Brief communication: Co-seismic displacement on 26 and 30 October 2016 (<i>M</i><sub>w</sub> = 5.9 and 6.5) – earthquakes in central Italy from the analysis of a local GNSS network

Abstract

Abstract. On 24 August 2016 a strong earthquake (Mw = 6.0) affected central Italy and an intense seismic sequence started. Field observations, DInSAR (Differential INterferometry Synthetic-Aperture Radar) analyses and preliminary focal mechanisms, as well as the distribution of aftershocks, suggested the reactivation of the northern sector of the Laga fault, the southern part of which was already rebooted during the 2009 L'Aquila sequence, and of the southern segment of the Mt Vettore fault system (MVFS). Based on this preliminary information and following the stress-triggering concept (Stein, 1999; Steacy et al., 2005), we tentatively identified a potential fault zone that is very vulnerable to future seismic events just north of the earlier epicentral area. Accordingly, we planned a local geodetic network consisting of five new GNSS (Global Navigation Satellite System) stations located a few kilometres away from both sides of the MVFS. This network was devoted to working out, at least partially but in some detail, the possible northward propagation of the crustal network ruptures. The building of the stations and a first set of measurements were carried out during a first campaign (30 September and 2 October 2016). On 26 October 2016, immediately north of the epicentral area of the 24 August event, another earthquake (Mw = 5.9) occurred, followed 4 days later (30 October) by the main shock (Mw = 6.5) of the whole 2016 summer–autumn seismic sequence. Our local geodetic network was fully affected by the new events and therefore we performed a second campaign soon after (11–13 November 2016). In this brief note, we provide the results of our geodetic measurements that registered the co-seismic and immediately post-seismic deformation of the two major October shocks, documenting in some detail the surface deformation close to the fault trace. We also compare our results with the available surface deformation field of the broader area, obtained on the basis of the DInSAR technique, and show an overall good fit.

Coseismic Slip Vectors of 24 August and 30 October 2016 Earthquakes in Central Italy: Oblique Slip and Regional Kinematic Implications

“…Moreover, the near‐field results yielded from our geodetic benchmarks are in agreement and can be extrapolated to the south‐westward far‐field GPS permanent stations showing the predominance of subsidence between the footwall and the hangingwall, coherent with a normal faulting dislocation profile (Figure ). Both near‐field (our study) and far‐field GPS data (Cheloni et al, ; De Guidi et al, ) show that the footwall of the SW°‐dipping Monte Vettore normal fault moved horizontally toward the ENE during 30 October (Figure ), suggesting a regional‐scale crustal motion.…”

“…The hangingwall has moved horizontally by 26 ± 2 cm, in a direction parallel to the fault plane toward the NW (azimuth N315° ±10°), and vertically downward 116 ± 2 cm. In Figure , we compare our results with far‐field coseismic displacements measured by GPS stations after 30 October event (Cheloni et al, ) and the data from De Guidi et al () that installed a GNSS network after 24 August event. Our near‐field displacement is remarkably consistent with the far‐field footwall motion measured on those others stations, both for the vertical and horizontal components (Figure ).…”

“…Black‐headed vectors are GPS velocities from Cheloni et al (), available online on http://ring.gm.ingv.it/?p=1304. White‐headed vectors are GPS velocities from DeGuidi et al (). Red and blue vectors are from the present study (photogrammetry and geodetic data; Figures and ) and belong to the Monte Vettore fault footwall and hangingwall, respectively.…”

Half‐Graben Rupture Geometry of the 30 October 2016 MW6.6 Mt. Vettore‐Mt. Bove Earthquake, Central Italy

“…We use a comprehensive geodetic data set composed of regional GPS measurements at 37 sites belonging to the Istituto Nazionale di Geofisica e Vulcanologia (INGV Working Group “GPS Geodesy”, ), to CaGeoNet (Anzidei et al, ; Galvani et al, ), and to the Istituto Geografico Militare (IGM, http://www.igmi.org) networks; of five local survey‐mode GPS observations in the near‐field of the MVB fault trace (De Guidi et al, ); and of six static displacements derived from the closest SM stations (Zimmaro et al, ), the Advanced Land Observing Satellite‐2 (ALOS‐2) coseismic ascending interferogram relevant to the 30 October event (Cheloni et al, ) and the Sentinel‐1 (SENT‐1) descending interferogram covering both the 26 and 30 October earthquakes (Walters et al, ). This combination of data provides good coverage in both near‐ and far‐field of the 30 October earthquake.…”

“…We use the GPS measurements of coseismic displacements from Cheloni et al (), which reveal a general relative normal motion SW‐NE oriented across the MVB fault system (Figure ). In addition, we also use the static coseismic displacements measured by a local GPS network deployed across the trace of the main fault (De Guidi et al, ), which had never been previously used in the source modeling of this earthquake. The latter GPS measurements provide another independent constraint on the fault location and coseismic slip.…”