Dottorato in Scienze della Terra, dell Ambiente e delle Risorse, Università Federico II, Napoli, Italy 2

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1 PS-INSAR DATA ANALYSIS: GROUND DEFORMATION IN PRE-SEISMIC PERIOD IN THE L AQUILA 2009 EARTHQUAKE REGION S. Nardò 1, A. Ascione 2, S. Mazzoli 2, C. Terranova 3, G. Vilardo 4 1 Dottorato in Scienze della Terra, dell Ambiente e delle Risorse, Università Federico II, Napoli, Italy 2 Dipartimento di Scienze della Terra, dell Ambiente e delle Risorse, Università Federico II, Napoli, Italy 3 Responsabile delegato Ufficio del Piano Straordinario di Telerilevamento, MATTM, Roma, Italy 4 Istituto Nazionale di Geofisica e Vulcanologia, INGV, Sezione di Napoli Osservatorio Vesuviano, Napoli, Italy Introduction. In the last decades, the development and growing use of new techniques, e.g. those based on satellite based information, has allowed the acquisition of huge amounts of data of unprecedented accuracy that permit not only identification but also quantification of millimetre-scale deformation of the Earth s surface. Among such techniques, those related to the use of radar orbiting satellites (SAR) are particularly suited to the detection of the vertical component of ground motions, thus being fit to the identification of areas affected by landsliding, subsidence/uplift phenomena, etc. With the aim of identifying unstable areas over the whole Italian territory, in 2007 the MATTM (Italian Ministry of the Environment), in the framework of the Piano Straordinario di Telerilevamento Ambientale (Special Plan of Remote Sensing of the Environment), started collecting and developing a set of information layers, including SAR satellite interferometric data (InSAR) by InSAR data processing. Through time, the MATTM website (Geoportale Nazionale - Roma) implemented a powerful interferometric database, which provides an Extraordinary Environmental Remote Sensing Plan (PST-A) as a support to Italian administrative regions (Costantini et al., 2017), and to date is a unique achievement in the European context. In recent years, growing interest has been placed on the use of satellite-based data analyses aimed at the detection and monitoring of ground motions associated with seismicity. In particular, the accuracy of the millimetre measurements so far realized by the C, X and L banded SAR systems and the multi-temporal analysis methodologies (DInSAR - PSInSAR) have provided impressive images of both coseismic and post-seismic (e.g., Atzori et al., 2009; Cheloni et al., 2017) surface modifications in areas affected by strong earthquakes. Such information bears crucial constraints to the geometric and kinematic features of earthquake generating faults. On the other hand, the interferometric PST-A archive retains the millimetre ground deformation data that could be the most important marker of accumulation of crustal seismogenic stress. Such a dataset provides fundamental information on the pre-seismic phase of moderate to strong earthquakes that have hit Italy in recent years (e.g., Lanari et al., 2010; Liu et al., 2010; Luo et al., 2014; Petricca et al., 2015; Moro et al., 2017). By these works, the ground deformation pattern predating the main shock of some months is very well imaged, while much less clear is the pre-seismic displacement pattern on a yearly scale. Our study focuses on pre-seismic ground deformation in the 2009 L Aquila earthquake, which was characterised by a normal faulting mechanism (e.g., Chiarabba et al., 2009). Coseismic 94

2 GNGTS 2017 Sessione 1.1 deformation was identified by different geodetic methods (Cirella et al., 2009; Walters et al., 2009), with SAR analysis constraining the April 6th 2009 main shock source properties, and pointing to the activation of a NW-SE trending, SW dipping normal fault (the Paganica fault; Atzori et al., 2009). SAR investigations point to subsidence since a few months before the main shock (Luo et al., 2014; Moro et al., 2017), while only negligible pre-event cumulative displacement has been detected to date on longer time windows through both SAR data analysis and other geodetic methods (Amoruso and Crescentini, 2010; Lanari et al., 2010; Liu et al., 2010). With the aim of outlining a comprehensive framework of the pre-seismic behaviour of the L Aquila region, we have investigated, through the multi-temporal PSInSAR technique, an around 20 years long time span predating the Mw L Aquila main shock. Materials and methods. Deformations are detectable as phase variations of the electromagnetic signal, through a multitemporal acquisition of SAR images. From the methodological point of view, in studies and research differential interferometry is applied in terms of stacking of interferograms using SBAS (Small Baseline Subset) and PS (Permanent Scatterer) techniques. In our work, we have used the PS-InSAR technique. From the interferometric PST-A database, we analysed ERS ( ) and ENVISAT ( ) datasets. For the ENVISAT dataset, the time span of best fitting of both ascending and descending orbits images is from January 2004 to June We have selected 24 pairsimages (24 satellite survey days) that cover an around 1500 km2 wide region spanning across the epicentre of the 2009 L Aquila earthquake. Single images or short period (up to a few months) without data-pairs images were not analysed. Using trigonometric relationships, from the two-point shape file (ascending and descending), we have obtained single raster images of the total vertical and horizontal displacement/ deformation (Up-Down/West-East; Lanari et al., 2010). Results. The PS-InSAR multitemporal analysis that we have performed in a wide region spanning over the 2009 L Aquila earthquake epicentre has allowed the detection of vertical component ground deformation predating the Mw 6.3 main shock. In particular, the analysis has shown that an about 450 km2 wide area bounded to the NE by the Paganica fault, has recorded pre-seismic displacement starting from about three years prior to the April 6, 2009 earthquake (Fig. 1). Fig. 1 - IDW raster interpolation between PS-InSAR, descendent and ascendent, displacement values in the L Aquila earthquake region. Left: uplift, in the 2005/ /09 time span. Right: subsidence in the 2008/ /02 time span. 95

3 GNGTS 2017 Sessione 1.1 Fig. 2 - NW-SE oriented topographic profile and relative vertical ground displacement, from IDW raster interpolation, in the 2005/ /05 time span. The geometrical combination of sets of images from both ascending and descending SAR orbits has allowed constraining the ground motion orientations, and identifying a change in the orientation of vertical-component ground motion. In particular, orientation of verticalcomponent ground deformation in the 2005/05/01 to 2008/09/01 time span (hereinafter Fig. 3 - NW-SE oriented opographic profile and relative vertical ground displacement, from IDW raster interpolation, in the 2005/ /05 time span. 96

4 labelled long-term pre-seismic phase ) may be distinguished from that which occurred in the following, 2008/09/01 to 2009/02/01 time span (hereinafter labelled short-term pre-seismic phase ; Fig. 1). In long-term pre-seismic phase we observe that vertical ground deformation in the region that includes L Aquila and encompasses the Middle Aterno valley Quaternary basin and the elevations to the SW of it, was characterised by an uplift trend (Figs. 2 and 3), while the horizontal displacement was oriented towards the east. Conversely, in the short-term preseismic period, i.e. starting from about five months prior to the main shock, we observe that vertical ground deformation was characterised by subsidence, while the horizontal component was oriented towards the west (Figs. 1, 2 and 3). Discussion and concluding remarks. The investigation of an about 20 years-long time window has allowed the recognition of pre-seismic displacement in the L Aquila 2009 earthquake epicentral area starting from about three years before the main shock. Crucial to the detection of pre-seismic ground deformation has been the combination of SAR ascending and descending orbits datasets. The displacement that has been identified during the long-term pre-seismic phase is consistent with the findings by Moro et al. (2017) for the Pizzoli area (Fig. 2). However, a much wider area to the south, which includes both the Middle Aterno basin and the ridges to the SW, is characterised by a different behaviour. The multi-temporal analysis of PS-InSAR data from both ascending and descending orbits that we have performed for this wider area has allowed the identification of a complex displacement sequence, which initiated with uplift (in the long-term pre-seismic phase) and was followed by subsidence. Our analysis points out that the change from one displacement trend to the other occurred around five months before the main shock (Figs. 2 and 3). References Amoruso A. and Crescentini L.; 2010: Limits on earthquake nucleation and other pre-seismic phenomena from continuous strain in the near field of the 2009 L Aquila earthquake. Geophys. Res. Lett., 37(10). Atzori S., Hunstad I., Chini M., Salvi S., Tolomei C., Bignami C., Stramondo S., Trasatti E., Antonioli A. and Boschi E.; 2009: Finite fault inversion of DInSAR coseismic displacement of the 2009 L Aquila earthquake (central Italy). Geophys. Res. Lett., 36, L Atzori S., Chiarabba C., Devoti R., Bonano M. and Lanari R.; 2013: Anomalous far-field geodetic signature related to the 2009 L Aquila (central Italy) earthquake. Terra Nova, 25, Cheloni D., De Novellis V., Albano M., Antonioli A., Anzidei M., Atzori S., Avallone A., Bignami C., Bonano M., Calcaterra S., Castaldo R., Casu F., Cecere G., De Luca C., Devoti R., Di Bucci D., Esposito A., Galvani A., Gambino P., Giuliani R., Lanari R., Manunta M., Manzo M., Mattone M., Montuori A., Pepe A., Pepe S., Pezzo G., Pietrantonio G., Polcari M., Riguzzi F., Salvi S., Sepe V., Serpelloni E., Solaro G., Stramondo S., Tizzani P., Tolomei C., Trasatti E., Valerio E., Zinno I. and Doglioni C.; 2017: Geodetic model of the 2016 Central Italy earthquake sequence inferred from InSAR and GPS data. Geophys. Res. Lett., 44, Chiarabba C., Amato A., Anselmi M., Baccheschi P., Bianchi I., Cattaneo M., Cecere G., Chiaraluce L., Ciaccio M. G., De Gori P., De Luca G., Di Bona M., Di Stefano R., Faenza L., Govoni A., Improta L., Lucente F. P., Marchetti A., Margheriti L., Mele F., Michelini A., Monachesi G., Moretti M., Pastori M., Piana Agostinetti N., Piccinini D., Roselli P., Seccia D., and Valoroso L.; 2009: The 2009 L Aquila (central Italy) Mw 6.3 earthquake: Main shock and aftershocks. Geophys. Res. Lett. 36, L Cirella A., Piatanesi A., Cocco M., Tinti E., Scognamiglio L., Michelini A., Lomax A. and Boschi E.; 2009: Rupture history of the 2009 L Aquila (Italy) earthquake from non-linear joint inversion of strong motion and GPS data. Geophysical Research Letters, 36(19). Costantini M., Ferretti A., Minati F., Falco S., Trillo F., Colombo D., Novali F., Malvarosa F., Mammone F., Vecchioli F., Rucci A., Fumagalli A., Allievi J., Ciminelli M.G. and Costabile S.; 2017: Analysis of surface deformations over the whole Italian territory by interferometric processing of ERS, Envisat and COSMO-SkyMed radar data. Remote Sensing Environ., in press. Lanari R., Berardino P., Bonano M., Casu F., Manconi A., Manunta M., Manzo M., Pepe A., Pepe S., Sansosti E., Solaro G., Tizzani P. and Zeni G.; 2010: Surface displacements associated with the L Aquila 2009 Mw 6.3 earthquake (central Italy): New evidence from SBAS-DInSAR time series analysis. Geophys. Res. Lett., 37, L Liu B., Luo Y., Zhang J., Gong L., Jiang W., Ren L.; 2010: PS-InSAR time series analysis for measuring surface deformation before the L Aquila earthquake. Geoscience and Remote Sensing Symposium (IGARSS), IEEE International, pp

5 Luo S., Bo W., Zhu S. and Fu L.; Ground surface deformation of L Aquila earthquake revealed by Insar time series. In Proc. XXV FIG Congress, Engaging the Challenges, Enhancing the Relevance, Kuala Lumpur, Malaysia, Vol. 7051, pp Moro M., Saroli M., Stramondo S., Bignami C., Albano M., Falcucci E., Gori S., Doglioni C., Polcari M., Tallini M., Macerola L., Novali F., Costantini M., Malvarosa F., Wegmüller U.; 2017: New insights into earthquake precursors from InSAR, Nature Scientific Reports, 7, Petricca P., Barba S., Carminati E., Doglioni C., Riguzzi F.; 2015: Graviquakes in Italy. Tectonophysics, 656,