Avallone, Antonio

This document describes the services for managing the Global Navigation Satellite System (GNSS) data that have been developed at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) within the context of the European-funded research infrastructure EPOS (European Plate Observing System) program. These services, optimised for solid Earth research applications, seek to harmonise and standardise the collection and quality control of GNSS data and metadata. The EPOS Thematic Core Services (TCS) GNSS developed an architecture based on Geodetic Linkage Advance System Software (GLASS) nodes which hosts the metadata information and allows access to the entire database from the web and a datacenter which hosts the data to distribute. INGV contributes to the EPOS TCS GNSS initiative by managing the GLASS Italian Ring Node (IRN) [1], to provide data and metadata from the Rete Integrata Nazionale GNSS (RING) network [2]. The RING network currently consists of approximately 250 permanent stations all over Italy and abroad (Greece and Malta) installed for the study of active tectonic deformation at regional (Eurasia-Africa plate boundary) and local (seismogenic faults) scales. In support of this infrastructure, INGV is developing and managing different software: Flask Web Service Server (FWSS) which is an interface with the local database to store the metadata; bancadati_sync which is the script to synchronise the RINEX data repository from the source to the local IRN node; gnss_indexer which automates the process to populate the database; ring_synchronization to upload the sitelog metadata of the GNSS stations, and other software tools to let the system working. All software was developed in Python language (version 3.10) while the PostgreSQL database is used to store the information.

The topography is the only ingredient of the kinematic finite fault inversion that is explicitly known. Nevertheless, such analyses commonly assume Green's functions for a 1D layered geological model with flat surface topography. Minimization of the complexity is needed to reduce the computational cost of the inversions in realistic conditions but such assumptions can significantly impact the retrieved source parameters. In particular, the lack of management of approximations and uncertainties could lead to overconfident and biased interpretations of the kinematic results. The increasing computational power available in the coming exascale era provides the opportunity to include the topography at a high resolution and low cost. We have modified the non-negative least-square inversion method of Dreger et al. [2005] for taking into account Green’s functions generated by SPECFEM3D including explicitly significant topography. We applied this new procedure to retrieve the kinematic rupture history of the 30 October 2016 Norcia earthquake (Mw 6.5), by inverting strong motion and high-rate global positioning system datasets. The considered complex fault geometry consists of a main normal fault striking N155°, dipping 47° and belonging to the Mt. Vettore‐Mt. Bove fault system (VBFS), and a secondary fault plane striking N210° and dipping 36° to the NW. The choice is supported by seismological data, geological constraints, and observed surface breakages, but also by inferences from dynamic simulations. We have inverted for slip and rake distribution on the faults while allowing a Bayesian exploration of all the remaining parameters (i.e., rupture velocity, rise time).

We assess the accuracy and the precision of the TanDEM-X digital elevation model (DEM) of the western Gulf of Corinth, Greece. We use for that a dense set of accurate ground coordinates obtained by kinematic GNSS observations. Between 2001 and 2019, 148 surveys were made, at 1 s sampling rate, along highways, roads and tracks, with a total traveled distance of ~25,000 km. The data are processed with the on-line Canadian Spatial Reference System precise point positioning software. From the output files, we select 885,252 coordinates from epochs with theoretical uncertainty below 0.1 m in horizontal and 0.2 m in vertical. Using specific calibration surveys we estimate the mean vertical accuracy of the GNSS coordinates at 0.2 m. Resampling the DEM by a factor of ten allows to compare it with the GNSS in pixels of metric size, thus smaller than the width of the roads, even the small trails. The best fit is obtained by shifting the DEM by 0.47 ± 0.03 m upward, 0.10 ± 0.1 m westward, and 0.36 ± 0.1 m southward. Those values are twenty times below the nominal resolution of the DEM. Once the shift is corrected, the root mean square deviation between TanDEM-X DEM and GNSS elevations is 1.125 m. In forest and urban areas, the shift between the DEM and the GNSS increases by ~0.5 m. The metric accuracy of the TanDEM-X DEM paves the way for new applications for long-term deformation monitoring of this area.

The Italian Tsunami Alert Center based at the Istituto Nazionale di Geofisica e Vulcanologia (CAT-INGV) has been monitoring the Mediterranean seismicity in the past 8 yr to get fast and reliable information for seismically induced tsunami warnings. CAT-INGV is a tsunami service provider in charge of monitoring the seismicity of the Mediterranean Sea and of alerting Intergovernmental Oceanographic Commission (IOC)/UNESCO subscriber Member States and the Italian Department of Civil Protection of a potentially impending tsunami, in the framework of the Tsunami Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (NEAMTWS). CAT-INGV started operating in 2013 and became operational in October 2016. Here, after describing the NEAMTWS in the framework of the global effort coordinated by IOC/UNESCO, we focus on the tsunami hazard in the Mediterranean Sea. We then describe CAT-INGV mandate, functioning, and operational procedures. Furthermore, the article discusses the lessons learned from past events occurring in the Mediterranean Sea, such as the Kos-Bodrum in 2017 (Mw 6.6) and the Samos-Izmir in 2020 (Mw 7.0) earthquakes, which generated moderately damaging tsunamis. Based on these lessons, we discuss some potential improvements for the CAT-INGV and the NEAMTWS, including better seismic and sea level instrumental cover- age. We emphasize the need for tsunami risk awareness raising, better preparation, and full implementation of the tsunami warning “last-mile” to foster the creation of a more integrated, interoperable, and sustainable risk reduction framework. If we aim to be better prepared for the next tsunami, these important challenges should be prioritized in the agenda of the IOC/UNESCO Member States and the European Commission.

We provide a dataset of 3D coordinate time series of 37 continuous GNSS stations installed for stability monitoring purposes on onshore and offshore industrial settlements along a NW-SE-oriented and ~100-km-wide belt encompassing the eastern Italian coast and the Adriatic Sea. The dataset results from the analysis performed by using different geodetic software (Bernese, GAMIT/GLOBK and GIPSY) and consists of six raw position time series solutions, referred to IGb08 and IGS14 reference frames. Time series analyses and comparisons evidence that the different solutions are consistent between them, despite the use of different software, models, strategy processing and frame realizations. We observe that the offshore stations are subject to significant seasonal oscillations probably due to seasonal environmental loads, seasonal temperature-induced platform deformation and hydrostatic pressure variations. Many stations are characterized by non-linear time series, suggesting a complex interplay between regional (long-term tectonic stress) and local sources of deformation (e.g. reservoirs depletion, sediment compaction). Computed raw time series, logs files, phasor diagrams and time series comparison plots are distributed via PANGAEA ( https://www.pangaea.de ).

We investigated the kinematic rupture model of the 2018 Mw 6.8 Zakynthos, Ionian Sea (Greece), earthquake by using a non-linear joint inversion of strong motion data, high-rate GPS time series, and static co-seismic GPS displacements. We also tested inversion results against tide-gauge recordings of the small tsunami generated in the Ionian Sea. In order to constrain the fault geometry, we performed several preliminary kinematic inversions by assuming the parameter values resulting from different published moment tensor solutions. The lowest cost function values were obtained by using the geometry derived from the United States Geological Survey (USGS) focal solution. Between the two conjugate USGS planes, the rupture model which better fits the data is the one with the N9° E-striking 39°-ESE-dipping plane. The rupture history of this model is characterized by a bi-lateral propagation, featuring two asperities; a main slip patch extending between 14 and 28 km in depth, 9 km northeast from the nucleation and a slightly shallower small patch located 27 km southwest from the nucleation. The maximum energy release occurs between 8 s and 12 s, when both patches are breaking simultaneously. The maximum slip is 1.8 m and the total seismic moment is 2.4 × 1019 Nm, corresponding to a Mw value of 6.8. The slip angle shows a dominant right-lateral strike-slip mechanism, with a minor reverse component that increases on the deeper region of the fault. This result, in addition to the observed possibility of similar mechanisms for previous earthquakes occurred in 1959 and 1997, suggests that the tectonic deformation between the Cephalonia Transform Fault Zone and the northern tip of the Hellenic Arc Subduction zone may be accommodated by prevailing right lateral low-dipping faults, occurring on re-activated structures previously experiencing (until Pliocene) compressional regime. Comparison of predicted and observed tsunami data suggests the need of a better characterisation of local harbour response for this type of relatively short-wavelength events, which is important in the context of tsunami early warning. However, the suggested dominantly strike-slip character would in turn imply a reduced tsunami hazard as compared to a dominant thrust faulting regime from this source region.

After large earthquakes, parts of the fault continue to slip for days to months during the afterslip phase, a behaviour documented for many earthquakes. Yet, little is known about the early stage, i.e., from minutes to hours after the mainshock. Its detailed study requires continuous high-rate position time series close to the fault, and advanced signal processing to accurately extract the surface displacements. Here, we use refined kinematic precise point positioning processing to document the early postseismic deformation for three earthquakes along the South American subduction zone (2010 Mw8.8 Maule, Chile; 2015 Mw8.3 Illapel, Chile; 2016 Mw7.6 Pedernales, Ecuador). First, we show that early afterslip generates significant surface displacement as early as a few tens of minutes after the earthquake. Our analysis of the time series indicates that, over the first 36 hours, more than half of the displacement occurs within the first 12 hours, a time window often disregarded with daily positioning. Thus, estimates of coseismic offsets can be biased by more than 10% if early postseismic displacements are acknowledged as coseismic ones. Finally, these results highlight the difficulty to accurately evaluate the different contribution to the seismic cycle budget and thus the associated hazard on faults.

On 18 January 2017, the 2016–2017 central Italy seismic sequence reached the Campotosto area with four events with magnitude larger than 5 in three hours (major event MW 5.5). To study the slip behavior on the causative fault/faults we followed two different methodologies: (1) we use Interferometric Synthetic Aperture Radar (InSAR) interferograms (Sentinel-1 satellites) and Global Positioning System (GPS) coseismic displacements to constrain the fault geometry and the cumulative slip distribution; (2) we invert near-source strong-motion, high-sampling-rate GPS waveforms, and high-rate GPS-derived static offsets to retrieve the rupture history of the two largest events. The geodetic inversion shows that the earthquake sequence occurred along the southern segment of the SW-dipping Mts. Laga normal fault system with an average slip of about 40 cm and an estimated cumulative geodetic moment of 9.29 × 1017 Nm (equivalent to a MW~6). This latter estimate is larger than the cumulative seismic moment of all the events, with MW > 4 which occurred in the corresponding time interval, suggesting that a fraction (~35%) of the overall deformation imaged by InSAR and GPS may have been released aseismically. Geodetic and seismological data agree with the geological information pointing out the Campotosto fault segment as the causative structure of the main shocks. The position of the hypocenters supports the evidence of an up-dip and northwestward rupture directivity during the major shocks of the sequence for both static and kinematic inferred slip models. The activated two main slip patches are characterized by rise time and peak slip velocity in the ranges 0.7–1.1 s and 2.3–3.2 km/s, respectively, and by ~35–50 cm of slip mainly concentrated in the shallower northern part of causative fault. Our results show that shallow slip (depth < 5 km) is required by the geodetic and seismological observations and that the inferred slip distribution is complementary with respect to the previous April 2009 seismic sequence affecting the southern half of the Campotosto fault. The recent moderate strain-release episodes (multiple M~5–5.5 earthquakes) and the paleoseismological evidence of surface-rupturing events (M~6.5) suggests therefore a heterogeneous behavior of the Campotosto fault.

When analyzing the rupture of a large earthquake, geodetic data are often critical. These data are generally characterized by either a good temporal or a good spatial resolution, but rarely both. As a consequence, many studies analyze the coseismic rupture with data that also include one or more days of early postseismic deformation. Here, we invert simultaneously for the coseismic and postseismic slip with the condition that the sum of the two models remains compatible with data covering the two slip episodes. We validate the benefits of this approach with a toy model and an application to the 2009 Mw6.3 L'Aquila earthquake, using a Bayesian approach and accounting for epistemic uncertainties. For the L'Aquila earthquake, we find that if early postseismic deformation is not an explicitly acknowledged coseismic signal, coseismic slip models may overestimate the peak amplitude while long‐term postseismic models may largely underestimate the total postseismic slip amplitude. This example illustrates how the proposed approach could improve our comprehension of the seismic cycle, fault frictional properties, and the spatial and temporal relationship between seismic rupture, afterslip, and aftershocks.

The 2015/11/17 Lefkada (Greece) earthquake ruptured a segment of the Cephalonia Transform Fault (CTF) where probably the penultimate major event was in 1948. Using near-source strong motion and high sampling rate GPS data and Sentinel-1A SAR images on two tracks, we performed the inversion for the geometry, slip distribution and rupture history of the causative fault with a three-step self-consistent procedure, in which every step provided input parameters for the next one. Our preferred model results in a ~70° ESE-dipping and ~13° N-striking fault plane, with a strike-slip mechanism (rake ~169°) in agreement with the CTF tectonic regime. This model shows a bilateral propagation spanning ~9 s with the activation of three main slip patches, characterized by rise time and peak slip velocity in the ranges 2.5-3.5 s and 1.4-2.4 m/s, respectively, corresponding to 1.2-1.8 m of slip which is mainly concentrated in the shallower (<10 km) southern half of the causative fault. The inferred slip distribution and the resulting seismic moment (M0 = 1.05 × 1019N m) suggest a magnitude of Mw6.6. Our best solution suggests that the occurrence of large (Mw > 6) earthquakes to the northern and to the southern boundaries of the 2015 causative fault cannot be excluded.