Fertitta, Gioacchino

Starting from 2001 INGV, in cooperation with INFN, performed several experiments with multidisciplinary submarine observatories installed at deep sea off the coast of Catania at the Western Ionian Sea site, the INGV Regional Facility that today contributes to the EMSO ERIC (European Multidisciplinary Seafloor and water column Observatory - European Research Infrastructure Consortium). Submarine equipment can provide real-time data to shore acquisition systems and are remotely accessible. For the management of several submarine platforms, a computer network was developed to support the systems for data management, acquisition and distribution. This technical report describes the network implementation for the simultaneous management of two submarine observatories and a Junction Box.

The InSEA project (“Initiatives in Supporting the consolidation and enhancement of the EMSO research infrastructure consortium (ERIC) and related Activities”) has the objective, as the full name of the project indicates, to consolidate and strengthen the infrastructures concerning the EMSO (“European Multidisciplinary Seafloor and water column Observatory”) ERIC (European Research Infrastructure Consortium) and all those technical-scientific activities related to it. In particular, the project is upgrading localized and distributed marine infrastructures, laboratories, observatories and spatial measurement activities in Southern Italian seas to support those activities of surveys in fixed time series points of observation of EMSO ERIC. The project is developing according to six implementation Objectives of Research (OR) that involve four National research Institutions: INGV, ISPRA, OGS and Anton Dohrn Zoological Station of Naples. The paper illustrates with more details the relevant objectives of the InSEA project and its most significant implementation phases.

We describe the first dense real-time urban seismic–accelerometric network in Italy, named OSU-CT, located in the historic center of Catania. The city lies in the region with the greatest danger, vulnerability, and earthquake exposure in the entire Italian territory. OSU-CT was planned and realized within the project called EWAS “an Early WArning System for cultural heritage”, aimed at the rapid assessment of earthquake-induced damage and the testing of an on-site earthquake early warning system. OSU-CT is mainly based on low-cost instrumentation realized ad hoc by using cutting-edge technologies and digital MEMS (micro-electro-mechanical systems) triaxial accelerometers with excellent resolution and low noise. Twenty of the forty scheduled stations have already been set up on the ground floor of significant historic public buildings. In order to assess the performance of an earthquake early warning (EEW) on-site system, we also installed wide-band velocimeters (ETL3D/5s) in three edifices chosen as test sites, which will be instrumented for a structural health monitoring (SHM). In addition to several laboratory and field validation tests on the developed instruments, an effective operational test of OSU-CT was the Mw 4.3 earthquake occurring on 23 December 2021, 16 km west, south-west of Catania. Peak ground accelerations (4.956 gal to 39.360 gal) recorded by the network allowed obtaining a first urban shakemap and determining a reliable distribution of ground motion in the historical center of the city, useful for the vulnerability studies of the historical edifices.

This work sets out to identify a state-of-the-art system to be used for the calibration of seismic sensors. The aim is to acquire such a system within the framework of the PON ARS01 00926 EWAS (an Early Warning System for cultural heritage) project, which seeks to develop new technologies for the protection, conservation and safety of cultural heritage and envisages creating a newly developed seismic monitoring system. This system will exploit the ETL3D/5s-H hybrid sensors, resulting from the integration of a precision accelerometer within the ETL3D/5s velocimeter [Fertitta et al., 2020]. The new calibration system, already acquired and being installed, can be used by the EWAS project partners (including the National Institute of Geophysics and Volcanology and the Kore University of Enna), to calibrate the ETL3D/5s-H sensors, and by external organisations to calibrate or gauge other seismic sensors, thus providing a useful service to the scientific community and supporting industrial activities. This paper presents the method used and the activities undertaken to define the technical specifications of the calibration system. A feasibility study of an electromechanical vibrating table and the testing of two electrodynamic calibration systems were carried out. One of the electrodynamic systems is the CS18P (Calibration System for Seismic Sensors) produced by the German firm SPEKTRA. The CS18P comprises two vibrating tables, one horizontal and one vertical, which, thanks to their fluid-dynamic suspension, eliminate the sliding and rolling friction associated with the movement of the moving part with respect to the fixed part. A hardware and software system monitors and controls the motion in real time, analyses the data and automatically processes a predefined set of measurements. In the light of the technical specifications and experimental results, the CS18P represents the ideal solution for the aims of the EWAS project and also in view of the possible future uses of the calibration system.

Seismological data recorded in the Ionian Sea by a network of seven Ocean Bottom Seismometers (OBSs) during the 2017–2018 SEISMOFAULTS experiment provides a close-up view of seismogenic structures that are potential sources of medium-high magnitude earthquakes. The high-quality signal-to-noise ratio waveforms are observed for earthquakes at different scales: teleseismic, regional, and local earthquakes as well as single station earthquakes and small crack events. In this work, we focus on two different types of recording: 1) local earthquakes and 2) Short Duration Events (SDE) associated to micro-fracturing processes. During the SEISMOFAULTS experiment, 133 local earthquakes were recorded by both OBSs and land stations (local magnitude ranging between 0.9 and 3.8), while a group of local earthquakes (76), due to their low magnitude, were recorded only by the OBS network. We relocated 133 earthquakes by integrating onshore and offshore travel times and obtaining a significant improvement in accuracy, particularly for the offshore events. Moreover, the higher signal-to-noise ratio of the OBS network revealed a significant seismicity not detected onshore, which shed new light on the location and kinematics of seismogenic structures in the Calabrian Arc accretionary prism and associated to the subduction of the Ionian lithosphere beneath the Apennines. Other signals recorded only by the OBS network include a high number of Short Duration Events (SDE). The different waveforms of SDEs at two groups of OBSs and the close correlation between the occurrence of events recorded at single stations and SDEs suggest an endogenous fluid venting from mud volcanoes and active fault traces. Results from the analysis of seismological data collected during the SEISMOFAULTS experiment confirm the necessity and potential of marine studies with OBSs, particularly in those geologically active areas of the Mediterranean Sea prone to high seismic risk.

PGS1 is a new compact portable seismic station, designed at INGV OBS and Earth Lab, that is specifically intended for the deployment of dense arrays of seismographs on-shore. With its low cost, compact design, high data-quality and long battery life, PGS1 is a perfect solution for seismic monitoring networks. PGS1 design is based on a solid polypropylene suitcase, containing a complete data acquisition system, two battery packs and a photovoltaic panel. The new Earth Lab 5s medium-period seismic sensor is included. The whole system meets the IP67 standard requirements both in transport and in acquisition configuration. PGS1 is normally equipped with one battery pack, one more pack can be added inside the suitcase achieving 40 days of battery life. The station is equipped with a photovoltaic panel, useful to extend the deployment length. Inside the suitcase, there are compartments where to store the seismic sensor, the photovoltaic panel and all the cables. Therefore, the station is very easy to transport.

This work presents a new low cost and low power consumption wide-band (5s) three-component seismic sensor, named ETL3D/5s. The sensor is suitable for seismic regional monitoring (local and regional earthquakes), HVSR measurements, seismic microzonation studies and Structural Health Monitoring (SHM) of civil structures. ETL3D/5s includes a set of three 4.5 Hz geophones and an electronic circuit that in-creases thegeophone’s natural period. The sensor exhibits a period of 5 s and a power consumption as low as 75 mW. Changes in ambient temperature have little effect on the frequency response because a temperature compensation system is also implemented. A small and sturdy cylindrical housing contains the electronic boards and geophones. The housing design was supported by a modal FEM analysis, in order not to affect the frequency response. The chosen materials and parts guarantee protection against atmospheric agents and watertightness (IP67 degree). The sensor noise model, partially confirmed by a field test, predicts a powerspectral density of 10 (nm/s)/√Hz at 1Hz.

The SEISMOFAULTS project (www.seismofaults.it) was set up in 2016 with the general plan of exploring the seismicity of marine areas using deep seafloor observatories. The activity of the first two years (Seismofaults 2017 and 2018) consisted of the installation of a geophysical-geochemical temporary monitoring network over the Ionian Sea floor. Eleven ocean-bottom seismometers with hydrophones (OBS/H) and two seafloor geochemical-geophysical multiparametric observatories were deployed to: (1) identify seismically active faults; (2) identify potential geochemical precursors of earthquakes; and (3) understand possible cause–effect relationships between earthquakes and submarine slides. Furthermore, five gravity cores were collected from the Ionian Sea bottom and ~4082 km of geophysical acquisition, including multibeam and single channel seismic reflection data, were acquired for a total of 4970 km2 high-resolution multibeam bathymetry. Using Niskin bottles, four water column samples were collected: two corresponding at the location of the two multiparametric observatories (i.e., along presumably-active fault zones), one corresponding at a recently discovered mud volcano, and one located above a presumably-active fault zone away from the other three sites. Preliminary results show: (1) a significant improvement in the quality and quantity of seismological records; (2) endogenous venting from presumably active faults; (3) active geofluid venting from a recently-discovered mud volcano; and (4) the correct use of most submarine devices. Preliminary results from the SEISMOFAULTS project show and confirm the potential of multidisciplinary marine studies, particularly in geologically active areas like southern Italy and the Mediterranean Sea.

The Ionian Sea area is a known site of seismic hazard. Several historical highmagnitude earthquakes occurred in the area (e.g., 1193, M=6.6; 1693, M=7.4; 1908, M=7.2) [Boschi et al., 1997], whose tectonic sources and generation mechanism are still debated. Due to the lack of a seafloor seismic network the detection and location of marine earthquakes are often elusive. The SEISMOFAULTS experiment [http://www.seismofaults.it/] was performed between 2017 May and 2018 May to increase knowledge on the seismicity in the western Ionian Sea. Seven broadband Ocean Bottom Seismometers and Hydrophones

Extending seismic monitoring to offshore areas is among main INGV’s aims; OBS Lab is contributing to the achievement of this goal with technological development of submarine systems and scientific missions. Offshore realtime systems not only provide oceanographic data but also allow improving the hypocenter computation, under certain operative conditions.