in a denser geodetic data set Given that most normal faults in the Apennines have slip rates around or below 1 mm/a, and most campaign GNSS velocities carry similar uncertainties, simple local back slip models cannot be applied More sophisticated modeling is required to extract reasonable bulk deformation rates and long-term fault slip rates at signal-to-noise ratio of order unity Given the spatial distribution of the GNSS network, we estimated the long-term slip rate of seven major fault systems that are in satisfactory agreement with available geological slip rates The resulting spatial distribution of bulk deformation rates locally fits short-term transients;in other cases, they represent the currently unclear signature of tectonic processes like upper-crustal viscoplastic deformation and aseismic slip, or indicate missing faults in the adopted database We conclude that the time is ripe for determining fault slip rates using geodetic and stress direction data, particularly where fault activity rates are hard to determine geologically

We investigate a large geodetic data set of interferometric synthetic aperture radar (InSAR) and GPS measurements to determine the source parameters for the three main shocks of the 2016 Central Italy earthquake sequence on 24 August and 26 and 30 October (Mw 6.1, 5.9, and 6.5, respectively). Our preferred model is consistent with the activation of four main coseismic asperities belonging to the SW dipping normal fault system associated with the Mount Gorzano-Mount Vettore-Mount Bove alignment. Additional slip, equivalent to a Mw ~ 6.1–6.2 earthquake, on a secondary (1) NE dipping antithetic fault and/or (2) on a WNW dipping low-angle fault in the hanging wall of the main system is required to better reproduce the complex deformation pattern associated with the greatest seismic event (the Mw 6.5 earthquake). The recognition of ancillary faults involved in the sequence suggests a complex interaction in the activated crustal volume between the main normal faults and the secondary structures and a partitioning of strain release.

We used continuous Global Positioning System (GPS) measurements to infer the fault geometry and the amount of coseismic slip associated to the August 24, 2016 Mw 6 Amatrice earthquake. We realized a three dimensional coseismic displacement field by combining different geodetic solutions generated by three independent analyses of the raw GPS observations. The coseismic deformation field described in this work aims at representing a consensus solution that minimizes the systematic biases potentially present in the individual geodetic solutions. Because of the limited number of stations available we modeled the measured coseismic displacements using a uniform slip model, deriving the geometry and kinematics of the causative fault, finding good agreement between our geodetically derived fault plane and other seismological and geological observations.

We analyze more than 100 GPS time series of continuous and discontinuous GPS stations located in the Abruzzi region (Italy) surrounding the epicentres of the L'Aquila 2009 seismic sequence. The purpose of this work is to reconstruct the coseismic displacement field caused by the 6th April (Mw 6.3) main shock from a dense network of survey-mode stations surrounding the epicentral area and to characterize the early postseismic deformation field. In the months following the main shock, an extensive GPS survey was carried out on the existing Central Apennines Geodetic Network (CAGeoNet), with the intention of collecting a robust data set and to study the co- and postseismicdeformation field of this Apenninic normal faulting earthquake. The analysis is carried out with two independent procedures and software (Bernese and Gamit) in order to provide reliable and validated geodetic solutions. The analysis of the postseismic transients and the knowledge of long-term inter-seismic velocities at all GPS stations, issued from permanent and CAGeoNet sites, allow us to derive a dense co- and postseismic displacement field for the L'Aquila Mw 6.3 main shock in a wide area around the epicentre. The highest deformation rate occurs during the first 4-5 months after the main shock and persists in the following at slightly slower rate throughout the whole monitoring period. Fast deformation rates imply that most of the observed deformation is due to a process different from a pure viscoelastic relaxation of the stress perturbation. Since the observed rates would imply a too low effective viscosity value (below 1017 Pa s), we rather suggest that most of the observed deformation in the first months after the earthquake is due to different processes, most likely frictional afterslip possibly modulated by the presence of fluids. The new coseismic displacement field is used to invert for the main shock fault geometry, analysing the consistency among the different geodetic solutions and the combined one, with the goal of validating the two data sets.

In this study we analyse coseismic GPS displacements and DInSAR data to constrain a dislocation model for the three largest earthquakes of the 1997 Umbria-Marche seismic sequence. The first two events, which occurred on September 26 at 00:33 GMT (Mw 5.7) and 09:40 GMT (Mw 6.0) respectively, are investigated using both GPS displacements and DInSAR interferograms. We discuss and compare the results of previous studies which separately modeled a smaller subset of geodetic data. We provide a dislocation model for these two earthquakes which fits well both GPS and DInSAR data and agrees with the results of seismological and geological investigations. The first event consists of a unilateral rupture towards the southeast with a uniform dislocation. The strike, rake and dip angles are those resulting from the CMT solution. The second event consists of an unilateral rupture towards the northwest and a variable slip distribution on the fault plane. The strike and the rake are consistent with the CMT solution, but the dip angle has been slightly modified to improve the simultaneous fit of GPS and DInSAR data. While the second rupture (09:40 GMT) arrived very close to the surface, the fit to geodetic data shows that the first rupture (00:33 GMT) is deeper (2 km), despite the more evident surface geological effects. The analysis of new SAR interferograms allows the identification of a 5‐6 cm additional displacement caused by the October 3 (Mw 5.2) and 6 (Mw 5.4) seismic events. We use data from a new DInSAR interferogram to model the displacement field of the Sellano earthquake of October 14, 1997. For this event significant GPS measurements were not available. We tested two different fault plane geometries: a blind, planar fault (top depth = 2.4 km), and a curved (listric) fault reaching the surface. The two models provide a generally similar fit to the data, and show that most of the slip was released at depths greater than 2.4 km along a gently dipping (40‐45) fault surface. They also show that a unilateral rupture does not allow fitting the interferometric fringes since there is evident surface deformation to the northwest of the hypocenter. Moreover, we suggest that the concentration of high residuals in the southern part of our uniform slip model may in fact indicate a certain slip variability in this area. We conclude that, despite the moderate magnitudes and the lack of significant surface faulting, the space geodetic data allowed to constrain dislocation models giving new insights in the rupture process of the three largest events of the sequence.

Geodetic data are providing a new prospective in studying active tectonic processes that are occurring in penin- sular Italy. In this paper we use a recently published GPS velocity solution, obtained by merging a data set of permanent and non-permanent networks spanning the 1991-2002 time interval, to provide new quantitative con- straints of the active deformation rates across the Apennines Chain and the Calabrian Arc. The velocity field, given with respect to a fixed Eurasian frame, has been used to compute horizontal strain-rates within polygonal regions that connect and include geodetic stations, and to draw velocity cross sections along 5 different profiles through this region. The computed strain-rates provide a picture of the regional deformation field, which is in agreement with other seismological and geological data, and show that the Apennines are mainly extending in a SW-NE direction, while in Calabria extension is NW-SE oriented. Indications of active shortening are present only in the outer Northern Apennines. The velocity profiles across the Northern and Southern Apennines, along the Tyrrhenian Sea and Calabria, provide a quantitative measurement of the active extension and shortening rates, which are taking up at a more local scale.

We computed the horizontal strain rate field for a sector of tbc Central-Southern Apennines (Italy) from GPS data collected during yearly repeated campaigns performed from 1994 to 2000 on tbc GeoModAp (Geodynamic Modeling of the Apennines) geodetic network. Site velocities were obtained starting from tbc daily coordinates and covariance solutions, using a Kalman filter approach. The residual velocity field with respect to a Eurasian 6xed reference frame shows two different prevalent motion trends, NE-ward for tbc eastern sector of the network and NW-ward for tbc western one. The mean strain rate tensor, obtained from a least square inversion method, shows a signifcant extensional deformation (1.2 x 10 ' strain/yr) normal to tbc Apennine chain, in agreement with seismological and neotectonic data. On the basis of tbc network dimension, of about 250 km, this value gives a well constrained estimate of about 3.0 ± 0.2 mm/yr of the extensional velocity oriented N55E, normal to the chain axis. Our results show a transition of the strain rate field from about N-S compression in tbc Tyrrbenian sfide to about NE-SW extension toward tbc Adriatic, which depicts a more complex deformation pattern.

During the time span 1999-2003 was set up and repeatedly surveyed a not permanent GPS network located across one of the highest seismic areas of the central Apennines (Italy). The Central Apennine Geodetic Network (CA-GeoNet), extends across Umbria, Abruzzo, Marche and Lazio regions, in an area of ?180x130 km, from Tyrrhenian to the Adriatic sea. It consists in 125 GPS stations distributed at 3-5 km average grid and includes 7 permanent GPS stations operated by the Italian Space Agency (ASI) and the Istituto Nazionale di Geofisica and Vulcanologia (INGV). With the aim to estimate the active strain rate across this part of the chain, the GPS sites have been located on the main geological units of the area and across the typical basin and range structures, related with the main seismogenic faults. In this paper we show the network and the first results obtained for a subset of 23 stations that have been occupied at least during three repeated campaigns, in the time span 1999-2003. Data analysis, performed by Bernese 4.2 software, shows an extensional rate normal to the chain, in agreement with geological and seismic data. The strain rates in the inner chain are ranging from 12x10-9±11yr-1 to 16x10-9±11yr-1 and from -14x10-9±11yr-1 to -3x10-9±11yr-1. This result provides an improved estimation of the ongoing deformation of this area with respect to previous studies and is in agreement with the style of deformation inferred from seismicity and with the features of the main seismogenic sources from recent geological and seismological investigations.

[1] On April 6, 2009, 01:32:39 GMT, the city of L'Aquila was struck by a Mw 6.3 earthquake that killed 307 people, causing severe destruction and ground cracks in a wide area around the epicenter. Four days before the main shock we augmented the existing permanent GPS network with five GPS stations of the Central Apennine Geodetic Network (CaGeoNet) bordering the L'Aquila basin. The maximum horizontal and vertical coseismic surface displacements detected at these stations was 10.39 ± 0.45 cm and −15.64 ± 1.55 cm, respectively. Fixing the strike direction according to focal mechanism estimates, we estimated the source geometry with a non linear inversion of the geodetic data. Our best fitting fault model is a 13 × 15.7 km2 rectangular fault, SW-dipping at 55.3 ± 1.8°, consistent with the position of observed surface ruptures. The estimated slip (495 ± 29 mm) corresponds to a 6.3 moment magnitude, in excellent agreement with seismological data.